Edge-lit back light unit using prism microstructures

Abstract

An edge-lit back light unit includes a specular reflector and an edge-lit light guide film positioned above the specular reflector, both configured to provide peak optical distribution and FWHM angle of diffusion along a light propagation direction. A diffuser film above the edge-lit light guide film has a bottom-side that faces the edge-lit light guide film and a top-side that faces away from the edge-lit light guide film, and has a plurality of parallel prism microstructures on the bottom-side, some have an apex direction that is generally along the light propagation direction. The diffuser film has a plurality of parallel prism microstructures on the top-side having an apex direction that is rotated with respect to the apex direction of the plurality of parallel prism microstructures on the bottom-side such that the apex direction of the parallel prism microstructures on the top-side is generally perpendicular to the light propagation direction. A pair of crossed BEFs above the diffuser film have a plurality of parallel prism microstructures on one side and face away from the diffuser film, wherein the plurality of parallel micro prisms of one of the BEFs is oriented perpendicular to the plurality of micro prisms of the other BEF. The apex direction of the plurality of parallel prism microstructures on the bottom side of the diffuser film is substantially aligned with the plurality of parallel micro prisms of at least one of the brightness enhancement films.