The backlight assembly includes a first lamp unit and a second lamp unit. The first lamp unit generates light. The light guide plate has a light exiting surface, a light reflecting surface and side surfaces. The light reflecting surface surfaces the light exiting surface. The side surfaces connect the light exiting surface and the light reflecting surface. The side surfaces include a first light incident surface. The first lamp unit is disposed adjacent to the first light incident surface, and the first light incident surface inclines inwardly from the light exiting surface to form an inclination angle that is smaller than or substantially equal to (90-2 sin.sup.-1(n.sub.2/n.sub.1)).degree., wherein `n.sub.1` is a refractive index of the light guide plate, and `n.sub.2` is a refractive index of a material between the lamp and the light incident surface.