Lightness change as perceived in relation to the size of recognized visualspace of illumination

According to the concept of the recognized visual space of illumination (RV SI) the lightness of an object surface is perceived in relation to its conc eptualized size. To prove this proposition the lightness of gray test patch es was judged when they were located at various positions inside an illumin ated 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 s urroundings, but the front room had walls, floors and furniture lower in li ghtness by the amount of N1.5 than the back room to make the RVSI of the fo rmer smaller despite the illuminance in the entire space being the same. Th e results showed that the apparent lightness of the patches was perceived h igher 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 s hould be conducted in a three dimensional space rather than tyro dimensiona l plane as done by several investigators.