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.