The first thing to know about LED (Light Emitting Diode) TVs is that they are simply LCD TVs with a different kind of backlighting. The screen remains the same but LEDs are used in place of Cold Cathode Fluorescent Lamps (CCFL) that are found in most LCD TVs.
The LEDs can come in two forms, Dynamic RGB LEDs which are positioned behind the panel, or white Edge-LEDs positioned around the rim of the screen which use a special diffusion panel to spread the light evenly behind the screen.
RGB Dynamic LED TV
This method of backlighting allows dimming to occur locally creating specific areas of darkness on the screen. This means you see truer blacks and much higher dynamic contrast ratios.
(Image courtesy of Sony)
This method of backlighting allows for LED TVs to become extremely thin. The light is diffused across the screen by a special panel which produces a superb uniform colour range across the screen.
(Image courtesy of Sony)
Currently LEDs are not small enough to be used for individual pixels in domestic televisions, and so the use of true LED TVs is restricted to much larger screens in places such as sport stadia. Don't let this put you off however, as there are some great benefits to choosing an LED TV over a standard LCD TV.
Improved brightness and contrast levels, with deeper blacks.
The use of Edge-LED lighting allows the TV to be thinner than standard LCD TVs.
LED TVs can consume up to 40% less power than a LCD TV of similar size.
They can offer a wider colour gamut, especially when RGB-LED backlighting is used.
LED TVs are also more environmentally friendly due to there being no mercury used during manufacture. Overall there are many benefits to buying a LED TV rather than a standard LCD TV. A comparison between LED and LCD can be found here on the LED vs LCD page.
Future of LED TV
The future of LED TV is expected to focus on the use of "Quantum Dots" as light emitting diodes to create QD-LED displays and QD-WLED (White LED) displays, which operate in a similar fashion to OLED displays in that light is supplied on demand. Quantum dots are valued for displays, because they emit light in very specific gaussian distributions. This can result in a display that more accurately renders the colors than the human eye can perceive. Quantum dots also require very little power since they are not color filtered. Research is still ongoing for this technology, and it is not expected to be put into use on commerical TVs until at least 2012.