The design of a day lighted space is both an art anda science. The biggest challenge facing the lightingdesigner is to admit only as much light as necessaryand distribute it evenly throughout the space withoutintroducing glare or heat. In warm climates such asFlorida, it has become common practice in windowedspaces to specify blinds and glazing with highshading coefficients to control glare and minimizeheat gain. However, this practice reduces theeffectiveness of lighting systems that dimautomatically. Improved systems are needed tocapture natural daylight and distribute it uniformlythroughout a space while controlling heat gain andglare. One such system is the light shelf. Lightshelves shade the space from direct sunlight andreflect this sunlight onto the ceiling for a deeper andmore uniform distribution. While this is not a newidea, little unbiased empirical data has been collected,outside the laboratory, that compares the performance(energy savings, uniformity, and level) of anautomatic daylighting system.This study measures the effectiveness of lightshelves and manually controlled horizontal blinds inan automatic daylighting system. Power consumptionand interior work-plane lighting levels werecompared in four essentially identical private offices.Two offices were configured with an interior lightshelf, one with a white diffuse top surface and theother with a specular surface. The third office had nowindow treatment and the fourth office had horizontalblinds, which were manually adjusted by the user.All offices had two lamp fluorescent luminaires withdimming ballasts (min. 20%) controlled by a ceilingmounted photosensor. The study showed thatdaytime savings ranged from 29% to 46%, with thelargest savings from the office with the light shelves.The office with horizontal blinds showed the poorsavings (32%) and also the poorest light uniformityand level.
展开▼
