Patent ID: 7738053

Claim:
A backlight unit comprising: a light-source substrate having mounted thereon a plurality of light-emitting elements that emit illumination light; a light guide plate having a side surface with the light-source substrate attached thereto so as to receive the illumination light from the light-emitting elements, the light guide plate also having a first surface extending substantially perpendicular to the side surface, and a second surface, wherein the light guide plate has a thickness extending between the first and second surfaces; a reflective sheet attached to the first surface of the light guide plate so as to reflect the illumination light from the light-emitting elements towards the second surface of the light guide plate; and an optical sheet layer attached to the second surface of the light guide plate and comprising a plurality of optical sheets in a stacked manner, wherein the side surface of the light guide plate to which the light-source substrate is attached is provided with a reflective portion that reflects illumination light received by the light guide plate from the light-emitting elements, wherein the light guide plate is shaped such that substantially all of the illumination light received by the reflective portion from the light-emitting elements is incident on the reflective portion at an incidence angle that is equal to or above a critical angle, such that the illumination light received by the reflective portion is reflected within the light guide plate; wherein the thickness of the light guide plate is gradually reduced approaching the side surface; and wherein a first thickness of the light guide plate at the side surface is smaller than a second thickness of the light guide plate at a central region of the light guide plate outside the reflective portion, wherein the reflective portion at the side surface of the light guide plate has a stepped profile.