Visual comfort in buildings is one of main demands for quality of indoor environment in buildings. Ensuring appropriate daylighting in interiors is architectural and technical problem. Tubular light guides serve opportunity to solutions of daylighting windowless interiors. Their function is based on the principle of light transport from outdoor to distant indoor places due to multi- reflections on their highly reflective internal surfaces. This presentation describes a method for evaluation of internal illuminance from light guides on the basis of determined luminance of a light guide ceiling diffuser. As luminance values of the diffuser are needed for indoor illuminance calculations under real daylight conditions the luminance camera was used and luminance photographs of the ceiling diffuser for clear, partly cloudy and overcast sky were monitored. The calculation results were compared with data from measurements on the practical installation of the light guide. The described method presents a design tool for the evaluation of indoor daylighting in rooms illuminated form tubular light guides.
2008 The Illuminating Engineering Institute of Japan