Full Color LCD Backlighting with LEDs - App Note

This application brief will describe the present and future needs for LCD backlighting and compare an LED solution against competing light source technologies. A full color back-lighting scheme with red, green, and blue LEDs is described. It will be shown that the LED solution is technically superior to other light sources that presently have a large portion of the LCD white (full color) backlighting market. The backlighting of an LCD has become a very popular aesthetic characteristic among all LCD product proliferations. The market demand will not allow for an LCD based product to be competitive without enhanced display visibility in a dark ambient. This backlighting requirement has placed some constraints on some of the major competitive attributes that an LCD without backlighting would have over one with it. These attributes are cost, power dissipation, weight, size, and reliability. Furthermore, most backlighting applications are finding demands to have full color capability. This adds complexity to the overall backlighting solution: lightguide, reflector, and diffuser system that can couple a large bandwidth of wavelengths towards the LCD with high efficiency. When using a white light source (i.e. cold cathode tube lamp, electro-luminescent, etc.), then a special filter system has to be implemented and there has to be at least three LCD pixels (RGB) for every viewer pixel. The filtering adds costs and reduces the efficiency of the lamp's light output. Using three LCD pixels to create one viewer pixel cuts down resolution capability.