Past studies suggested that sources with a high color fidelity may not always be preferred, while sources enhancing color saturation, especially the saturation of red colors, can result in higher preference. These studies, however, were typically carried out between 200 and 1000 lx. The color preference under a low light level was seldom investigated and illuminance was seldom varied in an individual experiment. This paper reports an experiment which was specifically designed to test a prior hypothesis that color preference reduced with illuminance level and sources with a larger gamut area can compensate the low preference caused by the illuminance reduction. Twenty-two observers compared the color appearance of an artwork under nine nearly metameric 3000 K stimuli under two illuminance levels (i.e., 20 and 480 lx). The stimulus with an R_g of 118 was the most preferred under 20 lx, while the stimulus with an R_g of 109 was the most preferred under 480 lx. The findings clearly revealed the importance of illuminance level in evaluating and specifying light source color rendition.