General > General Technical Chat
Why do backlight LEDs burn out and go blue?
james_s:
--- Quote from: dunkemhigh on November 12, 2021, 11:37:30 pm ---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).
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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.
amyk:
--- Quote from: macboy on November 12, 2021, 04:45:40 pm ---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.
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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 ::)
james_s:
--- Quote from: amyk on November 13, 2021, 04:08:59 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 ::)
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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.
eti:
--- Quote from: amyk on November 13, 2021, 04:08:59 am ---
--- Quote from: macboy on November 12, 2021, 04:45:40 pm ---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.
--- End quote ---
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 ::)
--- End quote ---
Yes, marketing people live in fairytale land.
wraper:
--- Quote from: james_s on November 12, 2021, 10:01:12 pm ---
--- Quote from: Zero999 on November 12, 2021, 09:50:11 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.
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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.
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And the amount of data and speed at which it would need to be processed are quite extreme.
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