Below we've gathered reviews of six different "LED TVs" that provide examples of all four LED backlight configurations, but first we'll provide a bit of context. All LCD-based TVs rely on a backlight of some kind to illuminate the liquid-crystal panel itself. The most common use fluorescent backlights, known as CCFL, but a growing number feature LED backlights instead. LEDs use somewhat less power, can enable thinner flat-panel cabinets, and--crucially for TV makers--provide a great excuse to charge more money. But make no mistake: despite the misleading marketing, LED TVs are just LCD TVs with fancy backlights.
Unfortunately for TV shoppers, the confusion just increases from there. To help cut through the clutter we're going to lengthen our descriptions beyond the "LED TV" shorthand, and tell you how picture quality generally compares with standard LCD. More details are available in our LED TVs: 10 things you need to know companion piece as well as the individual reviews.
Full-array without local dimming: The rarest of the bunch but the most familiar in concept. These models are just like standard LCD-based TVs aside from the fact that the CCFL backlight is replaced by LEDs. The "full-array" means that the LEDs themselves are arranged behind the entire LCD panel, not just along the edge.
Picture quality impact: No difference compared with standard LCD.
Example below: Sharp LC-46LE700UN
Edge-lit without local dimming: The most common today. Chances are if you see an "LED TV" advertised, it's this variety, which was first widely introduced by Samsung in 2009, then imitated in 2010 by just about everyone else. It's characterized by thin cabinet designs--around just an inch or even less in depth--that lead to decreased weight in shipping and wall-mounting, along with increased bragging rights (although we fail to see much practical appeal versus a standard, 3-to-5-inch-deep flat-panel TV). Unlike full-array models, the LEDs on these sets are arranged only along the edge of the LCD panel, and can illuminate the center and other areas of the screen using so-called "light guides."
Picture quality impact: No major advantage over standard LCD, and can have even more uniformity problems, such as brighter edges compared with the middle.
Example below: Samsung UNC6500 series
Full-array with local dimming: The original and still the best. There are exceptions, but in general, TVs with this LED backlight configuration are the best-performing LCDs you can buy. They're similar to full-array models, but the individual zones of LEDs can be dimmed or brightened independently.
Picture quality impact: Can have significantly better black levels and uniformity than normal LCD, but will also exhibit "blooming," or stray illumination, to some extent.
Examples below: Vizio XVT3 series, Sony XBR-HX909 series
Edge-lit with local dimming: A new innovation for 2010, currently available on select models from Samsung, LG and Sony. The idea is to allow some dimming of the screen in independent areas without having to place LEDs behind the LCD panel, just along the edge.
Picture quality impact: In our tests, the Samsung preformed relatively well and the LG did not, although neither matched the picture quality of full-array with local dimming and both exhibited more blooming.
Examples below: Samsung UNC8000 series, LG LE5500 series
Credit CNET full article: http://reviews.cnet.com/2795-6482_7-399.html
