An exemplary light guide plate (23) has a light incident surface (231); at least one side surface (232), the side surface being connected with the light incident surface; a light emitting surface (233), orthogonal connected with the side surface and the light incident surface; and a bottom surface (234) opposite to the light emitting surface. At least one of the light emitting surface and the bottom surface has a plurality of protrusions (235) spaced a predetermined distance, each protrusion having a plurality of grooves (2351).