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Philips Technical Review • DEALING ~TH TEC~CAL PROBLE~ RELATING to the PRODUCTS, PROCESSES and INVESTIGATIONS of the PIIILIPS INDUSTRIES

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Philips Technical Review • DEALING ~TH TEC~CAL PROBLE~ RELATING to the PRODUCTS, PROCESSES and INVESTIGATIONS of the PIIILIPS INDUSTRIES VOL.12 No. 7, pp. 185-212 JANUARY 1951' Philips Technical Review • DEALING ~TH TEC~CAL PROBLE~ RELATING TO THE PRODUCTS, PROCESSES AND INVESTIGATIONS OF THE PIIILIPS INDUSTRIES EDITED BY THE RESEARCH LABORATORY OF N.V. PHILIPS' GLOEILAMPENFABRIEKEN. EINDHOVEN.NETH,ERLANDC; THE "PHOTOFLUX" SERIES OF FLASHBULBS by G. D. RIECK and L. H. VERBEEK. 771.448.4 It is known that right in the beginning of photography, about 100 years ago, photographs were already being taken with a flash of light. This is probably even the oldest form of artificial-light photography, since with the means of permanent artificiallight available in those days and the very poor sensitivity of the sensitive plates of that time, the exposures would certainly hove been unduly long. The flash was obtained by burning i.a. magnesium powder. Nowadaysflashlight technique has reached a very high degree of refinement, as will be shown in this article. Introduction It was about 20 years ago that the "Photoflux" with in this journal as far back as 19362). The and similar flashbulbs were introduced to replace principle has not heen altered much, nor is there the old flashlight produced by combustion of a much difference in the appearance of the present- mixture of magnesium powder and an oxidizer day lamp compared with that described at the in air. Their success was remarkable -, Only in one time. The properties of the lamp however have application, for "magnesium flash bombs " when been improved or changed in a great many respects, photographing from aircraft, is the "open" flash- so that it is deemed opportune to discuss these light still in use, but otherwise it was very soon "Photoflux" lamps anew; they are now being ousted by the "closed" flashlight. "Ousted" is not produced in a series of five types, some of them in really the right word, since with their safe, clean different colours. We shall not particularly dwell and perfectly controlled working the modern upon the points of resemblance and difference flashbulbs have not only replaced the open flash- compared with the older types, since this is not light but by their introduetion have brought likely to be of much interest to the reader. about a vast exp ansion in the :field of flash photography. The flashbulb has become the insepar- General construction of "PhotoHux" Hashbulbs able companion of the press photographer - prob- The flashfrom the "PhotoHux" flashbulbs is brought ably the foremost user of this article - and also about by the combustion of :finewire of an alumin- in amateur photography it has taken a very import- ium-magnesium alloy (with 5-7% Mg). A certain ant place. Many are the accessories that have in quantity of this wire - it is only 32 fL thick - consequence been brought on the market for is placed loosely in a bulb like that of an incandescent flash photography, such as reflectors and syn- lamp, and during this process it is given a sort chronizers, and many are the types of cameras that of "permanent wave", so that it is uniformly distrib- have been :fitted with built-in synchronizers with uted all over the inside of the bulb in the form contacts for one or more flashbulbs. In this connec- of a loosely knit, resilient ball. The sealed .bulb tion mention may be made of the Philips flash is further :filled with oxyg~n under somewhat less camera, which has not only a synchronizer but than atmospheric pressure and contains also an also a lamp socket and reflector built into it 1). ignition filament which can be heated hy an electric The principle of the "Photoflux" lamp was dealt 2) J. A. 1\1. van Liempt and J. A. de Vriend, The "Photo- flux", a light-source for flashlight photography, Philips 1) See Philips Techn. Rev. 12, 149, 1950 (No. 5). Techn. Rev. 1, 289-294, 1936. 186 PHILIPS TECHNICAL REVIEW VOL. 12, No. 7 current from an external source (seejig. 1). When are cooled down before they are able to damage the filament reaches ~ certain temperature an the glass. Near the base of the lamp, where the explosivepaste applied to it ignites and the glowing •layer of lacquer cannot he applied owing to the particles scattered from it in turn ignite the ball sealing of the bulb, the glass is protected against of aluminium-magnesiumwire' at numerous points the glowingparticles by an aluminium plate moun- simultaneously, so that the whole ball burns away ted in the neck of the lamp (seefig. I). in a very short time. External damage, such as scratches, which may easily result when, for instance, .a couple of unpacked flashbulbs are carried in the coat pocket and rub against each other, may likewiseso weaken the bulbs that they are unable to withstand the pressure set up inside them when they are ignited. A coating of lacquer is therefore also applied to the outside of the bulb to prevent scratcHingof the glass. At the same time this outer coating serves to keep the fragments together and thus render the explosion harmless in the event of the bulb bursting in spite of these precautions. For that reason the coating is made fairly thick and with a tough kind of lacquer, while it is also coloured light yellow so that it can easily he checked; this colouringhas hardly any effect upon the radiation of the light. The effectivenessof these two layers of lacquer in preventing the bulbs from bursting is evident fro~ 63657 the random tests taken as a regular check in the Fig. 1. Construction of a "Photoflux" flashbulb. A a ball of manufacture oftheselamps. Ofthe tens ofthousands curled aluminium-magnesium wire, B ignition filament with of lamps ignited for these tests in the course of explosive paste, C aluminium plate, D spot of cobal salt, E fuse wires. the last few years less than onein a thousand have exploded. The electric current for the ignition is usually This applies to lamps where the bulbs were derived from a battery, but the large types of quite intact prior to ignition. Bulbsalready showing "Photoflux" lamps can also be ignited from the slight defects, from whatever cause, are more lighting mains, for which purpose these types likely to explode upon ignition, especially so when are provided with a quick-acting fuse :fitted in there are small cracks in the glass through which the lamp base and forming the connection to the air can penetrate. To avoid this increased risk mains lead; owing to'the arcirigin the gasfollowing with such lamps, a spot of cobalt salt is applied upon the ignition of the lamp a very heavy current on the inside at the top of the bulb of all "Photo- is . drawn from the mains,' but thèn this safety flux" làmps; in pure oxygen this spot is blue, but fuse burns through so quickly as to savethe fuse of whenthere is the slightest trace ofwater vapour (and the house mains. this is always present in the air) it changes to pink, The burning ofthe AI-Mgwire causesthe oxygen thus immediately betraying the presence of air in the lamp to be heated quickly to a high temper- in the bulb, in which case it is not advisable to ature, so that for a moment - until the gas has use the lamp 3). cooleddownagain- the bulb comesunderapressure that may amount to several atmospheres. A "Photoflux" lamps that have served their purpose some- times show amore or less extensive blackening of the laquer normal cold bulb can withstand this pressure, but l,ining, while in some cases a bulge is to be seen in the outer in the flashbulh the wall of the bulb is also sub- coating of lacquer. These two phenomena might give riseto jected to a bombardment of glQwing particles some doubt as to whether the layers of lacquer are after "';;il of ash which are apt to crack the glass where they the right solution of the explosion problem, since, if tI;, strike against it, and in that weakened condition the bulb cannot withstand the pressure. The bulbs 3) In addition to the slightly greater risk of bursting, when the lamps have sucked in air there is also the risk of faulty of the "Photoflux" lamps are therefore lined with synchronization, owing to their light-time characteristic a layer of lacquer in which the glowing particles undergoing a change; cf. the final section of this article. JANUARY 1951 "PHOTOFLUX" FLASHBULBS A B c D E F G IJ H 63701 115msec Fig. 2. Film of a burning "Photoflux" flashbulb taken at a speed of 3000 pictures per second. A number of cuts have been taken from the film corresponding to the moments indicated in the drawing (light-time characteristic) after the first picture reproduced (A). The film shows the formation of a black patch in the inner coating of lacquer. blackening takes place at the beginning of the generation of measurements of light output do not show any perceptible the light, this will absorb some of the light, whilst as regards difference either between lamps with and lamps without an the bulge in the outer layer, if this is formed at the moment inner coating of lacquer. of maximum pressure from within, it will make the hope of sufficient support for a bursting bulb illusory. The various types of ..Photoflux" lamps Photographs taken with a high-speed camera (3000 pictures per second) of a series of "Photoflux" lamps in the Fig.4 shows the five types of "Photoflux" lamps course of being ignited have shown that there are no grounds that are now being made, the PF no, PF 56, PF 45, for doubting the adequacy of the lacquer coatings.
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