Light-pipe prediction methods

Light pipes (such as tubular lighting) are simple structures that allow the transmission of daylight from outside to inside a room. They are an increasingly popular product, with CIBSE Building Journal (September 2003) stating that there are now an estimated three million pipes installed throughout the globe. They generally consist of a top collector (often just a polycarbonate hemispheric dome), the pipe itself, and an emitter. Light pipes have different designs and are constantly being improved and updated. Much of the work discussed here considers pipes of reflective aluminium sheets (96% reflectance) that transmits light through multiple specular reflection, but more reflective films are now available that produce even better performances. For example, a film developed by 3M has a reflectance of 98-99%, with the light transmitted via total internal reflection. Such innovations make the light-pipe increasingly efficient, but it is important to quantify this effectiveness by producing reliable predictive methods. The following article, as part of the CIE international technical committee TC3-38 contribution, provides a review of such models/methods and their applications.