Patent ID: 7628526

Claim:
A back light unit comprising: at least one lamp generating light; a light guide plate emitting light across a surface thereof using the light generated from the lamp; a diffusion sheet arranged above the light guide plate to diffuse the light passing through the light guide plate; a first condensing sheet condensing the light from the diffusion sheet using a plurality of first elliptical condensing patterns repeatedly formed on a surface of a first condensing film in first direction and second direction crossing the first direction, wherein each of longitudinal axes of the first elliptical condensing patterns is parallel to one another in the first direction and each of short axes of the first elliptical condensing patterns is parallel to one another in the second direction; and a second condensing sheet further condensing the light from the first condensing sheet using a plurality of second elliptical condensing patterns repeatedly formed on a surface of a second condensing film in the first and the second direction, wherein each of longitudinal axes of the second elliptical condensing patterns is parallel to one another in the second direction and each of short axes of the second elliptical condensing patterns is parallel to one another in the first direction, wherein the first elliptical condensing patterns are formed on a surface of the first condensing film to respectively have an asymmetrical or unbalanced elliptical shape of several μm using a holographic method, wherein the second elliptical condensing patterns are formed on a surface of the second condensing film using the same method as that of the first condensing patterns.