Evaluating the Material Appearance of Objects Under Different Lighting Distributions Against Natural Illumination

The recent development of new solid-state lamps including OLED lighting offered a wide variety of lighting conditions through controlling the spectral power distribution and the spatial distribution of light. The appearance of an object surface is largely influenced by lighting conditions and object materials. Variable control of lighting condition would be useful to offer an optimal material impression. We have investigated the possibility whether the subjective evaluation, comparing material appearance under different lighting distribution with that under natural illumination, is able to determine a lighting condition for an appropriate material appearance. We tested viewing condition consisted of three spotlight sizes and three illuminance levels. Participants chose one viewing condition in which the material appearance of fruits and vegetable food samples was closest to those impression learned from observing and holding freely in a reference natural illumination. In addition, they evaluated impressions of stimuli in each condition by the twelve questionnaires of seven-point scales. The result showed higher tendencies to select the wide spotlight size condition with higher diffuseness of illumination rather than narrower spotlight conditions, suggesting that diffuseness of illumination influences object material appearance. Results of seven-point scales showed differences between samples, but little differences among lighting distribution. It was thus suggested the possibility to provide an optimal lighting condition to offer material appearance similar to material impression learned with visual and tactile information in natural illumination.