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Feature: What is an LED TV?

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October 19, 2009

The Sharp Aquos LC32LE600E 32” full screen LED backlit TV - LED backlit LCD TVs have brigh...

The Sharp Aquos LC32LE600E 32” full screen LED backlit TV - LED backlit LCD TVs have brighter colors, deeper blacks and higher contrast ratios than CCFL LCDs

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Buying a TV has become as complicated as selecting the right mobile phone plan. Before large flat panel displays invaded our lives, the only real question when purchasing a CRT (cathode ray tube) TV was how big did you want it and how much space did you have in your room to house it? Sure, there were some quality issues but mostly it was dictated by how many diagonal inches you could get for your buck. While some of that justification still rings true with today's TVs, now there's the issue of plasma versus LCD to contend with, and just when you had that sorted out, LED TVs have entered the arena as an option. However, there still seems to be a fair bit of confusion surrounding what exactly an LED TV is. Well, basically, it's another form of LCD TV that uses LEDs to provide its light source.

All LCD TVs are backlit because LCDs are a transmissive type of display technology, which means they don't produce their own light. So for an LCD television to produce an image on the flat panel display, its pixels have to be backlit by a separate lighting source. Currently, most LCD TVs used CCFL technology (cold cathode fluorescent lamps) as their backlight source. They deliver good colors and brightness, and decent contrast, but not great blacks - the domain of the plasma TV. But TVs utilizing brighter LED backlighting can achieve much better blacks, as well as brighter colors and even greater contrast ratios (Toshiba Regza 55X1 is boasting 5,000,000:1). NB: Contrast is measured from the darkest lit area of the screen to the brightest area to give a ratio.

But just in case you thought your selection choice was now made easy, there are a couple of LED options - full matrix LED and edge lit LED TVs. Let's go through the differences and look at what some of the manufacturers are using as their preferred backlighting choice.

Clarification: is it really an LED TV?

A true LED TV is one of those giant screens you usually see at outdoor stadiums, at grand prix events and rock venues. They are large screens made up of thousands of extremely bright LED lights. But because the size of LEDs are mostly too big and chunky to use in TVs, but they are an ideally suited as a light source for backlighting LCD crystals.

How LED technology is used in LCD TVs

Edge lighting

Edge lighting is pretty much as described. In this method, a series of LED backlights are positioned along the outside edges of the screen. From there, the light is dispersed across the screen, which means the LED/LCD TV can be made very thin. And while the results may be better than CCFL screens, the black levels in edge lighting are not as deep and, if you look closely, the edge area of the screen tends to be brighter than the middle viewing area.

Full-array backlighting

To take full advantage of LED lighting, some manufacturers use full-array LED backlighting, where many rows of LEDs are placed behind the entire surface of the screen. Although this makes for a thicker TV panel, the LEDs provide more even, brighter colors and greater contrast. A measurable benefit of full-array lighting can be seen when "local dimming" is utilized, meaning that each LED (or more common, a selected "zone" of LEDs) can be turned on and off independently within the screen, thus providing greater control of the brightness and darkness for each of those areas. Greater contrast levels are achieved by diminishing the effects of light from brightly lit neighboring areas seeping into blackened areas of the screen, which is one of the downsides of LCD screens.

In other words, the greater level of dimming control, the better the picture quality.

A number of manufacturers are preferring this technology with impressive results. They include: Samsung, Toshiba, LG and Metz.

Speaking of quality, currently, most LED backlighting is provided by white LEDs that are plentiful and cost less than their red, green, blue (RGB) cousins. But as popularity and demand increase, and research continues to improve, expect to see RGB LEDs, that provide a much greater color gamut and therefore much richer, denser and varied colors, being incorporated into TVs. Already a couple of manufacturers including Sony and Sharp have models with RGB LEDs.

Features of LED backlit LCD TVs
  • An LED TV achieves deeper blacks as well as emitting brighter images, thereby producing better contrast ratios;
  • They are slimmer (especially edge-LED lighting systems);
  • They deliver better viewing angles than other LCD TVs;
  • LEDs are long-lasting;
  • LEDs are more energy efficient than their CCFL counterparts, and better than plasma Tvs and much better than CRTs;
  • LEDs don't use mercury like some other backlighting methods.

And then there are newer technologies ...

OLED displays make use of a thin organic film deposited on its surface with a simple printing process, and present several advantages compared to traditional LCD displays: most notably, they don't require a backlight to function, which allows for much thinner and power-saving displays. LG and Sony have dabbled in OLEDs, but expect to pay a premium for this cutting edge technology for the time being.

But for a lot of consumers, thinner is better, and OLED TVs almost defy logic they're so thin. The problems they encounter is where do you stuff all the things like speakers, tuners, storage drives, etc in around 15mm of space. Current OLEDs also suffer from a limited lifespan compared to other technologies - particularly the blue OLEDs, which have a typical working life of roughly 5000 hours, while, in general, LCD and plasma technologies log in around 60,000 hours, depending on the model.

Then there's Mitsubishi's Laser TV and Sony, Phillips and others will have 3-D TVs on the market from next year. Give it some more time and we'll also have holographic TV added to the mix. It's like I said, choosing a TV will be as easy as choosing a mobile phone plan - and don't expect it to get any easier in the near future.

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