Many technologies are currently being developed to provide the next generation of flat panel, projection, flexible, and micro-displays. Flat-panel emissive displays, which emit light in a lambertian behavior, are considered by consumers to be the most attractive display. Despite the human eyes natural affinity for emissive displays, liquid crystal displays (LCD) currently dominate the commercial display market. Because LCD's filter white light, which passes through polarizers, a perceptible variance in image quality is observed with view angle. Furthermore, the vast majority (approximately 90 percent or greater) of light in a LCD never reaches the viewer because of unavoidable absorption in thin film polarizers and color filters, and other optical losses in the LCD. Generally, polarizers transmit only about 40 percent of unpolarized incident light and color filters transmit only about 20 percent to about 30 percent of incident white light.
Cold cathode fluorescent lamp (CCFL) backlights, which provide about 80 Im/W efficiency, generally result in an LCD efficiency of only a few Im/W.
Furthermore, the LCD continuously absorbs light at a pixel regardless of whether the pixel is on (i.e., transmissive) or off (i.e., not transmissive). This insensitivity to pixel state leads to very poor panel efficiency for displaying images that utilize only a fraction of the overall number of LCD pixels. Alternative flat panel display technologies, such as inorganic electroluminescent, organic electroluminescent, plasma display panels, and field emission displays, do not require either efficiency-reducing polarizers or heavy color filtering. Regardless, even these alternative display technologies have comparable or lower efficiency to that of an LCD display panel.
The elimination of polarizers and color filters would significantly improve the efficiency of LCD's. Previous attempts to remove the polarizers from an LCD have included using focal conic domains to scatter light from a specular waveguide and replacing the inefficient liquid crystal cell with electromechanical light valves that involve a specular white light guides, diffuse light outcoupling, and heavy color filtering. Such conventional approaches provide only moderate, if any, efficiency improvements over conventional LCD's and suffer from significant inherent drawbacks, such as strong diffuse reflectivity of ambient light and poor contrast between pixel on and pixel off states.
Therefore, what is needed is a light emissive display that can use a highly efficient lamp or light emitting diode (LED) and that does not require either polarizers or color filtering of white light.
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