LED vs LCD

I'm wondering if LED screens dim over time like LCD screens do? I cant get a definite answer on google, some say they stay the same output as long as they are working and some say they dim at a much slower rate.

 

What? I think you're confusing LED-backlit LCDs vs. CCFL-backlight LCDs.

Anyhow, the issue isn't usually brightness, but whiteness. The same amount of light will usually still be emitted, but the color temperature will decrease so that the whites aren't as white any longer.

 

LED's do not dim over time. They either function or do not.

 

This. You'll notice over time that with CCFL based machines, as the screen ages, the whites will get a little more yellowed.

You'll probably notice that it gets a little more washed out as well over time, though this probably isn't specific to CCFL lamps.

 

^Yep. With a fresh CCFL in an old panel, it'll look good as new though. LED's don't really dim though. They maintain same brightness for the life of the individual LED.

IDK if the LED backlights can be replaced if they ever fail... which is to say they will... it'll just be a WHILE before they do.

 

LEDs dimm over time too.

 

Interesting spelling. Most LED's have an average life of about 100,000 hours. And I've not really ever known them to dim. Got any information on that?

 

There are several different LED backlit LCD types, like there is for the CCFL backlit LCD.

LED LCD have direct backlit version and edge lit version (the latter is used in laptops for thinness reason and energy saving reasons).

In addition, LED used for backlit comes in two flavours, one is the blue LED with yellow phosphorus (to produce a near white colour) and the other is the RGB LED (so Red, Green and Blue all have separate LED).

While, it is true that the LED life is around 100,000 hrs, i have found that with the blue LED and yellow phosphorus backlit LCD, there are severe discoloration after 2 years of continuous use. There is a clear yellow shift in the colour displayed by the LCD. I recently sent 2 of the Thinkpad X200 with the same problems in for repair.

 

Very interesting! I know that most of the consumer LED's are InGaN with the phosphorous coats like you said, but I never knew they had a color shift over time. But it would only make sense, as over time the coating of phosphor degrades. Does it decrease lumen output, or just yellow-shift?

 

The brightness also decreases, but much less than that of the ccfl one.

 

Also they are brighter than normal LEDs. They are not digital,the junction will degrade over time. It's a natural process not some logic function.

 

The issue with "white" LED color shift is the yellow phosphour degradation.
While LED itself will degrade very slowly, it's only blue led. Phosphour will degrade a lot faster (basically at same speed as CCFL phosphour will do), therefore yellow bit of spectrum will distort, causing colour shift.

 

Yes, LED's do shift and change.

There are some aquarium lights for marine fish that use LED and while (extremely) expensive and long lasting they too need to be replaced at a regular interval in order to support life in the aquarium. The lights still work, but not in the right spectrum and brightness needed (as mentioned, it is the blue ones that shift), but it is much longer than the CCFL and metal halide lights being used.


Honestly, I think the better question is how long do you expect it to reasonably last in perfect condition? 3-5 years is probably about all most expect from a laptop and these systems should provide that and then some. Oh, and most of the early change isn't perceivable by humans, expect a while before you could tell even side by side.

 

This thread is a treasure trove of information. It finally explains why my ~6 year old Samsung 971p has gone yellow. My most recent colour calibration says it all:

Red: 55
Green: 42
Blue: 70

 

i am not sure how the RGB LED version of the LCD stands to the test of time, and whether there is similar sort of colour shifts overtime.

Personally, i think the Blue LED + Phosphorus backlit LCD's only benefits is that they use less power, but the longevity of the backlight is no better than the standard CCFL one (unless you can stand the fact that the LCD have a strong yellow tinge after continued use). I am having second thoughts on leaving my LED LCD TV on 24/7 now, they are still a long way off from CRT's longevity.

P.S. one of my friend whom spoke to a TV repair person, says that those Blue LED/Phosphorus LCD would eventually get a strong green tinge after continued use, which may explain why there was a strong green hue on the bottom of the LCD panel on both of the X200 LCD panel.

 

Does anyone have any pictures or tutorials of LED backlit laptop or other LED LCDs being disassembled?

 

RGB LED backlights are virtually free from dimming and completely free from color shift.
They don't use phosphour, they use triads of "pure" narrow-spectrum R, G and B leds. Therefore there is nothing to "dim", as it was truly pointed out before, pure LED just works until it abruptly fails.
As for color drift, these leds have different "drift" over time right from the start, that was initial challenge with making "white" over three different color types of LEDs. Because of that, any RGB LED backlight now incorporates a feedback loop, using built-in simple color sensor to continuously monitor brigthtness of each primary, and continuously adjust them to keep sum "white". Therefore, regardless of how they characteristics change over time, result is always white, because white point is continuously calibrated there.
Another plus side of this approach is that on RGB LED backlights it's possible to adjust white point by truly varying a backlight color, and not applying curves to colors. This is usually done via I2C interface and most RGBLED-carrying laptops provide some kind of custom UI to control that.

 

The reason UV aquarium LEDs dim with time is NOT because the LED itself 'dies out', it is because the UV emitting coating inside of the LED wears out, mostly from heat.

Same reason colored LEDs seem to dim with time. It's the internal phosphor coatings that lose their effectiveness before the primary light emitter does.

This effect is very well documented for those who care to look up how colored and specialty light (UV & IR) LEDs really work.

 

You are mistaken if you think that all colored LEDs are using phosphour. There are many LED types that produce pure colored visible light natively, without phosphour.

 

not mistaken at all. nor did I say that.

I did encourage people to go and look up, for themselves, how the tech works.

They should also read the specific specs of the LEDs they are using if only to make sure that they are using the correct device for a given application.

But people generally depend on hearsay rather than doing proper research for themselves.

Wikia is as good a place as any to **start** with ones research, BUT ONLY if they follow on to the primary sources. One never knows what details have been omitted from any given wikia entry.

 

You said "Same reason colored LEDs seem to dim with time". This was not exactly correct, as most of colored narrow-spectrum LEDs don't use phosphour and don't dim. White LEDs almost always do on the contrary. I've posted reference to wikipedia only because it was quickiest way, if you search for many of phosphour-less materials listed you will see plenty of LEDs using them being in production for ages

 

That's why RGBLED backlights are so great. RGBLED's are true red, green, and blue... and not phosphor coated.

 

@Ingvarr, LED still dims overtime, this is why life of LED is quoted in L50 values, which is the time to reach 50% of the original light output. But most of the modern day LED in the visible spectrum have a very long service life.

However, as you have said calibration would usually solve the issues for colour accuracy on the RGB LED LCD.

Also, UV diodes emit UV ray directly not because of special coating, it is the materials used for the p-n junctions that determines the frequency of photons that is produced.

@newsposter. If there was a coating for UV ray, then the diodes would have to emit something close to the X-ray frequency. As the coatings would only emit light of lower frequency than they have absorbed.

The longevity of these UV LED depends on the type of materials used for the p-n junction and the environment in which they are used in.

 

I would guess there may be a coating converting far-UV emitting LED (very dangerous) to near-UV (a lot less dangerous).

 

Why 'guess', the info is available on the web although is may not be in Wikia form.........

 

They act in different manners on the organisms and their biochemical pathways. most of the UV emitting diodes are in the UVC ranges, which is what is needed for sterilisations of water. Near-UV is not effective for such purposes.

 

LCD easy, LED is old school.

 

^ Uh what?