What is LED TV?
An LED (Light Emitting Diode) display is a flat panel display that uses LED backlighting instead of the cold cathode flourescent (CCFL) backlighting used in most other LCDs. The use of LED backlighting allows for a thinner panel, lower power consumption, better heat dissipation, a brighter display, and better contrast levels. LED backlit LCD TVs use the same TFT LCD technologies as CCFL backlit LCD TVs. Picture quality is primarily based on TFT LCD technology independent of backlight type. While not an LED display, a television using this display is called an “LED TV” by some manufacturers and suppliers. In the UK, the Advertising Standards Authority has made it clear in correspondence that it does not object to the use of the term “LED TV,” but does require it to be clarified in any advertising.
To understand how LEDs function in an LCD TV, think of an actual liquid-crystal panel as the plastic pegs in a Lite Brite. They hold a translucent image, but without a powerful backlight to punch through and light it up like a signboard, you’re not going to see much. On your old Lite Bright, an inefficient incandescent light did the job, but pretty unevenly. On a typical LCD TV, fluorescent lights provide the backlighting through a special plastic sheet called a light guide that distributes light from a fluorescent tube evenly over the surface of the TV. On an LED-backlit TV, fluorescent tubes are replaced with light-emitting diodes – LEDs – the same technology that probably lights up your digital watch, the buttons on your monitor, and the indicators on your stereo. They can be either situated along the edges of the TV like a fluorescent tube, or arranged directly behind the screen in a grid. But what difference does it make, and why would anyone spend so much money on it?
How an LED TV is different from an ordinary LCD TV
The most obvious reason LEDs have fallen into favor in LCD TVs: they’re simply more efficient. Although fluorescent lights do a decent job converting electricity to light in the big scale of things, LEDs perform even better. Typically, manufacturers claim an efficiency improvement of up to 30 percent over fluorescent-based sets, which can add up significantly over the lifetime of a TV, especially on larger screens that use more juice to begin with.
LEDs are also much smaller than tubes, even after accounting for the number of them needed to light an entire TV. That means LED-backlit televisions can be manufactured significantly thinner than their tube cousins. For instance, many of the ultra-thin televisions that measure under an inch thick use LED backlights, because they add very little depth to the profile. Though commercial variants aren’t quite as dramatically thin as these prototypes, they’re significantly skinnier than their fluorescent-backlit counterparts, making them some of the most chic and living-room-friendly HDTVs out there.
For home theater enthusiasts, LEDs only matter for one reason: image quality. Because fluorescent tubes must light the entire screen evenly, designers have no way to vary the backlighting intensity in different parts of the screen. Even if you want to show a single white pixel on an all-black screen, the light needs to be blazing away in back. But with some LED setups, lighting different parts of the screen separately becomes possible, allowing the lighting to actually improve the image.
It’s made possible by a technique called local dimming, which can only occur on TVs that offer “full-array backlighting.” These TVs arrange the individual LEDs – up to 1,500 of them – in a grid behind the LCD, rather than clustering them around the edges as you’ll find on “edge-lit” screens. Because each LED lights a specific part of the screen, they can intelligently brighten or darken different zones of the screen to match the content being displayed on the LCD panel.
For instance, in a scene showing the Earth as viewed from space, the lights around the planet could be turned to maximum brightness, while those in the blackness of space could be dimmed or turned off entirely to help darken the screen. Not only does this improve efficiency, since not all the lights are running all the time, it improves contrast, producing blacker blacks and whiter whites on the same screen.
Keep in mind that not all LED TVs can achieve this effect. Many of the super-thin LED televisions you’ll find use edge lighting to reduce their side profiles, making them slimmer and more efficient, but unable to “turn off” different parts of the screen intelligently the same way a full-array set can. Always make a point of discerning between edge-lit and full-array backlighting, and go with full-array, unless a thin profile is your number one priority.
Differences with CCFL-backlit LCD displays
Compared to CCFL-backlit LCDs, LED-backlit LCDs
- produce images with greater dynamic contrast
- can be extremely slim, some screens less than half an inch (0.92 cm) thick
- offer a wider color gamut when RGB-LED backlighting is used
- produce less environmental pollution on disposal
- are more expensive
- have typically 20 to 30% lower power consumption
- are more reliable
- can allow a wider dimming range
TV manufacturers are still asking for a higher price for LED-backlighting when many cheap devices — particularly mobile phones and netbooks — use LEDs as backlights. As of 2009, Samsung said that LED backlights cost three times more in large sizes than the equivalent CCFL arrangement, and this is mostly due to a lower number of manufacturers. Presumably, as the technology continues to take a firmer hold, the price will keep coming down.
In 2011, only the budget LCD televisions use CCFL backlighting, and all of the major manufacturers use LED lighting in their mid-range and premium models. It won't be too long before it will become the default method of backlighting. While some people still prefer the look of a plasma, the LED's combination of thin design and sharp picture quality will soon find favour with many people. If you're looking for a further explanation of how LCD screens work, then you can try this video on the 3M site.
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