Author Topic: Why do backlight LEDs burn out and go blue?  (Read 19954 times)

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Offline james_s

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Re: Why do backlight LEDs burn out and go blue?
« Reply #75 on: November 12, 2021, 09:32:08 pm »
It's the contrast ratios and black levels that really sold me on OLED, they look absolutely stunning in a darkened room, and the color is also amazingly good. LCD looks washed out and bland in comparison. I think it's unfortunate that so many people don't care about picture quality and that has kept LCD going when it should have been largely obsolete by now.

I don't watch TV in a traditional sense, I use my TV for movies and streaming older shows and it is only on when I'm actively sitting there watching something so the potential for screen burn is not really an issue, and picture quality is very important to me. I have an LCD TV only because I got it for free, it's not nearly as nice as the OLED sets a couple of my friends have but it's good enough for the price.
 

Online Zero999

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Re: Why do backlight LEDs burn out and go blue?
« Reply #76 on: November 12, 2021, 09:50:11 pm »
If he had manually ran compensation cycle, most likely those issues would be gone.

I've seen no success with screen-burn reduction apps in other devices--is there something special about the compensation cycle in an LG OLED?  Does it know somehow which pixels are weak?  Does it store calibration data?
Yes, it is special.
LG engineers determined that the forward voltage of the individual OLED pixels changes predictably with wear. So if you can measure the forward voltage, you know the state of that pixel and compensate. The modern OLED TV panels are engineered with a substantial headroom in maximum brightness output. As the each pixel ages, the TV applies compensation to boost the output to match original specifications. Eventually of course, it will run out of headroom and won't be able to boost some pixels any further, at which time light output will decrease and burn in will begin to show up. I've read they expect this will occur after approximately 100000 hours, or around 10 hours a day for 30 years. This technology has improved over the years (and didn't exist at first) so don't be surprised to hear of burn-in issues from people with old OLED panels. It's highly likely that modern OLED TVs (just like LCDs) will be replaced due to technological obsolescence or some non-panel fault far before the panel is worn out.
Even if my OLED TV only lasts 5 years, I will get another OLED to replace it. There is no other tech on the market that comes anywhere close to the picture quality. The picture uniformity is perfect; in fact, I now find it almost painful to watch any LCD TV due to the subtle non-uniformity (blotches, brighter edges, etc.) that most people don't even notice because it's so "normal"/common. The black levels and shadow detail of OLED are amazing. The best zone-lit LCDs have narrowed the gap but don't and can't match the performance.
Wouldn't it have been much easier to allocate an area of memory to store how long each pixel is illuminated for and at what brightness? Then the wear can be calculated and compensated for.
 

Offline james_s

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Re: Why do backlight LEDs burn out and go blue?
« Reply #77 on: November 12, 2021, 10:01:12 pm »
Wouldn't it have been much easier to allocate an area of memory to store how long each pixel is illuminated for and at what brightness? Then the wear can be calculated and compensated for.

That would rely on the wear being absolutely predictable, which it may not be. If you can measure the actual condition of the pixel that is likely to produce much better results.
« Last Edit: November 12, 2021, 10:05:48 pm by james_s »
 

Offline PlainName

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Re: Why do backlight LEDs burn out and go blue?
« Reply #78 on: November 12, 2021, 11:37:30 pm »
Quote
I don't watch TV in a traditional sense, I use my TV for movies and streaming older shows and it is only on when I'm actively sitting there watching something

That's got me puzzled. What is the 'traditional sense' for a TV? Are they used instead of, for instance, a radio (I note Freeview over here has a lot of 'FM' channels).

 

Offline etiTopic starter

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Re: Why do backlight LEDs burn out and go blue?
« Reply #79 on: November 13, 2021, 01:45:34 am »
Quote
I don't watch TV in a traditional sense, I use my TV for movies and streaming older shows and it is only on when I'm actively sitting there watching something

That's got me puzzled. What is the 'traditional sense' for a TV? Are they used instead of, for instance, a radio (I note Freeview over here has a lot of 'FM' channels).

Streaming on demand, and/or YouTube as opposed to watching broadcast tv through the air, or via cable, I should think.
 

Offline james_s

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Re: Why do backlight LEDs burn out and go blue?
« Reply #80 on: November 13, 2021, 04:03:03 am »
That's got me puzzled. What is the 'traditional sense' for a TV? Are they used instead of, for instance, a radio (I note Freeview over here has a lot of 'FM' channels).

Loads of people just have the TV on for many hours of the day tuned to whatever happens to be on, whether it is being actively watched or not. My dad was like that, he'd have his TV on from the time he got home from work to the time he went to bed, and on the weekends it was on from the time he got up, he liked having it as background I guess. I turn on my TV when I want to watch something, I watch the show/movie I want to see and then I turn it off. It rarely gets used more than an hour or two a day and it is never displaying anything with a logo in the corner.
 

Offline amyk

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Re: Why do backlight LEDs burn out and go blue?
« Reply #81 on: November 13, 2021, 04:08:59 am »
As the each pixel ages, the TV applies compensation to boost the output to match original specifications. Eventually of course, it will run out of headroom and won't be able to boost some pixels any further, at which time light output will decrease and burn in will begin to show up. I've read they expect this will occur after approximately 100000 hours, or around 10 hours a day for 30 years.
Driving the worn ones harder to get the same light output just means they'll wear out even faster, so it's a very temporary solution and once the degradation starts it will quickly accelerate. It reminds me of CRT "booster" transformers that increased the filament voltage, more quickly destroying the cathode emission completely.

...and 30 years? They claimed the same 50-100k hours for LED lamps when they first came out... but look at what the actual lifespan in practice is ::)
 

Offline james_s

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Re: Why do backlight LEDs burn out and go blue?
« Reply #82 on: November 13, 2021, 04:14:05 am »
Driving the worn ones harder to get the same light output just means they'll wear out even faster, so it's a very temporary solution and once the degradation starts it will quickly accelerate. It reminds me of CRT "booster" transformers that increased the filament voltage, more quickly destroying the cathode emission completely.

...and 30 years? They claimed the same 50-100k hours for LED lamps when they first came out... but look at what the actual lifespan in practice is ::)

Well time will tell how it actually plays out, but in theory at least they are run well below their maximum output so there is a lot of room to drive them harder without exceeding the point at which lifespan is rapidly reduced.

I don't remember seeing 100k rated LED lamps but I do have some of the early ones that are 50k rated and most of those are either still going or they were replaced due to the availability of more efficient lamps. I have a Philips 8W LED bulb in my front porch light that I installed in 2011, it has been running dusk till dawn so around 12 hours a day average since then and still looks like it did the day I installed it. That's well over 40k hours so it may actually achieve the 50k rating.
 

Offline etiTopic starter

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Re: Why do backlight LEDs burn out and go blue?
« Reply #83 on: November 13, 2021, 05:44:46 am »
As the each pixel ages, the TV applies compensation to boost the output to match original specifications. Eventually of course, it will run out of headroom and won't be able to boost some pixels any further, at which time light output will decrease and burn in will begin to show up. I've read they expect this will occur after approximately 100000 hours, or around 10 hours a day for 30 years.
Driving the worn ones harder to get the same light output just means they'll wear out even faster, so it's a very temporary solution and once the degradation starts it will quickly accelerate. It reminds me of CRT "booster" transformers that increased the filament voltage, more quickly destroying the cathode emission completely.

...and 30 years? They claimed the same 50-100k hours for LED lamps when they first came out... but look at what the actual lifespan in practice is ::)
Yes, marketing people live in fairytale land.
 

Online wraper

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Re: Why do backlight LEDs burn out and go blue?
« Reply #84 on: November 13, 2021, 08:01:28 am »
Wouldn't it have been much easier to allocate an area of memory to store how long each pixel is illuminated for and at what brightness? Then the wear can be calculated and compensated for.

That would rely on the wear being absolutely predictable, which it may not be. If you can measure the actual condition of the pixel that is likely to produce much better results.
And the amount of data and speed at which it would need to be processed are quite extreme.
 

Offline PlainName

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Re: Why do backlight LEDs burn out and go blue?
« Reply #85 on: November 13, 2021, 10:46:07 am »
That's got me puzzled. What is the 'traditional sense' for a TV? Are they used instead of, for instance, a radio (I note Freeview over here has a lot of 'FM' channels).

Loads of people just have the TV on for many hours of the day tuned to whatever happens to be on, whether it is being actively watched or not. My dad was like that, he'd have his TV on from the time he got home from work to the time he went to bed, and on the weekends it was on from the time he got up, he liked having it as background I guess.

OK! Kind of wallpaper.

Got to admit I have a small 7" monitor hooked up to STB output which is on whenever my PC is. Reason is that when I was developing a CCTV DVR I needed a video source other than the DVD players being already used, and 24-hour news channel hit the spot. I just got used to it being there as a kind of ticker tape, keeping up with the world.
 

Offline Cerebus

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Re: Why do backlight LEDs burn out and go blue?
« Reply #86 on: November 13, 2021, 02:34:58 pm »
Driving the worn ones harder to get the same light output just means they'll wear out even faster, so it's a very temporary solution and once the degradation starts it will quickly accelerate.

Are you making assumptions from what you know about the wear characteristics of 'conventional' LEDs and applying them to organic LEDs? Straight question, because if you are then there's every possibility that those assumptions are wrong (they could also be right). One type are made out of elements, one out of compounds, they may wear/age in very different ways. I just don't know because I haven't looked into OLEDs in any more systematic a fashion than reading the odd article in the trade press as they started to emerge. So I'm not saying you're right or wrong, just asking "Is this an assumption or actual knowledge"?

...and 30 years? They claimed the same 50-100k hours for LED lamps when they first came out... but look at what the actual lifespan in practice is ::)

I have an unpleasant suspicion that the shorted life is down to value engineering and "Design it so they need to come back and buy more."
« Last Edit: November 13, 2021, 02:37:25 pm by Cerebus »
Anybody got a syringe I can use to squeeze the magic smoke back into this?
 

Offline james_s

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Re: Why do backlight LEDs burn out and go blue?
« Reply #87 on: November 13, 2021, 06:53:03 pm »
I have an unpleasant suspicion that the shorted life is down to value engineering and "Design it so they need to come back and buy more."

Unfortunately a lot of TV manufactures have miscalculated and gone too far. The number of late model LED lit LCD TVs I have been given with bad backlights makes me very hesitant to ever recommend buying one of those brands. I come from an era when a TV was expected to last around 20 years and I still expect that. Anything less than 10 years is absolutely unacceptable.
 
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Offline Cerebus

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Re: Why do backlight LEDs burn out and go blue?
« Reply #88 on: November 13, 2021, 08:12:02 pm »
I have an unpleasant suspicion that the shorted life is down to value engineering and "Design it so they need to come back and buy more."

Unfortunately a lot of TV manufactures have miscalculated and gone too far. The number of late model LED lit LCD TVs I have been given with bad backlights makes me very hesitant to ever recommend buying one of those brands. I come from an era when a TV was expected to last around 20 years and I still expect that. Anything less than 10 years is absolutely unacceptable.

We were talking of LED lamps, and that's where I suspect perhaps a little less good faith from their manufacturers towards the public than is properly warranted. One would hope that TV/panel manufacturers cared a bit more for their reputation. After all, you will remember whose TV brand you bought, the brand of that £4 LED lamp that lasted a disappointing time? Probably not.
Anybody got a syringe I can use to squeeze the magic smoke back into this?
 
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Offline james_s

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Re: Why do backlight LEDs burn out and go blue?
« Reply #89 on: November 14, 2021, 05:05:34 am »
We were talking of LED lamps, and that's where I suspect perhaps a little less good faith from their manufacturers towards the public than is properly warranted. One would hope that TV/panel manufacturers cared a bit more for their reputation. After all, you will remember whose TV brand you bought, the brand of that £4 LED lamp that lasted a disappointing time? Probably not.

The oldest LED bulbs I have are ones that cost me around $40 each back when I bought them. At the prices they were charging back then I think most of the bulbs were over-engineered because they knew a lot of early failures would risk killing the entire market, a lot of people already didn't trust them after experiences with CFLs not lasting as long as claimed. Then there was the predictable race to the bottom, although you can still get reasonably good ones. I've had good luck with Cree and Philips bulbs. 
 

Online wraper

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Re: Why do backlight LEDs burn out and go blue?
« Reply #90 on: November 14, 2021, 10:46:27 am »
 

Offline strawberry

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Re: Why do backlight LEDs burn out and go blue?
« Reply #91 on: November 14, 2021, 12:44:44 pm »
make so called old tech unappealing and degrade it and then replace it with more predictable (shorter) life product then add commercials at bootup and everyone is happy  ;D
LCD block ~1/2 backlight while white is displayed
 

Offline PlainName

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Re: Why do backlight LEDs burn out and go blue?
« Reply #92 on: November 14, 2021, 01:44:25 pm »
Quote
LCD block ~1/2 backlight while white is displayed

That makes sense - white is essentially unobstructed whereas other colours reduce the intensity because R, G or B are filtered, so without artificially reducing white it would appear too bright in comparison.
 

Online wraper

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Re: Why do backlight LEDs burn out and go blue?
« Reply #93 on: November 14, 2021, 02:02:16 pm »
Quote
LCD block ~1/2 backlight while white is displayed

That makes sense - white is essentially unobstructed whereas other colours reduce the intensity because R, G or B are filtered, so without artificially reducing white it would appear too bright in comparison.
What? White is not artificially reduced. There is a light loss because subpixels have color filter behind them and pass only narrow range of wavelength. When 3 colors are combined in your eye, you see "white". There are also RGBW displays which add a subpixel without a color filter for better brightness/efficiency, but it reduces picture quality.
 

Offline strawberry

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Re: Why do backlight LEDs burn out and go blue?
« Reply #94 on: November 14, 2021, 03:48:23 pm »
I think these are fancy RGB LEDs to increase efficiency and match LCD filters and some might be more fancy switching on/off at black spots

 

Offline etiTopic starter

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Re: Why do backlight LEDs burn out and go blue?
« Reply #95 on: November 14, 2021, 09:01:18 pm »
[1 of 3 messages with attachments]

I thought you'd like to see the bare die on the backlight strip, along with the special lens type device, inside which is a conical, hollow cavity, clearly designed for maximum dispersion (I'd think)
« Last Edit: November 14, 2021, 09:02:57 pm by eti »
 
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Offline etiTopic starter

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Re: Why do backlight LEDs burn out and go blue?
« Reply #96 on: November 14, 2021, 09:02:36 pm »
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Offline etiTopic starter

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Re: Why do backlight LEDs burn out and go blue?
« Reply #97 on: November 14, 2021, 09:03:51 pm »
[3 of 3 messages with attachments]

 


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