When the correlated color temperature of the test illuminant is different from that of the reference, a correction of chromatic adaptation must be considered in comparing color appearance under both illuminants on object colors considered. Four chromatic-adaptation formulas were selected and their influences were numerically compared for the following two kinds of object colors with respect to th reference illuminant C and the test illuminant A;(1) eight object colors used for the general colorrendering index and (2) thirteen metameric object colors including those derived by Wyszecki for defining an index of color-matching property.
The results obtained are as follows: (1) Correlation between predicted color differences by any two kinds of chromatic-adaptation formulas is extremely good for object colors considered on the index of color-matching property but not sufficiently good for those of the general color-rendering index.(2) In deriving the general color-rendering index, there exists an uncertainty caused by the inconsistency between the chromaticity coordinates of illuminant C and those corrected by a chromatic-adaptation formula for illuminant A. However, this inconsitency does not affect to the index of color-matching property.(3) The index of color-matching property of the test illuminant A is estimated at about ΔE_M=12 to 15 (R_M=31 to 46) for four kinds of chromatic-adaptation formulas with respect to the reference illuminant C, and the uncertainty of ΔE_M is about±11%.(4) These results may suggest the practical significance of using a single reference illuminant for deriving the index of color-matching property.

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