A surface light source (3, 4, 5) includes a light guide plate (32, 42, 52), which defines an incident surface (321, 421, 521), an emitting surface and a bottom surface (323, 423, 523) opposite to the emitting surface; and a light source (31, 41, 51) adjacent to the incident surface of the light guide plate for radiating light beams into the light guide plate through the incident surface. A multiplicity of generally rectangular dots (328, 428, 528) and generally circular dots (329, 429, 529) is formed on the bottom surface of the light guide plate. The rectangular and circular dots reflect and scatter the light beams in directions toward the emitting surface. The rectangular dots are distributed on the bottom surface corresponding to lower luminance areas of the light guide plate, so that the luminance over the whole emitting surface of the light guide plate is uniform.