FAQ: LED HDTV, LED versus CCF LCD HDTV

[Richard]

It would appear on the surface that many manufacturers are releasing a new kind of HDTV this year called LED HDTV. More than anything else this is simply a marketing scheme. LED HDTV is nothing more than current LCD flat panel technology using a different method of back lighting, LED rather than CCF or Cold Cathode Flourescent. LCD panels do not produce light, they block light or let it pass through therefore LCD requires a light source behind the panel which is called back lighting.

There are also LED displays in the market for commercial applications but have nothing to do with this technology. With these displays each LED is a pixel for black and white or a group of RGB LEDS for color representing one pixel. With either version you are directly viewing the LEDs and would correctly be called an LED display or LED direct view display.

LED Universal Advantage Over CCF
1. Consumes less power, roughly 40% less than CCF backlighting
2. About double the life in light output versus CCF back lighting
3. Environmentally Friendly when damaged* or disposed of. CCF technology uses mercury in the lamps.

*We have yet to see a CCF LCD damaged by a user in such a way to break open the lamp tubes. While I am sure it can happen it is a rare event at best. Projection lamps also contain mercury. Along the same lines of real or hysterical health and environment concerns, how about the current green promotion of CCF replacing incandescent lamps in your home?

LED Back Lighting versus Edge Lighting
1. The designation LED HDTV is directly related to LCD flat panel displays that are only 1 inch thick. This is made possible by putting the LED light source at the edge of the screen, rather than directly behind the panel, and the light is directed inward to the rest of the LCD panel using a thin light pipe diffusion layer(s) behind the LCD panel. It is this particular version of LED back lighting, correctly called LED edge lighting, that the marketing departments are promoting as some kind of new display technology because they are only about 1 inch thick. It is this factor along with their marketing allowing most shoppers to interpret these new skinny LED HDTVs as yet another new display technology.
2. You can also buy LCD panels using LED back lighting instead of CCF. These are NOT the 1 inch thick panels and retain about the same thickness as their CCF counterpart. Only this type of LED lighting provides the optional feature of local dimming to create a black level response similar to plasma or CRT display technology.

Two LED Back Lighting Versions
1. Thousands of single white LEDs are uniformly spread out behind the LCD panel.
2. Even more thousands of single red, green and blue LEDs (a group of RGB LEDs form a single light source) are uniformly spread out behind the LCD panel. This is an exclusive and far more complex technology called Triluminos by Sony claiming to improve the color gamut for performance enthusiasts and reduce power consumption due to additional light output by removing a color correction filter layer in the LCD panel.

Local Dimming
A feature of LED back lighting only. Neither LED back lighting system is capable of controlling light output at the pixel level and is limited to a small area of multiple pixels that can be increased in size based on picture content.


LED versus CCF Performance
First and foremost, LED back lighting or edge lighting is new technology. Sony is on their second generation for 2009 and most of the rest are releasing first generation for 2009.

It has been reported that LCD using LED lighting has a poorer viewing angle response.

There can be differences in color response for a variety of reasons mostly related to calibration. Users have reported LED as being whiter yet that could easily be due to a bluer grayscale; a notorious marketing ploy by manufacturers in the sale of displays. There can also be a difference due to color gamut and any performance enthusiast comparing CCF with LED needs to make sure the CCF version is also WCG or Wide Color Gamut.

While LED local dimming improves black levels this needs some real world perspective. Black level is a function of ambient light in the viewing area. In a well lit room there is no advantage since the black level would be below the light sensitivity of your eyes only burying content which you would otherwise see. LCD using CCF back lighting has come a long in this area improving black to perfectly acceptable levels for most users and their viewing environment. Like the highly touted black levels of plasma you would need a very dark room to take full advantage of this response.

While LED local dimming improves black levels it is not perfect. Recall that dimming only occurs in a small area and not at the pixel level. This can create an artifact of light leakage from a brightened area into a darkened area. Using a pattern of black and white squares you will be able to see the halo effect of light from the white boxes leaking into the edges of the black boxes.

Local dimming can easily affect the gamma response creating artificial images rather than hi-fidelity images. While this has not been reported I don