Abstract
It is our common experience that textures appear differently under different conditions of lighting. In order to manipulate textures in environmental design, it would be useful to know how they appear in a given situation. This paper. Part 4 of the studies, investigates the quantitaive relationships between lighting and perceived visual roughness by a psychophysical experiment. In the experiment, a pair of granular surfaced panels was visually presented to 9 subjects. The lighting conditions for one of the panels were systematically varied by changing the angle of incidence (from 15° to 75°) and the degree of illuminance (from 50 to 6 900 1x), while the other panel's lighting conditions were fixed (at 45°, 1 300 1x). The observation distance of the panel with the fixed lighting conditions was adjusted so that two panels appeared to have an equal degree of roughness. The effect of lighting on perceived visual roughness caused the change of the observation distance. For instance, if one panel appeared rougher by changing lighting condition, the other panel then had to be moved closer to the observer so that the visual perception of roughness between the two appeared equal. Based upon the result of Part 2 of the studies, the change of observation distance can be interpreted into the change of perceived visual roughness. Thus, a quantitative relationship between lighting condition and perceived visual roughness was obtained. The experiment revealed that the influence of both the angle of incidence and the degree of illuminance varied according to the projective image of the surface roughness (visual angle of the grain size). The finer the image of the surface appears, the more marked the effect becomes. When the surface appears as rough as the visual angle, over 7' (minutes), the lighting conditions have no effect on the subjective judgement of visual roughness.
