Technical Insight
LumiLeds' LEDs optimize backlights (LED News)
LumiLeds Lighting has introduced a backlight source optimized around its new Luxeon LEDs, a range of large-area, high-power devices employing high-flux chips (see Compound Semiconductor March 2001, p11). LumiLeds packaged LEDs now offer outputs upward of 20 lumens in certain colors (such as its 540 nm green device), and these emitters are being employed in the new backlighting system to enable features not currently available with conventional backlighting technology, says the company. In addition, this is the first source that targets medium to large LCD displays, including those used in PCs. LumiLeds is already working with LCD panel manufacturers and hopes to introduce Luxeon-powered backlights by the end of the year. LEDs offer a number of advantages over conventional light sources for this application. Solid-state emitters are more durable than fragile cold cathode fluorescent lamp (CCFL) sources, and at around 10 V their power operation is low enough to significantly reduce electromagnetic interference. LEDs also appear brighter, resulting in NTSC values of up to 130% being produced in the backlight. The NTSC is the color chart definition for typical cathode ray tube screens that defines color saturation e.g. how "red" an object appears. CCFLs exhibit only around 80% of the ideal NTSC value, resulting in paler colors. Added to this is the ability to "color sequence" the LEDs as a result of the Luxeon s very fast (100 ns) switching times. A higher resolution is afforded by the fast modulation and sequencing of the red, green and blue LEDs. Energy requirements are also reduced: in CCFL sources, filters are needed to display the required colors, and the LCD display has three different areas per pixel that open and close to show red, green and blue. This makes the LCD display more expensive and power hungry. As LED displays already consist of individual color-separated emitters, the LCD panel requires just one area that opens/closes per pixel and consumes less power. "This solid-state backlighting solution will allow the LCD display market to go head-to-head with the incumbent cathode ray tube market," explained Mark Pugh, LumiLeds vice-president of strategic marketing.
