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post #1 of 8 Old 08-11-2012, 04:12 AM - Thread Starter
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http://www.ravepubs.com/index.php?option=com_content&view=article&id=4570

Ever since I bought my Sharp 70LE845U, I've been trying to find out what the source of the backlight is.
The color gamut seems weak compared to a good quality CCFL set that I've been used to -- a 46" Toshiba.
The most obvious defect is the uneven white level, which gets bluer as the intensity increases.
There is also an excessive amount of red clipping and a lesser amount in the green spectrum.
This, from a company that touts the 4th pixel as a means to allow a wider color gamut!
It seems that all edge-lit sets use the same technology, so I don't single out the Quattron for condemnation.
Once calibrated to a much lower light output overall, the set performs beautifully, however.
There is a fundamental choice to have either a bright display or an accurate one.
I think the 3D capability is very good and takes advantage of the ultra-brightness to good effect.
Still, I have to think that the white LEDs are a step backward from wide-gamut color found in the earlier Toshiba.
Here is the above-referenced article, with mention of the properties of edge-lit LEDs:


Quantum Dots: The End of White LEDs in Backlights?
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In late January, Nanosys announced it had signed a "definitive commercial agreement" with LG Innotek (LGIT) for the use of Nanosys’ quantum-dot phosphors in displays. The agreement "represents the first real world commercial application of quantum dots in electronics," the Nanosys announcement said.

LGIT seemed equally enthusiastic. "Nanosys’ Quantum Rail technology is a solution ready for integration into backlight sub-assemblies without major tooling changes, making it our first choice for our next-generation high color gamut displays," said Charlie (Cheol-Kee) Hong, LGIT VP and head of the company’s R&D Center.

Nanosys fabricates what it calls a Quantum Rail (QR), a continuous component consisting of quantum dot phosphors in a polymer matrix. In a typical LCD edge light application, the QR is fastened with optical adhesive to the strip of blue LEDs that are the light source for the BLU. The "green" quantum dots down-convert the blue light to narrow-spectrum green and emit it into the light-guide plate. The "red" QDs do the same for red. The mixture is also carefully balanced to allow just the right amount of blue light into the light guide, too. This results in narrow-spectrum light sources for R, G and B, whose peaks can be tuned to suit the needs of the application. It produces a triangular color gamut that exceeds 100 percent of AdobeRGB and is considerably greater than the gamut of conventional modern LCDs. It also provides an improvement of 20 percent in power efficiency compared to existing backlight solutions, says Nanosys, probably because the color filter transparency can be increased due to the improved spectrum.

In addition, the approach is compatible with multi-primary displays. For a Sharp Quattron-type application, you can simply add quantum dots engineered to produce yellow, and you have the light source for a four-primary display.

This contrasts sharply with the most popular current approach to LED edge lighting, which is to use a white LED. A "white" LED is essentially a blue LED with the addition of a crystalline phosphor, cerium-doped yttrium aluminum garnet (YAG:Ce) being the most common. The blue light excites the YAG:Ce, which emits with a broad spectrum peaking in the yellow. The combination of the blue and yellow light yields a white. In an exclusive telephone interview, Nanosys CEO Jason Hartlove noted that white YAG LEDs were a step backward in color from CCFL, since both the green and red were relatively weak.

But, Hartlove said, image superiority is not the only reason panel makers are excited about the quantum-dot approach. The value proposition also includes reduced cost and better supply-chain control. Quantum dots permit the use of blue LEDs as the underlying light source for LCD edge lights instead of the white LEDs. The significantly lower cost of the blue LEDs compensates - or more than compensates - for the cost of the QR component, Hartlove said. He went on to explain that the price of a white LED of the kind typically used in LED edge lights is about 25 cents, while the cost of a blue LED is 5 or 6 cents if you have an internal source of supply, as Samsung (for instance) does.

Since a white LED is basically a blue LED with some YAG inside, you would think that the YAG is the source of the price differential. But YAG is not really expensive itself. It costs about $2000 per kilogram, but since only micrograms are used, the material adds little to the cost of the LED. However, Hartlove said, the IP is tightly controlled by Nichia and others, and this serves to keep prices high. (Nichia has been particularly aggressive in defending its IP.) Samsung, LG, and other panel-makers would like to get around this cost, Hartlove said, and gain greater control of their supply chains by creating their own blue LED solutions.

For its initial applications, LGIT is looking at notebook panels, smart phones, and tablet PCs. Hartlove expects QR production units to appear in a TV set in 2012, with demonstrators to be shown this year.

So how big a deal is this? Hartlove said that Nanosys customers are excited about the technology, and he believes that most LED edge lighting will make the transition to quantum dots and blue LEDs over the next few years.

Ken Werner is a senior analyst and editor for Insight Media. Reach him at kwerner@insightmedia.info
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post #2 of 8 Old 08-11-2012, 04:29 AM - Thread Starter
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http://www.maximumpc.com/article/features/display_myths_shattered?page=0%2C4

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January 08, 2011 at 7:00pm

To Dr. Raymond Soneira:

For the past several months, I have been noticing this very intriguing situation which contradicts our general notion that LCD TVs with white LED backlights are more reliable than those with CCFL backlight technology. The LED-LCD TVs that are in display in showrooms which have been running for a few months manifest lowered brightness and bluish screen as compared to the new units from the box. While the LCD TVs with conventional CCFL backlight have no or very little screen white balance and/or luminance change observed. It appears now that the white LEDs used for the backlight are deteriorating faster than what the manufacturers claimed 50,000 hours plus life span.

Could this be due to the technology implemented? Yellow phosphor degradation (bluish screen) and blue LED chip lumens down (lowered brightness) in producing white LEDs (yellow phospor + blue LED = white light).

I hope you can do some investigations on this issue as more and more LCD-LED TVs are coming out in the market.
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post #3 of 8 Old 08-11-2012, 08:26 AM - Thread Starter
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Hopefully, these articles are enough out of date that the problem of yellow phosphor decay has been solved.
Otherwise, calibrators will be busy trying to coax greens, yellows, reds, and magentas out of dying LEDs.
The fact that the brightest settings start out way too blue is alarming!...
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post #4 of 8 Old 08-11-2012, 09:02 AM
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Doesn't Sony build some TVs with tri-color LED backlights?

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post #5 of 8 Old 08-11-2012, 09:18 AM - Thread Starter
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I think the tri-colors lost the brightness war to the so-called white LEDs.
You can get an amazing amount of light out of these hybrids, but the quality of the light is lacking.
It's reminiscent of the brightness wars of the 60s and 70s, when phosphors became more orange and yellow to achieve luminance.
It became impossible to get cyan on a CRT and that started the Hollywood trend towards aquamarine backgrounds to distinguish themselves.
The current situation is not nearly so dire as that, but the white LEDs are quite blue to begin with and get bluer as the yellow phosphor decays.
It explains why the setting for Standard is so much brighter than than the more chromatically accurate Movie setting.
There is simply less available light in the Red and Green (and Yellow on Quattrons) channels, so they clip prematurely and the whites are too blue...
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post #6 of 8 Old 08-11-2012, 09:32 AM
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Check out Pg. 68 of this article to see how much the LED phosphor output decays with time. It doesn't take long.

100,000 Hour Lifetimes and Other LED Fairytales

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post #7 of 8 Old 08-11-2012, 09:43 AM - Thread Starter
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Told with a great sense of humor.
This past year has seen the end of CCFL and the almost-complete domination by edge-lit white LEDs.
I'm wondering if they had a breakthrough in the technology -- how far from the transistor blue emitter to place the yellow phosphor, etc. -- or if they just jumped off the cliff?
The dirty dishwater glow of solar garden lights is not quite what I'd expect to light up my $3,000.00 TV set. Maybe these articles are out of date? Please?...
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post #8 of 8 Old 08-12-2012, 05:16 AM
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There is a sticky in the Display Calibration forum - LED longterm performance?
http://www.avsforum.com/t/1278372/led-longterm-performance
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