Proceedings of the British Kinematograph Society (1936)

a source. With incandescent lamps, variation of voltage at the source is a very effective way. Unfortunately, at the present time changing of colour temperature is something which happens without the cameraman’s knowledge, and many times to his decided disadvantage. Importance of Voltage Control It is necessary to point out that in addition to using lamps of proper design, the studio electrical department must also appreciate the importance of voltage control so that the cameraman is not let into the pitfall of very different intensities at different times of day, or on different days shooting the same set. For some time past I have advocated a rather simple check which the cameraman can make which, while it in no way interferes with his artistry in lighting the set, gives him a check on those variables which too often work to his disadvantage. This is the use of a small light meter, which, with a little practice, can be a quick and effective check against the pitfall of this variable. This is a subject which does not necessarily fit into a paper of this scope, but I felt it desirable to at least mention it here. DISG4) $S1ON Mr. Jounson: Mr. Linderman mentioned the difficulties experienced with keeping sufficiently constant voltage control on arc lamps, and it would be interesting to know whether similar difficulties are found to a greater extent with the incandescent type. Tue AutrHor: The situation is more critical with incandescents than with arcs. Of course, in black and white photography it does not matter so much. It seems that you can shoot all the way from 100 ft. candles to 1,000 ft. candles and a lab. will eliminate your mistakes, but colour photography is very critical— even a variation of 5 volts gives trouble with incandescents, but we can actually stand for 7 or 8 volts before getting serious trouble with are lamps. Mr. Grary: Mr. Linderman has mentioned to us the difficulties and characteristics of arc and incandescent lamps, and it would be interesting to know what success attends the use of a mixture of them. Tur AutHor: You have to be very careful with mixing. You must put a blue filter in front of incandescents to take out the excess of red. When we wanted afternoon sunlight effects on a Spnanish Plaza set we used arcs, without filters, but for moonlight effects we did filter the ares with a blue filter, the evening interiors being lighted with the incandescents without filters. Mr. C. Vinten: Would Mr. Linderman tell us whether he has experimented with a high-pressure mercury type of lamp? 9 Tue Autuor: Yes. I find it has a few basic characteristics which make it impossible for use. One is spectral emission. Mercury vapour is very rich in blue-green and has almost no red, even at high pressures, which makes it difficult to use at the present time with existing filmstock. The operating characteristic is bad; it is a lamp that is actually on or off and, being used on A.C., you would have a lot of frames actually not exposed at all. These bad characteristics must be altered before we can see much use for it in cinematography Me. Warrexouse: Mr. Linderman, have you made any experiments on the effect on the life of an ordinary incandescent from the increased heat due to this restricted housing ? Tur Autor: The lamps are very well ventilated. The most we do is to put them up a few degrees, and the lamps are already operating at a high temperature. A trouble that we did find was bulb distortion or blistering, which took place when the gas pressure on the inside of the bulb was ereater than it should be. We actually have a splendid draught in our lamps which cools them quite well. Blackening inside the bulb causes distortion. The heat concentrates where the blackening is deposited, finally causing a large blister. The filament is not affected; it is only the glass you have to worry about. Mr. Morgan: I would like to ask Mr. Linderman what sort of filament structure is used now in the U.S.A.—whether it is bunch filament or bi-plane.