Daylight performance of lightpipes

Increasing the use of natural daylight for lighting purposes in buildings c an offer large savings in electricity usage, up to 20-30% of total building energy consumption. One solution is the use of lightpipes that can not onl y bring light into otherwise inaccessible or dimly lit places, but also imp rove the internal environment without generating excessive heat. The perfor mance of six light pipes has been monitored in three different areas, a wor kshop, a residential landing, and a small office. The highest illuminance w as 1538 lux, obtained underneath the straight lightpipe on the landing, wit h an aspect ratio of 2.1. The lowest was 41 lux in the darkest corner of th e workshop. The average illuminance for the whole landing was 366 lux and a mean internal to external ratio of 0.48%. The results show that lightpipes are proficient devices for introducing daylight into buildings, the most e ffective lightpipes being straight, short ones with low aspect ratios; cons equently, larger diameter lightpipes would probably be more effective. Howe ver, the benefits of lightpipes also include energy savings, user satisfact ion and a healthier and improved indoor environment. (C) 2000 Elsevier Scie nce Ltd. All rights reserved.