High efficiency quad luminaire prism light guide

Prism light guides are usually used in remote-source lighting applications, where the lamp is generally an intense point source with a high luminous e fficacy, and it is desirable to produce a uniform illumination. Typically a transparent protective housing is used to support a cylindrical prism ligh t guide, made of flexible prismatic optical lighting film.(1) The prisms in the film confine the light by means of total internal reflection(2-5) and scattering structures within the guide cause uniform light emission along i ts length. The advantages of using a prism light guide include lower maintenance costs because there are fewer light sources and lower glare as a result of a mor e uniform light distribution. However, there is some energy loss associated with guiding light, which results in a lower net system efficacy than that of some conventional fixtures. Although the light guidance loss can be sma ll, it is a common preconception that light guides are not efficient enough for conventional illumination. One of the motivations for the research des cribed here was to demonstrate high efficiency is indeed possible with a pr ism light guide luminaire system. In this paper, rue describe such a system, based on four-fold symmetrical i llumination of prism light guides having rectangular cross-section. We achi eve a net system luminous efficacy of 71 lumens per Watt, which is a 25 per cent improvement over the best previous system. The net system efficacy was determined independently by two groups. The fir st group at the University of British Columbia (UBC) measured the surface e xitance as a function of position and spatially integrated it to obtain tot al output flux. The second group at Queens University (QU) confirmed the ne t system efficacy using the same method and as a further verification, meas ured the luminous intensity as a function of direction and integrated over solid angle to obtain the flux. These tests agreed substantially and showed 76 percent of the lamp lumens are emitted from the output surface of the l ight guide.