A backlight system has a light guide plate. The light guide plate includes a transparent plate having a light incidence surface and an opposite light emitting surface, and a light transmittance enhancement layer. The light transmittance enhancement layer is provided on either or both of the light emitting surface and the light incidence surface, and is made of silicon dioxide or magnesium fluoride. The thickness of the light transmittance enhancement layer is in the range from 58.about.69 nanometers.