A backlight unit includes a light emission part having a lamp for emitting light beams and a lamp housing for mounting the lamp therein and for reflecting the light beams from the lamp; a light guide panel for guiding the light beams from the light emission part; a reflecting plate under the light guide panel for reflecting the light beams that progress to a lower surface and a side surface of the light guide panel; a diffusion sheet having a thickness of about 113 m for diffusing the light beams that have passed through the light guide panel; and a prism sheet having a thickness of about 165 m and having a half-power angle of at least about 40 for controlling progress directions of the light beams that have passed through the diffusion sheet.