Tailored edge-ray design for illumination with extended sources

The goal of the optical design of luminaires and other radiation distributors is to attain the desired illumination on the target with a given source. Usually there are constraints that should be satisfied, such as avoiding glare, maximizing the optical efficiency and respecting practical size limitations (not to mention considerations of fabrication costs, availability of materials and esthetics). While the required design procedure is well known for situations where the source can be approximated as a point or as a line, the development of an explicit analytical design method (as opposed to numerical search) for extended sources has begun only a few years ago. A solution for extended isotropic sources can be obtained by establishing a one-toone correspondence between target points and edge rays, using the tools of nonimaging optics. The designs are called TED (tailored edge-ray designs). Particular solutions have been found in separate papers by Ries and Winston^1,2 and by Gordon, Rabl and Ong ^3-6. The present paper presents a topological classification of all possible solutions in two dimensions and discusses their general characteristics. We show that any illumination distribution can be obtained exactly in the central region of the target, but in general there will be a certain amount of spillover outside this region. Some flexibility for tailoring designs to specific requirements (size, glare control, etc.) can be gained by the choice of the solution type, the choice of the boundary conditions, and by the use of hybrid configurations that combine several types of solution. The design method is illustrated with specific examples.