Before we delve into how an 'LED TV' differs from a basic LCD TV, it's worth noting how popular the new super-slim technology is becoming.

According to market research agency GfK, a total of 8,817,000 LCD TVs were sold in the UK in the 52 weeks ending in July 2010, with LED sets accounting for an additional 355,000.

That's a relatively small percentage, though it's also worth knowing that LED-equipped TVs have rocketed in popularity - just 41,000 were sold in the 12 months prior to July 2009.

AFFORDABLE: Sharp has taken LED tech down to entry-level prices

So LED is popular, but what is it? Effectively an LED-backlight is a replacement for the uniform CCFL backlight that gives a LCD TV its brightness.

Instead of being always on - and therefore not able to dim in specific areas of the screen - LED lights are arranged either along the sides of the screen ('Edge' LED) or arranged behind the entire screen ('Direct' or 'Full' LED).

These LED lights can switch on and off individually, which means the image can have greater contrast - bright whites and deep black in the same image.

LIGHTS ON:LED lights are sometimes arranged in clusters behind the screen

A good example of how this works is with a dark and dingy movie like Batman Begins. For night scenes a traditional CCFL-backlit LCD TV isn't able to dim sufficiently enough to make the black areas of the image convincing, and neither is it able to show night areas, such as headlights or street lamps.

The end result is a picture that isn't dynamic, and dominated by grey where there should be black, and indistinguishable details that ought to be brightly lit. Put simply, the contrast of the panel isn't very good.

A plasma TV doesn't have this problem - each pixel can light up, or switch-off, according to the demands of the picture.

LED vs CCFL

So to counteract its lack of contrast, LED lights are being used instead of CCFL backlights, though how many - and exactly how they're arranged - depends on the brand.

'Edge LED' systems use an array of LED lights along the side that fire light across into the centre of the screen. It's technically the least effective system in terms of achieving a high contrast ratio because it doesn't offer 'local dimming'.

As a rule of thumb this system does help produce the slimmest flatscreen TVs around. It's also cheaper to produce.

'Direct' LED systems, which could involve somewhere in the region of 200+ LED lights arranged all over the screen in clusters, is visually the most impressive technology, but it's more expensive - and adds a few extra millimetres to the depth of the TV.

Edge LED vs Direct LED

Which is better depends on what consumers want. "Edge LED offers various advantages over Direct LED such as a thinner chassis (meaning a larger TV in a smaller position in the home), it is more power efficient (saving the consumer money on utility bills), and picture clarity is improved," a Samsung spokesperson told TechRadar.

"Direct LED can create a 'halo effect' meaning that clarity from source content is lost. However, Edge LED suffers less from halo effect as the LEDs themselves are positioned around the edge of the TV, meaning the light source is emitting from the guide plate, producing less blurring of the image."

As you might have gathered from that, Samsung is committed to Edge LED tech, citing it as the "superior technology." It's 'halo' argument is valid; clusters of LED lights in the behind the screen can cause bright objects to appear with a slight ring around them. Edge sets do, however, struggle to produce as high a contrast - especially when compared to that other big-screen technology: plasma.

SLIM SET:LG's LEX9 'NANO Full LED' breaks the mould by combining local dimming and a 8mm depth. It goes on sale next Spring

Many manufacturers use both Edge and Direct LED systems for LCD TVs. "LED edge-lit backlighting produces excellent picture quality with high contrast ratios of 500,000:1 or more," says Tom Henderson, Trade Marketing Manager, Philips TV.

"The technology also allows exceptionally thin sets to be designed and produced. Edge-lit sets also have an obvious cost benefit over direct, local dimming versions.

"However, direct, local-dimming LED back-lighting means TVs produce best in class picture quality, with exceptional contrast of 10,000,000:1, new levels of peak light output and, partly thanks to the ability to have a scanning implementation, superb motion reproduction."

Henderson also points out that both LED-backlighting systems dramatically reduce power consumption by over 40 per cent compared to conventional CCFL LCD TVs.

Differentiating LED from LCD

Either way, manufacturers - and that certainly includes Samsung - are marketing the new technology simply as 'LED' without pointing-out that it's simply an update to existing LCD panels.

"For Samsung it is important that LED is differentiated from LCD," said the spokesperson. "Whilst the key part of the technology (the panel) is the same, the backlight is obviously entirely different and manifests a greatly superior picture when compared to CCFL-backlit LCDs.

"Samsung invests a vast amount of engineering and R&D into LED technology, which is why it is treated as a premium product above LCD - and why they are positioned separately."

PICTURE PERFECT:Philips has just released a new version of its super-wide Cinema 21:9 screen with all-new LED backlighting

Henderson at Philips thinks the industry should be completely clear about what an 'LED TV' really is. "As an industry we need to take ensure that the benefits are clearly explained and communicated, particularly at point of sale," he says. "Consumers need to understand that the benefit of LED applies to LCD TVs."

Manufacturers love LED tech because it commands a premium; the sale of flatpanel TVs has long been a commodity market with tiny - and shrinking - profit margins and prices; analysts at DisplaySearch report that the average worldwide price of a LCD TV have fallen by 24 per cent since 2008.

INTO EDGE: Samsung's high-end LED9000 series shows the brand's commitment to Edge LED tech

Samsung and Sharp - two of the planet's biggest manufacturers of LCD panels - are aiming to ship more LED-backlit panels than traditional CCFL models.

The market is shared principally by four companies, with Samsung and Sharp each with 29 per cent, LG on 25 per cent and Chinese company AUO taking 13 per cent.

Cheap LED TVs

LED-backlit LCD TVs premium prices are quickly shrinking. "LED panel prices are falling even faster than CCFL," says David Hsieh, Large-Area LCD Research Team Leader at DisplaySearch. "Panel makers are expecting to grow their shipments through the end of the year as LED panel prices and end-market retailer prices of LED LCD TVs fall rapidly."

With LED prices crashing, there doesn't seem much point buying a traditional LCD TV without LED backlighting of some kind, but which type should you head for - Edge or Direct?

Henderson sums it up nicely for us, saying: "If you want an exceptionally slim TV with excellent picture quality, contrast and power consumption, then buy a LED Edge lit set. If you want a slim TV with exceptional all-round performance, go for a direct, local dimming set."

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Liked this? Then check out LCD or plasma TV: which should you buy?

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