Presently, energy conservation and carbon dioxide emission reduction have become increasingly important because of global warming. Using solar energy, which is considered as one of the most important renewable energy sources, does not only decrease the consumption of fossil fuels, but also slows down the pace of global warming. For indoor illumination, our team has developed a technique called "Natural Light Illumination." Instead of using solar cells, our system directly guides sunlight into the interior of a structure. However, the efficiency of the light-collecting module is still low. To address this problem, we propose a new light-collecting module based on a prism array structure with high efficiency. We use optical simulation tools to design and simulate the efficiency of the module, which is found to be 57%. This value is higher than that of the original concentrator (i.e., 11%).

Natural light illumination system (NLIS) generates increasing research interest because of the recent trend toward green energy. Various crucial optical components used in a NLIS are analyzed, designed, and fabricated to obtain high efficiency. A large amount of light is loss because of the large viewing angle during light transmission. A tapered light pipe (TLP) is used to collimate light viewing angles. In this letter, we combine a TLP and a traditional lens as a new coupler based on Etendue theory. The original efficiency is only 17.54%, but the efficiency reaches more than 70% when the new coupler is applied.