A light guide plate is adapted for use with at least one light source that is capable of providing source light beams. The light guide plate includes a plate body, and a plurality of light-guiding structures that are distributed on the plate body. Each of the light-guiding structures is in a substantially quadrilateral pyramidal form, and includes a quadrilateral lower end that has four corners, and a tapered upper end that is disposed opposite to the lower end. Each of the light-guiding structures further includes four sides, each of which is defined by the upper end and a corresponding adjacent pair of the corners, adjacent ones of the sides being interconnected.