Computing evaluation of the combinations of uniform color spaces and chromatic adaptation correction formulae from the viewpoint of application to the absolute color rendering specification.

For calculating absolute color rendering indices which specify the color rendering properties of light sources referring to a single standard illuminant, independent of the correlated color temperature of the sample light sources, a proper combination of a uniform color space and a chromatic adaptation formula is needed. A method of computing evaluation for this combination is here proposed based on the assumption that the Planckian radiators and the CIE daylights in a wide range of correlated color temperature are quite similar to each other in their psychosensorial color rendering properties. Color rendering indices of various light sources are calculated, using several combinations of uniform color spaces and chromatic adaptation correction formulae by changing the reference illuminant. It is assumed here that the smaller the change in the color rendering indices with the change of the reference illuminant the better the combination of the space and the formula. The results show that the combination of the nonlinear transformation formula proposed by Nayatani et al. with the uniform color space CIELAB or Richter’s LABHNU is the best, confirming the results of the former experimental evaluation by the same authors.