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“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.”
“Local-dimming LED backlights can dim or turn off individually as needed.”
“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….”
“One downside to local dimming is an effect called “blooming,” where brighter areas bleed into darker ones and lighten adjacent black levels. This “blooming” effect varies widely from model to model; it’s pretty noticeable on the Toshiba 46SV670U, for example, and much more difficult to notice on the Samsung and LG 8500 sets. 4. Edge-lit TVs are really thin, but uniformity suffers.”
“As I said, the key benefit to an edge-lit LED-backlighting scheme is that manufacturers can make thinner TVs. However, the downside is that the backlighting isn’t quite as uniform. With edge-lit displays, if you put a white image up, you may notice that the outer edges of the screen appear brighter, or “hotter.” Also, when you put up an all-black image, the edges of the screen will appear lighter (grayer).”
5. LED backlighting of either variety doesn’t improve LCD’s poor off-angle viewing.
“Unlike with plasma, one of the big downsides to LCD TVs is that the picture degrades if
If this looks like your tv, you may be needing our ten facts about LED TV’s
…”Well, the problem is that you’re starting with such a good picture, so you’re more apt to notice the difference when you move to the side or stand up and look down at the TV. With a TV picture that doesn’t look as good to begin with, the difference doesn’t look as stark when you move off axis. Make sense?”
These are only half of the ten important facts about home theater design and LED TV’s found on Cnet Reviews, for the rest of the extensive information by David Carnoy and David Katzmaier you’ll have to read the whole article.
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