Backlight Output Enhancement Using Cholesteric Liquid Crystal Films

Dichroic polarizers are used to produce linearly polarized light in direct view displays; however, these elements introduce an inordinate amount of loss. Alternatively, a cholesteric liquid crystal (CLC) film and a quarter-wave plate (QWP) combination can be utilized in a display backlight to both polarize and enhance backlight output. A 45% increase in forward propagating light intensity from a notebook computer backlight outfitted with a broadband CLC film and a QWP is demonstrated here. Polarized backlight output is studied for two types of CLC films: one, a single layer broadband CLC, and the other, a stack of red-, green- and blue-reflecting CLC films. In addition, light output was measured at different positions on the backlight and for different types of rear reflectors.