[OPTICAL REVIEW Vol. 5, No. 5 (1998) 315-319]
Lightness Change as Perceived in Relation to the Size of Recognized Visual Space of Illumination
Yoko MIZOKAMI, Mitsuo IKEDA and Hiroyuki SHINODA
Department of Photonics, Faculty of Science and Engineering, Ritsumeikan University, 1-1-1, Nojihigashi, Kusatsu, Shiga, 525-8577 Japan
(Received May 25, 1998; Accepted July 22, 1998)
According to the concept of the recognized visual space of illumination (RVSI) the lightness of an object surface is perceived in relation to its conceptualized size. To prove this proposition the lightness of gray test patches was judged when they were located at various positions inside an illuminated space composed of two rooms in the depth direction from a subject. No retinal image arrangement was changed in the test patch and its immediate surroundings, but the front room had walls, floors and furniture lower in lightness by the amount of N1.5 than the back room to make the RVSI of the former smaller despite the illuminance in the entire space being the same. The results showed that the apparent lightness of the patches was perceived higher by amount of about 13 in L* units for the N4 test patch and about 20 for N6 when the patches were located in the front room, in accordance with the prediction. It was stressed that the experiment of lightness judgment should be conducted in a three dimensional space rather than two dimensional plane as done by several investigators.
Key words : lightness, apparent lightness, illumination, recognized visual space of illumination