A light blocking plate is adapted for being installed on a lens wherein the lens has an optical portion and a positioning portion surrounding the optical portion. The light blocking plate includes an annular body which is formed with a through hole at a central portion thereof. The annular body has a first face and a second face. The annular body has an inner rim and an outer rim. The through hole is defined by the inner rim. One of the first face and the second face is adapted for being disposed on the positioning portion of the lens. The inner rim is formed with a plurality of notches so that the inner rim has a contour which is not smooth circular. Thus, halo disturbance can be reduced.