The Influence of Material Colors on the Effective Color Rendering and Temperature through Mutual Illumination

In complex scenes, the light reflected by surfaces causes secondary illumination, which contributes significantly to the actual light in the space (the "light field"). Secondary illumination is dependent on the primary illumination, geometry, and materials of a space. Hence, primary illumination and secondary illumination can have non-identical spectral properties, and render object colors differently. Lighting technology and research predominantly relies on the color rendering properties of the illuminant. Little attention has been given to the impact of secondary illumination on the "effective color rendering" within light fields. Here we measure the primary and secondary illumination for a simple spatial geometry and demonstrate empirically their differential "effective color rendering" properties. We found that color distortions due to secondary illumination from chromatic furnishing materials led to systematic and significant color shifts, and major differences between the lamp-specified color rendition and temperature and the actual light-based "effective color rendering" and "effective color temperature". On the basis of these results we propose a methodological switch from assessing the color rendering and temperature of illuminants only to assessing the "effective color rendering and temperature" in context too.