Most of the current LED-equipped LCD TVs use edge-mounted designs that place the diodes at the borders of display. This allows for the thinner form factors that consumers appreciate, but it does not provide any major improvement in contrast ratios, according to Sweta Dash, director of LCD research for iSuppli. Contrast ratio is the ratio of the luminance of the brightest color to that of the darkest color that a television is capable of producing.

Televisions with superior contrast ratios get rid of excess off-state light when a LCD pixel is turned off, delivering a better picture.

“In terms of image quality, using a edge-mounted LED backlighting design in a large sized LCD TV is like putting a Ferrari engine in a Ford Pinto,” quipped Jagdish Rebello, director and principal analyst for LED research at iSuppli. “There is no improvement in picture quality and the color gamut of the display is actually less than when using a CCFL.”

An alternative approach to using LEDs in LCD TVs, the full-array backlight, provides sharp improvements in contrast ratio, according to Dash.

“The highest-quality images on LCD-TVs will be on sets that use the full-array backlight approach because it provides the best dynamic contrast ratio, which in turn improves perceived image color and sharpness.” said Randy Lawson, senior analyst, digital television semiconductors for iSuppli.

iSuppli expects LCD-TV makers will offer a mix of thin form-factor edge-mounted designs and high image quality full-array alternatives during the coming years.

LEDs: Now in living color
Another aspect of image quality hinges on the type of LEDs used in LCD TVs. Most LED-backlit LCD TVs now employ white LEDs, rather than the more costly Red, Green, Blue (RGB) alternatives. RGB LEDs provide a superior color gamut than white LEDs, providing richer and more varied colors in television sets.

“RGB LEDs are tidy and are the ideal best solution for LCD backlighting,” Patel said. “But pricing is still too high and these won’t show up in LCD TVs in significant numbers until 2010.”

Beyond televisions, LEDs are used for backlighting of desktop monitors and notebook PC LCD displays. LEDs also have strong growth potential as replacements for light bulbs in general illumination applications.