A display apparatus includes a display panel and a backlight unit for an embodiment. The display panel includes a plurality of pixels and the backlight unit supplies light to the display panel. The backlight unit includes a light source, which generates the light, and an optical sheet. The optical sheet includes a plurality of prism patterns formed on a surface of the optical sheet facing the display panel. The prism patterns include a plurality of peaks and a plurality of valleys to change the path of the light, and a plurality of diffusion patterns arranged at the peaks and valleys.