To set the record straight, it is important to note that the LED designation refers to the backlight system used in many newer LCD Televisions, not the chips that produce the image content.
LCD chips and pixels do not produce their own light. In order for an LCD television to produce a visible image on a TV screen the LCD's pixels have to be "backlit". For more specifics on the backlighting process needed for LCD Televisions, refer to my article: Demystifying CRT, Plasma, LCD, and DLP Television Technologies.
LED TVs are still LCD TVs. It is just that these new sets use LED backlights rather than the fluorescent-type backlights used in most other LCD TVs.
In other words, LED TVs should actually be labeled LCD/LED or LED/LCD TVs.
How LED Technology is Used In LCD TVs
The are currently two main ways that LED backlighting is applied in LCD flat panel televisions.
One type of LED backlighting is referred to as Edge Lighting. In this method, a series LED backlights are placed along the outside edges of the screen. The light is then dispersed across the screen. The advantage of this method is that the LED/LCD TV can be made very thin. On the other hand, the disadvantage of Edge lighting is that black levels are not as deep and the edge area of the screen has a tendency to be brighter than the center area of the screen.
Also, sometimes you may also see what is referred to as "spotlighting" in the corners of the screen, and/or "white blotches" scattered across the screen. When viewing daylight or lit interior scenes, these effects are not usually noticeable - However, they can be noticeable to varying degrees, when night or dark scenes in a TV program or movie are viewed.
The other type of LED backlighting is referred to as Full-Array (also referred to sometimes as Full LED or Direct Lit LED). In this method, several rows of LEDs are placed behind the entire surface of the screen. The advantage is that these sets can employ "local dimming" (if implemented by the manufacturer).
If local dimming is implemented, this means that each LED or a specific group of LEDs can be turned on and off independently within certain areas of the screen, thus providing more control of the brightness and darkness for each those areas, depending on the source material being displayed.
However, it must also be pointed out that some edge-lit LED/LCD TVs are now also claiming to feature "local dimming" or "micro dimming". Sony refers to their version of this technical variation as Dynamic LED. The technology employed consists of varying the light output using light diffusers and light guides, thus is less precise than the more direct local dimming method used in Full Array or Full LED backlit LCD TVs.
If you are considering the purchase of an LED/LCD Television, find out which brands and models are currently using the Edge or Full Array method and take of a look at each type when you go shopping to see which type of LED backlighting looks best to you.
LED/LCD TVs vs Standard LCD TVs
Since LEDs are designed differently than standard fluorescent backlight systems, this means that the new LED backlit LCD sets offer the following differences with standard LCD sets:
1. Lower power consumption.
2. No Mercury used as in some other LCD backlight systems.
3. More balanced color saturation.
4. In LED/LCD TVs using the Full Array blacklight method, there is little or no light leakage in dark scenes. This contributes to even better black levels than traditional or LED Edge-lit LCD televisions.
5. LCD TVs that employ full array or full LED backlighting are thicker than LCD TVs that employ an Edge-lit LED light source. In other words, LED/LCD TVs that use the Edge backlight method can be made much thinner than both standard LCD and Full Array LED/LCD televisions.
LED backlight does represent an advance in technology, mostly in bringing LCD TVs up to the performance levels of Plasma Televisions in terms of black level performance, and, at the same time, making even thinner LCD TV designs possible.
On the other hand, LCD TVs that utilize LED edge or full array backlighting are more expensive than non-LED backlit sets. However, as they have become more common, prices have gone down.
I have been generally impressed with the image quality of the LED/LCD TVs I have seen (see example shown by Samsung at a past CES) and feel that they do deserve purchase consideration. LED/LCD TVs are included on my latest LCD Televisions 40-inches and Larger Top Picks List.
For more information on LED technology used in LCD Televisions, check out a report from CDRinfo as well as our supplementary video tip: The Difference Between LCD and LED TVs
LED Use in DLP Projection Televisions and Video Projectors
LED lighting is also used in some DLP televisions and is also making its way into DLP video projectors. In both cases, an LED supplies the light source instead of a traditional projection lamp. In a DLP television or DLP video projector, the image is actually produced in gray scale form on the surface of the DLP chip, in which each pixel is also a mirror. The light source (in this case an LED light source made up of red, green, and blue elements) reflects light off of the DLP chip's micromirrors and is projected onto the screen. Using an LED light source in DLP projection televisions and video projectors eliminates the use of a color wheel. This enables you to see the image on the screen without the DLP rainbow effect.