Edge lit (good diffusser) vs. backlit non local dimming..Why backlit assumed better? - AVS Forum
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post #1 of 16 Old 03-19-2012, 09:18 PM - Thread Starter
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So I have been thinking about this:

If full array backlit LED cannot dim non uniformly (hence the need for local dimming), then why can't a edge lit be as good (also dims equally)? Seems to be a quality of the diffusing tech.

So is a good edge lit led ever "better" than non local dimming back lit?

I am debating between a 2011 70"735 (full array 3d) vs 2012 thinner edge kit 745
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post #2 of 16 Old 03-19-2012, 10:21 PM
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can someone explain to me how they manage to get even light distribution
from edge lit + diffusor on large screens ???

personally, i can only see a marketing ACT in the edgelit " LED " tvs ...

we should already have backlit LED with large array and high rez dimming
instead of this POS design ...

BUT NO .. we WANT THIN TV
like u can actually see how thin it is when looking in front of it ...

it's all about LOOKS!
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post #3 of 16 Old 03-20-2012, 12:31 AM
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Quote:
Originally Posted by JinMTVT View Post

can someone explain to me how they manage to get even light distribution
from edge lit + diffusor on large screens ???

They can't, so they shoot for the best approximation.

You can't actually run a true diffuser on a typical edge-lit TV. First of all, edge light doesn't lend itself to typical diffusion. Second of all, the depth doesn't permit would we'd normally think of as diffusion.

So edge-lit sets rely on two tricks to achieve light diffusion:

1) Light guides: long, thin pieces of plastic that the light it sent into from the side. These are crafted in such a way that as the light travels down the guide, some of it escapes at each spot along the way. The guides are shaped such that the light gets distributed across half the width of the TV (on most modern LED LCD TVs you have two LED bars on the sides, if you had top-bottom bars, which are used very occasionally like last year's Samsung 65D8000 apparently, you'd cover half the height). So basically, the guides are slightly wedge shaped. There are some examples here:

http://www.ciri.org.nz/downloads/Lightpipe%20design.pdf

2) Diffusion films: Typically, in front of the light guide (or bonded to it, depending on the design) there will be a layer of diffusion film which is designed to smooth out the light hitting it so it doesn't "hot spot" or appear to be a point source. This is a pretty good diagram of how a diffusion film is placed in concert with the light guide and light source.

http://www.kimoto.co.jp/english/products/light.html

Now, here's the thing. If the light guide is positioned perfectly with respect to the light source such that the angle and entry gap are as intended, even plastic light guides can theoretically provide a fairly uniform illumination. The problem is that the relative placement of all those items are rarely done with the precision of someone's CAD drawing.

It's fairly likely that if uniformity could be brought comfortably inside of +/- 10%, most people would never see any artifacts like flashlighting, clouding, etc. But it's clear that few TVs are anywhere near this good. And, in fact, variances of 20% or more are common.

The fact is that simply using an array of LEDs behind the display, it's easier to achieve uniformity. The consistency of output between LEDs is going to be easier to achieve than having to not only achieve that, but also spread the light around (edge-lit sets need to do both... there are still a lot of LEDs to be "uniform" with).

Now, if you give up some thinness and go behind the screen with full array, you can also diffuse the light more aggressively, making the job even easier. It's no surprise that sets like last year's Sharp 73x line did a very good with uniformity, except in the corners (which was mostly due to design decisions leaving those areas without enough lighting).

The new "direct LED" sets uses relatively few LEDs in a "full array" type design (relatively few vs. a true full array set). These are somewhat higher power, set somewhat farther from the LCD panel, and are therefore (a) somewhat better diffused and (b) somewhat more likely to cast overlapping light. Ironically, these cheap designs will probably outperform much more expensive edge-lit sets on uniformity, despite being thicker, cheaper, and somewhat less desirable.

Sharp claims that this year's edge-lit sets will compare favorably to full array sets on uniformity metrics. I have not yet experienced any of these sets, nor have I seen any reports about them. It will be interesting.

There is no difference in HDMI cables. If you can see the picture without visible dropouts or sparklies, the cable is working at 100%. No other cable will display a better version of that picture. You're simply wrong if you think there is a better digital cable than one that is already working. (Oh, and plasma didn't die because of logistics problems, nor does OLED ship in big boxes because it comes from Korea.)
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post #4 of 16 Old 03-20-2012, 01:48 AM
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Ît is important to notice that edge-lit problems stem not from principles but from the desgin/manufacturing. The main proponent of edge-lit is Samsung. It will be thus interesting to see if this year Samsung E series offers improvements over the last year D. But overall it seems full array backlit has limited future.
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post #5 of 16 Old 03-20-2012, 04:13 AM
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Quote:
Originally Posted by irkuck View Post

Ît is important to notice that edge-lit problems stem not from principles but from the desgin/manufacturing.

That's mostly true.

But getting even light distribution out of plastic light guides in 1-inch thick TVs is not a problem that better engineering and manufacturing will ever solve entirely -- at least not on larger screen sizes.

Assuming a world in which individual LEDs have an output variance inside of 5%, it's easy to imagine full-array sets having near-perfect uniformity and much harder to imagine any edge-lit sets consistently offering that.

There is no difference in HDMI cables. If you can see the picture without visible dropouts or sparklies, the cable is working at 100%. No other cable will display a better version of that picture. You're simply wrong if you think there is a better digital cable than one that is already working. (Oh, and plasma didn't die because of logistics problems, nor does OLED ship in big boxes because it comes from Korea.)
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post #6 of 16 Old 03-20-2012, 05:49 AM - Thread Starter
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Quote:
Originally Posted by rogo View Post

That's mostly true.

But getting even light distribution out of plastic light guides in 1-inch thick TVs is not a problem that better engineering and manufacturing will ever solve entirely -- at least not on larger screen sizes. .......

near-perfect uniformity and much harder to imagine any edge-lit sets consistently offering that.

Thanks for teh thoughtful comments, examples, and sources.

I am still struck, given the electronics involved, if the cost of Full array Backlighting+Local Dimming is licensing or development of the software. The actual hardware must not be any different itself unless, say in the Elite, there are alot more Backlit areas that can be made into Zones vs. the "735" series.

Again, this forum is fantastic. It is almost painful to listen to people talk in best, buy, frys etc. Makes you wonder why they are not required to read the FAQ on this site to have a job (no offense, I have met a FEW people who clearly love their job/tech).
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post #7 of 16 Old 03-20-2012, 06:07 AM
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Quote:
Originally Posted by rogo View Post

That's mostly true.

But getting even light distribution out of plastic light guides in 1-inch thick TVs is not a problem that better engineering and manufacturing will ever solve entirely -- at least not on larger screen sizes.

Assuming a world in which individual LEDs have an output variance inside of 5%, it's easy to imagine full-array sets having near-perfect uniformity and much harder to imagine any edge-lit sets consistently offering that.

Agree the non uniformity of edge lit without the LCD panel is very obvious. It is with LCD panel and content that it is so much less perceivable to the eye. Blooming and flash lighting would be much more perceivable than uniformity.
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post #8 of 16 Old 03-20-2012, 07:17 AM
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Quote:
Originally Posted by irkuck; View Post

But overall it seems full array backlit has limited future.

Every year since introduction of LED Local dimming minimum of LCd's models were LD, its no different this year. Hard to tell what LD future is. Hard to tell anything right now.

I made a 2012 LD list a few weeks ago
http://www.avsforum.com/avs-vb/showp...2&postcount=22
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post #9 of 16 Old 03-20-2012, 12:42 PM
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8mile, the future of full-array local dimming is bleak. It's never going to become much more popular. At best, you can hope it becomes slightly more popular and reaches a couple more models.

There is no difference in HDMI cables. If you can see the picture without visible dropouts or sparklies, the cable is working at 100%. No other cable will display a better version of that picture. You're simply wrong if you think there is a better digital cable than one that is already working. (Oh, and plasma didn't die because of logistics problems, nor does OLED ship in big boxes because it comes from Korea.)
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post #10 of 16 Old 03-20-2012, 04:57 PM
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Quote:
Originally Posted by rogo; View Post

8mile, the future of full-array local dimming is bleak. It's never going to become much more popular. At best, you can hope it becomes slightly more popular and reaches a couple more models.

They were not popular from day one, still making em. Logic dictates that Sharp Elite Pro should never have been made because of the lack of popularity. As long as LED manufacturers feel that their flagship should be a LD, as long as LED manufacturers need a show off its future is safe. Once OLED (and larger sized OLEDs) becomes mainstream there is no longer a need for LD (and Plasma), that should be the end then and there...
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post #11 of 16 Old 03-20-2012, 07:28 PM
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The bottom line for the demise of plasma and LCD will be the end cost of OLED's to the customer. That being said, it's just a matter of time. RIP plasma and LCD.
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post #12 of 16 Old 03-20-2012, 08:01 PM
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Quote:
Originally Posted by rogo View Post

8mile, the future of full-array local dimming is bleak. It's never going to become much more popular. At best, you can hope it becomes slightly more popular and reaches a couple more models.

Not so sure about this. Full array greatly reduces flashlighting and blooming. It was much more expensive 3 years ago as LED was like 5X the price now.

With LCD volume stagnant, the LED makers from Toyoda Gosei to LG Innotek has strong incentive to push full array. I would think 4k and huge TV is a plus for full array
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post #13 of 16 Old 03-20-2012, 11:15 PM
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Originally Posted by specuvestor View Post

Not so sure about this. Full array greatly reduces flashlighting and blooming. It was much more expensive 3 years ago as LED was like 5X the price now.

With LCD volume stagnant, the LED makers from Toyoda Gosei to LG Innotek has strong incentive to push full array. I would think 4k and huge TV is a plus for full array

I'm not sure about it, but I am sure that (a) cheaper is more popular with everyone in the industry, consumers and producers (b) full array is more expensive.

I will reiterate my strong doubt this ever gets beyond a small handful of products, especially given that two of the leading LCD makers -- at least -- intend to make OLEDs their flagship products over the next several years.

There is no difference in HDMI cables. If you can see the picture without visible dropouts or sparklies, the cable is working at 100%. No other cable will display a better version of that picture. You're simply wrong if you think there is a better digital cable than one that is already working. (Oh, and plasma didn't die because of logistics problems, nor does OLED ship in big boxes because it comes from Korea.)
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post #14 of 16 Old 03-20-2012, 11:42 PM
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Wasn't it samsung something like 5-7 years ago
that introduced LED backlight ( true backligyht) with LD ??
then they switched to edge lit ???

i am seriously fed up by the stupidity of regular consumer that drives
all this BS nonsense ...


Do we have a LIST of all the recent ( 09-12 ) LD LED array backlight sets ??
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post #15 of 16 Old 03-21-2012, 02:53 AM
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I don't think Samsung was the first (if my failling memory serves me correctly)... but I believe it was samsung that had their "kahonnies in a vice" with a lawsuit (from Sharp???) over their advertising that very thing. I also believe this is why Samsung does not have a full array set... they can't/aren't allowed to.

The first full backlit LED that was "successful" (ie. praised for it's picture quality) was the Sony XBR 8 with it's triluminous LED's... at the time considered to be equivalent to the Kuro in PQ

(8mile - where are the sonys on your list?)
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post #16 of 16 Old 03-21-2012, 07:48 AM
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Originally Posted by AVTrauma; View Post

I don't think Samsung was the first (if my failling memory serves me correctly)... but I believe it was samsung that had their "kahonnies in a vice" with a lawsuit (from Sharp???) over their advertising that very thing. I also believe this is why Samsung does not have a full array set... they can't/aren't allowed to.

The first full backlit LED that was "successful" (ie. praised for it's picture quality) was the Sony XBR 8 with it's triluminous LED's... at the time considered to be equivalent to the Kuro in PQ

(8mile - where are the sonys on your list?)

Heard that Sony will use the 2011 HX929 LD in 2012 so there is no ''fresh'' 2012 Sony LD.
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