A light guide plate (10) includes a light incident surface (12), a light emitting surface (14) adjoining the light incident surface, a bottom surface (16) opposite to the light emitting surface, and a plurality of holes (18). Each hole has at least one open end terminating at the light emitting surface or the bottom surface. The holes may be through holes or blind holes. When incident light beams reach the holes, the light beams are reflected or refracted in directions toward the light emitting surface. Therefore a distance traveled by a portion of the light beams in the light guide plate is shortened, and the loss of light energy is reduced. This enables the light guide plate to provide a high ratio of light utilization. Additionally, the through holes reduce the weight of the light guide plate. The light guide plate can be generally rectangular or wedge-shaped.