Corrections for chromatic adaptation in the determination of colour rendering indices

Abstract

The revised CIE Test Colour method for determining the colour rendering properties of light sources introduces a von Kries type of correction to allow for chromatic adaptation of the eye. Calculations have been made to discover the effect of this correction in comparison with other possible corrections, including that used in the original CIE method. A wide variety of spectral power distributions has been used to represent the test light sources, including many types of real lamps and some theoretical distributions. In general the von Kries correction produces an increase in the general index Ra if the chromaticity of the illuminant is on the purple side of the Planckian locus. Possible reasons for this bias are discussed. Details are given of a method of calculation with the use of 3 x 3 matrices as applied in colour television work.