Mirror lightpipes : Daylighting performance in real buildings

Mirror lightpipes are useful for providing healthy and energy-efficient daylight into buildings where windows and skylights are unsuitable, insufficient or generate too much heat gain. The lightpipes have been installed in dozens of buildings in the UK. Field monitoring has been carried out to assess their performance in four different buildings: the headquaters of a major insurance company, a health clinic, a residential building and a college dining hall In those cases where lighipipes with moderate aspect ratios were installed, good illuminance of up to 450 lux has been obtained with internal/external illuminance ratios around 1%. When long and narrow lightpipes with many bends are used, however, the ratio reduced to around 0.1%. These results showed that lightpipes can be effective daylighting devices provided that excessive aspect ratios and numbers of bends are avoided. Lightpipes with larger diameters should be used whenever possible. The lightpipes often improved signiScantly the visual quality af the interior environment, and high user satisfaction was found even in buildings where a relatively low level of daylight was admitted through the lightpipes