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Color Temperatures of Common Illuminants

D. .—All common illuminants having a Planckian distribution are of course characterized by a temperature lower than that of the sun and of the black body which emits normal gray light, and hence evoke an unsaturated yellowish or orange color. The spectral distributions of these various illuminants can obviously be specified by a statement of their respective color temperatures. lists these temperatures for a group of familiar light sources (). The radiation from Welsbach gas mantles cannot be matched satisfactorily with that from a black body at any temperature, and varies quite widely in distribution with the proportions of ceria and thoria in the mantle as well as with the average degree of incandescence. Probably the illuminant whose characteristics are best established at the present time is the acetylene flame produced by a standard burner under specified conditions. The spectral distributions for vacuum tungsten electric lamps are determined by the efficiency, or lumens per watt, at which they are operated, and extensive measurements made at the (), enable one to trans