Polymer LED display issue

I think it's poorly stated. All OLEDs will decay due to use, being at (for eaxample) 50% light output at 5000 hours illuminated. After 5000 hours, if pixel A is always on, and pixel B is never on, then when you want to light A and B, A will be 50% dimmer than B.

You need to think about this when designing displays, or live with the fact that they will look blotchy. light A and B together, you'll notice

Hi,

I have an application that just suits a Polymer LED display perfectly. I can get a 2 line 16 char display (such as a Delta PDC1602M), and all looks good (power consumption, life, interface etc)

The only problem is that buried in the specs is the line that says "Do not hold the same display picture over 1 min, because they will cause none uniformity in the display screen."

Ignoring the bad english, I think this is some kind of burn in phenomonon. Other makers mention a "differential burn in" issue, but put no time limit on it, however most manufacturers do not even mention this.

Trying it, so far, has produced no observable effects. I can see it would be easy to solve this on a graphics display, but much harder on a text display that never has quite enough characters anyway.

A web search has not prodiced any real useful info -- does anyone have any real experience with PLED displays and this issue in particular ?

TIA,

-- Regards, Gavin Melville snipped-for-privacy@acclipse.co.nz

Sure, but for a given set of display patterns, the difference in brightness of pixels due to burn-in should increase much more quickly (in relation to the expected life of product) at high temperatures.

Best regards, Spehro Pefhany

--
"it\'s the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

That too. I think the pixels'd be more or less isothermal though.

The application note that I have says "a long time" not "1 minute", which I would interpret as many hours (probably > 100 or >500). It also says that the effect of temperature < 50°C on life is small. They do go on at some length about automatically blanking the display, scrolling or doing other annoying things.

What's the document number of what you are looking at?

Best regards, Spehro Pefhany

--
"it\'s the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

I expect this to occur, but Delta indicate that it occurs over 1 minute, not 5000 hours, which in this use would be years.

-- Regards, Gavin Melville snipped-for-privacy@acclipse.co.nz

Thanks for the link. I see what you mean. Life appears to be 5,000 hours to 50%, since it's measured with 50% duty cycle. Still looks like it should be hundreds of hours to see a visible difference.

Have you talked to the office in Taiwan? (they'll probably refer it back to the dudes in FL, but it can't hurt)

Best regards, Spehro Pefhany

--
"it\'s the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

Hi Spehro,

, click on PDC1602M (a pdf file). Last page (22) , 15.4 says "(4) Do not hold the same display picture over 1 min, because they will cause none uniformity in the display screen."

Several other datasheets from Delta have similar warnings.

I have not found many other displays with reasonable power consumption

-- I can use either 16x2 text or 128 x 64 graphics.

-- Regards, Gavin Melville snipped-for-privacy@acclipse.co.nz

The reply from Taiwan was a bit of a stunner.

"Due to the display uniformity in the display screen , we advise our customer that don't hold the same display picture over 1 min.

Display skills : 1. Try to scrolling the pattern after 1 min. then return to the original pattern 2. After 1 min. turn off the pattern , when you want to see the pattern , try to contact some key button to start the pattern"

Back to the search for low power display, and don't go near Delta.......

They are lower power than an LCD + LED backlight.

Best regards, Spehro Pefhany

--
"it\'s the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

Yeah, what kind of useless product is this?

Even a CRT takes many hours to get burn-in images.

Hard to tell from their English, but I wonder if they mean that a picture would show up as an after-image if you change to an all-lit image?

Discrete LED brightness varies with temperature (brighter when colder), so maybe the lit pixels get warmer than the unlit pixels. They would then appear dimmer when the unlit pixels are turned on, at least until all pixels warmed to the same temperature.

Plastic isn't as good a heat conductor as glass or inorganic LED material.

I heard OLED displays are not actually very low power, they are emitting light energy rather than absorbing it as LCDs do.

Rather extreme CYA statement, though.

Best regards, Spehro Pefhany

--
"it\'s the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

I think this is just generic, and nothing specific to this OLED. They are not saying that after 61s, there will be damage. What they are trying to get across is that if you have the display static for long periods, you'll notice nonuniformity eventually.

I think it's possibly a case of the translator not fully understanding the engineers.

Hi,

I have one on test now -- completed 8 hours without showing any sign of degradation. Will keep the group informed.

Gavin Melville.