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Editors' note: Updated June 3, 2010

I've written articles in the past explaining various TV technologies, including the differences between 720p and 1080p and 120Hz and 240Hz LCD TVs. But with Samsung, LG, Sony, and other manufacturers pushing so-called LED TVs these days, it's high time that I--with an assist from our resident video guru, David Katzmaier--sort through all the marketing mumbo jumbo and provide some insight into just what an LED TV is. Here goes.

1. An LED TV is not a new kind of TV.

I appreciate a good marketing ploy as much as the next guy, but an LED TV is just an LCD TV that's backlit with light-emitting diodes (LEDs) instead of standard cold-cathode fluorescent lights (or CCFLs). And though they became well-known last year with Samsung's ultrathin models, LED-backlit LCDs have been on mainstream store shelves since 2007, when Samsung's LN-T4681F debuted.

Unlike plasma and OLED, which are emissive technologies where each pixel is its own discrete light source, LCD is a transmissive technology where each pixel has to be illuminated from behind, or backlit.

2.There are two LED backlight configurations

Initially, LED-based displays like the Samung LN-T4681F were backlit by what's referred to as a "full array" of LEDs behind the LCD, across the back of the panel--just like a standard CCFL backlight. But to create even thinner TVs, engineers needed to eliminate that extra layer of LEDs and move it to the sides of the display. With this form of backlighting, the LEDs are affixed to all four sides of the TV and light is projected inward to the middle of the TV via "lightguides." These types of TVs are commonly referred to as "edge-lit" LED-based LCDs, and are by far the most common available today.

3. Each configuration may also offer "local dimming."

All current LED-based LCDs with rear-placed, full-array LED backlighting--except the Sharp LC-LE700UN series from 2009--feature a technology called "local dimming." With local dimming, portions of the backlight can be dimmed or brightened independently when different areas of the picture get darker or brighter. For example, the LEDs behind the words in a credit sequence can illuminate while the ones behind the black background remain dim.

Being able to dim portions of the screen helps reduce the amount of light that leaks through to darkened pixels, and the end result is blacks that appear darker and more realistic. Since black levels are crucial to contrast ratio, the deeper the blacks, the more the picture--and colors--appear to pop. Also, the image as a whole will seem crisper. A couple of examples of local dimming done right are Samsung's UNB8500 series and LG's LH8500 series--respectively the best and second-best LCDs we've ever tested.

One downside to local dimming is an effect called "blooming," where brighter areas bleed into darker ones and lighten adjacent black levels.… Read more

There are now many different types of LCD TV backlights. This hasn't always been the case, though. Initially, the only option was a cold-cathode-fluorescent-lamp system, which essentially is made up of fluorescent tubes behind an LCD panel, providing the light that makes the picture visible. After several years, LEDs came into their own, with LED back- and edge-lit LCD screens becoming possible.

Now you can buy a TV with any one of four different types of backlight, but do you know what they all are and what they look like? As luck would have it, we fired off some … Read more

Yet another consumer electronics segment is bouncing back from the recession--demand for LCD TVs is showing new signs of life.

Third-quarter shipments of LCD TVs rose for the first time in a year, according to DisplaySearch's "Quarterly Global TV Shipment and Forecast Report," released Wednesday. That upward motion suggests that TV sales for the first quarter of 2010 could surpass those of the first quarter of 2009, the first gain in six quarters.

Total TV shipments will climb 6 percent in 2010 to reach 218 million units, versus 205 million for 2009, according to DisplaySearch's forecast. … Read more

Vizio is best-known for offering big screens at a low price, but the company's latest offerings straddle that thin line between small TVs and computer monitors. Vizio announced the 23-inch VM230XVT ($400) and 19-inch VM190XVT ($350) Wednesday, with both sets utilizing LED-backlighting technology usually seen on larger screen sizes.

The TVs have a slim profile, tapering down to less than an inch thick, although they fatten out to 1.65 inches at their thickest point. Sporting two HDMI inputs and a standard PC input, both models can technically be used as a PC display, although the VM230XVT's 1080p … Read more

The LED revolution has truly begun. In the last month or so, we've reviewed three LED-based LCD computer monitors, and we expect that they won't be the last.

Last week, we looked at the LG Flatron W2386L. It's an LED-based monitor that, while offering great game performance and a thin design, could not compare performancewise to the current LED king, the Samsung SyncMaster XL2370.

This week, we reviewed the AOC V22 LED monitor. Unlike many recent monitors, this one has a 16:10 aspect ratio instead of 16:9, Also, it has an extremely glossy screen--like "… Read more

If you watch football or read CNET, chances are you've noticed ads for Samsung's so-called LED TVs. The company has released three series of these super-thin LED-based LCDs so far this year, the 6000, 7000 and 8000 models, but it's saved the best for last. The fourth series is dubbed UNB8500, but you can remember it best as the king of LCD--for now.

Unlike the other three Samsung models, which use LED elements arranged along the edge of their screens, the company's two 8500 models employ a full array of local dimming LEDs behind the screen, … Read more

At CES this year, LG made a big deal out of its 240Hz technology, claiming it bested similar blur-busting tech from other LCD makers. The LH55 series represents the company's least-expensive HDTV equipped with a 240Hz refresh rate, and when it comes to that feature, as usual, we weren't particularly impressed. The results were similar to those seen on other 240Hz displays--reduced blur that was difficult for us to really discern, although test patterns prove it's there--but we were a bit annoyed that you have to engage the smoothing effect of dejudder if you want to reduce … Read more

Every year it seems there's a new catchy spec in the HDTV realm everybody likes to talk about. A few years back it was 1080p resolution. Then we heard about 120Hz, which is supposed to reduce motion blur in fast-moving images on LCD TVs. Well, this year, the latest and greatest spec is 240Hz, which is supposed to do what 120Hz does, but better.

Not too long ago, our video guru David Katzmaier gave his initial impressions on 240Hz in a post titled "Is 240Hz worth waiting for?" When he wrote that piece, he'd just seen his first 240Hz TV in action and wasn't sold on the new technology. Now that he's reviewed four 240Hz HDTVs and has a fifth review (the LG 47LH55) in the works, he's still not sold, but he admits the verdict isn't totally clear-cut.

Part of the problem is that there's a difference between what your eye sees in everyday material you watch and objective testing done with test patterns. As Katzmaier notes in his post, "Standard LCD and plasma TVs refresh the screen 60 times per second, or 60Hz, which is plenty fast enough to eliminate flicker and create the illusion of motion from a series of still images. In fact, most sources sent to your display arrive at the nominal rate of 30 frames per second, and each frame is repeated once by the television to achieve 60 total fps."

For most people, including me and Mr. Katzmaier, it's very difficult to see the impact that "faster" LCD sets have on picture quality. We spent some time in our AV lab watching various source material from 120Hz TVs and 240Hz models and it's really hard to detect any difference (it's hard to detect any difference between 120Hz and 60Hz models, too). To be clear, I'm referring here to motion-blur reduction because of faster refresh rates, not to dejudder processing, which smooths out motion and makes film-based material shot at 24fps look more video-like. When dejudder is engaged, you can easily spot its impact on the picture. (It's also worth mentioning that the dejudder processing on the 240Hz TVs we tested so far wasn't any better--or worse--than than the dejudder on 120Hz TVs). … Read more

As LCD and plasma vie for popularity and picture-quality bragging rights, one perceived weakness of the LCD camp has provided a reason for TV makers to charge more for step-up models: image blurring. Higher refresh rates like 120Hz and now 240Hz aim to clean up blurring with newfangled technology, and Toshiba's ZV650U series is one of the least expensive of such sets available.

Unlike such sets by Samsung and Sony, the Toshiba ZV650U uses a scanning backlight to reduce blurring--and, in fact, the company is careful to call its technology a "240Hz effect" to differentiate it from … Read more