This invention relates to an illumination apparatus. The illumination apparatus comprises a light guide plate and a light source configured to emit light into the light guide plate through a first surface, and the light guide plate comprises a concentrator configured to direct incident light in the light guide plate so as to radiate in a direction substantially parallel to a preset plane. The preset plane is perpendicular to any one of the top surface and bottom surface of the light guide plate, and intersects the first surface and a second surface of the light guide plate or intersects the first surface and one of the side surfaces at an angle that is substantially larger than the critical angle of a total reflection. In this way, unwanted light loss in the light guide plate is reduced, and the distribution of the light intensity or luminance along the light guide plate is improved, i.e., a substantially uniform distribution of the light intensity can be achieved.