Distribution of Border Luminance and Additivity Law in a Complex Illuminated Space

Abstract

We propose a measurement method for evaluating space brightness by measuring border luminance as it is very important for architectural design to assess space brightness quantitatively. Border luminance is the transition point of the color appearance mode. It is where natural object color mode changes to unnatural object color mode. Our previous work showed that the border luminance stays the same regardless of measuring position, if the room is uniformly illuminated. In such conditions, the border luminance is mainly determined by the illuminance and configuration of the interior's reflectance. We measured the border luminance at various positions in a non-uniformly illuminated room to examine how border luminances are distributed. Our results show that the illuminance distribution is not significant in determining the border luminance, but the distance between the measurement position and the wall, which might be used as the main cue for a subject to recognize the illumination of the room, is important. We also found that additivity law holds for border luminance. This rule is very useful for practical lighting design. For example, the border luminance of a room illuminated by two or more lights can be estimated from the border luminances under each single light.