Room Illuminance rather than Immediate Surrounding Luminance Determines Natural to Unnatural Color of an Object Border

The color of an object placed in a room goes through various modes of color appearance if its luminance is increased independently from the room illumination; from the natural object color to an unnatural object color, and to the light source color having two borders. We were interested in investigating the determining factor for the first border as it is useful in lighting design. It has been thought without a specific theory that it is the surrounding luminance that determines the border. According to a new concept of the recognized visual space of illumination (RVSI), the border is solely determined by the room illumination, and not by the luminance of the immediate surroundings of the object. In the first experiment of the present paper the border of a test stimulus was determined for various room illuminance while keeping the luminance of the immediate surroundings constant. It was shown that the border luminance was roughly proportional to the room illuminance, confirming the prediction based on the RVSI theory. In the second experiment the border was determined for varying luminance of the immediate surroundings while maintaining constant room illuminance. The border did not change, again confirming the prediction based on this theory.