A light blocking sheet includes a first surface, a second surface, an inner annular surface and an outer annular surface. The second surface is corresponding to the first surface. The inner annular surface connects the first surface and the second surface, and forms an inner opening. The outer annular surface connects an edge of the first surface and an edge of the second surface, and includes at least three notches disposed on the outer annular surface and at least three arc surfaces located on the outer annular surface, wherein the at least three notches and the at least three arc surfaces are alternately arranged on the outer annular surface, and the at least three arc surfaces are coaxial and have different arc lengths.