LED Backlighting vs. Edgelighting

I hear you talk about LED backlighting and edgelighting in LCD TVs, and I can't seem to find which one my Samsung UN60D7000 uses. I thought it was backlit, but hearing you talk about it made me wonder if I was right.

Joe Souders

All TVs in Samsung's 2011 lineup, including the UN60D7000, use LED edgelighting, with LEDs located along the edges of the screen—in this case, the side edges, not the top and bottom. By contrast, LCD TVs that use LED backlighting have an array of LEDs directly behind the LCD screen. Technically, both are "backlighting," since the light passes through the LCD panel from behind. The difference is where the LEDs are mounted—along the edges (with a diffuser that bends the light to pass through the LCD panel) or behind the panel.

Few companies make LED-LCD TVs with true backlighting, primarily because edgelighting allows the TVs to be thinner, which seems to be what consumers want. However, these sets almost always suffer from uneven illumination in dark scenes, an effect sometimes labeled poor uniformity.

One advantage of backlighting is a feature called local dimming, in which the LEDs behind dark parts of the image are dimmed while those behind bright parts are brightened, greatly increasing perceived contrast. In essence, the LEDs form a low-resolution, black-and-white version of the high-resolution image on the LCD panel, as depicted above. (Samsung's 2011 and 2012 models use a form of electronic "local dimming" to increase contrast.)

However, not all LED-backlit sets implement local dimming—for example, Sharp's current, non-Elite LED-backlit models and Samsung's 2012 entry-level EH series. LED-backlit sets that do implement local dimming include the Sharp Elite, Sony HX929, and several Vizio models. These sets are typically more expensive than comparably sized LED-edgelit models, but if someone is shopping for an LED-LCD TV, I generally recommend spending the extra dough for local dimming if possible and living with a slightly fatter flat panel.

If you have an A/V question, please send it to askhometheater@gmail.com.

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COMMENTS
utopianemo's picture

Scott, you start by saying all Samsung's 2011 lineup use edge lighting, but then later say that their 2011 and 2012 models use a form of local dimming. Are you saying they use a software-based local dimming 'trick' that is different from true LED backlit local dimming? I hadn't heard of such a thing.

Scott Wilkinson's picture
It's true that all TVs in Samsung's 2011 lineup use edgelighting. However, some models in the 2011 and 2012 lines use a form of electronic "local dimming" called Micro Dimming, in which the LCD pixels are divided into zones and biased to adjust the gamma curve in each zone. In the 2011 models, Micro Dimming included two controls—Dynamic Contrast, which controlled the LCD pixels as described here, and Smart LED, which dynamically controlled the side-mounted LEDs. This year, there is no Smart LED, only the electronic contrast enhancement, which is now called Black Enhancement. The original Micro Dimming had only a few zones, while Micro Dimming Pro in the 7500 and 7550 series has many more. Micro Dimming Ultimate in the 8000 series has twice as many zones as Micro Dimming Pro.
Old Ben's picture

Scott,

If memory serves, LED edge-lit was the first to appear, then back-lit, and the local dimming. I also recall that when back-lit LED sets and local dimming sets showed up in the market, both technologies were heavily marketed. Now it seems that both technologies are heavily scaled back in favor of edge-lit TVs.

I can't wrap my head around the notion that these technologies were scaled back because of thinness. What type of people are in the focus group that values a slightly thinner TV over a noticeably better picture? For me, that fraction of an inch that is saved by edge lighting is immaterial; especially when you consider that my TV is hooked up to a cable box, blu ray player, AVR, etc. that stick out from the wall significantly further than the fattest flat screen.

Do you know what cost increase is incurred to go from edge-lit to LED back-lit (and then to LED local dimming back-lit)? This seems to be a more likely argument is that edge-lighting keeps costs and therefore MSRP as low as possible.

Scott Wilkinson's picture
The trend toward edgelighting is driven by both factors—consumer preference for the thinnest possible flat panel and lower cost, though the cost factor only applies to local-dimming sets. Backlighting without local dimming needn't be more expensive—as I said in my main response, Samsung's 2012 entry-level EH series uses LED backlighting without local dimming. The processing required to do local dimming is sophisticated and thus expensive.

Sadly, many consumers do value thinness over picture quality, at least until they understand how much better local dimming looks compared with edgelighting. And while those who know better can talk about the advantages of local dimming until we're blue in the face, this understanding sinks in only when people experience the difference in a realistic setting, not a showroom floor, which means most of them will never know what they're missing.

Morvar's picture

Hey Scott, I just ordered one ES7005 for myself here in europe. Is it really true that this new ES7000 series still uses the worse Micro Dimming technique compared to old D8000 series' Ultimate version?

I'm planning to use the tv mostly just for pc and you said the ultimate version would have !double! the dimming zones so.. Have I just bought a bad tv for computer use? I don't understand why this brand new tv would have the worse version..

Proman's picture

I have searched for information about the microdimming technique. It seems to be impossible to get information about how it is implemented. I have even asked Samsung support.

First of all I would like to use the names "Full-LED" and "Edge-LED" as names for the two hardware techniques. Local dimming is easy to understand in the Full-Led case. But I don´t understand how local dimming is implemented in the case Edge-LED. Dimming means that the backlight is dimmed and how can you dim the edge leds without affecting the whole row. I think there must be some scanning technique involved. The picture signal moves forward column by column (similar to the old TV-CRT technique, but in that case we have line by line scanning) and the edge leds are modulated accordingly depending of which part of the picture you want to dimm.

If this is the way why doesn´t Samsung let us know how this technique works. People understanding electronics are also TV-byers. I am one of them. Are there some patents regarding this technique involved?

Proman

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