An exemplary optical plate includes a transparent layer and a light diffusion layer. The transparent layer includes a light input interface, a light output surface opposite to the light input interface, and a plurality of micro-depressions formed on the light output surface. The micro-depressions are arranged along a plurality of imaginary, separate, circular arcs. Each micro-depression has at least three side surfaces connected to each other, and a transverse width of each side surface increases 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.