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The General Requirements for Photographic Lighting
By R. G. LINDERMAN
Delivered to a Meeting of the British Kinematograph Society, held at the Gaumont-British Theatre, Film House, 142, Wardour Street, W.1, on October 12th, 1936.
_ SUMMARY
The paper discusses problems encountered in studio lighting and deals with the following points :—
1. The colour temperature of the lamps employed, and a rational method of lamp rating.
2. The errtical
nature of variations,
voltage
5. Vapour discharge lamps. 4. The use of spill rings and methods of
avoiding their use while securing greater lighting efficiency 5. Modern designs of lamps which
avoid ‘‘ hot rings”? between ‘‘ flood ”’ and “ spot’ positions. 6. The correct, use of diffusers. 7. The use of filtered are lamps combined with incandescents for colour work. ITHIN the scope of a paper to be delivered in a fairly short time it is possible to give only a general outline of requirements which lead toward ideal equipment for motion picture lighting, and I have, therefore, endeavoured to set forth a few essentials for such equipment to show how past experience has enabled us to construct lighting units of new design which more nearly embody these ideal essentials.
Importance of Colour Temperature
Although the ideal light source has not yet been evolved, generally speaking it is desirable to have a light source with a fairly large range of sizes, that is one which will emit different intensities with a more or less fixed spectral composition— which we usually describe as colour quality, or, more correctly, colour temperature of the source—the colour temperature, of course, depending on the film emulsion,
Since the advent of sound in motion pictures the prime essential has been quiet operation of the source. The incandescent lamp best meets the need of steadiness and quietness, and if adequate voltage control is possible, the colour temperature of this source can be held for very satisfactory use in exposing panchromatic film stock.
One of the very common practices which should be corrected is the general use of lamps which, when burned at their rated voltage, operate at considerably different colour temperatures. This is a practice which came into being by reason of the lamp manufacturers’ method of rating the lamp as to its average life rather than to its light output.
Rating Lamps by Filament Temperature
For photographic lighting it is much more desirable to rate lamps with regard to their lumen per watt or colour temperature characteristic. This step has already been taken in the production of Photo flood lamps which are designed to operate at a colour temperature of 3,440 dezrees Kelvin. As tungsten melts at 3,665 degrees Kelvin the life of a 250 watt lamp is approximately two hours, but by reason of the greater bulk of the filament, the life of a 5 k.w. lamp is approximately 40 hours.
It would be desirable to have a complete line of incandescent lamps to operate at about 3,275 degrees Kelvin, which is the rating of the present 5 k.w. lamp in general use, so that all lamps on the set would be operating at the same colour temperature.
In ordinary practice lamps vary from around 3,000 degrees Kelvin up to 3,275 degrees and, although this is not critical in black and white photography, it is not