cimedaca
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Only a 28 month backlight lifetime?

Sun Dec 16, 2018 2:47 pm

Is anyone else concerned that the 20,000 backlight life works out to only about 28 months if you use it for any always on function like an alarm clock or home control?

Specifications
Backlight lifetime: 20000 hours

David

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mahjongg
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Re: Only a 28 month backlight lifetime?

Sun Dec 16, 2018 9:25 pm

where does the backlit lifetime 20.000 hours come from?
I searched the site of the two manufacturers, and official resellers, and could not find an exception to the normal guarantee being made.
still 28 months means 2 1/3 year.... not *that* short a guarantee time.

But AFAIK the backlighting is done with LED's, which normally have an almost eternal burning time, they should last *much* longer than a few years.


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Imperf3kt
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Re: Only a 28 month backlight lifetime?

Sun Dec 16, 2018 10:47 pm

I wouldn't pay any heed to that. At my job we have a computer monitor that is on for 14 hours a day, 5 days a week. It has been working for over 5 years now and no sign of the backlight dying.
That's 70 hours a week, 3640 hours a year and a total of about 19,000 hours use so far.

By the way, there is a static image on screen the whole time which is yet to "burn in"
55:55:44:44:4C
52:4C:52:42:41

Rose tinted glasses are difficult to see through.

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mahjongg
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Re: Only a 28 month backlight lifetime?

Mon Dec 17, 2018 1:10 am

gordon77 wrote:
Sun Dec 16, 2018 9:47 pm
Here's one example...

https://www.samsung.com/ca/support/comp ... ys-a-week/
larger LCD screens use a different backlighting technique than using LED's, they use a technique similar to TL lamps, Cold-cathode fluorescent lamps (CCFL) with an "inverter" circuit that generates the required high voltages (>700 volt). it a technique that has a higher failure rate than LEDs.

https://en.wikipedia.org/wiki/Backlight#CCFL_backlights

PhatFil
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Re: Only a 28 month backlight lifetime?

Mon Dec 17, 2018 1:30 am

ccfl backlight tubes usually outlived the screens they were fitted to and are the subject of a few recycling/repurposing utubes ;)

If your backlight dies on you its do-able diy fix with a led strip.. https://www.youtube.com/watch?v=smrMoIpvYTk
Should be within the capacity of anone who has built n boxed a pi solution ;)

W. H. Heydt
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Re: Only a 28 month backlight lifetime?

Mon Dec 17, 2018 5:39 am

mahjongg wrote:
Mon Dec 17, 2018 1:10 am
gordon77 wrote:
Sun Dec 16, 2018 9:47 pm
Here's one example...

https://www.samsung.com/ca/support/comp ... ys-a-week/
larger LCD screens use a different backlighting technique than using LED's, they use a technique similar to TL lamps, Cold-cathode fluorescent lamps (CCFL) with an "inverter" circuit that generates the required high voltages (>700 volt). it a technique that has a higher failure rate than LEDs.

https://en.wikipedia.org/wiki/Backlight#CCFL_backlights
Well... Sort of... Newer monitors use LED backlighting. CCFL is now an "old" technology.

On the topic at hand, though, I suspect that "power on hours" isn't the only measure. It's pretty likely that the 20K hours expected lifetime is only if the backlight is at full intensity the whole time. On my alarm clock (the display is nowhere near 20K hours yet...ask me again in about 18 months) the setting is at 250 (of 255) during the day, drops to 50 for half an hour, and the goes to 16 so as not to light up the room at night, for 7 to 9 hours, depending on day of the week. It can be read easily in a dark room, but it won't keep you awake. I also use a black background for the desktop and dark colors for the control bar and such like. And if it dies after a couple of years... I'll get another. I expect it to last rather longer, though.

gordon77
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Re: Only a 28 month backlight lifetime?

Mon Dec 17, 2018 8:49 am

mahjongg wrote:
Mon Dec 17, 2018 1:10 am
gordon77 wrote:
Sun Dec 16, 2018 9:47 pm
Here's one example...

https://www.samsung.com/ca/support/comp ... ys-a-week/
larger LCD screens use a different backlighting technique than using LED's, they use a technique similar to TL lamps, Cold-cathode fluorescent lamps (CCFL) with an "inverter" circuit that generates the required high voltages (>700 volt). it a technique that has a higher failure rate than LEDs.

https://en.wikipedia.org/wiki/Backlight#CCFL_backlights
https://www.integral-led.com/support/la ... -lamp-last

aBUGSworstnightmare
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Re: Only a 28 month backlight lifetime?

Mon Dec 17, 2018 8:49 am

LED baclikght lifetime is usually specified as the time when the brightness is only 50% of the initial value.

Means it's not dead after 20k hours, it's only have of the brightness

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mahjongg
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Re: Only a 28 month backlight lifetime?

Mon Dec 17, 2018 10:10 am

One thing I know is that the lifetime of a LED goes down when it is hot, so its best to keep the LED's cool, or in other words, not at full brightness all the time, perhaps you can use a scheme where you dim them at night, and make them brighter during the day.
LEDs have a much better lifetime than alternatives, but after years of use their efficiency might decrease, nothing lasts "forever".

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bensimmo
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Re: Only a 28 month backlight lifetime?

Mon Dec 17, 2018 11:54 am

mahjongg wrote:
Sun Dec 16, 2018 9:25 pm
where does the backlit lifetime 20.000 hours come from?
I searched the site of the two manufacturers, and official resellers, and could not find an exception to the normal guarantee being made.
still 28 months means 2 1/3 year.... not *that* short a guarantee time.

But AFAIK the backlighting is done with LED's, which normally have an almost eternal burning time, they should last *much* longer than a few years.
It comes from the documents
https://www.raspberrypi.org/documentati ... /README.md

It'll be dimmer but usable , probably it is an average and it may have died completely.
Most devices for always on IoT style will use some sort of proximity sensor so it only on when you are near by.

It's much longer then the old cfl backlights of lcd screens.

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bensimmo
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Re: Only a 28 month backlight lifetime?

Mon Dec 17, 2018 12:06 pm

mahjongg wrote:
Mon Dec 17, 2018 10:10 am
One thing I know is that the lifetime of a LED goes down when it is hot, so its best to keep the LED's cool, or in other words, not at full brightness all the time, perhaps you can use a scheme where you dim them at night, and make them brighter during the day.
LEDs have a much better lifetime than alternatives, but after years of use their efficiency might decrease, nothing lasts "forever".
It's the cracks in the lattice from strain during the epitaxy of the layers (an old job of mine). These cracks, like all cracks propogate or are centres of propogation with expanding and contraction, also they can have photon accumulation iirc at unwanted frequencies.

At least that's one of the main factors
It probably the same in most semiconductors.

cimedaca
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Re: Only a 28 month backlight lifetime?

Mon Dec 17, 2018 12:16 pm

I do hope as suggested in this thread 20K hours is just when it is at half of its brightness and using it at lower levels will extend the life. Still, I think I would need to incorporate an unfortunate touch to start label or motion detection wake up. The problem is I wanted to use the Raspberry Pi for audio visual projector control at my college. I may want to install 20 or more. Once put in a room they may be expected to last 10+ years. Otherwise it may cost the college several thousand dollars to have the control system replaced in the future. I probably should consider an HDMI based touch screen that is more easily changeable. Given a local AV vendor wants a couple thousand dollars to change one code serial code on an eight year old Crestron touch screen control based system setup by another vendor, it will not be cheap if these start dying and they need to hire out the repair because I am no longer work there.

I have linked specification that show the back light hours below. I should have done this in my original post. It seems a 20-30K hours backlight rating is pretty common. The Nextion smart displays for Arduino I have looked at have similar ratings.
https://www.raspberrypi.org/documentati ... e/display/

David

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