Light-quality-tunable illumination system using a liquid crystal light control film for application to lighting for cultural properties

The light quality, i.e., the softness of the illumination, has a significant effect on both the color information and the roughness information of the surfaces of illuminated bodies, which are read by observing these illuminated bodies. Generally, to create soft light when taking photographs, tracing paper, white cloth, or similar materials are used as light diffusers. Consequently, the light quality must be adjusted by replacing or moving the light diffusing material, and fine adjustment can be difficult. Moreover, there is a high risk of physical damage being caused to the illuminated bodies because of the equipment falling over. In this study, we have applied a liquid crystal light control film of the type that is widely used to switch between transparent and opaque windows to adjust the light quality required for photography of chipped stone tools. The proposed illumination system can vary the light quality continuously using electrical control only, without using moving parts, and thus reduces the risk of physical damage to illuminated bodies during light quality adjustment. Therefore, the proposed illumination system using the liquid crystal light control film is extremely useful for photography of valuable cultural properties. As a result of the assessment of photographs of chipped stone tools that were taken under various light quality conditions, it was possible to change their states continuously from glossy states to matte states. Photographs of a chipped stone tool composed of obsidian acquired under hard light tended to make the roughness information easier to read; however, photographs taken under soft light tended to make their color information more readable. In addition to its use in photography of cultural items, the illumination system proposed here has potential for use as a lighting system that can guide each viewer’s point of view in real time by controlling the light quality during observation of cultural exhibits in museums.