1995 Volume 79 Issue 11 Pages 639-647
“Visual Clarity” or “Brightness Sensation” of colored objects changes by changing the color rendering properties of light sources. Though visual clarity is considered one of the most important characteristics of the color rendering properties of light sources, it can not be estimated adequately by using the present CIE Ra method. For this reason, we studied the cause of visual clarity and confirmed that visual clarity was caused by the feeling of contrast between the colored objects under the illumination. In addition, we proposed the method for predicting the illuminances for the same feeling of contrast under various light sources, based on the gamut area made by the four component colors of a four-color combination in a brightness and colorfulness space.
The purpose of the present study is, furthermore, to develop an estimation method of the feeling of contrast under test light sources and to propose a new index of the feeling of contrast under a test light source by using a simple transformation of the gamut area derived under the light source. The new proposed index correlated well with the illuminance ratio for equal feeling of contrast (or equal visual clarity) on various light sources reported so far. The new index is compared with the other indices, such as General Color Rendering Index Ra, Color-Discrimination Index and Flattery Index, and it is confirmed that the new index is a different measuring index from these indices. By using the new method proposed in this paper together with the present CIE Ra method, the color rendering properties of light sources can be well estimated from various points of view.