LED TVs compared: Local dimming versus edge-lit

David Katzmaier, Senior Editor October 28, 2009

If you thought all LCD TVs were created equal, you're underestimating the power of confusion as a marketing tool. In their continuing efforts to compete against the picture quality advantages of plasma-based flat-panel TVs, makers of LCDs have introduced numerous new technologies, but the most successful in our opinion is LED backlighting with local dimming. When you see the words "LED TV" in an ad, it definitely refers to an LCD TV, but there's no guaranteeing that local-dimming technology is also onboard.

Before we get too far ahead of ourselves, we need to explain some basic concepts. All LCD-based TVs rely on a backlight of some kind to illuminate the LCD panel itself. Most use fluorescent backlights, known as CCFL, but a growing number of sets use LED backlights instead. LEDs use less power, but their main picture quality advantage is the capability to deliver deep black levels that rival and in some circumstances surpass those of the best plasma sets.

There are two major versions of LED backlights illuminating today's LCD TVs. One is called local dimming, found on sets such as the Samsung 8500, the LG LH90, the Toshiba SV670, and the Vizio VF551XVT, that lets the backlight dim or turn off in different areas across the screen (more information). Edge-lit, the other version, is found on sets such as the Samsung B8000 models, and it gets its name from the arrangement of the LEDs along the edge of the screen, allowing for extremely thin cabinet designs (check out the slideshow). A third version is also available, but from only one manufacturer so far. Sharp's LC-LE700UN series uses LED backlights without local dimming that are arranged behind the screen instead of along the edge. In the Sharp's case, the LEDs don't have much on an impact on picture quality.

In our tests, we liked local dimming best of the three backlighting methods, and rank the so-equipped TVs below among the best LCDs we've ever reviewed. In comparison, the edge-lit models exhibited relatively poor uniformity and backlight fluctuations that can definitely be distracting--although a new firmware update by Samsung is aimed at correcting this issue. On the other hand, they're pretty good performers in their own rights--just not in the same league, so far, as the local-dimming models. For what it's worth, we still consider the best plasma TVs better overall performers than even local-dimming LCD displays, although Samsung's new 8500 series comes mighty close.

We're looking forward to testing more LED-based LCD models, including Sony's KDL-XBR10 series and LG's SL90 series before the end of the year.

More Resources

LED TVs: 10 things you need to know,

Best LED TVs,

LED-backlit LCDs of 2008: local dimming,

Samsung reveals its edge-lit LED-based LCDs,

Samsung LED TV ads called 'misleading'