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Led-Backlit Lcd Television

A LED-backlight LCD television is an LCD TV that uses LED backlighting instead of CCFLs used in traditional LCD televisions. It is not a true LED display but is often called "LED TV" by some manufacturers.[1] The use of LED backlighting has a dramatic impact, resulting in a thinner panel, less power consumption and heat dissipation, and a brighter display with better contrast levels.

The LEDs can come in three forms:

  • Dynamic RGB LEDs which are positioned behind the panel
  • White Edge-LEDs positioned around the rim of the screen using a special diffusion panel to spread the light evenly behind the screen (the most common)
  • A full-array of LEDS which are arranged behind the screen but are incapable of dimming or brightening individually

LED backlighting techniques

A LED TV.

RGB dynamic LEDs

This method of backlighting allows dimming to occur in locally specific areas of darkness on the screen. This can show truer blacks, whites and PRs[clarification needed] at much higher dynamic contrast ratios, at the cost of less detail in small bright objects on a dark background, such as star fields.[2]

Edge-LEDs

This method of backlighting allows for LED-backlit TVs to become extremely thin. The light is diffused across the screen by a special panel which produces a uniform color range across the screen.

Full Array LEDs

Many brands use LED backlighting technology and may offer a range of benefits over CCFL LCD TVs such as reduced energy consumption, better contrast and brightness, greater colour range, more rapid response to changes in scene and a capacity to provide the means to render an image more accurately.[3]

Differences between LED-backlit and CCFL-backlit LCD displays

LED-backlit LCD TVs differ from conventional CCFL-backlit LCD TVs in the following:[4]

  • Produce images with greater dynamic contrast.
  • With Edge-LED lighting they can be extremely slim. Models on the market can be approximately one inch thick.
  • Offer a wider color gamut, especially when RGB-LED backlighting is used.[5]
  • Less environmental pollution on disposal.
  • Higher price.
  • Generally 20-30% lower power consumption.[citation needed]

Technology

TV manufacturers can use an LED backlight instead of the Cold Cathode Fluorescent Lamps (LCD-CCFL) used in most LCD televisions. LCD-based televisions described as 'LED TVs' are different from self-illuminating Organic light-emitting diode (OLED), OEL or AMOLED display technologies. In the UK, the ASA (Advertising Standards Authority) has made it clear in prior correspondence that it does not object to the use of the term 'LED TV', but does require it to be clarified in any advertising. There are several methods of backlighting an LCD panel using LEDs including the use of either White or RGB (Red, Green and Blue) LED arrays positioned behind the panel; and Edge-LED lighting, which uses white LEDs arranged around the inside frame of the TV along with a light diffusion panel to spread the light evenly behind the LCD panel.

Compared to regular CCFL backlighting, an LED backlight provides higher brightness and improved color gamut. However advancements in CCFL technology mean wide color gamuts and lower power consumption are also possible. Cost is the principal barrier to wide use of LED backlighting on LCD televisions.

The variations of LED backlighting do offer different benefits. The first commercial LED backlit LCD TV was the Sony Qualia 005 (introduced in 2004) and featured RGB LED arrays to produce a color gamut around twice that of a conventional CCFL LCD television. This was possible because the combined light output from red, green and blue LEDs produces a more pure white light than is possible with a single white light LED. RGB LED technology continues to be used on selected Sony BRAVIA LCD models, with the addition of 'local dimming' which enables excellent on-screen contrast through selectively turning off the LEDs behind dark parts of a picture frame.

Edge LED lighting was first introduced by Sony (September 2008) on the 40 inch BRAVIA KLV-40ZX1M (referred to as the ZX1 in Europe). The principal benefit of Edge-LED lighting for LCD televisions is the ability to build thinner housings (the BRAVIA KLV-40ZX1M is as thin as 9.9mm). Others have also introduced Edge-LED lit LCD televisions with extremely thin housings.

LED-backlit LCD TVs are considered a more sustainable choice, with a longer life and better energy efficiency than plasmas and conventional LCD TVs.[6] Unlike CCFL backlights, LEDs also use no mercury in their manufacture. However, other elements such as gallium and arsenic are used in the manufacture of the LED emitters themselves, meaning there is some debate over whether they are a significantly better long term solution to the problem of TV disposal.

Because LEDs are able to be switched on and off more quickly than CCFL displays and can offer a higher light output, it is theoretically possible to offer very high contrast ratios. They can produce deep blacks (LEDs off) and a high brightness (LEDs on). However, measurements made from pure black and pure white outputs are complicated by Edge-LED lighting not allowing these outputs to be reproduced simultaneously on-screen.

In September 2009 Nanoco Group announced that it has signed a joint development agreement with a major Japanese electronics company under which it will design and develop quantum dots for LED Backlights in LCD televisions.[7] 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.

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