The major factors of an illuminative environment are a high rendering index and uniformity. The natural light illumination system (NLIS) is used to guide sunlight for indoor illumination. The NLIS consists of three subsystems: collecting, transmitting, and emitting. Nowadays, a variety of light emitters are available for different illuminative environments. This paper proposes a linear microstructure to diffuse parallel light for indoor illumination. To increase uniformity and promote the illuminative area, the light emitter includes two microstructures for the distribution of light. Finally, the proposed light emitter gives illuminance uniformity and efficiency of 0.55% and 74.18%, respectively.