LED-backlight feedback control system with integrated amorphous-silicon color sensor on an LCD panel

Ki-Chan Lee Seung-Hwan Moon Brian Berkeley Sang-Soo Kim Abstract — Thin-film-transistor liquid-crystal displays (TFT-LCDs) have the largest market share of all digital flat-panel displays. An LCD backlighting system employing a three-color red-green-blue lightemitting diode (RGB-LED) array is very attractive, considering its wide color gamut, tunable white point, high dimming ratio, long lifetime, and environmental compatibility. But the high-intensity LED has problems with thermal stability and degradation of brightness over time. Color and white luminance levels are not stable over a wide range of temperature due to inherent long-term aging characteristics. In order to minimize color point and brightness differences over time, optical feedback control is the key technology for any LED-backlight system. In this paper, the feasibility of an optical color-sensing feedback system for an LED backlight by integrating the amorphous-silicon (a-Si) color sensor onto the LCD panel will be presented. To minimize the photoconductivity degradation of a-Si, a new laser exposure treatment has been applied. The integrated color-sensor optical-feedback-controlled LED-backlight system minimized the color variation to less than 0.008 ∆u′v′ (CIE1976) compared to 0.025 for an open-loop system over the temperature range of 42–76°C.