The purpose of this study comprises three points: 1) creating a concept combining “brightness” and “vividness”, which was named “Brilliantness” :Brt; 2) expressing Brt by the numerical value; and 3) investigating the relationship of Brt between color image dimensions. 65 colors (12 tones by 5 hues [red, yellow, green, blue, and purple], and 5 achromatic colors) in Practical Color Co-ordinate System were used as stimuli. These colors were evaluated in terms of “Brightness,” “vividness”, and color images (15 adjective pair words). As a result, “brightness” and “vividness” were correlated. “Brightness” and “vividness” were analyzed by principal component analysis (PCA). PCA demonstrated a concept that combined “brightness” and “vividness.” The contribution ratio of the component was 88.2%. The concept was named “Brilliantness.” The color images were subjected to factor analysis, and three factors were revealed. The correlation coefficients between “Brilliantness” and factor scores were calculated. High correlation coefficients were found between “Brilliantness” and factor1(Evaluation-Potency) (r = .965) as well as between “Brilliantness” and factor2(Activity) (r = .937). These results suggest that “Brilliantness” can express these color images.

  Melanopsin has been reported to contribute to color appearance. Previous studies have examined the effects of melanopsin stimulation on the color appearance of small visual stimuli but not on the color appearance of the lighting environment. To determine the effect of melanopsin on the color appearance in a lighting environment, we conduct an experiment using an apparatus in which a multispectral light-emitting diode (LEDs) light source is placed on the ceiling. Eight light source conditions are prepared by combining the correlated color temperature (2700 K, 5000 K, and 8000 K) and melanopsin stimulation (low, normal, and high). The results showed that the higher the stimulation with melanopsin, the more the color appeared greenish under some conditions at the 5000 K and 8000 K. Melanopsin contributes not only to the partial visual field but also to the color appearance of the lighting environment, indicating that it must consider melanopsin stimulation as well as tristimulus values when designing the spectral power of lighting.

  There are individual differences in brightness perception; while some people do not feel glare even at the same luminance, others do. Extreme reactions to light stimuli can lead to visual perception disorders such as Irlen Syndrome. In this study, we conducted a correlation study betweenluminance difference threshold and brightness assessment in individuals in the mesopic range. The luminance difference thresholds were measured, and 30 subjects were surveyed on how they perceive brightness in their daily lives. As a result, we were able to confirm a certain correlation trend between the characteristics of luminance difference thresholds and the responses to the questionnaire regarding the sense of brightness.