The luminance, the luminance uniformity, the viewing-angle characteristics, and the luminance gain properties of 55-inch LED (light-emitting-diode)-type and CCFL (cold-cathode fluorescent lamp)-type backlights were investigated quantitatively. The luminance gain of the reflective polarizer, one of the most representative brightness enhancement films, was measured for several optical configurations of both backlights. The optical gain for the LED backlight, for which a light guide plate was used, was higher than that for the CCFL backlight, for which a diffuser plate was adopted. This result suggests that the luminance gains achieved by using brightness enhancement films are substantially affected by optical properties such as the reflectance, the absorption, and the polarization-conversion properties of the optical components and light sources in the backlight. This point may be useful in optimizing the optical performances of backlights for LCD applications.

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