Characteristics of the brightness perception under the dark adaptation - Aims to develop energy-effcient lighting system for signboard-

Outdoor signboards on the street provide not only advertising but also effective scenery of the town, and they are useful for the activation of the town. Sometimes they have different faces according to the effect of the lighting systems in daytime and night time. In this experiment, we use lighted signboards to examine how human eyes see "object colors" under the dark conditions. Advertising signboards that we recognize as "object colors" begin to change into "light source colors," when it darkens gradually in the night time. When this change occurs, the horizontal illuminance decreases from 1000 to 100 lx. In addition, "brightness feeling" and the ratio of "light source colors" rise rapidly when the luminance difference between the sky and signboard falls below 200 cd/m2. We think our results will be useful to develop and control signboard lighting in the field of energy saving technology.