Patent ID: 7583353

Claim:
A backlight unit equipped with at least a light source, a plurality of optical sheets and a chassis into which at least the plurality of optical sheets are assembled by placing each optical sheet in proper order and direction, the backlight unit comprising: a first optical sheet, which is one of the plurality of optical sheets, and provided with first identification parts at predetermined positions around the periphery thereof, wherein a number of the first identification parts is a same number as a rest of the plurality of optical sheets other than the first optical sheet; and a plurality of second optical sheets, which are the rest of the plurality of optical sheets other than the first optical sheet and to be placed following the first optical sheet in proper layer positions and direction when assembled into the chassis, and each of the second optical sheets being provided with a second identification part at a position corresponding to one of the first identification parts, wherein each of the first identification parts is allocated in predetermined order to specify a layer position where each of the second optical sheets is placed, the second identification part is so shaped that at least a part of the corresponding first identification part is visually recognizable when viewed from an assembling direction of the plurality of optical sheets.