An optical sheet includes a base film, a prism pattern formed in a first area of the base film, and a diffusion member formed in a second area of the base film. The prism pattern has a plurality of parallel prisms on a light-exiting surface. The diffusion member includes a plurality of scatter members in the base film to scatter light, or a plurality of irregularly arranged lenses on one or more of the light-incident surface and the light-exiting surface.