Colour rendering properties of light sources: New colour space for evaluation

A new colour space NC-IIIC, which is synthesized by nonlinear transformations of the tristimulus values X, Y and Z with nonlinear R-G and Y-B opponent colour response functions k1 and k2, is developed with proper correspondence to the physiological mechanisms of the visual system. This space can specify hue, lightness and chroma independently. The hue shift can be represented only by the difference of hue-angle. The chroma shift can be represented only by the variation of radial distance. Calculated colour shifts in new space NC-IIIC under the test illuminants are well in accord with practical colour shifts irrespective of the correlated colour temperatures of the test illuminants. This new space NC-IIIC is therefore considered superior to the traditional colour spaces for the specification of colour rendering properties of light sources.