Recently, CIE Sub-Committee SC-3.2 on “Illumination for Colour Reproduction” has been investigating an evaluation method for obtaining the index which can predict the degree of the color consistency of lamps in various fields of color reproduction. This work has been carried out as the activity of the Photographic Working Party of Japanese CIE SC-3.2, and the authors will propose here the new method for evaluating the photographic consistency of taking illuminants used in color photography. This paper is composed of the following three parts. The first part describes the derivation of the photographic consistency index “ P_c ”. In the second part, we show some numerical examples of P_c s by using seven fluorescent lamps as the test illuminants. In the final part, the reliability of the photographic consistency index P_c is confirmed by psychological evaluations of color pictures photographed under the test illuminants compared with those under the reference illuminant. It was found that the reliable correlation exists between P_c s and the indices obtained by psychological evaluations.