British Kinematography (1950)

March, 1950 HEWINS, HALLETT AND BOURNE [ STUDIO LIGHTING 95 Again, the colour of the radiation from the discharge lamp is not affected appreciably by the variations in supply voltage normally experienced in service. Future Scope of Compact Source Lamps The two lamps which have been described represent a great advance on earlier models. They have a light output comparable to the average carbon arc, they are practical in design, and their silence, steadiness and freedom from smoke will lead to their use in special cases where the use of arcs is impractical, where incandescent lamps do not give sufficient light, and where cost is relatively unimportant. The arc remains supreme as the most powerful and economical source of light, and there is little doubt that it still has a long and useful career before it, but the progress of the compact source lamp will be watched with interest. The closest collaboration has been maintained with the Research Laboratory of the British Thomson-Houston Co. during this development work, and the author would like to acknowledge his gratitude to Mr. L. J. Davies, Director of Research of that Company, for his assistance throughout the work ; also to Mole-Richardson for permission to publish this paper. REFERENCES 1 . Brit. Kine., 14, No. 6, June, 1949, p. 1 83. 2. Brit. Kine., 11, No. 4, Oct., 1947, p. 107. J. Soc. Mot. Pic. Eng., 50, No. 2, p. 122. DISCUSSION 3. " Discharge Lamps for Photography and Projection," by H. K. Bourne, Chapman & Hall. 1948. Mr. F. G. Gunn : Is it dangerous, or destructive to the bulbs, to operate them in steeply tilted positions? Mr. Bourne : No, these lamps will operate at least up to 45°. The chances of operating a lamphouse i pointing downwards for some hundreds of hours would be remote. Mr. F. N. Bush : What problems do you meet in designing lenses and reflectors? Mr. Bourne : The arc size in the compactsource lamp does not differ very much from that of the carbon arc ; the length is about 15 mm. and the width about 12 mm. But the brightness distribution is more "peaky" than that of the carbon arc, and this tends to make the beam somewhat narrower. Mr. W. Norris : In assessing the life of the lamps, have you a deterioration factor that you work to before the light goes off? Mr. Bourne : The life of any discharge lamp may end by gradual blackening, by failing to strike, or by being broken. A life of some 500 hours will take quite a long time to obtain in studio conditions. The life of a discharge lamp is said to be finished when the initial light has dropped to 75 per cent. When the lamp blackens to this extent it often fails soon afterwards due to failure to strike. Mr. F. G. Gunn : Does ageing affect the colour of the light ? Mr. Bourne : We have no evidence that it does to any appreciable extent. Mr. Gunn : What about de-vitrification ? Mr. Bourne : The lamp will de-vitrify, with considerable loss of light, if it is handled with bare hands and then operated without cleaning. Preferably the bulb itself should riot be handled at all — it should be held by the seals. But if it is handled it should be cleaned with a de-greaser before operating it. Mr. F. G. Gunn : As far as Technicolor are concerned, we are taking a very keen interest in the development of these lamps. They are still in the experimental stage, and so far we have not quite made up our minds as to whether they are applicable in all circumstances to our system. Mr. Waxman : Can you not build behind the lens a Venetian shutter of translucent material incorporated permanently in the lamp for diffusion purposes ? Mr. Heys-Hallett : We did try something like that, but it is very inefficient. Mr. R. H. Cricks : I saw a very interesting demonstration at the Philips factory in Eindhoven of small scale studio lighting by means of capillary lamps. Three small lamps, each running at 500 volts, 1 amp., were fed from three-phase supply and were housed in quite a small polished reflector. Dr. B. V. Bowden : We have analysed the records of a large number of productions, and have found that about 40 per cent, of the total time spent on the floor is devoted to lighting. Any new technical development which will in any way assist the lighting cameraman will therefore be of first-class importance in film studios. We have found rather surprisingly that the records do not reveal any significant variation of lighting time with intensity of lighting, and that the average time required to light a set with a key-light of 80-foot candles is about the same as that required when the key light is 800 foot-candles. Possibly the time spent in manipulating small lamps is as long as that required to adjust large ones. It would be most interesting to see how much these new remote control devices can help the cameraman.