Change of the Object Color Appearance by the Illumination Spectral Distribution

The spectral distribution of illumination light is a basic element deciding color rendering property, since the object color is dependent on the spectral distribution of the illumination light and the spectral reflectance of the object surface. Although the natural the sunlight is the standard light of the color rendering property, the sunlight spectral distribution changes to some extent according to time of day, weather, geographic position and season. It means that the color appearance of the object changes under the variable natural light from hour to hour in a day. In other words, it shows the possibility that daily fluctuations happen in the object color under the natural light. In this paper, we measured daily fluctuations of the spectral distribution of the sunlight and the spectral reflectance of various objects, in order to see if distinct change of the color appearance can be seen under diurnal change of the sunlight spectral distribution. As a result, we found the clear color appearance change of the object surface breaking color constancy under diurnal change of the sunlight spectral distribution.