You’ve heard about LCDs. You’ve heard about plasmas. Maybe even you even understand all the pros and cons between them. But what are all these “LED televisions” we keep hearing about?
With the crop of LED-backlit HDTVs announced at this year’s Consumer Electronics Show finally starting to hit the streets in force, it’s a question we hear a lot from budding home theater shoppers. Blame the acronyms. While yesterday’s consumers had to make a simple choice between CRT and rear-projection television sets, today’s consumers are confronted with plasma, LCD, DLP, OLED, and laser televisions. And now, the age-old term LED has been stirred into the mix. Let’s take a look at what those three magic letters mean, how they apply to televisions, and why you might want to consider buying one.
Not a Different Type of TV
It’s tempting to assume LEDs belong in a completely separate category beside LCD and plasma TVs, but in reality, an LED television is just a type of LCD TV. The proper term would really be “LED-backlit LCD TV,” but that always seems to get truncated to “LED TV” in everyday conversation, perpetuating the confusion.
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?
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, most of the ultra-thin televisions that measured under an inch thick at CES used 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.
What does all this mean for the befuddled TV buyer? LED backlighting boosts LCD performance in efficiency and image quality, while making TVs slimmer in the process. In our reviews of the first full-array LED pioneers like LG’s 55LH90 and Toshiba’s Regza 46SV670U, we found that LEDs and other technologies like 240Hz refresh rates have almost entirely closed the performance gap between LCD and plasma TVs. But as TV guru David Elrich reminds us in his review of the LG 55LH90, LED technology still carries a pretty price tag, making plasma a definite alternative for the less energy-conscious consumer until prices improve. Though LED backlighting undoubtedly remains the future of LCD televisions, current buyers should weigh the option – and price – carefully against plasma before diving in.
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