Optical transmittance of high-efficiency cavity with photon recycling

A planar-exit lighting surface is not only used in the luminaires but also useful in the display backlights and other illumination systems. Most planar-exit lighting surfaces are made by edge-lit with line light source or 1-D LED array. If it is not edge-lit type, the light source can be two-dimensional, but a cavity is required. In this paper, a high-efficiency cavity providing extremely high energy transmittance with photon recycling is reported and demonstrated. The cavity contains a diffuser and the high reflectivity surfaces. The optical efficiency of the cavity is calculated by a formula with considering photon recycling. Furthermore, various kinds of diffusers are applied to change the optical transmittance as well as the light pattern. When the reflectivity of the inner wall of the lighting cavity is about 96 %, the optical efficiency of the cavity is higher than 90 % with several diffusers. The experimental measurement as well as the calculation is demonstrated in the paper.