Patent ID: 7665876

Claim:
A backlight unit comprising: a light source; a light guide plate surrounded by two main surfaces and a plurality of end surfaces connecting the main surfaces, the main surfaces are substantially orthogonal to the end surfaces, one of the end surfaces facing the light source is designated as an entrance surface, one of the main surfaces is designated as an emitting surface; a first prism sheet provided above the light guide plate, having a plurality of first prism columns abutting each other on a top surface of the first prism sheet and a plurality of second prism columns abutting each other on a bottom surface of the first prism sheet, each of the first prism columns has a first ridge line parallel or perpendicular to the entrance surface, each of the second prism columns has a second ridge line extending in a different direction from the first ridge line; a second prism sheet provided above the first prism sheet, having a plurality of third prism columns abutting each other on a top surface of the second prism sheet, each of the third prism columns has a third ridge line extending in a direction different from the first and second ridge lines; and a reflection sheet facing the light guide plate below the light guide plate.