An exemplary optical plate includes a first transparent layer (21), a second transparent layer (23) and a light diffusion layer (22). The first transparent layer includes an outer surface (210) and a plurality of first conical frustum-shaped depressions (211) defined at the outer surface. The second transparent layer includes an outer surface (230) and a plurality of second conical frustum-shaped depressions (231) defined at the outer surface. The first transparent layer, the light diffusion layer, and the second transparent layer are integrally formed, with the first transparent layer in immediate contact with the light diffusion layer, and the second transparent layer in immediate contact with the light diffusion layer. The light diffusion layer includes a transparent matrix resin (221) and a plurality of diffusion particles (222) dispersed in the transparent matrix resin.