Abstract: A light guide used in flat panel liquid crystal display screens is provided. The light guide has triangular prismatic microgrooves cut within it to define a groove density that varies with distance from a light source. The microgrooves also have a groove angle that is based on two times the critical angle of the light guide, plus or minus approximately two degrees. This configuration of groove density and groove angle provides brighter back lighting compared to conventional flat panel displays with increased uniformity over the majority of the display. The maximized luminance and uniformity allows larger displays to be created out of a single light guide or multiple portions of light guides placed next to each other or in a stacked configuration.

Abstract: A first backlight light source is energized either at full or reduced rated power, until such time as the brightness which can be produced has reduced by a predetermined amount (e.g. half of the original level). A second or backup source is then switched on while the first is temporarily switched off. When the backup light source has degraded to the point where the brightness which can be produced by this light source has reduced by a second predetermined amount (which is the same as the first predetermined amount, e.g. 50%) the first light source is switched back on so that both are simultaneously energized. When this measure fails to maintain the required level of brightness, the power with which the light sources are energized is increased.