Color Temperature: Its Use in Color Photography

Color temperature as a specification for light sources is inadequate to define any light source for color photography which departs appreciably in energy distribution from the black body. It should probably be restricted to use with tungsten incandescent lamps only. Meters devised to measure color temperature by means of measurements of the relative energy in two wavelength bands are likewise not trustworthy when applied to any but the black-body sources. A "three-point," rather than a "two-point," meter is needed for the precise control of photographic exposures. Such a meter should have sensitivity distributions that match those of the three emulsion layers of the color film.