Design guidance of backlight optic for improvement of the brightness in the conventional edge-lit LCD backlight

An edge-lit backlight as a surface illuminator in the liquid crystal display achieves high brightness illumination with the light-condensing optic, composed of lamps, a light guide plate, a reflection film, a diffuse film, and a brightness enhancement film (BEF). This paper dealt with a technique to improve the brightness of a LCD backlight by increasing the light-condensing efficiency of an existing BEF. First, the technique was proposed; the efficiency of a BEF can be improved by a proper shaping of the angular luminance of lights entering the BEF. Then, its validness was experimentally proved with investigation of the brightness change of a test monitor backlight, varying the angular shape of the incident light to a BEF by adjusting the scattering power of both a diffuse film and an ink material printed on a light guide plate. It was revealed that the improvement range of the brightness by the proposed technique is about 5–9%.