How the spectral structure of the light source determines colour rendering

Abstract

Light sources with almost arbitrary spectral distributions, like LED and DLP based sources, are today available to the general public but their colour rendering properties are still not well characterized. In this work we studied, computationally, the chromatic effects of a large set of illuminants with almost arbitrary spectral structure. The illuminants were metamers of a Planckian radiator with colour temperature of 6500 K and metamers of non-Planckian radiators with chromaticity coordinates uniformly distributed over the same isotemperature line. The metamers were generated by the Schmitt’s elements approach and were parameterized by the spectral distance to the equi-energy illuminant E. The colour rendering properties of each illuminant were quantified by the CIE colour rendering index (CRI), by a chromatic diversity index (CDI) and by the number of discernible colours estimated for a set of indoor scenes digitized by hyperspectral imaging. It was found that CRI decreases as the spectral structure of the illuminant increase and that larger values of CDI could only be obtained with illuminants with a small number of non-zero spectral bands, that is, with highly structured spectra. In conclusion, highly structured illuminants produce larger chromatic diversity than more uniform spectrum and may therefore be best for applications where maximization of chromatic diversity is important.