A backlight unit according to various embodiments of the present invention includes a light source, a color conversion sheet disposed above the light source for converting a color of light emitted from the light source and an optical film disposed on the color conversion sheet. The optical film further comprises a first sheet having a first pattern layer including a plurality of pyramid patterns formed on one side of a first base and a second pattern layer including a different pattern from the plurality of pyramid patterns disposed on the other surface of the first base and a second sheet having a third pattern layer including a plurality of pyramid patterns formed on one side of a second base and a fourth pattern layer corresponding to the second pattern layer formed on the other side of the second base. The second pattern layer and the fourth pattern layer include a plurality of irregular protrusion portions. The first sheet and the second sheet is laminated by an adhesive material disposed between the second pattern layer and the third pattern layer.