E Lectric Arc Lamps 73

E L E C T R I C A R C LA M PS

T H E I PR IN CI PLE S CON STR UCTI O N R , AN D WO R KI N G

Z E I D ER J. L

I AL E IN EER THE A G BE RL IN W C NG . JL

M . sc . T T U G R E . J L S A N,

LECTUR E]! m EL T L E I N EERI HO L I? E N LOGY EC RICA NG NG . SC O O T CH O , MANC HESTER UN I VE RSITY

PR OFUSE LV I LLUS TE A TE D WI TH O VE R 1 60 I LLUS TR A TI ON S

N EW YORK

V AN R D . N O S T AN D CO MPAN Y

2 3 M URRAY AN D 2 7 WARRE N STREE TS

1 908

PR E FA C E

THE present volume is a st udy of arc lamps and their applica

f n r d n tions, and is intended to be use ul to lighting engi ee s, stu e ts, and those engaged in the manufacture of the modern arc lamp or n o interested in its applicatio f r artiﬁcial lighting . The

n w Mr. Z e J. l origi al ork , writt n by eid er and published in

G m has re En has er any, in the p sent glish edition been g tly

r e o h e enla g d and br ug t up to dat , additions having especially

m the m E of been ade to chapter on Fla e Arc Lamps . xamples ma nufactum for n of E chosen descriptio are recent nglish,

G m n m t er a , and A erican prac ice, so that the book will also be useful for reference to those to whom a complete survey of the vi PRE FACE

Who English edi tion. Thanks are due to the va rious ﬁrms have kindly supplied the blocks a nd information relating to

m s to Mr Pe e Ma for r of the their la p ; . W. rr n ycock desc iption

B h s m a rc a m and f e d ta l ritis Westinghou e ﬂa e l p ; to ri n s, no b y

Mr r B for ea f f o . . Arthu entley, the r ding proo s

' Ma nona srsn,

December, 1907 . C O N T E N T S

Li st or Pu m a

CHAPTER I THE E LE CTRIC

GENERAL REMARKS

The Open Arc The Enclosed Arc

Current Arc

CHAPTER I I TH E E LECTRICAL PRINCIPLES OF ARC LAMPS

I I R TI N . NT ODUC O

I IF E E I . D F RENC S OF CONSTRUCTION

SERI ES ABC LAMPS

Regula tion

‘ Con of L n stancy amp Curre t . De end n of Ar P u on Su l P ure p e ce c .D. p pp y ress

Exrnm mx. Coxxnc rl os s viii CON TE N TS

SHUNT ARC LAMPS

I NTE RNAL CoNNE cn oNs Regula tion

ns c of PD. a cross the r Co tan y . A c .

D ndence of PD. a cross th A u n the re ula tin epe . e rc po g g mechanism a nd increa se in temperature of the wi ndi ng of the solenoid Dependence of the Lamp Current upon the Supply Pressure

EXTE RNAL CONNE CTI ONS

DIFFERENTIAL ARC LAMPS

INTE RNAL CONNE CTI ONS Regula ti on Consta ncy of the Arc Resista nce Dependence of the La mp Current and across Arc upon the Pressure of the Ma ins

EXTE RNAL CONNECTI ONs

CHAPTER III CONSTRUCTION OF ELECTRIC ARC LAMPS

WITH OPEN s a cs AND C- AXIALVERTICAL LAMPS , C CARBONS

E AILS A. D T

1. The Base Pla te

r - n 2. The Elect o Ma g ets Th Le r Fra m 3 . e ve e, etc.

4 . The Detent

ula n S rin a nd Le r 5 . Reg ti g p g ve he Da s ot 6 . T hp m 7 . The Guide Fra e Th er a nd Lower Ca r on Holders 8. e Upp b a r on la m s 9 . C b C p

10. Terminals

11. Reﬂectors a nd Economisers 1 2. The Casing CON TE N TS ix

B D ' L . sscmr rm or LI T m s roa Di nner GH I NG .

S unt L o the C h amp f AB .

A E G. Differentia l . . Arc La mp ’ Johnson a nd Phillips Differentia l La mp Twin La mp (shunt) (di ﬁerential)

E G Alterna tin Current M La m A. . . g otor p C 0. Si zes or m oNs

D. La w 103 INDIE EOT Lla m a Sizes of Ca rbcns a nd La mp Pressures

FLAME ARC LAMPS

A GE NE E AL Bm s

B. Fan s As e Lm s wrrs Co - a m r. Cm oxs

Sim of Ca rbons a nd La mp Preu ur-os

F t 0. u n Ana Lu res wrrn INOLJN ED Ca neens ' ni n o s E ll U o M o C . xce o La mp

’ Union Electric Co. s A.O Fla me La m . p ’ Britis Westin ouse Co s Fla me La m h gh . p

Sizes of Ca rbons and IA mp Pr-eesures

S A. Germa n . REMARK

B. Dan na or CoNsTEncrroN

lu 2. The C tch

Th Clutc - 3 . e h fra me 4 n . The Carbo Holders

h a s 6. T e D hpot

he Ad ustin Pa r s 7. T j g t

8 . The Termina ls

9 The La m asin a nd Outer lo e . p C g G b ENCLOSE ARC — D LAMPS Conti nued.

- C. Decca n mos or ENcw sE D Aa c La u re

Jenda s E nclosed La mp (New Model)

America n GE O . Multi le La m f A p p or C.

- Multi La m f B. T H le or . . p p DC.

America n G E.C Di r n a l F s . . ffe e ti eed Lamp

Foster Hoto wire EnclosedArc Lamp

D i s r a ns AND Ln sr P a . S n o C no a n am

CHAPTER IV

IGHT I TE ITY IGHT DISTRIBU L N NS , L TI AND TH E I TI OF ON, APPL CA ON THE E LECTRIC ARC FOR PURPOSE S O F ILLUMINATION

' of Vaxi ous Lamps for Diﬂerent Currents Table of Pola r Curves of Arc Lamps ’ Determination of by Roussea u s Method

I I LLUMINATION I .

Units

Horizonta l Surfa ce Illumina ti on

Exam le of Li h p g ting of a n Interior . Exa mple of Lighti ng of an Interior with Inverted Arcs

“ Ta le of M He - ea n xmenta l Illumina tion for Various ooms etc . b R , CON TE N TS

CHAPTER V E X TE RNAL CONNE CTIONS (INSTALLA TION) O F ARC LAMPS AND ACCE S SO RIE S

I EXTERNAL E . CONN CTIONS 15 7

General 15 7 External Connecti ons a nd Adj ustment of Direct Current La mps 160 External Connecti ons a nd Adj ustment of Shunt Arc Lamps 161 Externa l Connections and Adj ustment of Differentia l Arc La mps 163

I I AC E RI E FOR EXTER AL NECTI NS . C SSO S N CON O

La mp Resista nces Sta rting Resista nces Automa ti c Sta rti ng Resista nces Choking Coil ! Arc La mp Tra nsformer Automa ti A liance c Substitutions ] pp . Com ensa tin il p g Co s .

Minimum Automa tic Cut - out

Current I ndi ca tor

APPENDI X I ABLE A TITI ES . T OF PHOTOMETRIC QU N

A I TA LE M ARATI VE COSTS OF THE PPENDI X I . B OF CO P USUAL SOURCES OF LIGHT

A I X I II A A A LES O PHOTOMETRY PPE ND . ST ND RDI Z TION RU N AND LAMPS OF THE AMERICAN I NSTITUTE OF ELECTRICAL ENGINE ERS

INDEX

LIST OF ILLUSTRATION S

Poi nted sha pe of ca rbons of a di rect current open a rc Fla t form a ti on of ca rbons of a direct current enclosed a rc Reﬂection in i ndi rect lighti ng I ncli ned ca rbons a s in ﬂam e a rc

N on - focu ssing a re Focu ssi ng a rc

Clu tch - feed

B ra ke- wheel feed Clockwork feed Al terna ti ng cu rrent m otor feed Seri es a rc la mp connecti ons i nclu di n resi stan ce n n g t rc la m c nnec i ons Shun a p o t . i nclu ding resi sta nce Shunt a rc la m ps working in seri es Diﬁeren ti a l a rc lamp connec ti ons i nclu di n resi sta nce n n g

Horseshoe electro- ma gnets Solenoid wi th tu bula r core la mi na ted core Solen oids wi th horseshoe core of sheet sta mpi ngs ’ Uni on E lectri c Com pa ny s a ltern a ting current electro- m a gnet

i s E . G m otor r la m D c of A. . a c p

Si em ens- Schu ckert m otor a rc la mp r of E G loc wo ea r A. . la m C k k g . p Wheel m echani sm a nd di sc of m otor a rc la mp Detent of clockw ork la mp Regula ti ng spri ng a nd lever of clockwork la mp Da shpot Guide fra me of a rc la mp consi sting of tu bes soli d rods Ca rbon clamp (upper) (lower) i n pa rts Termi na l xiv LI S T OF I LLUS TRA TI ON S

FIG.

r f r 48 . Reﬂecto o a lterna ting current la mp

4 4 . E conomi ser .

4 5 Casi n f A E . g o a n H G. la mp ’ i la m 46 . a Un on E lectri c Compa ny s p

4 a Si m s- e la m 7 . e en Schuck rt p

48 . Di r t curren t s u n a rc M A E G. ec h t p ( . . ) 4 r m f 9 . Di a g a o connecti ons of sa m e

5 0 T ra ture m r o he of Kot tin a ndMa thi esen Ltd. . empe co pensa to f t firm g , 5 1 n r l E G . Direct curre t difl n ia l c a m A . . e e t a r p ( . 5 ra 2. Di a g m of conn ecti ons of sa m e ’ n n P illi ere la m of ra e w eel t e wi t 5 8 . Joh so Jr h ps di fi n tia l p b k h yp h globe lowered rea dy for trimm i ng

5 3 A. Di tto wi t lo e ra ised la m trimmed h g b , p 4 5 . Di agra m of connecti ons of sa m e 5 5 Twin s u nt l . h amp wi th m ec ha ni sm i n seri es

5 6 . Di a gra m of conn ecti ons of sa me 5 7 Di ra m of connections of twi n differenti a l la m wi th m ec a ni sm s . ag p h i n series

Dia ram of onn ti n of l e i m i n 5 8 . g c ec o s twi n shunt a m p wi th m cha n s s pa ra llel Dia ra m of onn ti n in l wi t m e a ni sm s 5 9. g c ec o s of tw diﬂ crenti a la mp h ch in pa ra llel

60. Alterna ti n urrent m tor la m of the A E .G. g c o p . 6 1. Di a gram of connecti ons of sa m e

62. E lectr m a ne s f sa m e a d usta l o e o g t o showing j b e y k . 68 r r . I nve ted a rc la mp Wi th m eta l reflec to 64 e r . tra nslu cent gla ss refl cto 65 r t r o er . m eta l eflec o a nd gla ss c v i a l a l a st r owl a n tra nslu c ent 66 . spec a b e b d linen reflector

Fl a r la m Wi t cc - a i l a r ns 67 . a m e c p h x a c bo s o e il tio ou tl s 68 . h wing v nt a n et

- 70A 708 00. Blow down ma net Of a a me a rc la m , , 7 g ﬂ p

1 Cr - secti on of economi s r in E xcello a r la m 7 . oss e ﬂa me c p

72 i ew of A.E .G. a m e a rc la m for conti nu ou s urren t . V ﬂ p c

8 Anot er i ew of A.E . G. a me a rc la m for conti nu ou s cu rren t 7 . h v ﬂ p Di a ra m of connecti ons f sa m e 74 . g o i ra m of connecti ons of E xc llo a m e a rc la m for conti nu ou s 76 . D ag e ﬂ p current

f A E lterna u r e e r iew o . .G a tin r nt a m a c la m 77 . V . g c ﬂ p

Ano r i ew of A E . G . a ltern a ti n cu rrent a m e a rc la m 78. the v . g ﬂ p r of onn i f 79 . Di a g a m c ect ons o sa m e Cords a nd ulle i n E xcello la m 80. p y p ecia l clu tc conta cts for am e ca o 81A. Sp h ﬂ rb ns

813 .

2 Dia ram of connecti ons of E xcello la m for alt r n cu rr nt 8 . g p e na ti g e

ketc of ra e- w eel mec ani sm of Briti s o 85 . S h b k h h h Westi ngh u se ﬂam e a rc lamp LI S T OF I LLUS TRA TI ON S xv

ti ons ci Di a grsm of connec sa me . “ " Orifla mme flam e a rc la mp of the 01i ver Co. The ca rbon maga si ne oi the same “ " Another view of the Ori fla mme la mp of Dia gra m of connecti ons aw e .

G f h cla w- cl utc food t e lam . o t e Diﬁerenti a l enclosed p (A.E . ) h yp Ring clutc h

wi th spring sti rrup

“ r s N ew m odel Ja ndu s enclosed a c lamp of Mes rs. Drake

ci osedM p of the seri es type for a lterna ti ng current

the America n G.E .O.

' connecti ons of Bri ti sh Thomson - Houston Compa ny s multiple la mp for contin uous curren ts

he i i or la m i n Fi 105 T choke co l p g. The electro magnet core for sa me Seri es m ulti ple enc losed a rc la mp of the di ﬂerenti al food type for

r t of h eri ca n G E . 0 continuous cu ren t e Am . .

for a lt a n current Di tto, ern ti g A i enclosed wi t the two a rcs in seri es of the Am rica n G E 1 tw n h e . .C. 14

r va ri ous la mps

th a nd wi thout a globe

n m A O n

D C a m e a rc ith vertica l - a . . ﬂ w co a xi al ca rbons , with a nd without a globe

wi th verti - Pola r cu rves c f a n A. C. ﬂa me a rc ca l oo a xi a l ca rbons wi th a nd Wi thou t a globe

Pola r curves of a D .C. a me a rc wit inclined ca r ons wi t d ﬂ h b , h a n

A.O. a me a rc wi t incli ned ca r ons wi t ﬂ h b , h a nd

C enclosed a rc wit inner no ou t r , h and e wi th opa l inner a nd ala ba ster

clea r inner globe xvi LI S T OF I LLUS TRA TI ONS

Pa .

ma ll o a lescent 182. enclosed a rc wit s Pola r curve of a sma ll D .C. , h p ova l globe ’ Roussea u s pola r di a gra m Tria ngle for determini ng the ground illumina ti on

o o s f a n O en D C. a rc la m P la r a nd illumina ti n curve o p . p D a m e a rc la m 186 . a .C. ﬂ p 18 ni t i ll i a ti e 7 . U um n on curv 1 C ti i o r u c r wi t en r s 88 . a lcula on of illumi na t n fo a p bli squa e h op a c f n i n or ua re wi t o en a rea 189 . o a teri sq h p wit i n erted o en 140. h v p a rea 15 4

14 1 e tor a m f r ri w r i of a lterna ti current a re la m s 15 9 . V c di a gr o se es o k ng ng p o o of t e la m s i n ulti le 160 142. E xternal c nnecti ns seri es yp p m p . u nt i n ti le d ri 148 . sh type la mp mul p a n se es m ul tiple A possible combina ti on of lamps M p resista nces showing a djusta ble meta l colla r A sta rting resista nce Di a gra m of connections of sa m e ior three la mps In seri es Di tto wi t a dditiona l resi sta nce , h Dia gra m of connecti ons of sta rti ng resi sta nce with six la mps I n seri es A a ti a rt re i a n or l utom c st ing s st ce f a re a mp . Di a gra m of connections of sa me for three la mm Arc la mp choking coil E G c la m o A. . . a r p tra nsf rmer Di a gra m of connec ti ons of sa me connected a s a u to tra nsform er or n coil for n C la m eco omy o e A. . p tto for two A C la m s i ri es Di , . . p n se

Di t o for two A.C. la m s I n a ra llel t , p p

Direct la mps wi th a u toma ti c cut- ou t a nd substituti onal resi sta n ces

Di a gra m of connections of diﬁerenti a l la mp wi th a utoma ti c cu t- out a nd substi tu ti ona l resi sta n ce m e tin oil to u se wit motor la m Co p nsa g c h A. C. p Cur es s owin a ri a ti on of current lam ressure consum ti on v h g v , p p , p

- of wa tts ower fa ctor etc . for six A. C. la m s i n series ein , p , p , b g extingui shed consecu tively a nd repla ced by compen sa ting c oi ls

Mi ni m um a utoma tic cut- ou t

Current indi ca tor LIST O F PLATES

10 7 5 08 I“ F — wi nc osed a rc I . ronti spi eoa Exa mple of decora ti ve lighting th e l l m s in e c h lo h ster “ne a p th School sc no gy, Ma nc e w — Figa l and 2. Di rect cu resnt open a rcs 2 2 — Fig. L Alterna ting cu rrent a re 8

- . 5 D Fig . irect current ﬂa me a re burning norma lly 8 F — r h d i t ol ig. 6 . Di sct cu rrent ﬂa me arc od short lengt a n n a c

- Direct c urrent ﬂa me a rc wi th diﬂerent i nc lina " tions ol the ca rbons up to a n a ngle OI QO

6 t - r with i M 9 (x o n) . Alterna ting current fla me a c d flerent " i ncl ina ti ons of the ca rbons up to a n a ngle oi w so “ ” F 5 - Re la i e c l ig. 7 . gu t ng m cha ni sm oi the E xcellO fla me a r a mp 88

B ottoms; 88 a nd as

- Fi . 84 . Di tto a not er i ew g , h v

- - Fi . 86 . Ditto s owi striki le er a nd low down t g , h ng ng v b m agne

— of a tis T o on - Hou F 9 7. Lower lam mec sm Bri ms ig. p ha ni h h ston ’ Comm y s Drop Frame enclosed a rc lamp

- - F I m ri sus ensi on (or B .T. H. l m ig. p Sp ng p a ps . “ Fi — - H r Fr me wi t r i r K. g . 98 . B.T. . D op a M p h oute a nd nne globes together wi th reﬂector — F . 1 I si e a nd ou er snctosin lo es ig 02. nner, ngl , t g g b — B - l l la m r con uous currents Fig. 1m. .T. H. mu tip e p fo tin

— - E i l . e ti a l lam o i the salt contai n Fig. I la ma diﬂer n p sh w ng ed stu dyi ng a nd su bstitutiona l resista nces

— - l l B H tor i ndi rect l wi concen tri Pig. 7 . .T. . la mp ighting th c light di ﬂussr — i . 118. Di tto s owin acti on of di ffuser Fg , h g

— - Fo r hot wi re a rc la m s ow n cons ru ti on Fig. l2l . ste p, h i g t c

' ‘ I nn rted a m whting in ths Pattern- wea vi ng room l extile De l olo Ma c ester rtm nt Sc hoo ol Techn n . pa e , gy, h

E LE CTRI C A RC LAMPS

horizontal, and the discharge , inﬂuenced by an upward current of hot air together with its tendency to enlarge due to

of f m o f the expansion the vapour, causes it to take the or

a rch 1820 n eff of m an ; and in , in describi g the ect a agnet on

m ri ﬂ — a c r ame r . the discha ge, he deﬁnitely na ed the elect c the

W of cc - ith the advent vertical axial carbons, although the

- m of are i discharge is no longer arch shaped, the na e st ll

Ow ing to the intense heat, charcoal burns away very

i r m m 184 3 rapidly, and a cons de able i prove ent was made in by

of f h for the use carbon rom gas retorts, w ich lasts a longer period, though it may be pointed out that charcoal gives a

m ff m . 1 m e 8 7 . larg r and ore di used ﬂa e In 7 , Sie ens Bros intro “ duced the cored carbon, in which the carbon is provided with

of m f r a central core carbon uch so te than the rod. Modern arc lamp carbons (excepting ao- called chemical or treated

O carbons) are generally made by mixing retort carbon With soot

- f m and coal tar to or a thick paste, which is afters forced

u n s thro gh dies under pressure, the resulti g rod being baked to m f a high te perature . The so ter carbons are rich in soot, whilst

d m r n the har er ones contain ore reto t carbo . A needle, placed of in the centre the die, leaves a central spa ce in the carbon rod for the core consisting of a mixture of carbon and sodium or potassium silicate which is squirted through ; the cored carbon f m being a terwards heated to dry the ixture .

As the distance between the carbon tips in either the horizontal or verti cal position is increased by actual burning w or m i a ay, by hand anipulation, the res stan0e of the arc m beco es greater, and with a given constant P.D. across the c f arbons the current alls until a point is reached when the a rc will fail (unless the carbons are brought nearer to one another

Th are again) . e is thus broken and the current can no longer h a pass throug the c rbon vapour that ﬁlls the space between the brou tips , until the carbons are ght i nto conta ct once more and

E LE CTRI C ARC LAMPS T

also wi th an n of arc very short arc, but ; y le gth (open) , provided f The s m that the current is su ﬁciently increased . hi sing see s to be due to the crater extending and bw oming too large to occupy The the positive carbon tip. extension is up its side and

wh n r exuemn onl and tha n e the c ater, occupying the y y protected from the direct inﬂuence of air by the surrounding

The large consumption of energy at the crater produces i W l A 1881 a high temperature there, wh ch Sir il iam bney in

" ° 5 u i 900 3 00 C. Rossett 3 C about , tho gh estimated it at . t tem m ture The nega ive carbon tip has a lower p , probably ° 3 000 C. The

i f m r and very rap dly ro the c ater the negative hot spot. For a parti cula r quality of carbon the brightness or intri nsic tuillia ncy i c of er of h . r ( . amount light p unit area) the c ater will t ere?

consta n irres e ti v of u r n fore also be t p c e the c r e ts used. A

l of r e m ra ure b greater supp y ene gy do s not raise the te pe t , ut aim l increases the area or de th of the cra ter M p y p , and M morea se r s of i m An in the p e sure the surround ng edium would, on the other ha nd ca use a rise in the temperature of vapori za i and u a n t on, would also res lt in incre si g the minimum RD.

“ “ Mm A rton The Electric Arc y , , p. 308 : The sudden diminution of

P.D tha t a ccom anieo the hi sin th o . p s g of e pen arc is due to the oxygen in the

i - sir getting d rectly at th crater and combining with the ca rbon at its THE E LE CTRI C ARC

have a lower intrinsic brightness than graphitic ones.

Mrs. Ayrton suggests that the carbon vapour leaving the crater for a small distance is practically unaltered in tempera i n n ture and inv sible, but beyond this distance, owi g to cooli g of of the surrounding air, it condenses into a mist ﬁnely i of i m of divided part cles carbon. Th s ist is the portion the a u t re which is violet . The s rrounding air not only cools his of f vapour, but unites with a certain thickness it, orming an envelope of burning gases around the invisible carbon vapour

and a s of . the mist, as well part the carbons themselves It is w the la tter porti on of the a rc whi ch burns i th a greenish ﬂa ms. The current passes mainly through the carbon vapo ur and

c of the ﬁnely divided carbon mist , sin e the speciﬁc resistance

v f the gaseous en elope is very high . The speciﬁc resistance o the va our is of mist and p higher than that the , owing to the

t c PD of i . of . thin layer a large part the energy, the . , is absorbed

crater.

a The arc when burning between pure solid c rbons, with

if E F of 9 r direct current, acts as a counter M . 3 volts we e set

a nd P.D. h 4 up , is unsteady with a less t an 0 volts. It is a f f P almost greed that this all o D . is due to the red sta nce

of the aboveo men i n d r t o e thin layer. The a e voltage 6

1 A PD f m ( ) . . to overcome the fall ro the positive carbonto the are

2 A P. D for ( ) . the arc proper ; and A PD 3 . f of E D. ( ) to overcome the all (probably. a true E M F f . the back ) rom the arc to negative carbon. The a pproximate formula for c is

b ’ e : a + 6 E LE C TRI C ARC LAMPS

' a P .D c where . at the positive arbon, ' c M E . F n ar true back . . at the egative c bon, 1 n of I m b le gth arc, current in a ps ., a consta nt .

' ' - M F of a c a = ao E . ar s The called back . . the c is +

c = a +

m f m Mrs. A rton A ore general or ula given by y , including f ’ the inﬂuence of the current on the sum o c and the inﬂuence ' f o a 18 of the length o ar on ,

a b c d are a a o where , , , and const nts depending on the c rb ns

uri PD C ng the carbons reduces the total . which reduction is of m due, no doubt, to the presence the ore conducting vapour . Carbons treated with chemicals will have a lower value for a of owing to this increased conductivity the arc, the salts

a M being e sily led into the arc . oreover, the other constants

— r will also be altered and, in gene al, will depend on the

h m m are m pa rticular c e ical ﬂa e e ployed . For a consta nt arc length

I a 6 f f Showing that as incre ses, alls, ollowing a hyperbolic THE E LE CTRI C ARC

cl I constant constant . A' B' l .

for PD c of l which gives a linear law the total . in terms . The positive carbon is consumed about twice as fast as the

m 1 to 2 negative, and the consu ption amounts to inches per hour,

of r the aw a rding to the diameter and hardness the ca bons . In

i cured f arc lamp the pos tive is usually with a so ter carbon , and eff t of this has the ec steadying the arc, which otherwise tends ﬁ to wander and gives an undesirable ﬂuctuating lighting e ect.

The l m of m i m e negative is, as a ru e, solid and ade a s aller d a et r in order to obstruct as little of the light as possible and to — The Enclosed Ara I n 184 6 Sta ite discovered that the ca rbons enclosed in a glass vessel to which the access of fresh air is checked burned away at a less rate than in open air. It was not until 1880 that various constructions of enclosed arc

a m t m l ps were at e pted, but with poor results, as the attempts PD w 40 . . m ere made with volts , which required such a s all distance between the carbon tips that very little light was

. f f the n given out In act, it has been ound that negative carbo

m m for builds up a ushroo tip voltages below 65 . But 1893 of m J was the year a marked i provement, when andus burned 80 his enclosed arc with nearly volts . The longer are nocessi

‘ mting this high voltage causes a distinct diﬂerence in the light

cepted much by the negative carbon. Though its distribution is better than that of the open arc it requires more energy for the

of l of same amount light given out . The princip e the enclosed

m l Bein enclosed in a vessel wi h a arc is si p e. g t closely ﬁtting the cap through which the upper carbon enters, ﬁt being as 8 E LE CTRI C ARC LAMPS

l f i the e c ose as proper eed ng permits , oxygen is rapidly burn d up and the resulting heated gases check a further supply of

f ca r n in h resh air. The bo wastes a way a t the rate of of an c

is per hour, hence the lamp requires less attention. There no

e r f d a s i n the o en arc the ti s of both deﬁnit c ater orme p , p

carbons become ﬂat. Since the section of the arc does not cover the area of the carbon tips and the arc seeks the shortest ‘ dista nce between a constant wa nderin of arc results , g the , e n of which, alt ri g the distribution the light, may vary it by 3 0 per cent.

. 3 P Fig ( late II .) represents an enclosed arc with solid n is carbons . The positive carbo tip very slightly concave, whilst are the negative carbon tip is somewhat convex . The has the

m - f rm r of O a re sa e pear sham o as the interio violet zone the pen ,

for m of a re t i not the constant move ent the , hence h s is termed “ ” n ar fr the crater. A cored positive does not preve t the e om of i wandering . Only by the use th n carbons, so that the whole of ca n m m of section the arc covers the tip, the ove ent the arc be prevented ; but the advanta ge of increased time of burning is then lost . The dark band and the greenish shea th are missing i n the

of the tips is therefore accounted for by the absence of the i i i n n green sh ﬂame, wh ch the open arc bur s the sides of the v s carbons and gi es them their pointed hape, the hot ca rbw i O vapou r at the same time shap ng the crater. f the 80volts 3 9 as across the arc, about volts are needed, in the case of the

e for PD . f op n arc, the drop in rom the positive carbon to the

If the ti s of enclosed a rc ca r ons be exa mined closel p b y, they will be

THE E LE CTRI C ARC 9

- . f r PD f the arc About 4 volts o the . . rom arc to the negative — Alterna ting Cu rrent Arc With alternating current there m will evidently be no arked crater on either carbon, and the m O two will burn at about the sa e rate . wing to the current

i turn changing s gn, each carbon in will become the positive, thus the positive crater will change its position at every half r of n C pe iod the curre t. onsequently, the carbon tips will have

m 4 P i f c the sa e shape (Fig. , late And we onsider the

i nsta ta neous f D n o the of P. are values distribution . in the they

of di m the are similar to those the rect current arc, na ely , that

P D of dro a t he su rfa ce of ord er total . . consists a p t the to i n o the cra ter arc, a drop the arc m m , and a drop at ; the

P. D w . drop at the crater being al ays greater than at the

. PD u crater Since this total . . is p lsating in value, there is m of obviously an inter ittent supply energy to the arc, and

m of ul . hence the light ust be a p satory character, which is m f In f t if ore pronounced at the lower requencies . ac , the hand be moved rapidly to and fro i n the light of the arc with low

r of i for alte nations, we shall see a number mages, one each

i u alternat on. Thus the arc is extinguished once in each p lsa of tion, and evidently the duration extinction is increased with

n f re- It has bee ound that the P.D. required to light the arc a of incre ses rapidly with the longer duration extinction. A

high E MF impressed on the are in series with a self- induction

f are (choking coil) would there ore give stability to the , as it E MF t would ensure a high . when the curren vanishes . i of m The alternate arc causes a d stortion the wave for . The rs Ju 1880 m ﬁrst pe on to note it was o bert, in , since which ti e m me i any experi nters have invest gated this reaction, and the reader- is referred to Experiments on Alternate Current Arcs by ‘ of Oscillo ra D d M r for aid g p by ud ell and a chant, a very

Jou rna l I nst E . E2 Par s 138 and 189 vol. xx iii . . , t , v t o E LE CTRI C ARC LAMPS

f n i ff of a etc . reque cy, and d erent makes c rbons , , on the arc The results of their experiments show that with a high voltage and

c sma ll f - he c solid arbons and sel induction in t ircuit, the arc

P.D. ﬂa - f a wave is t topped with a high ront pe k, the current remaining low for a consi derable part of the period ; the power

PD w m u induction makes the . . ave ore rectang lar, the current

ai m for no longer rem ns s all any sensible period, the power

c m l n peak, espe ially pro inent in o g arcs , is due to the high resistance of the gaseous column after each extin ction of the

f i . the power actor is nearly un ty, and the arc is very stable In c are i pra tice, cored carbons used in the alternat ng arc lamp ;

of P.D. for tral position the arc and a lower the arc . Two solid 48 carbons would require about volts, whereas two cored

for nl t 2 carbons the same current o y need abou 8 volts . One cured and the other solid would similarly require an PD f 3 o 5 . intermediate . . volts An objection to the alternating current arc is the humming

r r noise produced by it . This is pa tly due to the vib ations in the lamp mechanism and partly to the pulsati ons impressed m

f m b in the arc. The or er vi rations are reduced by correct

u of m i design and constr ction the la p, and the latter by us ng a

' or tw o volts with cored ca rbons ma ke a large diﬂerence te the a rc as to whether it is too or too short Wherea s i h long . , w t

three times as much. THE E LE CTRI C ARC n

and has only a small eﬁ ct on the current wave ;

the gaseous column. The change produced by

MS of P. D. for am on the R . value the total the and current amounted to no less than 65 per cored carbon used in Duddell and Mar Enclosing the are reduces the power n s but the stabili ty of the arc i crw se .

of burning will be increased, but not as of current enclosed arc. The period burning urrent open a rc is a lso less tha n tha t of the n i of open arc , owi g to the nrushes oxygen b e a re caused by the rapid expansion and

gaseous column. i n the light is somewhat reduced in the

(see p. or Fl m — a e Arc . Bremer in 1898 discovered with a metallic salt like he was able to ' obtai n a Whilst the chief source

not so . A arbon arc was found to have a crater only

the area of 10- ampere ordi nary carbon arc brightness less even than that of the soft of the 275 0hemispherical

- di e power is emitted by the positive crater. shows the more modern method of burning

“ - me La m s Jou rna l I nst. E . 5 1 Long ﬂa Arc p , ,

also 1905 vol. xx i . 67 a rticle Dr. , v , p. , by 12 E LE CTRI C ARC LAMPS

i the flame arc by inclined carbons. This gives a h gh light emcienc r ra s y, as the c ater and the negative carbon y are not m n of l f m m intercepted . The ajor portio the ight comes ro the fla e , and is doubtless due to the small particles being rendered highly n of m incandesce t. The intrinsic brightness the fla e is about one i of of o . 6 P th rd that the p sitive crater (Fig , late but the area

of e the ﬂame visible is m any times greater than the area the crat r, which therefore accounts for the large amount of light given out

The m f by it. a ount o light given out is practically proportionate “ of w a n to the quantity salt used . But ith a very heavy s lti g

fo m of ob ec a slag r s around the tip the carbon, which is very j

' ti onable. m n lowm Hence , as a co promise, a carbo with a per of m m centage salt beco es necessary . The che ical carbons now

’ m of of made are co posite. Blondel s carbons consist an outer zone c m of m arbon, to give echanical strength, then a zone carbon ixed m m n e with a etallic salt, such as calciu ﬂuoride, the an inn r softer core of the same mixture intended to hold the crater. The essential point seems to be the use of ﬂuorine com n t m r pounds, and only the i ner part (about one hird) is ine al ” m m . in d. So e makers i pregnate only their positive carbons — The colour of the arc depends on the base used barium gives

ﬂm e m i u . a white , strontiu p nk, and calci m a golden yellow

The calcium ﬂame is the most efﬁcient.

- of The salts are non conductive, and make the carbon much e m et high r resistance ; oreover, to g anything like a long u m m f b rning la p, the carbon ust be at least two eet long, and, m m of i of with the e ploy ent th n carbons, the question their m h i n resistance is very i portant . T in carbons are used the

of sta nce of inclined type, because the variation the ohmic rw the ﬂame when on the two outside edges as against the two inside edges of carbons of large diameter would not make it possible to burn the lamp with a fairly constant terminal

d l f which, the wan ering would cause a variation in the co our o THE E LE CTRI C ARC 13

e the the light, depending on wheth r arc was on the hard carbon — — shell in which case it would be white or whether it was M al i ntroduw d on the impregnated zone. et lic insertions are into the carbon electrodes for are lamps for the purpose of m f di inishing the resistance o the electrodes.

f of has To increase the li e the electrodes, a departure been m ade by usi ng as a large constituent of the electrode a refractory

i r of a f conduct ng mate ial (instead c rbon) . This takes the orm of o u r h a metallic xide, and to it is added a ﬂ o ide or p osphate or a mixture of a ﬂuoride and oxide of calcium or thorium or ‘ ” i The stront um, etc. magnetite lamp used in the States has

r and of m i n b illiancy, closely resembles that a candle ﬂa e, hav g

- a bright and non luminous zone. The bright zone is contiguous the to negative electrode which is made the upper electrode . A good air ci rculation is necessary in the lamp to remove the f m h u es , ot erwise the latter deposit on the globe as a solid. It 10° gives a maximum light intensity at below the horizontal, f f for and there ore avourable street lighting . It is supposed to

' i ve a useful life of 15 0 200 hours burni n and g to g, takes CHAPTER II

THE E LECTRICAL PRIN CI PLES O F ARC LAMPS

I . INTRODUCTION

THE utilization in practice of the light produced by an arc between two carbons requi res a mechanism which strikes the of arc, and automatically regulates the position the carbons , f of l eeding as they burn away during the continuance the ight, m a and aintaining a constant distance between the c rbon ends .

B m m r a r roadly speaking, this echanis , gene ally known as the e

(a ) An electrical portion which regulates the potential difference across the arc ; (b) A mechanical part to support the carbons and to regulate the feed ; and c m l ( ) The la p case, which is provided with a g ass globe in order to protect the regula ting mechanism against dust a nd m a re f at ospheric inﬂuences and to shield the rom draught, etc .

II. DIFFERENCES OF CONSTRUCTION

The differences in the construction of modern arc lamps

— l l i a l . a rdi o A. Pu re y E ect r c ( ) Acco ng t the internal con nections ff , into series, shunt and di erential arc lamps .

6 i of re re ( ) Accord ng to the kind cur nt, di ct or alternating. 14

16 E LE CTRI C ARC LAMPS

- e cc . 7 are situat d either above one another ( axial, Figs and

r or inclined (collate al, Fig .

Fm. 9.

(b) Lamps OI as the are changes or maintains its relative 11 position in the glass globe (Figs. and (c) Clutch feed lamps i n whi ch the clutch is attached directly to the

l r Fi carbon or carbon ho de ( g.

- f m brake wheel eed la ps (Fig. and lamps in which a c lockwork mecha

u rr holder or s pport and the a est, in order to secure a more exact and frequent feed

Fi cases the su er ( g. In all these p

FIG. 10 1. P N RI CI PLE S OF ARC LAMPS 17 — or pivoted the latter is the more

Fm. 18 .

I II . SERI ES ARC LAMPS

INTERN AL CONNECTIONS

In series are lamps the main current delivered to the

‘ e - m eﬂects a rc serves to xcite the electro agnets (Fig. 17) ,

u the of s. thro gh the latter, separation the carbon ends, i

rt cu i w c l a pa i lar d stance bet een the arbons, the re e se

M al ce] f of the i portion and the eed carbons, as O l 8 E LE CTRI C ARC LAMPS

soon as the cnrrent falls short of the normal

of m rt hand, an arrest the echanical po ion by

l - m n of e ectro agnets , with a conseque t increase

between the carbon points, takes place as soon as m m exceeds the nor al a ount . 18 shows diagrammatically a seri es clutch

Fm. 14 .

arc la m in whi ch : S is a solenoid feed p, ,

o er wi re of c pp , the diameter taken by the lamp ; M is an solenoid when the current

clutch fastened to M ; A is a contact ; 0, and

c and B is a re ula ti n resi sta nce. arbons, g g THE E LE CTRI CAL PRI N CI PLE S OF ARC LAMPS 19

i i n. f w c i curr n takem f m switch ng A ter s it h ng in , the e t ro a

of u E t supply press re volts , passes hrough the solenoid S, the of C C upper carbon Cg, the point contact between ; and a, the to a regulating arc lamp resistance R (usually

Fro. 18.

M p), the latter having a resistance I

to . - equal B ohms . The resulting current I m I (assu ing we are deali ng with direct current and neglecting heat loss in the circuit as well as the usually small loss in the solenoid and the m bone) excites the solenoi d so strongly that it pulls up M the iron core . At the same time the clutch F is pulled up s ri n w on one ide , g ps the upper carbo , and raises it along ith 20 E LE CTRI C ARC LAMPS

M e a ch c . The carbon points are h reby separ ted, an arc is u k , and the circuit is maintained through the carbon vapour pro

u d ced between the carbon points . The arc now introduces an

s f additional re istance in the lamp circuit, in which that part o

m m n the the ain pressure necessary to ai tain arc is consumed . Thus the arc causes a reduction of the current I with

and of PD c increasing arc length with corresponding increase . .

E 6 a cross the arc u l , g ) only excites the so enoid to such an extent that the attraction of the solenoid is i n equili briu m of r with the weight the iron co e and the upper carbon. But the striking of the arc occasions a consumption of the car bons and a correspondingly increased arc length , an increase

PD . in the . . across the arc Hence the current I and the of l f i attraction the solenoid are sti l urther d minished, so that f the iron core and the upper carbon both all . Hereby the

the iron core to fall so far that the clutch F touches the t f f h contac A, a urther eed occurs t rough the release of thi s

. core sinks still m the clu tch arrest When the iron ore, essu mes

r n f r u a ho izo tal position, so that the carbon slips reely th o gh the hole in the clutch and the distance between the carbons is

arrest te- occurs according as the lamp cu rrent exceeds or fa lls m short of the nor al . — Const ancy of La mp Cu rre nt Let IT equal the number of

ampere- turns of the solenoid where T number of tu rns on

Then the attraction of solenoi d K x IT where K

is a cc - eﬂi ci eu t dependent upon the ma gnetic arrange THE E LE CTRI CAL PRI N CI PLE S OF ARC LAMPS 2 1 m en t of the solenoid and the position of the iron core

If P represents the total weight of the portion moved by the

solenoid, a balance is maintained when P K.I T.

i of Since, however, under normal conditions, the posit on the

r a m for r iron co e rel tive to the solenoid re ains, p actical purposes ,

c n K m for m un ha ged, re ains constant this nor al position. Since the number of turns on the solenoid and the weight of the iron of n core and the clutch are co stant, and , moreover, since the consumption of the upper carbon only affects the weight very sli i tl of s g y (this, course, must be so arranged in its de ign) , P

t in m re : t. wi h practical li its, the cur nt I RT constan A l — Dependenc e of rc P. D. u po n S u pp y Pressu re Since i R and the n t f m the res stance curre t I are cons ant, it appears ro

E 8 that the fall of pressure across the are a

can only rema in constan t if the supply pressure E is constant ; otherwise a alters with a variable main pressure by exactly the

a ri l m s me amount as E varies . Se es a ps which burn with a short arc f m h require, there ore, that the ains pressure s ould be as

t s constan as pos ible.

E XTE RNAL CONNECTIONS

ri ca n Without special accesso es , several series type lamps only

be t B . 18 ins alled in parallel , in which case a resistance (Fig ) s If l m mu t be connected with every lamp. two a ps were to be

c B e E the P.Ds. e I , , and ev n remain constant, individual , and ,

' w m ma di ﬂerent if i across the arcs of the t o la ps y be , only the r m mu e u sum be constant. In both lamps there ight be a si ltan o s Md t m , al hough one la p is already burning with too short and 22 E LE CTRI C ARC LAMPS

m of the other with too long an arc. Only by eans auxiliary

O r PD apparatus pe ated by the . . across the arc, which inserts

t l i a a resis ance in para lel with the solenoid, and thereby

ﬂuences m - n of er the the a pere tur s the latt , can series type

w series M lamp be orked in in practice . oreover, with

m ca n alternating current, series type la ps be used in series by by using choking coils with strongly saturate d cores in parallel with the arcs .

IV. SHUNT ARC LAMPS

I NTE RNAL CONNE CTIONS

In these lamps

m ' the series la p, the coil must have a

high resistance, and consequently consist of m of any turns ﬁne wire, so tha t in order to obtain the same number of

m - m a pere turns as in the series la p , only a small exciting current i is necessary ,

for 6 10- m tem s m which, to a pere p , a ounts

3 4 E LE CTRI C ARC LAMPS

of l m t ma tion the so enoid upon the iron ar a ure) , which y be

h r m w replaced by a weig t. s is an escape ent wheel hich, when

' oh a t the lamp is switched , grips a detent or st p , B, at ached to

. D for c the base 9 is the holder the upper arbon, the weight of fﬁ n me r which su ces, whe the escape nt is eleased, to set the e m o b of m wheel g ar in oti n and, y means the echanical con

nection u n the c E (us ally a chai ) , to pull up lower arbon and D holder 9 . H is an air dashpot to weaken the momentary pull

of i r the soleno d when car ying a large current, which usually a w N N m 0 h ppens hen the arc is struck . 1 and 9 are ter inals , 1 C and a are the carbons . As the operation of the solenoid only serves to bring the f in carbons together, the separation o the carbon po ts with a

' n view to striking the arc must be eﬂecwd by the spri g F. Since the spring deﬁnitely comes into action when the lamp is

ff e the f L si tua ted i n its limi ti n switched o , nd since rame is g In of the M om must not position a separation the carbons, touch whm tke la nw is out mmbu t must be separa ted by such a 8 to 10 m as for t of distance ( .) is suitable the s riking the

arc R d a n c l m . is a stea ying resist ce, onnected in the a p of i R the of circuit, such an ohm c value, , that with passage

m m is PD of u the nor al la p current, there a . . across it abo t

3 0 of the P.D u E per cent . arc . Hence the mains press re, ,

PD c m If the must exceed the arc . . by just that a ount. lamp n R is connected to the mai s, the circuit through the resistance m c and shunt coil i s ﬁrst made . The resulting current is u h m n f less than the normal la p current, and he ce the all in s R pressure across the damping re istance is insigniﬁcant. The coi l ends thus have across them a pressure which is very li ttle 5 f m m m less than the main pressure ; is there ore a axi u , and excites the solenoid so powerft that the iron core M is

drawn as far as possible into the solenoid. In this movemen t e r the lever pivoted at A participat s, and b ings the carbons THE E LE CTRI CAL PRI N CI PLE S OF ARC LAMPS 25

e B f r has w tog ther . e o e the iron core reached the lo est point the

m r from if escape ent s slips away the detent B, and , the separa tion of the carbons was previously so great that they do not

m of L f f of touch by the swinging ovement alone, a urther eed the carbons takes place by mea ns of the weight of the upper carbon holder cau sing the train of wheels to revolve until the

. of carbons touch At this moment, since the resistance

r i l . the ca bons is very small, the lamp is pract cal y short

r circuited th ough the steadying resistance, which will absorb

the of m u H t practically whole the ains press re . ence he pressure on the lamp terminals and at the terminals of the

m s MI r solenoid is al o t , and the solenoid S is p actically without

C e of current. onsequ ntly, under the inﬂuence the spring F,

h f m L a nd t e ra e separates the carbons, raises the upper carbon ,

ch . I ops the lower one The current g), produced at the

mom a m n ent the c rbons co e into co tact, heats the carbons and

m the e As in the series la p, pressure betwe n the terminals

of m of c the la p increases with the separation the arbons, and

current until a balance is reached between the attraction of the i h of soleno d , S and t at the spring F. As the carbons burn

f s of e of away , a urther eparation the carbons and an increas the

D w a n of i t of are P. ., together ith increase , or at raction the

i . c soleno d, take place The iron ore is drawn down whilst l r the ever gradually b ings the carbons together, and strains

n il u um a If c of the spri g F unt eq ilibri is obt ined. , on a count the continuous burning away of the carbons and the gradually

PD s l m increasing . . acro s the arc , the so enoid has oved the

iron core and the frame so far that the escapement rs comes of f f qui te clear the detent B , then a urther eed is supplied by

P.D the clockwork. The arc length is hereby diminished, the .

across the arc is reduced, the spring F outweighs the attraction 26 E LE CTRI C ARC LAMPS of r B the solenoid and ar ests the wheel train by the stop , until Th the regular play is resumed. e lamp has reached its normal

P.D. c across the arc , and maintains it constant, independently of m the la p current. — C nsta nc of P. D. a c R o y ros s the Arcs epresenting the .

n r K f r resista ce , and a coe ﬁcient, which is constant fo the normal position of the iron core ; and representing the opposing force of

P for the spring by , which is also constant this position, then the equation is P K i t ,

fu 12 r f since, rther, and is likewise constant, there ore

constant .

n a c r ss t he a rc u n he l Depe dence of P. D. o , po t reg u a ti ng m ec ha ni sm a nd i ncrea se in t empera t u re of t he w i ndi ng of — I n t he solen oid . practice it is only possible to obtain an

m of 6 e 6 m m a approxi ate constancy , sinc ust be so ewhat gre ter

f r for the release of the feed than o the arrest . The value of

ff e e m of this di erence m m , which constitutes a easure the

f of regulation, depends upon the riction the dashpot plunger

of n m and the tension the spri g F, which have to be overco e, n m m and also , with direct curre t, upon the residual agnetis

m m f m a m in the agnetic syste . Apart ro this, is so ewhat less when the lamp is cold (immediately after the striking of a rc m of the ) than when it is war , because the resistance

f n m r the thrns o the sole oid increases with a rising te pe ature.

i of the f re Hence the strength eed cur nt is, in the heated of m n condition the la p, only reached with a correspo d

in l PHD a m 10 m . g y higher arc In l ps taking over a ps , this THE E LE CTRI CAL PRINCIPLE S OF ARC LAMES 27

D . disadvantageous heating ma y produce an increased P.

m 10 of the m if a ounting to per cent. la p pressure, the winding f of of . the solenoid be copper wire It is usual, there ore, to wind it partly with a resistance material which has a smaller

em f P.D. m a t perature coe ﬁcient, whereby this increase in y be m of reduced to about 2 or 3 per cent. Si ilarly, the application

m s o m of F hea t co pen at rs, which di inish the tension the spring m m of when the la p beco es heated, or which alter the position

n e f a . the dete t B , serv s to neutralize this de ect due to he ting Dependenc e of the La m p Cu rrent u pon the S u pply — o ar Pressu re . From the description of the stri king f the e it is evi dent that a steadying resistance is absolutely essential to the

m . not shunt arc la p Were this so, that is , were the supply n pressure equal to the pressure at the lamp terminals, the ,

f t i of f of e be ore the s rik ng the arc, no urther increase pressur at c the terminals of the solenoi d would be possible. The attra tion

of suﬁ f m n the solenoid would not ce to ree the escape e t, since

m fri r m so e ction must be overcome to set the clockwo k in otion . Bu t if the stri king occurred by a slight increase of the main b m pressure, no steady arc could be o tained , because the la p f PD current itsel , with absolutely constant . . across the arc, wou ld vary between zero and an exceedingly high value according as the main pressure equalled or slightly exceeded

P.D i for the . across the arc. The equat on the resulting current

E s Bu t since 8 and R

R w ff E e If for are constant, I varies ith the di erence . ,

m l m o m n w m 1 exa p e, the nor al pressure f the ai s ere ade volt

i e P.D. if of h gh r than the across the arc, and the variation E n m 1 m o ly a ounts to volt, then the nor al current would be 1 i I ; 1 ressure I ; and with 1 11 with volt increased p Ii volt O decrea sed ressure I h the case of a n p i t T at is to say, in 28 E LE CTRI C A RC LAMPS

l of 1 I l increased supp y pressure volt, wou d reach double the

r of 1 re z no mal value, and in the case volt dec ase, would be ero, ti e i n . the arc would be extinguished . Hence, practice, about 25 of per cent . the supply pressure is dissipated in the steadying

n 75 . m I f resistance and the remaini g per cent in the la p . the m r ains pressure varies per cent. above or below the no mal, 2 5 u — 100 10 the c rrent varies x . , 25 per cent above or below m l which is per issib e in practice.

a P K it 6 In the equ tion , and the resulting equation g m f f the la p current I is not included , rom which it ollows that I has no inﬂuence upon the regulation ; and from the equation

E 8 I g we see that the strength of current with which shunt m arc la ps ought to burn depends, with a given supply pressure m entirel and with a suitable pressure across the la p terminals, y

m n advantage which these la ps possess, because by alteri g the

e n in the r a ext rnal resistance, and without any cha ge egul ting m of mechanis , the strength the current, and hence the intensity

of the m ma light, may be varied within such li its as y appear

of t d. proper, and provided that carbons suitable diame er are use The value of the resistance (including the resistance of the leads in a single burning lamp) ma y be found from the equation

E - c R I

E XTERNAL CONNECTIONS OF SHUNT ARC LAMPS

° r — —i c 6 B F om the equation I R since l , g, and are

f d h m t a constant a ter a justment, we see t at two or ore shunt la up E of can be connected in series . ach the lamps connected in series

m the u ma receives, however uch s pply pressure y vary, an equal THE ELECTRICAL PRINCIPLES OF ARC LAMPS 29

m of a the PDs e a ount energy, bec use . . a and g, with a given n of desig , depend only upon the tension or regulation the spring

of F each lamp, which may be made

series in a circuit it sumces to have

e of the r sistance the leads) , which must absorb the difference between the su m of the lamp pressures and the supply

r ff r n p essure (Fig. The latter di e e ce m m 2 ust also a ount to at least 5 per cent .

then E

c 6 c of where l , g, g, denote the pressures the individual m la ps connected in series .

S V . DIFFE RENTIAL ARC LAMP INTERNAL CONNE CTIONS

The diﬁerentia l arc lamp uni tes in its electrical mechanism of n the current and pressure regulation the arc. Its i ternal Fi 22 m n of ri and connections ( g. ) are a co binatio the se es

m ne connected in series wi th the arc tends to form the ag t ,

rd with the arc , tends to shorten the arc length. Acco ing 30 ELECTRIC ARC LAMPS

as the attraction of the series electro- magnet or that of the

- r a shunt electro magnet predominates, an inc ease or decre se of the arc length occurs until the inﬂuence of the two

m i ri m agnets produces equ lib u . With increased length of a re PD are 8 n the . . across the i creases, and with it, as in the shunt

Fro. 22.

m of ma c . arc la p, the pull the shunt gnet in reases

u m E n of time, pres pposing a constant ain pressure , the stre gth R 6 r current I the se ies I;

u E a n PD a cross the a rc ence between the ma i n press re d the . .

3 2 ELE CTRIC ARC LAMPS

i s h etc to portion , . the iron cores, olders, , are supposed

of are immMeria l the dif For the stri king the it is , in ferentisl f arc lamp, whether or not the carbons touch be ore the m If la p is connected into circuit. they do not touch, only l ll m i the shunt so enoid S wi ﬁrst carry the s all current , so that M as the iron core g is drawn downwards , and, in the shunt arc

m a i s. a s la p, will bring the c rbons together, rele es the arrest l m until the carbons touch. The moment they touch, the a p

E of t ri e devoid current, whils the resulting se s current I E

(R steadying resistance) is considerably greater tha n when

the lamp burns normally. Hence the decreased attraction of shunt coil is opposed by the increased attracti on of the series C n u l M the coil . o seq ent y, the iron core 1 is raised by coil S, and swings the lever so that the upper carbon holder is raised

ra sepa ted and the arc is struck . With the stri king of the

B 6

of , I . m the the arc) so that now I2 At the same ti e

s t P hun coil S, receives the current corresponding to the .D .

throu h the stri ki n of n the across the arc, so that g g the arc, o

u of r one hand. the c rrent I, and hence the attraction the se i es

e f m L i the lev r ra e in its ﬁnal posit on is swung to right, so B m that the detent grips the escape ent wheel 7 , ﬁrmly .

r arc P As the carbons bu n away, the length and the .D . n across the arc increase, whilst the curre t I decreases. The THE ELECTRI CAL PRINCIPLES OF ARC LAMPS 3 3 a slow downward movement of the iron core and a motion of f f the lever rame towards the le t ensue . The carbons are

il of a e uili hereby brought together unt , with a given value , q b rium if fa r is again reached . Finally, the lever is turned so

’ r f of e n that the scape wheel s is quite ree the det nt B, the , m f f as in the shunt arc la p, a urther eed is provided by the

l a clockwork , whi st necessarily decreases and I increases .

e er of H nce, owing to the great attraction the series solenoid, the lever frame is again turned towards the right and the

l r il m m whee t ain checked unt the nor al play is resu ed . I and e have then reached the normal values determined by the construction and regulation of the lamp and the supply

i t f m - of X , as be ore, as the a pere turns the two solenoids , and 1 a nd K coeﬁi ci ents for , the respectively, which are constant the n ma n i m or l positio (see p . Then equ libriu is reached w ith IT R I it Kg ; assuming that the mechanical portion is b c of t alan ed, so that, with the exception the solenoids , here is n othing else to inﬂuence it.

of ma Since resistance shunt winding) , then we y substitute for the above equation

I . T K t K . l ; o . 3

T. K1 . r f. ' t . Kg I

PD m 3 ' ' a the The ratio , which indicates the I lamp current

a a rent resista nce of the arc remai ns consta nt beca use all pp , , the terms on the left side of the above equation possess ﬁxed

d a u a ro n si stm m lam p i a rayrdc tc by cm tm t . 34 ELECTRIC ARC LAMPS

h Dependenc e of the La m p Cu rrent a nd t e P. D. a c ros s — the Arc u pon the Pressu re of the Ma ina As a result of the constancy of the tota l resistance (arc resistance steadying

of t u with the pressure the mains (assuming direc c rrent) .

8 of if 6 Further, the value I remains constant only changes

awp cmied i n thc p rodw tion of thc a ro w rics by m a s much

W w he m ria tion ar csnt o thc rc c o tha . t . m w ma i ns m p f p f , But since the intensity of the light i s proportional to this

r for of m ene gy small variations the nor al current, it follows

must not vary beyond certa in limi ts if a stea dy light is to

EXTERNAL CON N ECTIONS OF THE DI FFE RE NTIAL ARC LAMP

f lamp with constant arc resistance, it ollows that the external

resistance of the circuit has theoretically no inﬂuence upon the

of variation of the intensity light. It may therefore be omiM d , ti e e . the external resistance is only nec ssary to the stri king of

are i i n the as a start ng resistance, order that the curren t may m of not be too great at the mo ent striking . In practice ,

with a large external resistance are of less importance than m c with a s all resistance, be ause however accurately the m ma u i mechanis y be constr cted, st ll some inertia and i n exactn ess occur in the ﬁtting of the regulating solenoids due , m f on to residual agnetism and ricti , and, in consequence, there m i ma y be some s all var ation in the ratio Also the adjustment described above requires some change in this THE ELECTRICAL PRI N CI PLES OF ARC LAMPS 3 5 r t o uri e mi f of u a i d ng the int r ttent eed . This change is, co rse , so slight that the eye does not note the consequent light

ri ur ul of di ff r arc va ation. F ther, the reg ation the e ential lam p with a constant arc resistance renders the possibili ty

of n m e m s s e n e e m s a worki g two or or la p in eri s . Si c u t v ry

P r s m ro o i e the s .Ds. c ss p p rt onat ly with I, variou a ro the a c ust

r u f m w t l r ssu Hen va y ni or ly i h a ﬂuctuating supp y p e re . ce,

w us m e s r m s m ith one adj t ent, the light int n ity e ain the sa e in a ll the lamps . CHAPTER III

CON STRUCTION O F ELECTRI C ARC LAMPS

l . LAMPS WITH OP N A S - E RC , AND CD AXIAL VERTICAL CARBONS

DE AI LS A . T

I N m m these la ps , which are now always ade with a ﬁxed f i arc position, the ollowing constructive deta ls have to be

1 The Ba se Pla te —Ou u fac of . . the upper s r e the base plate is l erected the regu ating mechanism , and on the under surface f i m attached the hollow rame tubes, on wh ch or through which

c n l e s slide the rods ca rrying the arbo ho d r . The diameter of

m e d i u m c u r r e n t strength (6 to 12 m a ps .) is about 6 ins ;

2. The E l ec tr o

ourrent lamps thu s

m f of rse ﬁxw frequently ade in the orm a ho shoe, with

r m r re f the massive iron co es, and a ovable a matu , which aces

are n f m wit poles (Fig. They also constructed in sole oid or h CONSTRUCTION OF E LE CTRIC ARC LAMPS 37

and armature must be well - annealed soft iron retaining very t l lit e residual magnetism, since the latter has an injurious

‘ eﬂect of m upon the regulation the la p. The pivot upon which

24 e the armature (Fig . ) works is placed as n ar as possible to

m i m a nd . the base plate, in such a anner that an aginary ne drawn through this pivot and the centre of the pla ° ° makes an angle of 3 0 to 45 with the plane which

w as alternating current, in which the n of iron tubes slotted le gthwise (Fig.

Fm. 26. Pro. 27 .

or made out at (05 mm. iron sheet stampings v o e ri eted t gether (Figs. 26 and In order to r duce eddy ff currents and their consequent heating e ect, the iron sheets are electrically insulated by the insertion of thin paper between m them . The bobbins which w ry the windings are usually ade of r a nd s i b ass, in that ca e are insulated with mica, paper, l nen ,

of or other insulation, and covered with a varnish capable with

a n standing temperature. For alternating current

of f eddy currents . The internal diameter o the bobbin is 3 3 ELECTRIC ARC LAMPS

15 2 ems 8 1 to , the available winding space about x cm . The bobbin windi ng must be su ch that the watts lost per m 2 coil in a la p burning normally do not exceed about 5 . The m . 25 26 2 ovable iron cores , shown in Figs , , and 7, are m t f ade at least as long as the coil i sel , and sink into it to about

of of the to ii their total length in the normal position lamp . With alternating current these solenoids have the dis advantage that the self- induction of the winding increases the deeper the iron core penetrates into the solenoi d ; hence the attraction exercised upon the iron core does not increase to m the sa e extent, with an increased pressure the coil as

. 28 in the case with direct current Fig. shows a type of

Fro. 28 .

electro - magnet for alternating current (employed in lamps of w the Union Electric Co. ) in which the iron cores as ell

n m v as the exciti g coils are stationary . The o able portion

o e ti e. k n m n which perat s the lever, the stri i g echanism, co sists

m m i of m e of alu iniu r ngs a co paratively larg transverse section , which to a certain extent form the short - circuited seconda ry windi ng of a transformer of considerable leakage on account of the juxtaposition of the primary winding and the short n circuited secondary . In these ri gs large currents are induced which weaken the ma gnetization of the portions of the iron

r i m co es under the r inﬂuence, increase the agnetic leakage

40 ELECTRIC ARC LAMPS

another, a torque is exerted between the ﬁxed copper plates

m the of and the ovable disc, so that uncovered portion the

s . the disc as hown in Fig 29 revolves towards copper plates. Fi 3 0 In g. the poles are not covered, but beneath each is ﬁxed

of n a solid piece iron, B , which has eddy currents i duced in it

e f by some of the lines of force which leak into it . The lin s o force produced by these eddy currents combine with the leakage l l i Z w of ines and produce a resu t ng ﬁeld, g, hich is out phase

w m a l 2 . m ith the in ﬁe d, 1 The agnetic conditions are thus the

m 2- m sa e as exist in a phase otor, and consequently the disc has

ma etic relucta nce a nd hence the . n a torque exerted on it g ,

sel - induction is i n both a rra n ements o the ma net f , g f g s

o the osi tion o the mova ble di sc f p f .

3 The Lever Fra me eta — f s f . , The rame invariably con ists o f to n n brass plates astened gether, betwee which is a chai pulley and a wheel train which is so gea red that the feed per tooth

of 005 01 mm a u the escapement is about to . The ch in p lley

is connected with the gear - wheels by the interposition of a

- - ratchet wheel and a pawl. The ratchet wheel is ﬁxed to the f chain pulley, whilst the pawl and its spring are astened to one

- of . the gear wheels Hence, although the chain pulley serves to f f m eed the carbons, it can be reely oved in the reverse direction CONSTRUCTION OF E LE CTRIC ARC LAMPS 4 !

with the lever fra me is the movable part electro- magnet

(viz . the iron plunger or armature), as well

. Fi 3 1 the dashpot g. shows the lever frame

drive are made of hmdened bronze , so

Onthe axle of the es c a pement wheel i s ﬁxed a f a r centri ug l b ake, the m ovable porti ons of side plate when the r otation is too rapid. vanes are m d mm of the

f of m ff t brake. The regulation the la p is not a ec ed by

so they need not be considered in detail, but they am of importance if for any reason there is too great a distance

f e between the carbons be ore switching in ( g. when carbons

e n for m short r than the correct le gth the la p are inserted), as the of wheels revolves quickly owing to the weight of the upper holder or to a downward pull on the upper carbon by

1 of n operator. The sudden arrest the wheel trai when the

m of touch mi ght otherwise bend or da age one the parts.

i construction of the wheel mechanism must be very exact if it is to run smoothly for years without repair ; and it 42 ELECTRIC ARC LAMPS

- su mcient the w gear wheels and to leave clearance between heels, i s nce the collection of dust is unavoidable and m ay increase the friction so muc h that the weight of the upper carbon support ma f m y no longer su ﬁce to set the wheels in otion . The axles m f d ust be care ully polished and ma e as light as possible . The

o r s pivots sh uld be lub icated sparingly. For this purpo e it is desirable to use an oil which dew not harden or oxidize in

Fro. 3 2.

the greatly varying temperatures to which the mechani sm of an

m On of m arc la p is subject . account these great te perature

ri a u h ex a n va tions, the pivots must be s ch t at a contraction or p

sion does not produce a jambing of the axles .

3 2 m w m u ’ Fig. shows a wheel mechanis ith an alu ini m du c f A G n n m or E u . an . alter ati g c rrent motor arc la p Escapement CONSTRUCTION OF ELECTRIC ARC LAMPS 4 3

by a pull upon the chain - wheel and the arc is not struck by m of n m m n f w the eans a swingi g lever ove e t , but they ollo as

r esult of the torque on the disc in either direction . The move ment of the disc is transmitted to the chain pulley by a trai n of m wheels . Hence in si plicity and reliability this construction is superi or to the previous one ; especially is the deposit of dust

on of a the wheels less inﬂuence, bec use the drive is direct upon n f the quickly (relatively to the chain pulley) rotati g sha t, and because the power of the drive i ncrea ses wi th a n i ncrea sed

ine ua lit o ctri cal m q y f the ele condi ti ons. It is i portant in motor lamps to bring the magnetic pull in unison with the inerti a of

n d of m the rotati g isc and the train wheels , so that an inad issible oscillation or swinging movement of the disc ma y not occur w r ith a va y ing main pressure. — 4 . The Det ent . rs m of The detent usually ade hardened steel , a d w n e Fi . is scre ed to a lever, and adjustabl ( g The lever

u he is us ally hinged to a pillar mounted in t base plate, and is connected with a weak spring or a weight in order that it ma y

m of have a steady otion. The purpose the hinge is to render a striking of the are still possible even if the edge of an escape m t t of ent ooth comes into con act with the edge the detent, since in that case the detent participates in the swinging movemen t

of the f lever rame. It ma y be mentioned here that the escape m as ent or brake need not have teeth , and the arrest shown in

of l m m detent. In the latter case the regulation the a p is so e m ti mes even more exact than in the la ps above described . The

e u friction brake, howev r, has the disadvantage that it is inﬂ enced

of m by a shaking the la p.

ula ti n S rin a nd Levon— 5 . Reg g p g The regulating or counter Fi 34 c acting spring ( g. ) tends, espe ially in shunt arc lamps, to oppose the swinging movement of the lever frame exerted by

h - t c n t e electro magnet. At one end it is at a hed to the swi ging 44 ELECTRI C ARC LAMPS

f m m l u m a nd clockwork ra e or the ovab e iron pl nger or ar ature,

h other end r l n at t e to a egu a ti g lem a s i n the ﬁgure. The

n of e m spri g is made hardened steel, and it is d sirable to te per it after it is ﬁxed so that its tension ma y not be further alte red n m under the i ﬂuence of the lamp temperature . The dia eter of of the spring, the number the coils, and the tensile strength of the wire must be proportioned to the power of attraction of m m n the agnet. The ore coils the spring has, with a give P m r .D. agnet const uction, the higher will be the across the

Fro. 88 .

a re mm d f i e iately a ter switching in , because then, with a given movement of the clockwork lever frame in the direction for the

of are of re striking the , the tension the spring alters latively

f Bu less than if the spring had ewer coils. t this alteration in the tension of the spring must be i n a certain proportion to the alteration in the attraction of the core or armature of the

- m u of f m electro agnet, because either the ret rn the lever ra e CONSTRUCTION OF E LE CTRI C ARC LAMPS 45

too PD with low a . . across the

n of n u These consideratio s , course , o ly apply to sh nt arc m n la ps . To stretch the spri g in order to obtain a certain arc m . 34 . length, the regulating lever (Fig ) is e ployed It is usually ﬁxed in the base plate i n such a way that it ma y be a n adjusted, and is held by the spring against an djustme t screw .

6 The Da sh t — m . po . The air dashpot consists al ost inveri

of 20 3 0 mm . e ably a brass cylinder, about to diamet r,

c f m atta hed to the lever ra e , in which works a brass piston to secured to the base plate (Fig. Its purpose is prevent

u m me of f u the s dden ove nt the lever rame, which wo ld otherwise occur with the considerable current ﬂuctuation as produced in the of w s striking the arc. With the delay hich the da hpot causes i n ra on of f e the sepa ti the carbons a t r contact, a greater heating of the s carbons takes place, and consequently an ea ier striking of W h the arc. t ou t the damping arrangement it is scarcely possible to stri ke an are in lamps with such a swinging lever

rea f m the tips are al dy ormed. The da ping must have a deﬁnite of relation to the pull the magnet. It depends (with a given movement of the lever frame and a sudden moti on of the same) upon the difference in pressure between the air withi n the

e of cylinder and the out r air, as well as upon the size the

. dam in is f m piston The p g there ore greater, the larger the dia eter of n m of ai r the pisto , the greater the change in volu e the in

the cylinder, and the deeper the piston plunges into the

. o f cylinder The cylinder and pist n must be per ectly round,

The and the contact surface well poli shed. longer the piston the more easily it will move with a given amount of damping

s l The piston is provided with groove , into which any possib e 46 ELECTRIC ARC LAMPS

ma f . L dust y settle, and riction is thereby prevented ubricants m ust not be used .

The Gu id e F — f m ll of 7 . ra me The guide ra e usua y consists

a . two pinchbeck tubes (Fig. or else solid br ss rods (Fig

Fro. 87 . which are fastened to the base plate a nd connected at the

m - a - botto by a cast iron or br ss cross piece, which keeps them

of parallel . Their length depends upon the size the carbons .

m t of u 10 13 mm The dia e er the t bes is usually to ., that of the 0mm solid rods about 9 to 1 .

48 ELECTRIC ARC LAMPS

of ff m . Fi 3 8 carbons di erent dia eters g. shows an upper, and

. 3 9 40 Figs and , a lower carbon clamp. The latter M p

Fro . 40.

d t f d m e is so a jus able that a satis actory a just ent is possibl , even

a m with crooked c rbons . The cla ps are usually made of bronze.

The depth of the V - shaped part of

l m 1 for the c a p is about 3 to in . 1 m a currents of 6 to 5 a ps . The cl mp without a spring attachment is nu

f the satis actory, owing to unequal of w e expansion the metal and h n ,

a ltm' na tin curmnt especially with g , and often results in the carbons

falling out . Both must be capable of adjust ment on their holders in ordm' to facilitate the placing of w hom of

ne e m . O holder, at l ast, ust be insulated

. 4 1 M 42 usually constructed as in Fig . One is ﬁxed in the hm plaw

insulati n with or without p . current is led from the termina ls or

from the electro- magnet winding to the movable carbon holders by mea ns p m. 4 1. Fm 42. CONSTRUCTION OF ELECTRIC ARC LAMPS 49 guarded

Al ternating current lamps require a

e r ﬂector above the arc, because the stream of light as the upper w hen

ﬁxed to the guide

43 shows such a reﬂector as in the

‘ The 9 is atta ched to the

ﬁxed to it is bent so ELECTRIC ARC LAMPS

fastened to the cross—i b r w The inner surfa ce of p ece y sc e s. the of i reﬂector is enamelled white, so that the reﬂection l ght is as

r of c o u l of la ge as possible. The shape the reﬂe t r is us al y that

c n ma a trun ated co e, but it y also be made curved. In the is concentrated and the illuminati on beneath the lamp is But the exact shape of the reﬂector does not appear to be of

m u im of the m para o nt portance, since the distribution light ainly ’ depends upon the power of diﬂa si on of the globe. The use of a reﬂector over the arc has little appreciable value with direct

of of l w current, because the distribution light the o er negative

d . have a natural reﬂector alrea y to hand It is possible, how

e m m of ver, to e ploy an econo izer over the arc instead a reﬂector Fi m f m ( g. The econo izer or s a closed hollow space above

n e the arc, the air in which is lacking in oxyge , wh reby the

m of l s a nd consu ption, especially the upper carbon, is e sened, a

n of longer burning is obtai able . In spite this advantage, the

n t i - u m eco omizer is lit le used with ord nary direct c rrent la ps,

e w a arc, g . when bad carbons are used, or hen a dr ught (caused

f f of by aulty globes , and thus preventing the ormation carbon

m of onoxide) is occasioned ; and also, on account the paucity of of oxygen at the carbon tips, the intensity the light appears t m to be less wi h an econo izer than without .

12 1718 a s — w . C i ng The ca sing in hich the Whole la mP m m of echanis is enclosed usually consists an upper part, which s m m contain the regulating echanis proper, and a lower part,

c for of new n deta hable the purpose inserting carbo s, to which

the glass globe is attached. The upper portion, again, consists

of a - w as a a suitable ﬂanged c st iron ring, to hich the b e pl te On of (insulated if it carries current) is screwed . top the ring

a metal cover is ﬁtted as closely as possible. The close ﬁtting

of m rta to m m the latter is very i po nt, as it reduces a mini u the CONSTRUCTION OF ELECTRIC ARC LAMPS 5 !

c l mecha nism and kee s ou t a ll ac ess of a ir to the regu a ting , p

s a du t . To the ring is also att ched the hanger carrying the

m d a e to fold back, in order that the

m the echanism readjusted. In this ring are also ﬁxed the porcelain

so arranged and of such a shape that rain cannot ﬁnd its w a y into m the la p . The lower portion of the lamp consists of a meta l cylinder with a suitable stamping or casting at its

ow rim l er , to which the globe is

c u atta hed . The latter is us ally atta ched by a wire netting (copper

W of 1 mm m ire about . dia eter) with the assistance of a metal ring ﬁtted

nd of to the lower e the globe. In

d r l f or e to secure the globe stil urther, Fro. 45 . especially if the net attachment is

s m r not de ired , an indented etal st ip may be attached to the

t m of u w bo to the cylinder, its teeth being bent o t ards , so that

it grips the globe inside . On the cylinder are also placed the hooks necessary for

i of t m attach ng it to the upper portion the casing. This at ach ent, t ff m m ff whils o ering the si plest possible manipulation, ust e ect an

f n m uf i absolutely sa e and rigid co nection , and it ust be s ﬁc ently rigid to prevent the lamp swinging against its support in windy

. F 4 5 a i weather In ig. construction ) this is att ned by the hanger being hooked at its lower ends and provided at its 5 2 ELECTRIC ARC LAMPS the upper rim of the metal cylinder presses against the pro

ectin w the a j g ring, hich causes latter, together with the l mp f m m of mechani sm, to be li ted up through the ediu pins (pivots) in the long slots of the hanger until the lo

o with the hooked ends f the upper hanger. f ﬁxed to the hanger acilitate the hooking on. — Another modiﬁca ti on a rigid connec tion between the upper and lower portions of the casing to effect an easier

Fro. 46.

ff m of is e ected by a crank otion the lower hook .

m U E Co. l . 4 7 the sche e in the nion lectric amp, and Fig in the

m - m w f Sie ens Schuckert la p . In both cases the lo er per orated hooks engage in the projecting lugs or hooks by a downward

m of si excentric ovement a lever ﬁxed to the lower ca ng. In order that it could unhook of its own accord the axis of rotation CONSTRUCTION OF ELECTRIC ARC LAMPS 5 3 hook pivot lay outside the line joining the crank pivot and the

of of i s . point support the hook ( . the projecting lug) (see Fig 4 In Fig. 7 the b ook , by being bent

m r has so e sp ing, so i n execution are not of

The lamp casing m ust admit of a certain constant ﬂow of air to

the arc, since the car

3 p, ) and would ” tend m m to ushroo ,

of light rays. Hence, according to the construction the lower

ro portion, it sometimes becomes necessary to int duce special

m - plate , so that the war , ash laden air beneath it obtains

an outlet. Fresh air is partly introduced in the same way, partly betw een the globe and ring where they do not ﬁt

- m of . exactly, and partly by eans an ash pit The latter is

m of in clw e ade either glass, zinc, or p chbeck , and serves to

of - the lower opening the globe . Frequently the ash pit

ia n of is provided with spec l ve ts, closed with a netting a

r f m f ll ou t ﬁne mesh, in order to p event sparks ro a ing .

The ash - pit must be so arranged that it scarcely closes the of o lower opening the globe and is not dislodged by vibrati n . Its function is partly to catch sparks so that they may not l f of crack the g obe, and partly to acilitate the cleaning the 5 4 ELECTRIC ARC LAMPS

The globes are almost exclusively made of opal or alabaster 4 n of O glass about to 6 mm . thick . The thick ess the pal or . alabaster covering must be such as to secure the most uni form illumination (which cannot be obtained without such a globe by

arc s u i of the exposed , owing to the irregular di trib t on its light) h with t e least possible loss of light due to absorption. In the globes used in practice thi s loss usually amounts to 20 to 3 0 per cent . With opal glass the arc appears as a point of light ; with m m of of alabaster glass ore as a ﬂa e . The power dispersion

f li for the latter is there ore greater, and its app cation internal

ta eous g . For outdoor lighting purposes, on the other hand , the

r m of opal globe is gene ally chosen . The sa e distribution the rays as with the alabaster globe (together with a smaller loss of ma t m f light) y be ob ained by globes with a att sur ace, produced

f . by sand blast or etching, provided the grain be ree enough m These globes , however, easily beco e dirty on their rough f of sur ace so that they appear unsightly , and the loss light soon

C a f m'ds increases . le r glass globes are o ten used in railway y e m with alt rnating current la ps, partly because the distribution of light with the alternating current a re with a suitable

ﬂ m w m f m . re ector placed over it, is so e hat ore uni or Hence the more transparent opal a nd alabaster globes are often chosen for

are On the use with alternating current lamps . the other hand, illumination on the ground with alternating current lamps of equal consumption is appreciably less than with direct

ma e ear current lamps . The globe y be ither spherical or p shaped . The whole regulating mechanism must be so ﬁtted within

n the casing that the latter shall carry no curre t .

5 6 ELECTRIC ARC LAMPS

aud an exact regulation is m of m obtained. Another ethod eliminating the te perature error is to be found in the alteration of the tension of the spring or in the

tion of the dete nt (according to the kind of lamp) by means of tempera tu re compensa tors as em ployed by the ﬁrm of Kbrti ng and M i L td. I n ath esen,

com principle, the

upon the expansion , with increased tem

Fro. 5 0.

a u of m t of M . p rat re, e al tubes in the interior the p CONSTRUCTION OF ELECTRIC ARC LAMPS 5 7

i m t expans on is com unicated by a bent lever, ei her with the

the e or det nt, in

u m er PD. for s ch a ann that the . the lamp rem ains constant in spite of the increased t emperature of the magnet winding and the uent weakening of the elec

- et tro ma p . In order to secure a su mciw t increase in length with

of m tubes s all size, several , or

er alt nate, iron and zinc tubes are used and built up so that the elongations of the more readily

M«si i VB 800 zinc are added ( Fig.

1 a n 3 n u bes 2 a n d are iro t , d

' 4 m Th iron tube l i a re nc. e s a tﬂ ched to a support in the base

Fi 5 1 - g. is a direct current ,

A of AE G. are lamp the . .

f u 40 PD. or abo t volts . across the m Two to three of these lamm

r for 110 a e used in series volts, or ﬁve to six for 220 volm or for a

s: . of 3 7 5 5 m p to volts per la p .

ha ve alrea dy been described on

3 1. i di ﬁers p. Th s lamp in e n on from the shunt arc lamps only in the addition of the

1 o- ma em electr gnet, in the

u of a stronger air dashpot

F m 5 1° a r k of a l ger stro e, in the use a

r tro m n of wea ke con lling spring, and in the eli inatio the 5 8 ELECTRIC ARC LAMPS f m for f m ra e the resistance or the shunt coils. The te perature error of the shunt coils has not su ch a great inﬂuen ce on the

' P D are diﬁerentia l m a e . . across the in a la p, because to the g e t r attraction of the shunt in the cold condition of the lamp there is

s m h a m i n a o ew at gre ter la p current, which turn strengthens the

of - f attraction the opposing series electro magnet. There ore the

o in t err r is, with similar conditions the shun

w n f i ding, only hal as great in as in shun t

. ff m of lamps Hence, in di erential la ps, the use a special

rc m a an resistance in the shunt coil ci uit y be dispensed with, d

of r the winding ma y consist simply insula ted coppe wire . In the 2 of . 5 o of above lamp, as shown in Fig , a porti n the winding

Sh ir of he the coil is wound with resistance w e , and a portion t

latter spirals BS is short- circu ited by the teeth of the escape m — R n o of ent wheel and the dete t or st p S, as in the case shunt CONSTRUCTION OF ELECTRIC ARC LAMPS 5 9

m h la ps. T e regul ati on of the lamp is therefore extremely

exact . Naturally the whole electrical behaviour of the lamp f m of depends on the or the pole pieces of the electro magnets. I n the lamps shown these pole pieces are so constructed that

the m ll - f B ar ature approaches tangentia y to their pole aces . y this means it is possible to alter at will the pull of the electro n of magnets with respect to the positio the armature . For shunt lamps these conditions are so arranged that for the extreme

o of m PD positi n the ar ature against the detent S, a . . across the

of 3 5 m PD . m arc about to volts below the nor al . aintains ili m of n I f the equ briu the opposing or regulati g spring. the pole pieces are so formed that the norm a l tension of the spring maintains an equilibrium for every position of the armature

' (possible with a suitable form of the pole pieces and taking

of r i of n if account the alte ing tens on the opposi g spring) , or the

' D extreme osi ti on i n m P. . is higher in the p than the nor al v m position, then the disad antage arises that the la p ﬂares up too readily with every disturbance of the a re through loose

t of e par icles carbon , and another disadvantag is that the striking of the arc with partially consumed carbons is only

of m effected after much jerking the carbons . The agnets in

A. E G m m a ll . . la m are ovable horizont y (through the provision

of m of for slots), whereby an adjust ent the pull is possible

different lamp currents without altering the windings.

5 3 Jo P ff m of bra ke Fig . is a hnson hillips di erential la p the

wlwd The - m o o of type . electro agnetic contr l c nsists a series

e c in solenoid, Se, and a shunt sol noid, Sh , a tuat g respectively

C C . the cores , (Fig These solenoid cores are pivoted to ' of a rm R w opposite ends a balance , , hich is centrally pivoted at

P f - B . o w rim The brake gear consists a brake wheel, , having a

st Eh rim on which re two brake blocks, , one inside the and the

h rim e ot er outside the . Thes brake blocks are so pivoted on a

r brake lever, Bl, that when the lever is ho izontal the wheel ca n

f u slip reely thro gh the brake blocks , but a slight tilting of the 60 ELECTRIC ARC LAMPS

c Eh of B lever auses to grip the rim w. One end of B1 is ' arm R connected to the balance , and the other end rests freely on a support S . H The carbons are gripped in tube holders, 1 and Hg,

m attached to rods, ensure their ovement being

ri of st ctly along the axis the carbons . These rods are connected m n of by ea s ﬂexible, braided copper tape to two wheels, both

mounted on m ft as - Fi the sa e sha the brake wheel ( g. but are CONSTRUCTION OF ELECTRIC ARC LAMPS 6 1

e f insulat d rom each other. The connections are so arranged

one m n that as carbon descends the other ascends, thus aintaini g

alwa s in the arc y the same place.

ea h vier than the negative, so that the carbons approach each other f B1 by gravity. The position o and the carbons touching shown in

. 5 4 f Fig , is the normal state be ore

i - in of m the sw tching the la p . When current is supplied to the lamp the series core is power fully magnetized and pulled into

its solenoid, Se ; this tilts the balance a rm and ca uses Bb to grip

l r to rotate slight y, thus st iking

As the carbons bu rn away

Fro. 5 4 . PD. and arc . increases, the shunt solenoi d gets gradually more powerful and causes B1 to assume a position in which the brake wheel can slip back a little owing

to the greater weight of the positive carbon holder, thus

dashpot preven ts too rapi d a motion of the cores and brake

. 5 3 f u . system . The action of the feed is ai rly continuo s Fig m Fi 5 3 A of m shows the la p closed, and g. another view the sa e,

O for r mm pened t i ing.

Fi . 5 5 shows a twi n arc la m of the sa me t e as in Fi 48 g p yp g.

for of ms direct current. It consists two independent mechanis m t of . wi h a double set carbons, constructed within the sa e casing This la mp was the outcome of an increase of the supply pressure 9 for mi of the C 8. o which had its object a di nution lead l sses . F i n m r or example, any towns the mains p essure has been 62 ELECTRIC ARC LA MPS

e f m 110 220 f incr ased ro volts to volts . This object requently conﬂicts with the number of lamps required for a certain purpose

- for i for as, nstance, tradesmen needing only two ordina ry single m m la ps. Since transfor ing to the lower pressure could not be en terta i ned for such and similarly

m ur om sem a s all lighting p p , on nt of the expenses of transformation

m neces and attendance , it beco es sary to employ the high voltage m enclosed arc la ps, which burn

w PD . of ith about double the .

the l m ordinary open arc a p. Owi ng to the relatively smaller illumination and the consta nt

of m wandering the arc, these la ps have not met with general approva l

E of a e in urope, in spite the advant g of prolonged burning which they

w s of n give ith a ingle pair carbo s,

for li at any rate, street ghting ; though i n America it has driven out the open a re for both indoor l n illumination and street ighti g .

I n E ngland, at the present time, we ma y say fairly that the most popular type of arc lamp for

m d globe enclosed (see p . the ﬂame arc lamp is rapidly superseding the ordi nary 0pm

e- mendened lighting. In Germany especially, it was the abov

5 4 ELECTRIC ARC LAMPS

of r e . m r of both which, the arcs are in se i s The ter inal p essure 8 these lamps is about 0 volts . With a resistance they can be

100 t or m on burned singly on vol s, with two la ps in series 220 volts supply . I f it is desired to bu rn the lamp for a longer period with of m only one renewal the carbons , these la ps be con

Frs . 5 7 . nected so that the two pairs of carbons burn in which

and the terminal pressure of the lamp then corresponds only to CONSTRUCTION OF ELE CTRIC ARC L AMPS 65

t he P.D of . across one arc. Fig. 5 8 shows the connection a

m l a p. In the latter lamp the main current passes (on entering the lamp) from one termi nal to the series coils of both

m m or of e echanis s in series, and then passes to one other the s ts

of m m . carbons, and thence to the other la p ter inal Both the

Fro. 5 8.

coils connected in parallel with the Current

for thus passes through all the coils, although the time being

are few m only one is struck . Hence the lamp consumes a ore m On watts than a single la p. the other hand, there is a greater certai nty of acti on with the above connection than if an automatic switch inserted the coils of the second pair of carbons f a ter the ﬁrst pair burnt out . In the case considered the r 66 E LECTRIC ARC L AMPS bnrning pai r is so adjusted with non nal cunent tha t the relesss

1 to 2 volts a m the

sa w other est. Since the me ma in current ﬂo s through both the

M 5 9.

e and l e s ries coils, since both the shunt coils have the same vo tag ,

D are e the er for P.D P. . k pt apart until oth pair ( a lower .) CONSTRUCTION OF ELECTRIC ARC LAMPS

n of PD m co sumption the carbons ; thus the . . across the arc beco es greater until the other mechanism controlling the second pair of

a r re n of c bons is leased. In co sequence the short circuit, due to the ri of i u st king the second arc, the ﬁrst is ext ng ished and the

e consumption and feed of the second pair b gin. The two

' nw d not require the above- mentioned (constant) di ﬁerenoe in

f r i e . of i P. D. o the r r gulation By the choice pole p eces the

ment a diust may be so arranged , that at the ﬁrst attraction the 68 ELECTRIC ARC LAMPS

f armature o one mechanism requires a somewhat higher P.D.

m of P.Ds. across both arcs . The connections and echanisms

for of substitution it suitable springs or weights, the same.

. 60 A E G er a Fig is an . . alt nating current motor arc l mp . Between the s and the shunt map ets a meml disc capable of rotation is inserted . The pole pieces are partly covered with

i ro n co

ﬁxed copper plates or and the metal e currenm i o uc o the magnets induc eddy , wh ch pr d e a t rque on

6 e ; o the movable disc. As shown in Fig . l , the a;

ro o osi te o n so arranged as to p duce pp t rques . The

“ the series magnet is to strike the arc ; W e a CONSTRUCTION OF ELECTRIC ARC LAMPS 69

series magnet The latter alteration is effected by means of 62 m e of the adjustable yoke shown in Fig. . The ovem nt the me tal di sc is transmitted to the carbon holder by gear- wheels of and a chain pulley. A lengthening or a shortening the arc occurs according to the way in whi ch the equilibrium of the

r f e cou to ques is disturbed. The lamp is there ore r gulated

m n is the case in lamps provided with a clockwork escape e t. Since the motor lamp is not affected in its working by any f m has heating, as lamps with a swinging lever ra e are, it the advantage that immediately after the striking of the are the

electrical conditions become normal. All the lamps heretofore described are only suited for use m a with ordinary pure carbons, and cannot be e ployed to advant ge r with chemically treated carbons or othe electrodes .

0. SIZES OF CARBONS.

The following tables give the sizes and lamp pressures for

pure carbons. For direct current the positive carbons are cored n of and the negative carbo s solid, and in the case alternating

n t r m t f curre t bo h carbons are co ed . The consu p ion o the positive carbon with direct current is greater than that of the negative a m f c rbon. In order to secure an equal consu ption , the ormer is

chosen with a correspondingly greater diameter.

Sm or Ca nnons AND LAMP Pa sssuass son D C Aa Two . . c La mps m cams ON 110 ow on Fons TO I E S V s , F V ERIES on 220 ow s on ron m an m ea ms S V , o S wrrn ABOUT 45 TO 5 0 ot ra m LAMP V .

TABLE I . 70 ELECTRI C ARC LAMPS

SI s o ARBO r C Ns AND LAMP PamsURss rOR THREE D .C. LAMPS IN Sca ms ON 110 ow s on Sa t LAuPs IN eams FOR V , S 22 V 0 onrs, OR FOR MORE IN Sea ms wrrn ABOUT 3 7 TO 40 VOL'rs PRR LAMP .

TABLE II .

of 8 10 12 s The length each carbon is usually , , or inche

200 25 0to 290 3 25 for the ( , , or They burn correspond

of 8 18 0r 15 20 hours lea vin ing periods to to , to , g a m Of 4 5 0 mm I 2 m re ainder 0 to . ( i to inches approxi ately) for length open arcs . With the smaller currents they burn for m for a shorter ti e than with a greater current, so that a m m of 8 m ediu current strength a ps . , with the given lengths ,

for 10 14 16 18 . ri they would burn about , , , or hours In inte ors

the 1 2 s they burn on average to hours longer, owing to decrea ed m r air circulation. In la ps provided with an economiser ove the

1 mm . arc, the positive carbon is usually . less in diameter Positive carbons of inferior quality (producing more ash) require m w i a so e hat thinner (solid) negat ve carbon, but these, as a rule , a re only adapted for lamps which burn with a pressure Of at 0 least 5 volts .

LAMP POR P A . SIZES or CARBONs AND LAM Pa sssuans FOR AN .O 0 4 s P Y POR Tw 2 TO 80 V om s 0 VoLr SU PL , o LAMPS wxru 7 Y O EE ON 1 5 PO 12 rs OR FOR SIX ON SUPPL , F R THR 0 0 VOL , 200 TO 220 O 'rs O FO MORE ca ms WITH A V L , R R IN S TERMINAL PRESSURE or ABOUT 3 6 Von'rs PER LAMP AND AN RM ALTERNATING CURRENT wrrn A SINR WAVE FO .

29—3 1 29- 81

72 ELECTRIC ARC LAMPS

- lower carbon is the positive. These are the cc called inverted e w to arc lamps, in which the crat r casts its rays up ards on the l cei ing . The latter then serves , in rooms from 11 to 16 feet (3 5

5 metres hi h as to ) g , a large

e r m r ﬂecto , and hence ust be kept

hi The a re f a w te colour. itsel can be either entirely obscured by means of a metal reﬂector F ( ig. or partly obscured by reﬂector (Fig.

64 i to m . ), accord ng the require ents

In the latter .; e some light

principally from the upper new

tive carbon. In spi nning mil ls

material is likely to drop into

be entirely enclosed, owing to the

e n v air. dang r e , explosi e This may be e of a glass cov r, ﬁts over the

16 f c height than eet, or in rooms in whi h the ceiling is

not as ﬂ hi e a; a c i suitable a re ector, a special w t l ed reﬂector,

3 0 3 5 800 900 m . to inches ( to mm.) dia eter, is ﬁxed over the arc The arrangement of the positive carbon as the lower carbon hem has, however, the disadvantage that particles dropping the r f ll r e m uppe carbon a in the c at r, and disturb the arc ore or less

u until they are burnt p . For this reason it is desirable to a a s i to choose the c rbons thin as poss ble, having regard the

r of for l pe iod time which they are reu d, and on y to

e w rbons of o m constm cwd h m g od quality . La ps with t is of gement the carbons, and having an open arc (and also CONSTRUCTION OF E LECTRIC ARC LAMPS 73

t l n g those wi h a clear g ass cover) , throw on to the ceili g a stron

of r of the la m Of shadow the upper po tion p, which is ten s de irable . This dis a dvantage disappears

rangement of the posi tive carbon as the

upper carbon, and with a reﬂection of the rays from the

crater to the ceiling .

rdi n Here, too, acco g

ena melled reﬂectors

(Fig. or trans Fi lucent reﬂectors ( g. which allow some of the light to pass

downwards , but throw

con chosen. In se Fro. 65 . qu ence Of the double

the of and ceiling) , loss light in n this a rrangement is comparatively large . Hence the illumi a

O ai ca rbon as the lower carbon, is only bt ned with a greater

i of . expend ture energy But still , where it is applicable, this is the best in quality for artiﬁcial lighting of interiors f in which work o any kind is conducted. A special device for Obtaining light indirectly with an ordinary direct curre nt are m m - la p is the Sie ens Schuckert reﬂector (Fig. It

of - e consists a large, bell shaped, transluc nt, linen reﬂector, 74 ELECTRIC ARC LAMPS

m h 0 a nd s A, a s all hemisp erical alabaster bowl, , a clear gla s

of m ring, B, pris atic section. The large reﬂector is situated ' ° m and u of 25 above the la p, receives p to an angle below the horizon the upper portion of the rays emi tted from the arc . ff These rays it di uses and reﬂects downwards. The alabaster globe encloses the lower portion of the lamp and permits som e

u rays to pass thro gh, whilst casting others up to the reﬂector of m f m A. The intensest portion the rays, which is e itted ro ° the are wi thin an angle Of 25 to must pass through the

glass placed slightly below the arc, and is thus

FI G. 66.

so refracted that it also stri kes the reﬂector. In

of of ﬂ o i of the transparency the large re ect r, a port on the light

f m of i passes through it, and thus a so t illu ination the ceil ng w and the upper alls is obtai ned.

Alternating- current lamps may also be used for indire ct

m x of r the lighting, though with the sa e e penditure ene gy illumination is considerably less than with direct c urrent

mm of fre lamps, and the hu ing noise the arc is quently CONSTRUCTION OF ELECTRIC ARC LAMPS 75

SIZES or CARRONs AND LAMP Passsuars FOR DIRECT- CURRENT ARO LAMPS FOR I NDIRscr LIGHTI NG WITH APosrrrvs LowaR OAR sON .

LE I V TAB .

L e of re 10 25 0 mm. of ngth co d carbon, inches ( ) length 6 h 15 0 P of 7 8 solid carbon , inc es ( eriod burning, to hours .

Le a 8 h 200 P of ngth per c rbon, inc es ( eriod burning, JO f about hours. A so ter light is obtained with the sizes given

I . in Table V. than with those given in Table V The sizes given

t for int n . in Tables I . to III . apply to all o her lamps lighti g

A LAMPS . ll . FLAME RC

GENE R AL REM RK A. A S.

m Lm B W n The Fla e Arc a p, ever since The ritish esti ghouse C m n o pany introduced it into Great Britai , has rapidly gained i n ul pop arity. Its warm , attractive glow has caused it to be

u f for of much so ght a ter shop lighting, places entertainment,

On c u f of etc . a co nt o the brilliant appearance the lamp ,

the a greater efﬁciency than ordinary open type arc, and an

of t lighting large spaces, such as railway sta ions, engineering ” - - r . ao ya ds , parks, etc The called Sun ray, or golden ﬂame

has fo - e s e of arc, a g penetrating pow r, and thu r nders it special

s m is value for dock and harbours . The ﬂa e arc lamp also being 76 ELECTRIC ARC LAMPS

B. FLAME ARC LAMPS WITH CO- AXI AL C

The ﬂame arc lamp is simply an ordinary open type of are ’ m r la p, but with certain modiﬁcations, and can be ar anged to burn with direct or alternating current .

(a ) Chemical carbons mi nerali zed with certain m (or electrodes with a refractory conducting material a n 13 c rbo , see p. ) (b) Suitable alteration in the striking working with a greater length of the ﬂ of ordinary open type. The length ﬂame

15 16 mm . volts is about to , whilst

r fo PD. wo the o dinary open type r the same .

are bowl, ﬁtted above the (Fig . In order to obtain a light sufﬁciently

of r o of ments exte i r lighting, as little as possible the

the are f should be exposed to , there ore carbons

m - m possible are e ployed . In the direct current la p the uppermost or positive carbon is made the same size as the negative. But

i i m the since, under ord nary c rcu stances, positive carbon burns if d away twice as quickly as the negative, it is necessary , a ﬁxe n l burning position is to be retai ed, to supp y a hollow space, as

of co m ﬁ in in that the e no izer, in which an atmosphere de cient a oxygen can collect around the upper c rbon . The combustion of the latter is thereby retarded, and the automatic equalization of the combustion of the two carbons is thus effected l o In certain ﬂame arc lamps the ower carbon is made p d tive. In that case it must be proportionately thicker than the negative m carbon. The light is then ore steady and the colour more — uniform than in the former case presumably because the added

A ra ctica l enclosed ﬂa me are la m has een aten p p b p ted by M. Andre B a ri Britis n londel. P s. h pa te t No. 4 677 CONSTRUCTION OF ELECTRIC ARC LAMPS 77

' a ﬂ a chemic l substances o er a steadier resistance, and bec use the

of r of currents air. In spite of the abso ption light due to reﬂection of light at the surface of is not

h e. 68 . h e. 67 .

r n less of light with ar angement, because the m delivers more of the added che icals to the ﬂame .

It is necesas ry to isolate as far as possible the portion in which 78 ELECTRIC ARC LAMPS

ﬂa mc i n d the the burns , or er that injurious gases produced by the chemically prepa red carbons should not reach the lamp

68 al a ffected, as shown in Fig . , by a met cover ﬁtting in a groove in the lamp casing and ﬁxed to the lamp frame a nd

r of r in the outer po tion the lamp, and these are p ovided with a ou t cover, in order to keep rain . With alternating current the special arrangement of an m m of economizer may be o itted, since the consu ption both of carbons is the same. Instead the economizer a re ﬂector is M generally introduced. otor lamps also do not require a

i eﬁort modiﬁcation of the str king .

Srzss or Cu rsor s AND LAMP Paassua ss FOB FLAME Aa c

Lm rs WI TH - a x a nn s Cc nu . C on .

TABLE VI .

80 E LE CTRIC ARC LAMPS

‘ — - - 00 hrou i so called blow down magnets (Figs. 7os 7 ) t gh wh ch the current taken by the lamp passes ; the a o

tion of the blow - down ma gnet upon the arc

repellant effect that the magnetic lines exert

ﬂecti on and h e. 7OA. ,

then readily

ﬁeld may be strength ened or weakened a o

i n o esi re cord g t d . The stronger the ﬁeld the more the ﬂame ex

Fla . 7013.

a wea keni ng of its own

of net, are advantage.

See a lao p. 91, Fig. 86. V PLAT E I .

Direc t u en ol s 10a m ree. C rr t, 45 v t , pe

w - Without the blo down ma gnet.

Alterna tin urrent 45 olts 10 a m eres . g C , v , p

F I G . 69 .

To a ce a e 80 [ f p g .

82 ELECTRIC ARC LAMPS

e hot carbon tips in an atmospher deﬁcient in oxygen , thereby

of both cost carbons and trimming. The economizer also serves

e ash as an excell nt reﬂector, as it is covered with the white m deposit and protects the ﬂa e from draughts . To get the best

of results, the carbon tips should not project below the level the

m of 1 - ri the economizer. Fig. 7 shows the cross section of an economizer in an Excello arc lamp (Union Electric and h of ex ibits at the same time the correct position the carbons. of is e of The position the carbons dep ndent on the length the arc, and this is naturally controlled both by the voltage available for of m the arc and the quality che ical carbon used . In this lamp great stress is laid upon the correct elevation of the a re in the

m z I f f o econo i er. , a ter it has burnt long en ugh to be properly f m or ed, the carbon tips remain too high inside the economizer, it of too is evident that the voltage the arc is high, indicating at

m m the . m the sa e ti e that current is too great To re edy this, it is only necessary to increase the steadying or line resis tance ; m n and conversely, to di inish the resistance whe the carbon tips l of m a re below the leve the econo izer.

On n m m the whole, the regulati g echanis is usually the same

ff of The only di erence lies in the ﬁxing the carbon holders . These must be so arranged that both carbons may be fed down

the m m m wards at sa e ti e, and to the sa e extent, as they burn

ff m of a the a away . There is also a di erent ethod separ ting c rbon tips in the act of striking .

l m . 72 80 ff e The regu ating mechanis in Figs to is di er ntial,

A.E G m m 2 the magnet system in the . . ﬂa e la p (Figs. 7 to 74)

' m n i on r 5 . being the sa e as in the ordi ary type desc bed p. 7

- m t U E m m The electro agne s in the nion xcello ﬂa e la p (Figs . 5 P V 76 It in 7 , late ., and ) are at right angles to one another, be g

i m n . m of the ser es agnet, and the shunt magnet Both la ps are w a i f the clockwork type, but here s the swing ng rame in the E PLAT V .

Fro. 75 .

T e of ac e p a g 82.

84 E LECTRIC ARC LAMPS

The feed in all the ﬂa me arc lamps described, except in the

- O of alternating current motor lamps, is perated by the weight the i m carbon holders . In order to nsert new la ps 2 of of the type shown in 7 , upward movement the

Fro. 76. Fm. 77 .

l r ff ho de s is e ected by a pull on the loose chain,

d - whilst in lamps with a cor or chain pulley, a third cord or

for u r chain use by hand is us ally inse ted Gig.

The shunt magnet brings the carbons together, and the CONSTRUCTION OF E LE CTRI C ARC LAAI PS 85 m agnet separates them and checks the feed. For striking the areand separating the carbons a few millimetres they wouldlneed

F Fro. 78 . ro. 79.

f of to to be raised up considerably a ter contact the tips, owing the

acute angle at which they are placed. This is generally 80 only possible with motor lamps (Figs . 77 to ) which are not 86 ELECTRIC ARC LAMPS

' limited to an ﬂ r Lam s wi th a y ﬁxed stri ki ng e ort o pull . p

u i s - l m h r deﬁnite striking p ll, . all direct current amps, ust t e e f be f ore provided with a system o levers which, when the

en s curr t passes through the serie coil, participates in the of m of movement the ar ature, and so causes a separation ar the c bons . This movement either the whole carbon holder f 74 or only the carbon itsel ma y share . In Fig. the con necti ng rod and crank lever controlling the negative ca rbon

6 i d con is attached to the armature A . In Fig . 7 the sl der is

nected to the rod b whi ch i n turn i s ﬁxed to the swi n i n , g g frame a in such a manner that the movemen t of the armature towards the series magnet causes a side movement of the i of extrem ty the carbon rod . m m m i n In all these ﬂa e arc la ps the carbons ust, the

of i m ra thi nmar interests a steady l ght, be chosen co pa tively

m f . C if than in the la ps described be ore onsequently, they are

for 6 18 m to burn the usual time ( to hours), the carbons ust e be considerably long r, and thus their ohmic resistance, which

cannot be neglected , is introduced. For this reason, in lamps burni ng more than 6 hours it is not sufﬁcient to conduct the

a i n current to the c rbon holders , but special clutch contacts, as 81 81A 8 113 m Figs . , , and , ust be introduced in the neighbour

hood of the carbon points (w e also Fig. It has also been

ducti vi ty increased by means of a copper deposit or a zinc

v . i n the gauze co ering or core, etc , so that this case special

contacts may be omitted.

r m as m of In o der to prevent the econo izer, as well so e the

f s c a re metalwork, rom possible de tru tion by the travelling up

far m e when the carbons have burned away as as per issible, g . n d r whe the hol e s have reached the lowest possible point, there

u ishi n are t i ng g the in such cases . These contrivances may

r L . 18 Cha pte , p .

88 E LECTRIC ARC LAMPS

f - m lamps, and there ore the blow down agnet, which is excited

i r by a ser es winding whilst the lamp burns, has an ext a shunt

of switching out the shunt

the magnetization and extin

bent in such a way that an increased separation of the ca r bons occurs when the carbon t holders reach the lowest posi ion . All these devices have the same are object, viz . to extinguish the by a sudden separation of the m carbons, and the si plest device of all is to insert carbons whi ch are not cord at the a nd inserted

into the holder. Then as the carbons burn down to the un cored conductivity is suddenly reduced ; thus the

a re current is not so readily conducted, and the is extinguished as a direct consequence. The case must be constructed so that the globe space which

' contains the light shall be entirely shut oﬁ from the upper

of d to portion the lamp , in or er exclude the injurious nitrous

i f m a vent h les ox de u es which are generated, and the necess ry o ' a ar a ree outlet for a efi must f f these gases. This is usu lly ected 4 9 by a special protecting cover (Figs . 7 and 7 ) at the lower f m f n end of the lamp ra e, to which is astened a plate fitti g the O of case as closely as possible . wing to the presence these f m nitrous u es, it is desirable that in all flame arc lamps with ia clined and cc - axial carbons all iron and steel parts should be

LATE I P V .

FI 3 . twee a : 88 a nd 89 . G. 8 !Be n p ge

CONSTRUCTION OF ELECTRIC ARC LAMPS 89 enamelled or lacquered with a heat- resisting and rust- preventing en m a el. It is also better to avoid the use of steel in delicate parts. — The Bri ti sh Westinghouse Fla m e Arc La m p The ﬂame

— duced into this country was the Bremer lamp the pion eer — of magazine lamps but it was rather too complicated for or m m C m a dinary use . The ﬂa e la p the o p ny now supply is m very simple and of substantial construction. The la p is a good example Of the distin ctively British type Of brake- wheel feeding mechanism with the see- saw striking lever (see p. For this reason we propose to give a detailed description of their lamp for direct current. m m ffe s Of The agnetic syste is di rential , consi ting a series s ri f olenoid, Se (which st kes the arc and arrests the eed in the f usual manner) , and a shunt solenoid, Sh, whose unction on switching the lamp is to bring the carbons together before the a re is struck and to feed the carbons after it is struck

i . 83 84 P of (F gs and , lates VI . and The cores the ' f O of R solenoids are suspended rom the pposite sides a rocker, , m of D the ovement which is steadi ed by the dashpot .

C C l e The carbons , are ﬁxed in ho d rs which slide on the

of n - f m pairs incli ed guide rods g, g, and which are hung ro the

Of o - CP two opposite ends a centre cr ss piece, , which slides On ‘ 7 r - of the tubes , . The cross piece is attached to the end a chain l which passes over a chain pul ey, T, the guide pulley p , and ’ r m through the slotted tube , ter inating in a short rod with a

K c . d knob, , proje ting through the slot Thus in a justing or re- ca rboning the lamp the holders may be raised by pulling K

- . c of down T is atta hed to the side the brake wheel B , round

a be whi ch the brake ch in passes (see Fig. One end of be r l is ﬁxed at f, and the othe is attached to a ever pivoted at X ; the helical spring S tends to keep L down and be taut a B, B f i . round so th t and T are prevented rom rotat ng When,

h . 84 n however, the s unt solenoid (Fig ) pulls its core dow , 90 ELE CTRIC ARC LAMPS the li nk rod [ (and wi th it the lever L) is ra ised by the tilting Of the rocker (whose posi tion when the lamp is out Of circuit

' oﬂ B - i is as indicated), so that the brake is taken ; the cross p ece

It should be noted that the upper end of I has a long slot in f ff m m of it, and is there ore una ected by the ove ent the

l latter is tilted in the reverse direction by the series so enoid. As soon as the current passes through the seri es coil (when the m m v w and carbons co e in contact) , its core o es do n, the long rod

Ir i f of lam rt , wh ch passes right down to the oot the g pa icipates s ri s in this movement and actuates the t king mechani m . This is more clearly ill ustrated in Fig. 86 (Plate VIII ”) where the

CONSTRUCTION OF ELECTRIC ARC LAMPS 9 1

On as - f i as - plates the c t iron oot F, to wh ch the c t iron economizer

One of ca n is ﬁxed. the plates move sideways, and is con

use Ir throu h h m r ted to the long rod g t e s all c ank and the lever.

the energizing Of the series m e Of coil, the side ov ment one carbon occurs and the arc is

. C r l struck onve se y, the shunt

ul ir coil wo d cause to be raised , be brought a cerar te the other

of f for the eeding, as the carbons burn away, with a resulting lengthening Of the are Zr , Sh raises , and the plate m oves inwards . This action

before the brake- wheel is re leased and the carbons feed downwards . The ﬂame arc is Of a colour depending upon the carbons m e ployed, and is deﬂected downwards by a blow- down

a M m gnet, , excited by a wind ing connected in the mai n m u ll in Fi 8 7 showin la p circ it, as wi be seen g. , g the diagram f s O connections and also the substitutional circuit, consi ting

of m C n BR. an auto atic switch, , and substitutio al resistance, This circuit is dispensed with in lamps intended for working s m e ingly, but is provided when two, three, or or are connected 92 ELECTRIC ARC LAMPS

on - n constant pressure circuits . We shall have occasio to f r m 1 2. e er to this co pensating circuit on p . 7 — The Ma gu lne Fla me Am u mp The ma gazi ne lam p has been designed to burn longer with ﬂa me ca rbons and to save tri mming. It has the further advantage that the carbons ma y be burnt to a stump . ” In the Oriﬂa mme arc lamp made hy the Oliver Arc Lamp

C . ha ve a ma azine M con a ini i n i ts stor e o , we g p t ng ag

3 6 40 O to hours . It is claimed that by using ﬂame carbons f cheap quality and Of small diameter a saving in carbons is

e m r eﬂected and a st adier burning obtained . As the la p wo ks f on new lines, and scarcely alls into the classiﬁcations we have m m of its ade, it is desirable to explain at so e length the details construction and working. 88 In Fig. the two downwardly extending limbs of the f m fo ramework , ter inating at a point just above the arc, rm

Of - a the poles the blow down magnet, excited by winding ,

n a which is placed horizo tally and connected in the m in circuit. f of m The framework orms the positive pole the la p . m 89 of The carbon agazines (Fig. ) consist ﬂat receptacles , in which the carbons are contained one behind the other. Pro vision is made at the back Of the magazines for inserting the b m carbons. Spring arms, , bear upon the carbons and keep the o he discha r i n side of C pressed u p t t g g the magazines. lose up Of m l to the inner edge the agazines and c osing it, is an endless

. c a chain rotating over sprocket wheels Two projections, , on e ch of chain, the length a carbon apart, project in turn into the

m f f for agazine and engage with the oremost carbon , eeding it

ward from the magazine through the carbon holder. As each pa ir

fed f r o Of carbons is orward , othe s are pressed int position by the m f r o spring ar s, to be pushed o ward in turn by the pr jections to c of e a on the chain . The p spro ket wheels ach m gazine are

94 E LECTRIC ARC LAMPS is connected by mea ns of a bell cra nk lever and link j to the

n m m h m e regulati g echanis w ence it derives its ovem nt . m s Of of l k The regulating echanism consi ts a pair so enoids , , m f m w ounted side by side in the ra e ork, and having a horseshoe E l di ﬂeren iron plunger working within them. ach so enoid is tia ll w i s of n i y ound, . consists a series and a shunt wi d ng in o f - pposition. The movable plunger is pivoted on a kni e edge

ma l m bearing a king crad e, , which in turn is also pivoted on ” f - a f m kni e edges, , to the ra ework . The link 9 is pivoted on

i of m m m m this cradle, so that the t lting i parts a ove ent to the point of the carbon projecting below the swinging magazine.

f m e Be ore the la p is switched on , the two carbons are s pa

he e 1 n i n rated and t plung r is in the lowest positio . Switch g in causes the shunt winding of k to tilt the rocker so that

c m of the carbons come into conta t. Si ultaneously the drop

e c voltag auses the solenoid to be weakened , and the movable

r f r i n Of the are u plunger d ops, and there o e a str ki g ens es ; a

o n m m of dashpot, , damps any viole t ove ent. The pull the regu

Of t lating solenoids against the action gravi y, depending upon

t m n an ' e uilibri um the vol age across the arc, aintai s q and keeps

n PD and Of the are at its correct bur ing . . The reverse the rocking cradle is weighted to Obtain a balance corresponding to the volta ge of the are it is desired to maintain. The side movement of the magazine feeds the carbon until no further m n f d move ent is available. It is then that a mag etic ee ing motor feeds the carbons from the magazines by rotating the ratchet wheel and shaft connected with the chains Of the two

The m of s o magazines . otor consists a horse hoe electr magnet,

r v m p, p o ided with a loosely pivoted iron ar ature, q, and excited

m - by a s all shunt current . In its circuit is the make and

' r Oﬂ break switch , which is normally in the position. The

8 i switch is provided with links, , both connect ng with the regu

arm l lating cradle and with the ature. The crad e, by its move m r f O ent, closes the switch, and the armatu e, when it li ts, pm s CONSTRUCTION OF ELECTRIC ARC LAMPS 95

i t and allows the arma ture to fa ll a a in. arma ture ro g The , p m i entioned, by its reciprocat ng action causes rotation, and unti l of current and voltage restored. The

9 Fro. so. h e 1

swit c h is an exha uswd glass tube containing

- in of l platinum leading wires, one end the tube being en arged

i g of (F . To prevent a possible breakdown the insula ﬁon h w i Of on e c a on t e ind ng p br aking this ircuit, a sp rk gap is

placed screw the winding as a protection.

to O e in of as closely engages with the p and only p n g the globe , 96 E LE CTRIC ARC LAMPS

- and is also air tight. The heated gases pass through the cen tral m passage , which connects the globe with the space y above the ventilation being facilitated by a small supply of air

r l z l . ente ing the globe through ho es, , in the reﬂection p ate A glass and copper gauze tray at the bottom Of the globe catches the short ends Of carbons as they are discharged from the

The lamp works with a substitutional resistance a nd an

- automatic cut out (see p. which take the place of the lamp

m of f h for when the stu p the ﬁrst carbon alls throug , and also Of r series working lamps, so as to keep the remainde burning . D of n m uring interruption the series curre t in the la p , the shunt winding of k swings the magazine inwards and starts the il 20 3 0 o ratchet magnet p, unt in about to sec nds the arc strikes

c fed m on the new arbons through the holders, the auto atic switch opening to allow the arc to stri ke when the carbon s

o come t gether. The alternating current magazine lamp by the same ﬁrm ha s laminated cores and a tchoking coil instead of an adjustable

di r » urrent m line resistance used in the ect c la p, otherwise the ct a movement is exa ly like the l tter.

All ﬂame arc lamps with inclined carbons are generally a P e for .D . regulated, both with direct and lternating curr nts, a

of 45 . n 11 120 l across the arc about volts He ce, with 0to vo ts 220 f two lamm, and with volts our lamps, can be connected in ri a 5 5 60 of se es ; th t is, about to volts the supply pressure per

of m of r Both kinds ﬂa e arc lamps may, course , bu n in seri es wi th ordina r lam s in so fa r a s the y p , y regulate with

Of l m them, but the light the latter wil be ore inﬂuenced by the s e m are i less t ady ﬂa e , so that such ser es working is not always l suitab e.

98 ELECTRIC ARC LAMPS

m of entirely re oved, though at the expense the intensity of the 20 m light, which is decreased by about per cent . or ore .

E N C LO S E D ARC LA M PS .

. GENER AL REM RK A A S .

rin0i le m ff r f m In p p , the enclosed arc la p di e s ro the open

are of re type lamp, in the provision an arc enclosu , which pro n f m m n tects the carbo tips ro the at osphere, and thereby re ders

potential difference across the enclosed arc is also considerably 80 m 4 5 5 0 higher, being about volts as co pared with to volts PD of . . the open type .

al To keep out the air, a small, elongated glass globe, c led the n o n n i ner or encl sing globe, is used , which co tai s the lower f m t carbon , and is there ore either sealed at the botto , or res s quite

i- - air tight in a removable holder upon a lower cross piece of the

f O of l rame . The upper pening the enclosing g obe is closed by

m as as m m a etal cap (the g cap, it is so eti es called), which has

l for of on y a hole the insertion the upper carbon. The oxygen

r m of a the enclosure we have p oduced a ixture g ses, consisting

of m i i etc w nitrogen, carbon onox de, and carbon d oxide, , in hich

m of the the consu ption carbons is retarded . The consequence

m as n is that the carbons do not assu e a pointed shape, happe s

Fi 3 . f of v shown in g. The sur ace the positi e tip is very slightly of v concave, and that the negative very slightly con ex, the edges

are r of f usually employed, the only cove s a portion the sur ace,

h ' m are nearest to each ot m. This ovement and the consequent unsteadiness of the light becomes greater the larga the carbons

e the stren th of Th n h of t are in pr portion to g current. e le gt ime CONSTRUCTION OF ELECTRIC ARC LAMPS 99 during which a single pair of ca rbons will burn is greater if the

n u for if m off bur ing is continuo s ; , the la p be switched , the gases c f ool, and resh air is drawn into the enclosing globe and, having

ff a a stronger oxidizing e ect, c uses the carbons to burn more l h m rapid y w en the la p is switched on again .

e of f m of In cons quence the ﬂat or ation the carbon tips, enclosed lamps must necessarily burn with a longer are (and D the P. hence a higher . across arc) than is the case with open are m w of the type la ps, other ise the distribution rays would m of f m not be good, and a large a ount light ro one carbon would t be s opped by the opposite carbon . They are therefore regulated t PD of 5 80 wi h an average . . across the arc 7 to volts with direct 65 70 e h current, and to volts with alt rnating current, whilst t e volts consumed in the lamp (line) resistance amount to about

4 . of m 0per cent the nominal la p pressure. Owing to the length of the arc and the slow combustion of

mad for of m like open type lamps, and are e, the sake si ple and

r n n t of . l m st o g co struc ion , a clutch type The enc osed arc la p ' O di ﬁerent mm em is adapted to perate on the co ercial syst s , such i m m as incandescent l ghting, power, and tra way equip ents. For

are m l m the ﬁrst system the lamps styled u tiple la ps, and operate re 110 on 110 and 220volts direct cur nt, and volts alternating u a m current constant potential circ its, in which c se the la p is best of the series magnet type ; whilst in the second class of m r equi p ent, lamps operating in series on both alte nating and — dim t constant current circuits and in the thi rd class of c .

m enclosed arc lamp is not suitable as a shunt agnet type, owing to the movement of the arc and the consequent great

m rre cha nge in the a rc resistance. In such a case the la p cu nt l w ELE CTRIC ARC LAMPS

011 page 19 a series magnet type of lamp with m m a clutch is shown, and the echanis explained.

Fig .

for of 2 m currents about a peres , with

- f m a claw clutch eed. The echanism m is very si ple.

B f tc i - in m e ore swi h ng the la p, the

M o u core , t gether with the s pport and F the clutch F, sink until rests upon

the globe cap, and the claws open.

fr The upper carbon is then ee, and falls into contac t with the lower m carbon . When the la p is switc hed

in , a strong current passes through the carbons and the series coil Se ; the latter pulls up the iron core and

the clutch F, which then grips the upper carbon and lifts it away from

the lower one, whereby the arc is m m struck . At the sa e ti e a current

r passes th ough the shunt coil Sh, whereby a pull in the opposite di rec tion to that of the series coil is exerted

u pon the iron core, and this pull PD increases with the . . across the

are. As the carbons burn away, the attraction of the shunt coil preponde

rates, and the iron core and upper

carbon are pulled down, so that the

Fr 92 of m . o o. attractions the two c ils aintain li m I f an equi briu . the downward movement extends so far that the clutch rests upon the globe

r cover, then the claws open and libe ate the upper carbon. The electri cal conditions in the coils will alter accordi ng

102 ELECTRIC ARC LAMPS

5 PD. c the With direct current and 7 volts . a ross the arc, 8 mm ll carbons are separated by about . But in order to a ow for etc the backlash between the clutch and the carbons, , the ull f l i p of the iron core must be a bout hal as arge aga n.

2 clu tch ff . The may be constructed in di erent ways, and, as

m of f m i ff f m of c a atter act, ore d erent or s clut hes have been made than of any

. 92 the clutch (Fig ) and disc or ball clutch (Frg. 94) show the e f m I f m en ral or . the clutch be ade of metal it should be well g .

of “ the point contact with the carbon . In the Westi s a c a CONSTRUCTION OF ELECTRIC ARC LAMPS £03

- t u m h c sheet me al basket or p nching, and is thus ec ani ally

m fr m i in The clutch ust prevent the upper carbon o sl pping, m m f u na void case the la p is shaken, and ust adapt itsel to the of able variations in the diameter and smoothness the carbon, so that the latter neither sticks nor ca uses too grea t a difference as of the o m in the rele e the clutch, which would inﬂuence n r al

i of n . 94 posit on the iro core . In this respect the disc clutch (Fig )

r f m f and e the carbon ve y tight, requires care ully anu actured v ry

- f s a of even sur aced carbon . The rele se the disc or ball clutch

occurs as soon as the trough - shaped case has sunk so fa r that the discs m' balls rest upon the ﬁxed uprights whi ch enter the ca se i f , and the d scs can no longer participate in a urther down

w m m o ard ove ent f the case. Balls have the disadvantage that ‘ m ll they oder too little fricti on as the contact surface is so s a . Both discs and balls must be so arranged that they cannot fall f out when the carbon is removed . Both are there ore protected

are by a slotted plate surrounding the carbon, and the discs

provided with short axles .

3 ra me m of . Thef connecting the core to the clutch is ade din brass rods or tubes accor g to the type of construction . 4 m bon holders ma f m . The y be made ro split bronze

le v 3 8 m s e es, or as in Fig . ; since, as a rule , enclosed arc la ps

only burn with small currents of about 3 to 6 amps. The lower carbon holder is generally held in a metal socket and

u - sec red by a set screw . All kin ds of metals and alloys have been tried for the carbon holders in the enclosing globe ; but the metal whi ch

of are i withstands the heat the best, and wh ch is not deposited on the inside of the globe either in the form of dust or a brownish

as as m scale (which unites with the gl s and is not e ily re oved) ,

n i ca st . is iro , e ther or wrought ‘04 ELECTRIC ARC LAMPS T 5 he ot . 95 . m oring globe is of the shape shown in Figs and

96. n m e The pattern , open at both e ds, can be ore easily cl aned , whilst the other pattern possesses the advantage of having only f one aperture to keep tightly closed, and is there ore more air f tight . In both patterns the edge o the apertures must be very m c . evenly ground, so that special etal rings need not be atta hed t m vm- i f w With hese rings the arrange ent is y d ﬁcult, o ing to the

of the me unequal expansion the glass and tal, set up by the

unavoidable variations of temperature.

Fr . 6 Fro. 95 . o 9 .

m m m I n 97 (Plate IX .) is shown the lower la p echanis ’ ” m - o s m Co D . of a British Tho son Houst n . rop Fra e lamp The

n l m e lower carbon and e closing globe are he d in a re ovable hold r,

- tu m of device . A quarter a bayonet catch allows the outer globe

to be lowered and gives access to the inner globe and carbons . By loosening tw o thumbscrews the removable holder can be f mne taken out and a resh lower carbon and clean r globe put in . i m The lower carbon and enclos ng globe being cla ped in, the

CONSTRUCTION OF ELECTRIC AR C LAMPS 105

re din globe, when lowe d, is rigidly held by the sli g rods, and

Thi s fo of m a for s cannot swing. makes this rm la p suit ble treet

’ l 98 P . ighting and places exposed to high winds . Fig. ( late X )

B T- H D shows the . . . rop Frame lamp with the outer and inner globes together with reﬂector. te of t m In the pat rn enclosure sealed at the bo to , the lower . carbon holder must be so arranged that the former entirely m encloses it . The enclosing globe ust also be able to

M produced when the p is switched on , E without cracking. nclosing globes which t0 are only open at the p, are screwed to a

ca or m m gas p, globe cap , as it is so eti es called, an asbestos ring being inserted w bet een (see Fig. They may also be

r in p essed against the cap, and held place

n be eath the globe (Fig . In the m ” m 104 Fixed Fra e la p, shown in Figs . 105 t and , it will be seen hat the lower

t the enclosing globe, which is kep in position by a bail hung on two piston

f The gas cap sur ace, against which the enclosing globe rests , should be machined true and smooth in order to make the joint

- m as nearly air tight as possible. The cap ust rest with a m re oderate pressure on the globe, otherwise it will sult in m cracking and chipping at the edge, with the obvious di inution

if of M re v f m of in the l e the carbons . o o er, this sur ace ust be a

The ﬁner grade of soapstone has been successft used for this

ca to f m purpose . The gas p is attached the ra e and is provided 106 ELECTRIC ARC LAMPS

the f rod holds lower carbon, and is ﬁxed to the cap or rame, then the centre must have an insulated bushing of soapstone . The best practice seems to consist i n making the ga s ca p of m l for etal , with an insu ated centre bushing low tension lamps , mice w ed n and in high tension lamps . The bushi g is designed i “ to n an; m one is a the s g ve two req , th t upper carbon not

u wo ld considerably shorten the period during which the carbon , is that it shall act as a relief valve for the explosion of gases i n

the m v 0118 inner globe . This is ost n when the inner 81 is generally when the lamp is l -cd on after being out from

ten m n to a cw ss of a ir seven to inutes, when, owi g the , there is an explosive mixture inside the globe which would probably

i i m u shatter t. In the West nghouse la p the b shings are arranged to have a

m them ent, allowing to lifwd e be by the gas s, in such a w a y as to

m the at osphere . In some makes of lamps

the cenma l hole is

to adopted, carry away and In othm

f I f i rs access o air . the nner globe only lightly

ca m of al c eni r the gas p by eans a spring, then the v ve and p m

CONSTRUCTION OF ELE CTRIC ARC LAMPS 107

om Inner globes, open at the top and bott , are usually m f screwed to the la p rame at the lower end , whilst at the top the gas cap can be carried loosely by the guide rods of the frame 100 and rest upon the globe (Fig. ) or be pressed down upon it n by a spri g. In the latter case the screwing of the bottom is

of unnecessary, as also the valve in the cap, provided, course, that the latter is not attached to the globe so secure ly that it

6 da sh . The p ot is similar in construction to that of open m e m m m arc la ps, exc pt that in enclosed arc la ps it ust be so e w ma hat stronger in its action . This object y be attained by

s m increasing either the ize or the nu ber of dashpots. In

of f m m i and as uni or a dia eter as possible, the valve seats be ng m accurately achined and the plungers ﬁtted with care, so that each dashpot will operate in about the same time as every

r f m m other one . And to prevent the plunge s ro ja bing in the

s a e f m a re m cylinder when the lamp is trongly he t d, the or er ade of m u graphite, which has practically a negligible te perat re

f r v coefﬁcien t and satis acto ily pre ents any sticking .

i n m a d usti n s ri n s 7 . To adjust the current some la ps, j g p g

wei hts d or g are provided accor ing to the particular construction . The former are ﬁxed to one end of

The an adjustable screw pin . latter m a y either be attached to the rocking lever in the form of

as small additional weights, or, in a weight mounted on a threaded Fl a . 101. f stud on the rocking or eed lever,

- ti of and kept in position by a set screw, thus permit ng a very

accurate a re (or current) adjustment.

termi na ls m to those shown in Fi s. 4 1 8 . The are si ilar g

ri m a m and 42. Ame can ﬁr s ne rly always place the ter inals r08 ELECTRIC ARC LAMPS

m on ta of n re outside the la ps , p the casi g. They are the fore petticoated to protect the insulation against deposits

I n order to a tta i n a lon er er od of i it is desi ra ble g p i burn ng, to protect the casing against the admission of air ; on the other

to their expansion at high temperatures . For this purpose, one n of or two valves consisti g simply ﬂat springs, cover

T- H m i for B . . . open ngs in the casing. The casings la ps

9 . (Fig . 8) are made of solid copper in one piece Three h m t0 r bayonet catc es in the la p p suppo t the casing, and a

se - F ﬁ f m single t screw holds it rigidly. or the xed rame la ps

fra m m the casing is the same as the drop e la ps, except at the lower end where the ﬁxed frame ca sing is arranged to s l hi fr m upport the outer g obe, w ch , in the drop ame la p, is supported by the telescopic globe - lowering device. In the f m e u m i w or er, the out r globe is s pported on a etal r ng hich f n the aste s to casing by bayonet joints , and hangs by a chain

O e . uter globes may be either clear, opalescent, or alabast r

ma i fa r The lower opening y be om tted, except in so as it is

for m necessary attach ent, because in this lamp the ashes are

c r l already aught up in the inner globe, and it is are y necessary

r to clean the outer globe . For streets, dockyards, and gene al

n results. For interiors the opalesce t or alabaster outer is to

f re be pre er d .

If of a rc both globes are opalescent, the movement the is not so noticeable from the outside on account of the reﬂection

al of between the two globes, though the loss light is naturally Al m f considerable . abaster inner globes i prove the quality o

CONSTRUCTION OF ELECTRIC ARC LAMPS 109 l as ight, but do not resist heat well as opalescent globes, which m o are re durable . Sometimes the outer globe is dispensed with and the inner

globe is made rather larger than usual . The spherical globe

g Fi . 102 P XL in ( late ) , which, with a shade or a reflector, is ffi e very e ci nt, and concentrates the light in a downward ‘ re i s di ction, is such a s ngle enclosure . The first two globe

for are the usual enclosing globes, the third is a twin carbon

m f - m la p, the ourth the above entioned single enclosure globe ,

f e for f m m the ﬁ th is a cylindrical out r drop ra e la ps, the sixth

for f m for f m m . an outer ﬁxed ra e, and the last drop ra e la ps boo 10. sus ensions of i r k. The p are two k nds, sp ing and f m 103 P of e The or er (Fig . , late IX .) consists a highly insulat d f m in spring support astened to the la p by a cotter p , and tapped

for w on scre ing to a bracket. A spring absorbs vibrations ,

m fr m whilst the support keeps the la p o swinging. The lead

wires run through the support into the la mp . b ook 98 f m The suspension (Fig. ) is astened to the la p top

m m arr in the sa e anner. It has two lugs c ying a porcelain m insulator with a link for hanging the la p on a hook.

DE C L MP C CR P O F EN LOSE D AR . . S I TI N O C A S

104 andu m of M Fig. indi cates the new model J s la p essrs .

D o ai m f rake and G rham, which, whilst ret ning the ain eatures of t of of m the old pat ern (one the pioneers enclosed la ps) ,

m m - m m e bodies several improve ents . The iron clad agnet, ar a f m n ture, carbon holding ra e, and enclosi g globe are concentric

r m m m to the cent al ste , ensuring correct align ent when asse

n of m for bli g . The dashpot is placed on one side the la p

e of of eas access, and by means a lever is geared to the

a m u m of 2 1 r at re echanism in the ratio to , giving a ff powerful and quickly operating dashpot e ect. The clutch

‘ 104 800 alsc ﬁ g. . n o ELE CTRIC ARC LAMPS

3 of weighs nearly lbs . The great inertia this heavy weight natura lly acts somewhat as a ﬂywheel in steadying

small ﬂuctuations. The total weight of the me

held in a loose sheath and current is led to it by

give a a n th a nd fric

ti onless n c co ta t, and thus ﬂ avoid exihmcords . The negative carbon and en

a ud i r nne globe holder, which supported by f m the negati ve spring ra e.

frame are insulated from the body me of the lamp and sm' ve to ca rry

as curm t. The g cap is made by ma chined meml facings to Fro. 104 . the lower w t of the

‘ f m diﬂuser lamp body ra e, which acts as a light .

w The lamp has a selfc ontained resisMnce in . ta p of the m la p. The circui t through the lamp is as follows : current

1 12 E LECTRIC ARC LAMPS

f in Fig . 105 is a multiple lamp of the series type or alternat g

m of 10 P . Fi 10 . 7 6. sche e connections in g. Fig ( late XII ) shows

B T- H m m for u a . . . ultiple la p continuo s current circuit with

e of 108. i for schem connections in Fig. It w ll be noted that direct

l for al current an adjustab e resistance, and ternating current an

d l - for ro a justab e choke coil , adjusting the arc voltage, are int duced d 110 ff t . An a justing clip (Fig . ) e ec s the adjustment on F this resistance ( ig. which consists of bare re

e c m m 011 8 Ro sﬁggn c o sist n e wire

u t rn in a separate groove,

the turns to be short

Fi 111 ( g. ) is made with a laminated iron core and with separate form er m wound coils, so that ore or less turns can be con

s 108 u eted. In Fig. the lamp has adju stment for

n a 5 two curre t c pacities , 4 m d or § a ps. To a just the lamp for its higher

r cur ent rating, connect the

wires A a nd B to the Fro. 108. lower

112 shows the shape of the magnet core for alternati ng u c rrent. To it is attached a ﬂat spring which is fastened to the

of e the core by the pulsation the alt rnating current, and thus

simultancous of r ar of prevents a vibration the othe p ts the lamp . I PLATE XI .

Fm . 116.

e 11 [ Ta j a ce pa g 2.

1 14 ELECTRIC ARC LAMPS

n 116A m of t . resista ces, and Fig. is a sche e its connec ions In resistance is introduced by

through the shunt

Fro. 115 .

of an interrupted series coils . Inclined f m i of The trouble ro accumulat on dirt. turns of the

arra n f sma l r sh coils are ged or the lest cu rent, and unwd across m them is an adjustable resistanoe. In this way the la p current m ay be altered without any altera tion of the magnetic

1 16 E LE CTRI C ARC LAMPS

m . 11 1 XIV . Figs 7 and 1 8 (Plates XIII. and ) show a la p for indirect lighting with a Concentric Light Diffuser above the

— of m arc enclosing globe. This diffuser is made etal with a v f f cur ed reﬂecting sur ace, by which a particularly avourable of l dispersion the rays is obtained. Beneath the g obe is a white glass shade which permits a little light to pass through.

- ff f for ofﬁces . This di user is use ul drawing , etc All the American lamps are provided with a single pole m switch, ounted on the lamp top, and intended to be switched f f back and orth by a long pole in the hands o a janitor. It consists of a blade made entirely of insulating materi al with a conta ct button inserted in it which is forced between two o stati nary contacts to close the circuit. There still remains to be mentioned the construction of an enolow d arc lamp for direct or alternating current in whi ch no f magnets are used. In their place the expansion o a hot wire

119 and 120 show the principle of such a lamp Foster

System).

h m 0 c of i t In t is la p a bar, , one end, l , wh ch res s in a pivot,

r m k f e has its other ext e ity, , astened to the levers j l , j ; the latt r l mi k a re l bent ever, j , works a clutch. To the extre ty a so

d r a nd attached the hot wire and the sp ing 9, as the spring expa nds or contracts the point k is deﬁected to the right or

f Th is so a rra n ed tha t if current a ss s le t. e lever g no p e through the wire or M p the clutch liberates the upper carbon On and allows it to make a contact with the lower one. n k f a nd switching on the curre t, d expands, g pulls to the le t, f u the lever j li ts up the clutch and hence the pper carbon,

so that the arc is struck. The play between the tension

1 18 ELECTRIC ARC LAMPS

t of the cannot be ob ained, an occasional renewal wire is

. This la m m uires ca n used necessary p q no dashpot, and be with direct and alternating current without a ny further

D ARBONS FOR E CLO ED ARC L MP . C N S A S .

The ca rbons used i n enclosed arc lamps must be of a quali ty m especially suited to them. They ust produce little ash c f and must not cra k easily, as both these aults produce a very W m unsteady light . ith direct current la ps, two solid carbons

SIZES or Om ens AND Lm Panssuaas roa Dmaor LA P TE XV .

Fl 1 o. 21.

Ta a ce a e 1 [ j p g 1 8 .

CHAPTER IV

I T IN TENSITY LIGHT DI S L GH , TRI BUTION AN D THE APPLI , CATION O F THE ELECTRIC ARC FOR PURPOSES OF I LLU MINATI ON

I . LIGHT INTENSITY AND LIGHT DISTRIBUTION

IN spite of the efforts of the International Electrica l Congre ss and other Congresses there is at present no international

n f of m co vention with re erence to the unit lu inous intensity,

a 1896 C nor a practical st ndard in general use . In this ongress

u é m o proposed the bo gie d ci ale as the unit, but th ugh its relation with common ﬂame standards has been determined with

m c m r so e pre ision , it has never co e into unive sal application.

The legal standard in English - speaking countries is the m 120 ai 77 76 m of m sper candle, which burns gr ns ( gra s) sper a of n ceti per hour. This legal unit is spoken as the sta dard " is to u e of n candle, and said give a lumino s int nsity one ca dle m n n n power . It co es nearer to bei g an internatio al unit tha

a n y other standard.

The boo ie decimals is one- twenti et of the iolle sta n r w i g h V da d, h ch is the luminous intensit emitted normal to its surfa ce one s uare centi y , , by q f mol n la tin lidif i t m ra meter o te p um a t its so y ng e pe ture. LIGHT INTENSITY AN D LIGHT DISTRIBUTION 12 1

The omcia l a for L stand rd testing gas in ondon , also recently a the n P a L dopted by Natio al hysic l aboratory, Bushy House, is ’ m ni of - of the Harcourt la p, bur ng pentane, and a candle power 10 c legal andles .

f m e m f m The He ner la p ?used in G r any, and so o ten e ployed

e for of ef in oth r countries purposes r erence, burns amyl acetate .

used in France and Italy. f m The He ner lamp is si pler in construction than the pentane, m m of small, and ore easily set up, but the ﬂa e the pentane is d M a f easier to a just oreover, a we k point with the He ner lamp n is its colour, being disti ctly reddish orange , whereas the pentane is much whiter. Expressing the values of the units in terms of tha t of the legal candle, we have 1

The ligrt intensity of an a rc lamp in a certain direction can be measured by a photometer by comparing its illuminating power of the photometer screen with that of a standard light

ll m n as of intensity . The i u inati g power me ured is the amount light recei ved per unit area of photometer surface placed at right angles to the rays . If we imagine a source of light at the centre of a hollow

l r sphere of unit radius and emitting light equal y in all di ections, then it is evident that the ratio of the quantity of light received

r of of on an a ea, S, the unit sphere to that the whole sphere is

For descrhrtion see The Notiﬁca tion of the Ga s Referees for the Yea r i e published by Eyre and Spott swood . ' ‘ i tion see the EZektrotodmisch Zeitachr vol. iii . . 445 and 1 For descr p iﬂ , p , 20 vol. v . p. .

rson Journa l I nst. E . E . Ja nua r 1907 . See a lso footnote t C. C. Pa te , , y,

Appendiz l . 122 ELECTRIC ARC LAMPS

of w f equal to the ratio the solid angle, , enclosed by the sur ace, S, to 2 h the solid angle, 1 , enclosed by t e sphere . The surfa ce enclosed by the solid angle 21 x since

Hence

ﬂ ris ill umina ti ng power is equa l in all directi ons i n the

' above e of arc la m whioh has a diﬂ r nt ca s . In the case an p e e ff intensity in di erent directions , the mean illuminating power of 4 would be the total quantity light given out divided by a .

The light eﬁ oi ency of the arc is obtained by dividing the

of n of diameter and position carbo s, the supply air to the arc,

124 ELECTRIC ARC LAMPS

122 i to a greater ex ten t. In Fig . are plotted l ght intensity

i of ri curves, showing the relat on between the va ous m e ff . On la ps without outer glob s, and di erent current values

f i s the other hand, the e ﬁc ency diminishe with the increase in of length arc (viz. but to a less extent. The eﬂi ci ency m PD increases so ewhat on increasing the . starting with a very

Di rect Current Open Arc. o L WIthont s gIob c. IL Wlth s gl he.

1000000800700000 600400300M0 100 0 100 200 300400 600 600700 800 900 1000

Fro. 123 .

ac m. m short arc, but soon re hes a maximu For, although ore i light is exposed by the crater, a large absorpt on takes place ‘ m i s f c of in the carbon ist wh ch it traver es . The e ﬁ iency arc m m lamps is di inished so ewhat when worked in series, on account

s of the extra power spent in the steadying re istance. The effect of the quality of commercial carbons upon the

" Mrs A rton The Electric Arc . 3 45 . . y , , p LIGHT INTENSITY AND LIGHT DISTRIBUTION 125

of f m m intensity the light, apart ro its steadiness, consists ainly

of is ri i qualities a smaller angle d t but on), and in the dirty of e ing the globe due to large deposi ts of ashes . With treat d

si dera bl n e of of . y i cr ased, in spite the increased deposit ashes

l. With reﬂector bnt without s globo.

1000 900 800 700600 5 00 400300 200100 0 100 200 300400 600 600 700 800900 1000

Fro . 124.

With increa sed diameter of the carbons the light inte nsity is m of di inished, on the one hand, because, in consequence the

re s f n inc a ed sur ace (increased heat radiatio ) , the carbon tips

for e glow a short r distance, and on the other hand, because m l the angle of distribution becomes s al er . With an increase of oxygen the burni ng of the carbons is increased per uni t of

im an of t e, d hence the temperature the tips, and hence also the 126 ELECTRIC ARC LAMPS

l B t a dmi sd on ight intensity, are increased. u since the increased

of are l m m t o s air depends in a ps ainly upon ven ilati n, so al o

i m m m of is the heat radiat on so ewhat greater . The echanis the lamp itself has only a secondary inﬂuence upon the light

f m the e of h intensity, and shows itsel ainly in st adiness the lig t. For most purposes only the hemispherical light intensi ty and

- Di rect Current Fla me Arc wit ertica l cc a xia l ca r ons. h v , b

s L WIthout globo. m m n globe.

“gu m -try . 1000 900800700600 5 00400800 200 100 0 100200 300 4005 00 600700 800 900 1W0

Fro. 125 .

i of a the light d stribution the are re of practical intemst. ri of h 123 13 2 characte stics the latter are s own in Figs . to . These polar curves indica te by their radii vectors the different

H f units and u m E are in e ner , to red ce the to nglish standard

v m mu use. candles, the alues ust be ltiplied by l z8 ELECTRIC ARC LAMPS

It ma y be seen from the curves that the distri bution is not m though not at all disadvantageous to the illu ination.

Lamps contain the greatest light intensity within angle of 20° 0° to 7 below the horizontal. LIGHT I NTENSITY AND LIGHT DISTRIBUTION 129

’ n a r ns di ﬂ a nd o incli ed o bo er in this respect possess, with ut a ° o e m of 90 . gl b , a maximu angle below the horizontal The polar of 124 126 13 1 curves Figs. , , and only appear in alternating current lamps provided with a reﬂector. The polar curves of lamps with cc- axial carbons may be ima gined as the

' cross- section of a surface of revolution with the va ti cal as

ui wi axis, which conception does not apply q te to lamps th inclined carbons . In alterna ting current ﬂame arc lamps with

n in rbom Alterna ti ng Ourrcnt Fla me Aro wi th i ol ed oa . IL s lobe LWlthoot a gloho. Wlth s . t Ligh in ﬁ nity .

t of carbons, a par icular value the light intensity on one side of the axis of rotation possesses an equal value on the

i re other side (Fg. whilst with the corresponding di ct current flame arc lamps the distribution of the light is some w ri hat unsymmet cal, because the positive carbon emits more f light than the negative (Fig. The influence o the globe is f o loss of io elt, not nly in a light, but also in a certain reduct n of the ma M um and minimum of the light intensifies and x 130 E LE CTRIC ARC LAMPS

l n m distri g obe, as is usual with e closed arc la ps, the maximum b uti on of light occurs usually at a somewhat smaller angle

m 130 of globe (co pare Figs. and The inward bending the

With lnncr globs and no outer.

“ M M !” 0 W 200 ”

. 127 128 he curves II . in Figs and , to the vertical , is due to t presence of the ash tray in the lamps during photometric observations . It has been stated that the lighting power of an arc M p is

ri l - c e given in mean hemisphe cal cand e power, the andl power which would occur if the light below the horizonta l were if m m f un or ly directed towards a he ispherical sur ace . This light

13 2 E LE CTRIC ARC LAMPS

’ s the pola r curve may be obtained by Bon sea u s method. In

Sm ﬂ Dheot Onrt o-ed m

M M .

' ' o g g‘ s s s e e s s s g g

F m. 132.

1 2 3 4 etc f md i o r the sections , , , , o the i mot rs are p ojected on cc- or OY of oo- a the dinate axis a rectangular ordin te system,

l m len th of the r J J J etc . bein made a to g o dinates l , ; » , g equ l LIGHT I N TE NSI TY AND LIGHT DISTRIBUTION x33

OX CY the m of the and an area, ean ordinate which gives quantity of light received by the hemisphere (of radius R) 2 R f ’ r x Area of the Rousseau sur ace. Hence the mean quantity of light received per unit area of

m i a m c i we the he isphere, . . the mean he ispheri al lluminating po r,

’ Zr R x Area of Rousseau s surface

“ (Since 2x11 area of hemisphere)

the sca le of ordina tes bein tha t of sta ndard ca ndles g .

- In Fig . 122 are plotted the mean hemispherical candle powers of for ff various lamps di erent currents . It must be noted here that in alternating current ﬂame arc a - l mps, with super imposed and with inclined carbons, the consumption of wa tm in the arc is less than the product of

a m a a . f 08 5 09 current and la p w sur The power actor is to ,

a r PD r a i n as . although the current and e . . are p actic lly ph e

The r f 1 m powe actor is less than , because at the maxi um v of arc current value (at e ery pulsation) , the conductivity the , owing to an increased heating of the carbons and the generation of of a greater quantity conducting vapour, becomes so great

the PD m m that decrease in . . in the arc is less at that o ent than f f m of be ore or a ter the maxi um value the current. The f l terminal pressure, there ore, shows during each current pu sa

m m m i s. n of PD tion two axi u values , a be ding in the . . curve when the maximum value of the current occurs.

“ ” See Mrs. A rton The Elec ric Arc . 45 4 . y , t , p 134 ELE CTRIC ARC LAMPS

The lamp pressure is about equal in direct and a lternating w t i current ﬂame lamps ith inclined carbon . Hence, ak ng

of f c s m of of account the power a tor, the con u ption energy a

10- m amp . alternating current ﬂame la p is not greater than that of - m an to 9 a mp. direct current ﬂa e lamp . The quantity

of f f . 122 m light is, there ore, as may be seen rom Fig al ost equal .

On all u - m the other hand, in lamps with s per i posed carbons, the of li of quantity ght, with equal consumption energy in the

re di ct current. The lower carbon tip, with alternating current, emits just as much light above the horizontal as the upper

w far m carbon emits below, whereas, ith direct current, by the ost

di ed light is emitted by the positive carbon. The light mct upwards is only partly reﬂected by the reﬂector and is partly absorbed by it.

er e r f r te m Th e are , howev r, clearly othe acto s which de r ine the lower candle - power per unit of energy of the alternating cu rrent

re are in comparison with the direct current a . The power f f a m e 1 actor o the usual alternating current re is approxi at ly .

in s of Also, neglect g the greater lo s owing to the presence two

s a - s m globe , the c ndle power is le s in enclosed arc la ps than in n of lamps with an ope arc and an equal consumption energy . The values of the mean hemi spherical intensity given in

. 122 of nl c Fig are, course, o y approximate, be ause, as already m m a . entioned , many circumstances y inﬂuence the absolute value In using these values the loss due to the use of an outer globe

II. ILLUMINATION.

In planning out lighting schemes for outdoor work the f n general principle ollowed is to obtain the most inte se and,

s m f l t n . at the a e time, uni orm horizonta illumina io This wi ll be better attained the more lamps there are and the higher they x36 E LE CTRIC ARC LAMPS the square of the distance of the ll to be i uminated . This will be di cula r to the rays emitted by

nation becomes

The unit of illumination is that obtained by light intensity the candle - power) upon a unit surface placed at a unit distance perpendicular to the rays . En i f t In gland, the unit distance be ng the oo , the unit chosen 1 foot a nd is that produced by a standard candle at , is con

ca ndle- oot veniently called the f .

of i n H ner- M rs The unit illumination Germany is the ef , " - Em f . n th or , and is sel explained by its name In Fra ce e unit

Ca mel- metre f th is the . The ollowing table shows e relation between them

And since 1 Lux 0085 5 candlefoot

Illumination 0- 085 5 ca ndle foot

See A endix I . P o metri i i pp h to c qua nt t es. A ILLUMIN TION. 137

I n Fi 134 Jis a g. soume of light of candle - power Jat a height a above

The ground or horizontal illumina ti on at unit surface distant b from the pillar or vertical a is equal to

'h l - f R m f 18 1?cand e eet, where eet Fro. 184 . the slant distance from the source of light and a the angle which the rays make with the normal

to the surface. Al so b = a ta n a . The horizontal illumination becomes

Joos u

008 0

° 1 x 008 a x Jcandle- f 5, eet

or without reference to the angle of inclination a

g ? JCOS a d a - Lb

x Jcandle - feet

I f the source of light Jbe that of an arc lamp whose polar of curve light intensities is known , the horizontal illumination of the surface to be illumi nated ca n be calculated for the various 8 values of a by multiplying the value of cos a by the corre spondi ng value of Jand dividi ng by the (height of the 138 E LE CTRIC ARC LAMPS

Fi 13 5 i a of D. C. In g. the characterist c pol r curve a arc lamp of the Open type is given in English standard candles ; and for a i 2180 - the light intens ty is candle power . The value s ° of a for a 3 5 5 4 9 If m nd so cos is 0 . the la p is suspe ed, 25 f for that crater is eet above the ground, we have the ° horizontal ground illumination for a 3 5

05 4 9 x 2180 Ill tion

- f candle eet.

ff to di erent angles . and plotting these any scale as ordinates,

the ﬁ . 13 5 . 13 6 and curve in g is obtained In Fig. , the polar

t n of D. m illumina io curves a C. ﬂa e arc lamp with inclined carbons are similarly plotted. The curve shown in Fig. 135 is = ° plotted from a 0 to and from it the domes of

140 ELE CTRIC ARC LAMPS

u and minimum illumination to the m m illumination .

ma ximum solid angle of radiation « 1 upon the area of illumi na ted f rt sur ace pe aining to the solid angle. The value of the mean illumination for a given angle may 1 1 ILLUMINATION. 4 be o by regsrdi ng the curve of illumination a s the boundary line of a rotating body, with the vertical through

of a s l f the point the light axis, and the il uminated sur ace

rotating body to a cylinder of equal ba se and volume . The height of the cylinder gives the value of the required

ll m a E i w a mean i u in tion “ , For a sol d angle (

i 13 5 . This mean value is candle feet for the curve in Fig .

In order to obtain the candle- power necessary for a given m of mean horizontal illu ination, with a given source light, it is necessary as the basis of the calculation to construct the

- a 1 f of candle power at a height oot. The values the mean ° horizon tal illumination for the different solid angles from 60 ° to 15 0 of i (in increments are then obta ned, and the products of these illumination val ues and the corresponding of these products gives the vertica l component or useful part of the quantity of light radi ated within the pa rticular solid angle

If (P o ri e a w is the t tal light dist but d within the solid ngle , m f f i and , the vertical co ponent or use ul part all ng on the f S f E m m sur ace (in square eet) , , the ean horizontal illu ination

« 1 within the angle , then

t P E . , , S

P ri the Lumen In the hotomet c units, Appendix I is the

m 1 possessing a mean illu ination of m .

. 13 7 of w ri t As an example, Fig shows the construction a i llumi na taon cu rve for the polar curve of an ordinary direct

are m for current la p with globe, to be a basis calculation, and

XV. v of (P for ff l in Table the alues , calculated di erent ang es ‘ 42 E LE CTRI C ARC LAMPS l 44 ELECTRIC ARC LAMPS

25 . of . say, about per cent the light We must decide at what height the lamps are to be suspended . For streets (including

ar r a of squ es) , poles are gene ally employed, so that the height 20 the sourceof illumination is about to 3 5 feet. For simplicity 3 0f 10 as let us take eet ( yards in the ﬁgure) the height. We can reckon that per lamp a circular su rface of diameter about three timss the height of the lamp will provide us with

m . l c . s of good illu ination (For practica reasons, g toppage trafﬁc

u of the f thro gh use too many poles, or cost thereo , this diameter m f al d is someti es increased to our times the height, though the

i f d 2a most un orm illumination is obtained with .) Taking f 3 0 f m f the height o the lamps as eet, the dia eter o circular

er M 3 0 r f 00 surface p p equals ya ds, and the sur ace about 7 the of e f square yards . Hence number lamps r quired or the

1 square equals W 4 . It depends upon the shape of the surface to be ill uminated whether this number of lamps ri u can be suitably dist b ted, or whether a greater or smaller ou number of lamps sh ld be employed. We shall choose m r 138 thirteen lamps, distributed and nu be ed as in Fig. .

of d ri or The maximum solid angle ist bution (see Fig. ° u 15 0 a for of practical val e, may be taken as ( ordinary for t r n direct current lamm ex erio lighti g.

For a height a 3 0 feet and the angle a the maximum circle of illumination a per lamp has a dia metm'

- a tan a = 75 rd . a are 2 x ya s These circles, , drawn to

ﬁ . 13 8 l for scale in g , and so also the circ es the side lamp ;

corresponds 6 te en angle ° ° 10 0 0 of 130 n of 1 ( circle to an angle ( and, ° r d of 140 a : lastly, ci cle to an angle (

for From Table XV . can be taken every proposed lamp the of

1 8 of h rt lamp No. 7 (Fig . 3 ) the approxi mate value t e ve ical luminous ﬂux given by a source of light of a mean hemi

° 6 corresponds to an angle of distribution of 15 0 and lies of entirely within the surface to be illumina ted. For each the ° 4 5 9 10 of (P for 140 d lamps , , , and the value , (circle ) is

Fm. 188.

’ and to thi s must be added a fraoti on of diﬂerence in tP for the , ° 140 . di ff 04 8 and According to Table XV this erence is , and repru ents the vertical luminous ﬂux falling on the surface

for of 4 5 9 10— l — n each the lamps , , , and about !o lies upo the round to be illumi nated 9 of thi s ff 048 g ; so that only 1 6 di erence , L 146 ELE CTRIC ARC LAMPS

i s. 048 043 2 ( x , D need be added to the value ,

v . of (D for a of 4 5 9 given abo e The value , e ch the lamps , , , ) 10 for M 1 01 of 1 - to 4 and 1 . candle power is equal 8 82.

ma f r The same method y be ollowed with the othe lamps , except

of 0 for al of di stri that here the value , is chosen a sm ler angle bution f c for m 2 6 8 12 of rom the table ; g. la ps , , , and the value

l t illuminated square. It is not practicable to se ec the added ' ° r as f of di ﬂerence

r to e t s but it is necessa y use one or two int rmedia e angle , viz . ° ° 110 (P for 90 19 d to To the value , must be a ded ° ° the fractions of the values between 90 and 110 and ° 130 lr and and The added amounts depend, as a eady of f i f stated , upon the amount the overlapping sur ace wh ch alls

urf illumina wd. m Fi within the s ace to be For the la ps in g.

138 XVI . a ul for n , Table gives the c lc ated results a u it For the surface to be ill uminated the average value of

spherical candle- power amounts to which value corresponds approxim m to an angle of distribution of (For approxi mate calculation of the illumination of a public square of n different dime sions than the one worked out, assumption of this of f angle of distribution , or rather the value the use ul quantity

s i of light corre pond ng to this angle, gives a sufﬁcien tly exact

for are result ordinary direct and alternating current lamps. ) For the surface under consideration we said that the total

a m (I) ui for vertic l lu inous ﬂux , req red a mean illumination E ,

- f E S of l candle oot was , x 5 x This

m of m . i e n ME OHP and the nu ber la ps , viz th rt e , gives the M necessary mean hemispherical light intensity per p.

per lamp

143 ELECTRIC ARC LAMPS

s i u n r C and D. Poin E The ame ll mi ation occu s at points B, , t is i ed m s n a ein ence only lluminat by three la p , the a gle b g h the ill uminati on at this point will be

0-08 x 3 x 85 0 nale- f ca oot,

l na J K L which il umi tion applies also to the points F, G, H, , . . a n M d .

i n Fi 13 is n ar the m l m . 7 The maxi um i lu ination, as seen g , e

se of 4 a r fr a n an l a ba each lamp, at about 4 y rds the e om, at g e ° approximately 25 (0 a tan a 10tan 25 o m No il als be A point ya rds t the right of la p . 7 w l o f ula te i ﬂ 8 5 and 10. a u o a a c n uenced by lamps , , The v l e (c l d)

for 8 for ea of la s 5 a nd 10 a From lamp is ch mp ,

d . 13 7 for stan curve, Fig we have, ° Lamp 7 a 25 Candlefoot 8 74 o per 1 0 5 a 68

1 f . ° oot high 10 a 68

Ma u lu i 0 - xim m il minat on 8 candle foot.

The degree of va riation of illumination for the centra l part of the square is 08 03 05 _ 05

or 100per cent .

xa m le of Li h — a nin a n E p g ti ng of a n Interi or. I n pl n g ri t ll sa m f e x inte or ins a ation the e method may be ollow d, e cept of of that the power reﬂection the walls must also be considered . ’ S 4 5 x 4 5 ar f e 21 fe has to uppose a room squ e e t, and et high,

- I n Fi s. 138 140a ll num ers sta ndin f r i n hs and hei hts g b g o dstances, le gt , g f n enienc are or co v e expressed in yards only. LIGHT INTENSITY AN D LI GHT DISTRI BUTION x49 b e illumina ted b ordinar di rect curren arc la m s so y y t p , that at f m to eet. The necessary luminous ﬂux ust amount 4 5 4 5 4 8100 of x x . The arc, considering the size the

m m a 3 f a t la p, y be assumed to be eet bene th the ceiling, so hat i f m 15 f its he ght, reckoned ro the table, may be taken as eet. The diameter of the useful circle of illumination of each l m ma for as f a p y be suitably chosen , interiors, one and a hal to

i s 22 3 0 f m a 4 5 4 5 twice this height, . } to eet. Fro the rea x 2025 f f the f u square eet, and rom use ul circ lar areas controlled m of f by a lamp, the necessary nu ber lamps is ound to be three m o m to ﬁve. Three la ps, h wever, in a square roo , distribute f the light badly, hence our, or, better, ﬁve, are chosen, which Fi 13 9 mi may be arranged as in g. . By drawing the illu nated ff f circles belonging to the di erent angles o distribution, as

13 8 for of 15 f shown in Fig. , a height eet, and by proceeding as f f in the ormer case, then the mean vertical use ul light, per

i h - 2 9 hem sp erical candle power is 7 , disregarding the gain by

f m w . m 40 reﬂection ro the alls Assu ing that per cent. (see Table XIX ) represents the power of reﬂection of pure white

ll two- i of i etc wa s, and that th rds them is occup ed by windows, , then abou t a quarter of the light falling upon the walls ma y be utili zed for the room illumination and a corresponding additi on v must be made to the abo e calculated amount.

i i a This add t onal amount cannot be calculated exactly bec use ,

m after repeated reflection , and so etimes it does not reach them n f at all. But si ce the sur ace to be illuminated does not absorb f u it all the light which alls pon , but partly reflects it, and f m n of il partly receives it back ro the reflectio walls and ce ing , 15 0 E LE CTRIC ARC LAMPS the reflecti on may be a ssu med for prac tical purposes to be that

13 9 tha In Fig . it will be seen t the circle for lamp 5 lying , e wholly on the plane to be illuminat d, has an angle of dialri bution w the next circle (to lies partly on the

plane and partly on the walls . The maximum circle of b uti on m e am 1 2 3 ( li s wholly on the walls. For l ps , , , and 4 the smallest circle is for w All other circles (not

. XV . for m s all drawn in Fig chosen in Table II these la p , lie partly on the plane and partly on the walls from whence

1 5 2 ELE CTRI C ARC LAMPS

a ( 3 0”

for reﬂecti on .

ore? n 0 Average value of gi7 4 x 00444 0945 088

0- 12

f From the mean value o Q . and the required total amount of Q 8100 m for light . , the light intensity per la p the case of 5 ﬁve lamps at a height of 1 feet can be calculated. 0

. . E d f a c A l xclu ing reﬂection rom the w lls 2 333 .p. 8100 2 1110111 = 480 C . n W .p.

For the same number of lamps at a height of 10feet

B 1. i f l c . Excluding reﬂect on rom the wa ls .p.

8 100 2 I ncludm = 4 40 c . g .p 3 68 x 5

Fi . 122 f 15 f I . for o From curve , g , a height eet direct

m of 8 . for of 10f r current la ps 4 amps , and a height eet di ect m of 8 i current la ps amps . capac ty would then be necessary . Of course the smaller height requires a lesser consu mpﬁon of t of energy, but the degree variation in illumination is grea er ;

ve are ra cti cal r w moreo r, there p reasons in pa ticular o es which determine the minimum height at which lamps shall be placed. LIGHT INTENSITY AN D LIGHT DISTRIBUTION 15 3

f m s of f m al In the or er ca e, A, the gain light ro the w ls amounts, i m 16 t accord ng to our assu ption, to about per cen ; in the

a 1 i s m the an le of distri 0 t . latter c se, B , to per cen , the s aller g b uti on withi n which the illuminated plane obtains primary or di e m the rect light, or the high r the lamp is ounted, greater is m the inﬂuence of the walls upon the ill umi nation . In ost

of ma m cases the gain light y be greater than is here assu ed, and the ill umi nation with the lamp considered will then be somewhat higher than the value u sed as the basis of the calculation . m l mi wi c With a given ean il u nation and th indire t lighting, it is more difficult to calculate the required lamp current owing to f the inexact determination of the amounts o the reflections. It must be pointed out tha t in the first place the ceiling ca n only be

reﬂector i n of 12 15 f i considered as a suitable rooms to eet he ght, u f n 40 5 0 and even tho gh the ceiling be painted o te , about to

er n of . p ce t. the light is only reflected With higher or dirty ceilings it is better to attach enamelled reflectors to the lamp itself. These have been shown by experience to reflect 5 0 to

60 . of e A roxi per cent the light, and they are asily cleaned. pp mately correct values ma y be obtained by supposing that the

o 6 indirect light f a direct current lamp (Fig. 3) with a lower posi tive carbon is brought about by an image of the a re above

i u n the ce ling, and contin ing the calculatio in the same way as

f for of be ore, allowing absorption by the ceiling. With a power of 5 0 t reﬂection per cen , double the calculated light intensity l wou d be necessary . Exam ple of Lig hti ng of a n Int e rior with Inverted — Area Suppose that a room 4 5 x 4 5 square feet and 15 feet high has to be illuminated by the indirect light of ﬁve lamps a of (Fig. so that on a pl ne, the height a table, there is a

o - mean illumination f 4 candle feet. The source of li ght is

3 f ma situated eet below the ceiling, so that it y be considered

3 f n . The far as an image eet above the ceili g example, as as x54 ELECTRIC ARC LAMPS

dimensi ons o is the sa me as the la st. ca l ul i g , The c a t on would then result in a candle- power per lamp equal to abou t 2 double that given in previous example, A. (p. ’ 480 2 9 . are of x 60c.p The the lamp in question is open

I Fi . 122 m at the top, so that curve g , gives the la p current in

Fm. 140.

11 m r i n this case as a ps . In o der to secure an equal illuminat o with the same lamp and the double reﬂection (the upper carbon

This w not quite cormog a s the sta ndard or unit illumination curve for

it lo e a s aro been assumed. For in erted arcs n mel lu n a la mp w h g b b h v , a y, 0 1 ou d g es the unit illumina tion cur a nd ence er c. . c l withou t glob , ve, h p p , m la r r e obtained fro the po cu v L, Fig . 128 .

LIGHT INTE NSITY AN D LI GHT DISTRIBUTION 1 5 5

Tables XIX. and XX. some values of the reﬂecting powers of surfa ces and approximate values of the mean horizontal

o SURFACES on s ru m m useu m or u ni ns ( . e ) .

w m m ummw on nn m z m m n m m d.

ha lls m

side streets CHAPTER V

EXTERN AL CON N ECTION S (IN STALLATION ) OF ARC LAMPS AND ACCESSORIES

l . EXTERNAL CONNECTIONS GENERAL

GENERALLY in all t es of arc la m s a resis a noe is se yp p t u d, r which, according to the lamp const uction, may be in the lamp circuit either continuously or only for the time during which the lamp is burning. The continuous connection is required by all shunt arc lamps , and also by series and m m differential arc la ps with a long arc, viz . enclosed and ﬂa e ’ I n series and diﬂeren tia l arc lam s with a short arc la mps. p a re (1 to 3 the resistance may be cut out in pro portion as the lamp pressure (or the sum of the lamp pressures) of increases with the consumption the carbons, till the normal regula ti ng pressure is reached. I t is assumed in this ca se tha t the mains pressure amounts to one or more times the lamp

E LE CTRIC ARC LAMPS

The ohmi c value B of the resi sta nce may be determi ned by the formula

E c e where supply pressure, l, a,

al of In general , the v ue the resistance is only determined r of app oximately, but is made capable variation, and is adjusted with the help of a voltmeter and an ammeter until the heated

r e for lamps maintain the co rect and constant electrical valu , ’ which they have been previously adjusted in the works test

ls room. With inductive resistances (choke coi ), which are only

for e of used alternating current, the r sistance the winding is

r esistances cause the arc to be struck more quickly, but are t f little used owing to their cos . It usually su ﬁces to determine the reactance pressure to be created by the choke coi l with

r the m adjustment is only made whe e la p is connected in circuit,

necessary reactance pressure a. of the choking coil is calculated by the formula

or more accurately

i n I R i of o a the which is the ohm c drop the ch ke coil and ,”

dro in the l ds The t a of the pressure p ea . erminal pressure

We? (I R)’ X A E C OF ARC LAMPS E TERN L CONN TIONS , ETC. 15 9

The choking- coil terminal pressure may be easily obtai ned

ll . 141 E graphica y as in Fig , in which is the mains pressure to

c of - a given s ale volts . On E a semi circle is drawn with half

Then the sum 26 of the lamp pressures e e etc x, g, ,

F1c . 14 1.

if n n plus the mains drop (and, k ow , the ohmic drop in the choking coil) 18 drawn to the same scale of volts as E in the diagram by describing an arc with centre on the extreme and of E and radius 26 and j oining up the point of intersection with

- nd semi circle to the extreme a chosen .

rea cta noe 8 of E The pressure , the choking coil is times the sine of the angle by which the lamp current is out of phase with m I ﬂ m the ains pressure. As the lamp current ( a e arc lamm excepted) 18 in the same phase with the lamp pressure the con 160 ELECTRIC ARC LAMPS

EXTERNAL CONNECTI ONS AND ADJUSTMENT OF DIRE CT CURRENT LAMPS .

W of m ithout accessory apparatus , series type la ps, as al a m l a for s n r re dy entioned, are on y suit ble i gle or pa allel

as . 142 u connection, shown in Fig . With the mains press re,

110 220 u h to volts us ally employed, the only series lamps whic m PD need be considered are enclosed la ps with a . . across the 1 1 arc of 70to 80or 3 0to 5 0volts. A voltmeter placed across the terminals su ﬂi ces to adju st m the la p resistance . The latter must be so adjusted that the lamp burns with the correct

PD r f . across the a e in the

normal condition. As the bu rning away of the carbons in enclosed arc lamps is

f e exceedingly slow, it o t n happens that the normal regulation is only reached

m To save ti e, the inner globe is removed (if pra c ti cable) until the resistance

Fro. 142. is correctly adjusted . By this means the carbons burn away more quickly and the electrical conditions of the lamp adjust themselves in a of m shorter time . The correct connection the ter inals to the mains for direct current is checked by switching off the lamp an d observing the carbon points : that carbon which glows longest is obviously connected with the positive pole of the the supply, and with enclosed lamps must always be upper f s carbon . I f thi s is not ound to be the ca e, the connections

must be reversed .

162 ELE CTRIC ARC LAMPS

Fi g 14 3 number of lamps and a resistance in series as in . . The current with which the lamps burn depends upon the value of

the resistance. In mder to ﬁx the

e m o in latt r, an a meter sh uld be

serted i n each m ci rcuit i n la p turn , and the resistance increased or

cates the required lamp curren t. This should be done when the m la ps are heated to their maximum, w hich is generally reached , at the

fte for latest, a r burning an hour

By the use of a regulating resistance (with a lever handle) the current and the light intensity can be regulated at any time within

the limits of 25 per cent. above or

below. The permanently connected

adjusted for the maximum curren t. 144 such as shown in Fig . may be m m e ployed. It ust be pointed out that in this case the

r resistances must be connected to the individual b anches , and the desired current in these must be correspondingly regulated. The sum of the currents in two adjacent branches will be the current passing through the lamp connected to the junction of r L these b anches, and so on. For instance, lamp , burns with of L ma ms the sum the lamp currents Ls and e, which y the elves

m a off if be unequal . Lor L; y be switched necessary, provided L s that ; burns correspondingly thin carbon . E X E AL E OF A MPS TC 16 T RN CONN CTIONS RC LA , E . 3

DIFFE E I AL R NT ARC LAMPS.

s l r ingle, multiple, in multip e se ies, or in series .

The regula ti on of the electrica l condi tions of the a rc is more

since both the PD . across the arc exact, and the lamp cu rrent u the e nis t i s of inﬂ ence m cha m, and the uns ead nes light, due to va r i n mains ressu is less tha n i n shunt la m s y g p m p . A dis of r t i advantage this lamp, as cont as ed w th the shunt, is that the light intensity ca nnot be obtained by altering the resistance

s m bu t m - re only, as in the hunt la p, the a pere turns in the gula t ing magnets must be also adjusted . The alteration of the turns is effected by providi ng tappi ngs to particular porti ons of i m the winding. These tapp ngs ake it possible to put in or cut m of out a nu ber turns . Further, an adj ustable resistance may

of m re he a part the la p cur nt passes through its turns . T of d of the alteration the electrical con itions one lamp, by above

m d tm of la ps in series . An a jus ent the lamps (already installed) for another current is therefore generally not practicable without auxiliary apparatus. A voltmeter placed across the terminals

‘ of direct current diﬁerential lamps is used to ﬁx the resistance i of lam exactly, so that in a heated cond tion the g the latter

PD . burns with the correct . . across the arc The lamp current

a u i t will then be correct, ss m ng that with above adjus ment the lamps ha ve been regulated in the works for the desired

With alternating current a subsequent adjustment of the i c f m of lamp cannot be avo ded, be ause the wave or the current

m i s. t e PD. inﬂuences both the ost suitable arc length ( h . ) and 164 ELECTRIC ARC LAMPS

lamp was regulated by the ma kers. It is desirable to connect an ammeter in the lamp circui t when adjusting the rea ctance

of m i ls by means the volt eter across the lamp term na . I f in la mps wi th an open arc and unheated carbons the li ht is of a violet hue too lon an arc or the li ht i s too little g ( g ) , g

o shor he a c an mu in r d or decrea sed (to t a n a rc) , t re t ce st be c ease

r l the desired current, eadjustment is necessary . This shou d il only be done by a sk led hand. I n adj usti ng a lterna ting sw ea t ﬂa me a rc la mps of both

var ieties onl mea surin i nstru n s M e dm t o wa ve orm , y g m e t pm f f

a nd re nc o the current must be used f t y f .

NNE TlONS . ll . ACCESSORIES FOR EXTERNAL Co C

The most necessary accessories are the frequently mentioned mai sta nces resistances ; of the others, we have regulating with

Fro. 145 .

e automatic resistanc s, choking

' the exhncti on of other

ou t.

166 ELE CTRI C ARC LAMPS considered in those hand - ma nipulated

Fm. 148 .

r a suita ble, eithe owing to l ck ARC LAMP ACCESSORI E S 167 unreliability of the persons to whom the switching on of the m la ps is entrusted . They usually consist of a solenoid lamp current passes. At one end of the iron

which over a At the other end is a spiral of the solenoid and form a r k m n of a f b a e to the movement. The seg e ts the cont ct sur ace a m a nt ra ” : a m ' i i fi pfl d fi m su m in th u h s d cu - fi - b h l él h m h a d fi d a fi q d a m inn s - c b l i n d -h i p wi t h i n-r i b bon“!

and the com . parts ca n be bolted so tha t a n a ir space ma y be

tw e em- and the wound limhs in orda w be e n the or pieces , t 7o ELECTRIC ARC LAMPS

the product of the primary current and the secondary

I f E u m u pressure . is the s pply pressure, then the pri ary c rrent

watts of f m the trans or er.

hence m and the la p . This holds good with single lamps or la mps

1 Fm 1 Fl a 15 7 . h a . 5 5 . . 5 6 . .

m i i m ser es , assum ng in the latter case that the la ps 15 5 always burn together (800 connections in Figs . and

15 r m ma With the connections as in Fig . 7, whe e one la p y be d c switched out, the stea ying resistance must be pla ed in the

r d I s ur se with a c la mps connecte in series. t p po is to ensure the i of t r cont nuous burning lamps connec ed in se ies, should one of e h them be extinguished. It is also intended to prev nt a hig m ELECTRI C ARC LAMPS pressure at the termina ls of the indi vi dua l lmnps whi ch would m e unduly hea t the la mps or fuse the winding of the shunt a g x t.

Beneath these limits the use of the appliance depends more or upon the construction of the the

Fro. 15 8 .

d etc r by the shunt win ing , ), and upon the deg ee

of s f . a ety desired with a given installation In railway stations,

for u m . example, s ch an appliance is generally e ployed It

tmwc a resis . The latter is switched into the lamp circuit inste d of the arc resistance, when a lamp is extinguished.

3 74 ELECTRIC ARC LAMPS operated by the lamp mechanism and the substitutional resis

' i er n i l current d ﬁ e t a arc lamp (Fig . The current ﬂows as

(A) When a la mp is bum ing : The ma in current ﬂows from the positi ve termi na l through the series magnet coil Se to the c r H are upper arbon holde 1, to the B, the lower carbon holder

H and . ﬂ f m g, to the negative terminal The shunt current ows ro r m n Sh the positive te minal to the shunt agnet windi g , the e m R e detent S, the scape ent , to the base plate and n gative

i e - u (B) When the lamp is ext nguished, owing to us d p carbons or any obstructions which prevent the separation of the carbons : The armature is drawn down by the shunt magnet Sh further than is necessary for the release of the esca pement 00 t R from the detent S. The pieces 0; and Ca then touch

m fr switched in . The ain current then ﬂows om positive termi nal

s B u c 0 through the resi tance , thro gh the conta ts 1 and (3 . back to

the base plate and negative terminal. The shunt current ﬂows from posi ti ve termina l to the ma gnet RS a nd ba ck to the ba se plate and negative terminal . The shunt magnet is continuously excited and maintains the contact between C; and C, so long as the remaining m m of m e f f I f echanis the la p do s not per orm its unctions . the

i s. if n latter works, the carbons touch, the shunt mag et is

- e o of rr n short circuit d and consequently bec mes void cu e t, whilst the seri es magnet is strongly excited and draws the c 0 f t f armature up and the conta t , away rom the contac sur ace Q . With alternating current are lamps a similar apparatus may

ma r be used, or choking coils y be connected in pa allel with the

15 er of (about p coil), but have the great advantage absolute ARC LAMP ACCESSORIES 175

f of sa ety, owing to the elimination contrast to the

o t n Coil C mpensa i g .

l - these choke coils have a constant we l closed magnetic circuit. They are so take little 176 E LE CTRIC ARC LAMPS

for a ny rcsson the feed of a la mp cea ses the la mp pressure immediately and of the

0 N

0 OJ IO IGOO

1 70 1000

0] “ 1200

6 OL SO IOOO

3 M a shhad 5

Fro. 161 .

n u s f i t mai current will ﬂow thro gh these a ety co ls, un il, ﬁna lly, the arc is extinguished a nd the whole of the current passes

178 E LE CTRIC ARC LAMPS

the P.D. the arc i ncreases th consumed, then across and c

he is s run out of contacts G and a t and t switch p g the , the r same time the circuit is broken. The p otection given by this

m s one the P.D . the la p pressure increase in lamp only, in with

Fro. 162.

i i lamps) . Under certa n condit ons the terminal pressure of one lamp may attai n a value which is dangero us for great enough to bring the minimum switch into operation and

is the undesired breaking of the circuit if for any reason there the is a temporarily large decrease in supply pressure .

It is connected in the lamp circuit in those cases in whi ch the ARC LAMP ACCE SSOKIE S l 79

sw hin - in of la ff f a hi itc g .the mps is e ected rom a pl ce at w ch it is not si F 1 3 if i . 6 pos ble to see the lamps are burning or not. g of shows It consists a solenoid,

m a w which the la p current p sses, hich attracts an iron core with

m of a ark on it. From the position the iron core the operator can discern the presence of the correct lamp current.

DIX II

USUAL Sensors or LIGHT

01148

n rice of electrici t as i a. er B .T.U. a nd spirit as 7d. per gallo ; p y p APPENDIX III

STANDARDIZATION RULES ON PHOTOMETRY AND LAMPS OF THE AME RICAN INSTITUTE OF E LECTRlCAL ENGINEERS — 3 4 s. Ca ndle - Pow er . The luminous intensity of sources of light

be derived from the standards mainta ined by the National B of W D ureau Standards at ashington, . which sta ndard uni t of candle- power equals of the Hefner unit under

m e m la ps are mor reliable and accurate than the pri ary standard . — l - m n . f 3 42 . Ca nd e Lu e The total ﬂux o light from a source is

a m m 7 equ l to its ean spherical intensity ultiplied by 4 . The

- - unit of ﬂux is called the candle lumen. A candle lumen is the

th of of i o 72 part the total ﬂux l ght emitted by a s urce having

of - a mean spherical intensity one candle power. — dh - M tra of the a 3 4 3 . Ga n e The unit illumination is c ndle o d b metre. This is the normal illumination pr duce y one unit

of candle- power at a distance of one metre. — a Ca ndl - FooL Illumina tiom n 3 4 4 . ( ) e is occasio ally expressed in

- A d - f m i r candle fest. can le oot is the nor al llumination p oduced

- by one unit of candle power at a distance of one foot.

- - f 107 64 m . of the 3 4 5 . 1 candle oot candle etres The use candle f mm metre unit is pre erable and is reco ended . fﬁci c of Elect ric La m s 3 4 6 . The E en y p is properly stated in terms of mean spherical candle- power per watt at lamp es f terminals. This n o the term emci ency is to be considered fu as special, and not to be con sed with the generally accepted i deﬁni tion of efficiency n Sec. 85 .

186 APPE N DIX 11]

screened. The angle below the horizontal at which the measurement is made should be speciﬁed when it exceeds 1

3 5 7 . i n Compa ri ng Different luminous sources not only should

e c d - m ar but e at e f rm th ir an le power be co p ed, also their r l iv o ,

of light. IN DEX

Aom eories for externa l 164

tim e a re, 11 168 Gun-ant

- 6 Out out, minimum a utoma tic, 177 c emi ca l or a 11 h ﬂ me, D

the enclosed, 7 the, 45

169

E nclosed 98 Distri ution li t 120 , b , gh ,

Fla me, 75

Series, 17 S unt 22 h ,

Economisers, 49 B

Enclosed are, the, 7

e m. f of a re . , 5 .6 wa ve

Excello ﬁa me are la m p, 82 closed arc la m 104 gghuee F

America n are l s 1 2 ( ) amp , 1 G b 1 lo es, 08 ma nnf c Guide-fra m a ture of, 2 es, the, 46 97

' M l- mm m m H m ml Oa si n t w Harcourt sta nda rd la m the ha p, , 120

coi l th ﬁS Hefner- m re e g eJ et , th , 166 188 INDE X

Hefner l the 121 standa rd a mp, ,

“ ” Oli er Arc La m h ri a ca rbon, 4 7 v p Oo O ﬁ mme

la in 92 p,

Illumina ti on, 184 uni ta of 136 I i r t i s nd ca to , curren , 7

In nsit ﬁ t 1 te y, gh , 20 “ L. cti ro surfaces 15 5 on f m va rious , Beh w tore, 49 E ula ti n le er 48 m g v ,

1 Jandus enclosed a re im p, 09 ’ 5 lli n t la m a u i c ta rtin 16 Johnson and Phi pe ope ype p, toma t s g,

5 9 h

Shunt a re Im pe tus Sim s motor a rc la mp

dim , 89 9 Siaee of m bcna w, 75 , 78, 7 , 97

H co rt 120 h M ty, 120 a r u , Li hﬁn la m . for di rect 5 5 Hem 121 g g, p , , . ” ind 71 S o ub i0 s a re 148 the arc 8 f a p l qu , , 9 of a n interior, 14 with eleva ted T

arcs, 15 8

r em ains “ M , i Twi n nrc la mm s‘i e 92 la mp, oriﬂa mm , U

’ Unim Elw trle 0c. s A.O. fla me

- Minimum a utoma ti c cu t out, 177 88 er-m a of 1 2 det nna . 8 Uni ts of la na tion of 1 2 exp , 2 from pola r curve by Rous ’ sea u s met od 18 h , 1 la na tion of 1 exp , 22