An exemplary optical plate includes a transparent layer and a light diffusion layer. The transparent layer includes a light input interface and a light output surface opposite to the light input interface. A plurality of micro-protrusions formed on the light output surface. The micro-protrusions are arranged along a plurality of separate, circular arcs. Each micro-protrusion has four side surfaces connected to each other, and a transverse width of each side surface decreases along a direction away from the light diffusion layer. The light diffusion layer is integrally formed in immediate contact with the light input interface of the transparent layer, and free of air or gas pockets trapped in an interface therebetween. The light diffusion layer includes a transparent matrix resin and a plurality of diffusion particles dispersed in the transparent matrix resin.