Fluorescent Lamp

Patentamt JEuropaischesEuropean Patent Office

Office europeen des brevets © Publication number : 0 586 1 80 A1

EUROPEAN PATENT APPLICATION

© Priority: 31.08.92 US 937083 © Inventor: Roberts, Victor David 3 Garrison Road _ Burnt Hills, New York 12027 (US) @ Date of publication of application : 09.03.94 Bulletin 94/10 © Representative : Pratt, Richard Wilson et al London Patent Operation G.E. Technical (S) Designated Contracting States : Services Co. Inc. Essex House 12/13 Essex DE FR GB NL Street London WC2R 3AA (GB) © Applicant : GENERAL ELECTRIC COMPANY 1 River Road Schenectady, NY 12345 (US)

(54) Fluorescent lamp.

© An electrodeless fluorescent lamp has an envelope configured to have a height-to-width ratio of less than one. According to one embodiment, the envelope is ellipsoidal. Advan- tageously, such lamps operate at high efficacies and are useful for replacing incandescent lamps in standard fixtures.

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LU Jouve, 18, rue Saint-Denis, 75001 PARIS 1 EP 0 586 180 A1 2

Field of the Invention vention will become apparent from the following detailed description of the invention when read with the The present invention relates generally to fluor- accompanying drawings in which: escent lamps and, more particularly, to a high- Figure 1 is a partial sectional view of an electro- efficacy electrodeless fluorescent lamp including an 5 deless fluorescent lamp envelope of the prior art; envelope configured to have a height-to-width ratio of Figure 2 is a partial sectional view of an electro- less than one. deless fluorescent lamp envelope of the present invention; and Background of the Invention Figure 3 is a graphical comparison of average arc 10 efficacy for standard spherical electrodeless flu- Fluorescent lamps generally require lower electri- orescent lamp envelopes and electrodeless fluor- cal power to operate than conventional incandescent escent lamp envelopes according to the present lamps and are generally more efficient than incan- invention, each lamp envelope having the same descent lamps on a lumens per Watt basis. Some flu- diameter. orescent lamps have therefore been designed to re- 15 place incandescent lamps in standard fixtures. How- Detailed Description of the Invention ever, the use of fluorescent lamps as incandescent lamp replacements is limited by the fact that practical Figure 1 illustrates a typical electrodeless fluor- fluorescent lamps are generally larger (i.e., longer) escent lamp 10 having a spherical bulb or envelope than incandescent lamps which produce the same 20 12 containing an ionizable gaseous fill. Asuitable fill, light output. for example, comprises a mixture of a rare gas (e.g., As a class, electrodeless fluorescent lamps are krypton and/or argon) and mercury vapor and/or cad- generally smaller, i.e., shorter, than conventional flu- mium vapor. An induction transformer core 14 having orescent lamps, but are still not as short as desired. a winding 16 thereon is situated within a re-entrant Typical electrodeless fluorescent lamps use an envel- 25 cavity within envelope 12. (However, it is to be under- ope with a height greater than or equal to the width. stood that some fluorescent lamps do not employ a Many envelopes are spherical. By way of illustration, transformer core, and the principles of the invention exemplary electrodeless fluorescent lamp configura- apply equally to such lamps.) The interior surfaces of tions are shown in: commonly assigned U.S. Pat. No. envelope 12 are coated in well-known fashion with a 4,01 7,764 of J. M.Anderson; commonly assigned U.S. 30 suitable phosphor which is stimulated to emit visible Pat. No. 4,187,447 of V.M. Stout and J.M. Anderson; radiation upon absorption of ultraviolet radiation. En- and in the advertising brochure distributed by Philips velope 12 fits into one end of a base assembly (not Lighting at the Hanover Fair in April 1991. shown) containing a radio frequency power supply For fluorescent lamps in general, there is a well- with a standard incandescent lamp base at the other known trade-off in size versus lamp efficacy. That is, 35 end. for a given light output, efficacy decreases as lamp In operation, current flows through winding 16, size decreases. The reason is that discharge current establishing a radio frequency magnetic field in trans- density and electron density, and hence discharge former core 14. The magnetic field within transformer loss mechanisms, increase as a result of a smaller core 14 induces an electric field within envelope 12 discharge space. 40 which ionizes and excites the gas contained therein, Accordingly, it is desirable to reduce the size resulting in an discharge 18. Ultraviolet radiation from (more specifically, the height) of an electrodeless flu- discharge 18 is absorbed by the phosphor coating on orescent lamp without sacrificing efficacy. the interior surface of the envelope, thereby stimulat- ing the emission of visible radiation by the lamp en- Summary of the Invention 45 velope. Disadvantageously, for a lamp with a spherical An electrodeless fluorescent lamp has an envel- envelope such as that shown in Figure 1, there is a ope configured to have a height-to-width ratio of less trade-off between height versus lamp efficacy. That than one. According to one embodiment, the envel- is, for a lamp having a spherical envelope, to de- ope is ellipsoidal. Advantageously, electrodeless flu- 50 crease the envelope height, the diameter of the en- orescent lamps configured in accordance herewith velope must be decreased, leading to lower efficacy. operate at higher efficacies than incandescent lamps For example, an electrodeless lamp having a spheri- and are useful for replacing such lamps in standard cal envelope with a 68 mm diameter and producing fixtures. 1300 lumens is known to have a lower efficacy than 55 a lamp constructed with a spherical envelope with 80 Brief Description of the Drawings mm diameter also producing 1300 lumens. In accordance with the present invention, Figure The features and advantages of the present in- 2 illustrates an electrodeless fluorescent lamp 20 hav- 2 3 EP 0 586 180 A1 4 ing an envelope with a height-to-width ratio of less terior phosphor coating for emitting visible radia- than one. Since the top and bottom portions of the en- tion when excited by ultraviolet radiation, said envelope have very low discharge density, these por- velope having a height-to-width ratio of less than tions of the envelope can be substantially reduced in one; size according to the present invention without creat- 5 a magnetic core contained within said en- ing the increase in current density that would other- velope; wise decrease the lamp efficacy. In particular, the flu- means for establishing a radio frequency orescent lamp of Figure 2 comprises an envelope 22 magnetic field in said core; and having an ellipsoidal (or "flattened spherical") shape. an ionizable, gaseous fill contained in said A preferred height-to-width ratio is in the range from 10 envelope for sustaining an arc discharge when approximately 0.5 to approximately 0.9. Advanta- subjected to said radio frequency magnetic field geously, the shortened configuration of such fluores- and to emit ultraviolet radiation as a result there- cent lamps, without sacrificing efficacy, render them of. as desirable replacements for incandescent lamps in standard base assemblies. 15 2. The electrodeless fluorescent lamp of claim 1 wherein said envelope is substantially ellipsoidal. Example 3. The electrodeless fluorescent lamp of claim 1 Two spherical electrodeless fluorescent lamp en- wherein the height-to-width ratio is in the range velopes, each having an outerdiameterof 80 mm, and 20 from approximately 0.5 to approximately 0.9. two ellipsoidal electrodeless fluorescent lamp envelopes, each being 80 mm high by 70 mm wide, were 4. The electrodeless fluorescent lamp of claim 1 constructed. Each lamp envelope was dosed with wherein said means for establishing a radio fre- mercury and 0.5 Torr of krypton; and was operated quency magnetic field comprises a drive coil with an air core transformer. At five arc power levels, 25 wound about said core. from 15 Watts to 35 Watts, each lamp envelope was allowed to warm up through its optimum mercury tem- 5. An electrodeless fluorescent lamp, comprising: perature. Peak lumen output and power output were a light-transmissive envelope having an in- measured at each arc power level, and peak efficacy terior phosphor coating for emitting visible radia- was measured. A graph of average peak efficacy ver- 30 tion when excited by ultraviolet radiation, said en- sus arc power for each pair of lamp envelopes is illu- velope having a height-to-width ratio of less than strated in Figure 3, the solid line representing average one; efficacy of the standard spherical lamp envelopes a drive coil situated within said envelope; and the dashed line representing average efficacy of means for coupling a radio frequency sup- the ellipsoidal lamp envelopes. 35 ply to said drive coil so as to generate a radio fre- Advantageously, as indicated by the data of Fig- quency magnetic field about said coil; and ure 3, the efficacy of an electrodeless fluorescent an ionizable, gaseous fill contained in said lamp is not sacrificed (and may even be improved) by envelope for sustaining an arc discharge when configuring the lamp envelope according to the pres- subjected to said radio frequency magnetic field ent invention, resulting in a small, high-efficacy re- 40 and to emit ultraviolet radiation as a result there- placement for incandescent lamps in standard fix- of. tures. Specifically, lamp efficacy is not sacrificed by the shortened envelope configuration because cur- 6. The electrodeless fluorescent lamp of claim 5 rent density is not increased. wherein said envelope is substantially ellipsoidal. While the preferred embodiments of the present 45 invention have been shown and described herein, it 7. The electrodeless fluorescent lamp of claim 5 will be obvious that such embodiments are provided wherein the height-to-width ratio is in the range by way of example only. Numerous variations, from approximately 0.5 to approximately 0.9. changes and substitutions will occur to those of skill in the art without departing from the invention herein. 50 Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.

Claims 55

1. An electrodeless fluorescent lamp, comprising: a light-transmissive envelope having an in- 3 EP 0 586 180 A1

4 4° I CM EP 0 586 180 A1

European ratcnt EUROPEAN SEARCH REPORT Application Number Office EP 93 30 6713

DOCUMENTS CONSIDERED TO BE RELEVANT category citation ol document with indication, where appropriate, Relevant CLASSIFICATION OF THE of relevant passages to claim APPLICATION (Int.CI.5) bUVlbf PATENTS ABSTRACTS 1,2,4-6 H01J65/04 Section EI, Week 8546, 13 December 1985 Derwent Publications Ltd., London, GB; Class X26, AN 85-289032 & SU-A-1 156 168 (LIGHT-TECH RES DES) 15 May 1985 * abstract *

US-A-4 727 294 (H0UKES ET AL.)

TECHNICAL FIELDS SEARCHED (lnt.CI.5) H01J

i ne present search report has been drawn up for ail claims rinc ill aC4Tln i iate or completion or the search Examiner THE HAGUE 2 December 1993 Schaub, G I : theory or principle underlying the invention E : earlier patent document, but published on, or X : particularly relevant if taken alone after the filing date Y : particularly relevant if combined with another D : document cited in the application document of the same category L : document cited for other reasons A : technological background O : non-written disclosure & : member of the same patent family, corresponding P : intermediate document document