The numerical values which specify the suitability of fluorescent lamps as a light source of taking color photographs were obtained by the experimental evaluation method which was described in the previous paper. In this paper, the authors examined the rationalization of the values by a view point of practical use of the light sources in photographing colored objects. The suitability factor calculated by the mathematical formula modified by the authors showed high correlations to the result of practical use of light sources. Additionally, it was found that the flattery indices, for individual object colors which recognized as important in color photography, have to be introduced in the evaluation method. As the discrepancies on the metamerism between the human visual system and the color photographic system play significant role in use of the color charts, the consideration on spectral characteristics has to be given to specifing the characteristics of the charts intended to be used in the evaluation method.