Consideration of light level in specifying light source color rendition

Abstract

In lighting practice, light level is seldom considered when specifying light source color rendition. Many past studies found that sources that can enhance color saturation within a certain range, especially for red colors, were preferred, but the experiments were typically carried out with an illuminance between 200 and 500 lx and the illuminance was seldom varied in individual studies. This article reports a psychophysical study that was designed to test whether illuminance affected color preference. Four nearly metameric stimuli with a correlated color temperature (CCT) around 3000 K and a Duv of −0.005 were produced to illuminate an oil painting at two illuminance levels (that is, 20 and 500 lx). These four stimuli were carefully designed to cover a range of relative gamut (that is, IES Rg) from 100 to 125 and enhance the saturation of red and green colors (that is, Rcs,h1 and Rcs,h8). Observers compared pairs of light stimuli at a same illuminance level in a sequential mode and selected the one under which he or she preferred the color appearance of the painting. It was found that the Rg of the most preferred stimulus decreased as the illuminance increased. The stimulus with an Rg ≈ 117 was the most preferred at 20 lx, whereas the one with an Rg ≈ 100 was the most preferred at 500 lx. The interaction between illuminance and saturation enhancement caused by the stimuli with larger gamut areas revealed the importance of considering illuminance when specifying light source color rendition, especially when an application requires a low light level and good color rendition.