Patent ID: 7905619

Claim:
A backlight device for a display device, the backlight device including: a light source emitting light; an optical sheet having a notch formed in a side thereof and arranged to adjust an optical path of the light emitted from the light source to direct the light to a back side of a display panel; and a frame arranged to attach the optical sheet to the back side of the display panel; wherein as seen in plan view, a maximum width of the notch as measured in a direction substantially parallel to a line connecting both ends of a mouth portion of the notch is greater than a width of the mouth portion; at least one projection with which the at least one notch in the optical sheet respectively engages is disposed on the frame so that, by making the at least one notch in the optical sheet engage with the at least one projection on the frame, the optical sheet is positioned in place; and in a two-dimensional rectangular coordinate system having an origin G(0, 0) thereof at a center of gravity of the optical sheet, having a y-axis thereof running perpendicularly to a side of the optical sheet that is located highest in a direction of gravity in actual use, and having an x-axis thereof running parallel to said side of the optical sheet, a sum of an x-coordinate of a location at which the at the least one projection on the frame respectively engages with the at least one notch in the optical sheet equals zero.