Leds dimming under heat?

[Itzamna]

Hello!


I have a early 2011 Macbook Pro and lately i started to notice that when my computer reaches high temperature (above 70ºc) i can see a dark shadow in a cone shape right above the CPU and GPU fans.

I can only see them IF my screen image is black (in this case there is a difference between the black of the rest of the screen and the black of the "shadow") or a dark almost black gray. The last scenario is the one that the shadows are most visible.

If the screen image/color is lighter its perfectly normal. For example in the Solid Colours available on the wallpaper preferences, i can't see the shadows with any of them, it must be darker then the darkest gray there.


The higher the temperature the most visible the shadow is. If i'm doing some very intensive stuff and the computer is like 1 hour near 90ºc, then the shadows are easy to see on a dark background.

As the temperature drops, the shadow tend to disappear.




My first thought was that this could be the leds right above the heat exits getting dimm due to the hight temperature (they get brighter on colder situations), but i would like to know if this is a normal behaviour.

Should i get worried that somewhere in the near future i will be short of 2 leds?! Or is this normal?

Anyway, here are 2 pics of the situation. The first one is with 80'ish ºc the second one is with 30'ish ºc.

Its a lot more visible in the naked eye. The camera didn't make it justice. But even so, its perfectly visible.


So, should i be worried?

 

[Big-TDI-Guy]

Only when hot? While LEDS to shift in intensity over temperature - with the diffuser, it shouldn't be localized like that.

I'd guess it's stress induce birefringence caused by thermal expansion, allowing light bleed-through.

If it's only noticeable with darker tints - that's when the liquid crystal is at extinction to the polarizer, and SIB will reduce your extinction ratio, causing light bleed. If you can't see it on white screens, then it's very likely SIB.

Not awesome, but likely not a progressive failure - it should return to normal with cooler temps.

Edit: The only other thing I can think of that'd have a similar behavior, would be a dying GPU, that starts artifacting when hot - but what I see in your pics does not look anything like artifacting.

 

[grahamnp]

My older non-unibody MBP had a screen that looked like yours, only worse. I can't tell if it is heat though. Idle temps never dropped below 50 and it developed over time.

 

[Itzamna]

Only when hot? While LEDS to shift in intensity over temperature - with the diffuser, it shouldn't be localized like that.

I'd guess it's stress induce birefringence caused by thermal expansion, allowing light bleed-through.

If it's only noticeable with darker tints - that's when the liquid crystal is at extinction to the polarizer, and SIB will reduce your extinction ratio, causing light bleed. If you can't see it on white screens, then it's very likely SIB.

Not awesome, but likely not a progressive failure - it should return to normal with cooler temps.

Edit: The only other thing I can think of that'd have a similar behavior, would be a dying GPU, that starts artifacting when hot - but what I see in your pics does not look anything like artifacting.

birefri-what? lol I have to google that.

Thank you for the swift response.


But yes, only when its hot. The first pic was after deliberately rising his temperature to high 80's ºc and the second picture was at 30'sºc.

And yes, only on very dark backgrounds i can see it. On white or light gray backgrounds its bright as always.

I know it doesn't look like a dark background, but the one on the picture is almost black. The camera gave it that bright to dark gradient.

I only noticed that by accident, but now that i know about it, i'm always searching for it. :/




About the GPU artifacts, so far i haven't see any wierd behavior, be it on video/image processing or gaming.

----------

My older non-unibody MBP had a screen that looked like yours, only worse. I can't tell if it is heat though. Idle temps never dropped below 50 and it developed over time.

Well, as long its not harming my screen and as long it happens only on very heat intensive conditions and as long i can only see it on dark backgrounds, i'm not to worried about it...



My fear is that it becomes permanent or those leds simply go off... :/

 

[Itzamna]

Now that i'm searching closely, when the temperatures are low (about 30ºc) i can see that in the same spot of the shadows the screen is a tiny tiny tiny bit brighter there.

Its really a faint difference and only noticeable when looking at it from like a 45º angle. And again only seen on very dark backgrounds.

If i look at it from the normal straight angle i can't see it.


I tried to take a picture of this, but its so subtle that the camera didn't picked it.


Does this help on the stress induce birefringence hipotesys?

 

[randomrazr]

just take it to the apple store yeesh

 

[Itzamna]

I will, but the nearest Apple store is like 300km's away... Not the easiest thing to do. I'll probably go there is some weekend or so.

 

[Itzamna]

Ok... So i talked to some guy in a Apple Service Provider and he said that while its not normal, its within the anomalies that are accepted in the construction of the LCD.

Its like the dead pixels thing... Its accepted because it would be extremely expensive to check and discard any LCD that had 1 or few dead pixels. This is the same stuff.


He said that i should not be to worried about it, and near the end of the Warranty i should take it to a Apple Service Provider to do a full check-up to the screen.

 

[Itzamna]

I asked a second opinion from another Apple Services Provider, and he basically told me the same stuff.

He also said that if the "smudges" were distracting me in any way, i could try to lift up the back of the laptop so more fresh air could enter in the right side of the hinge, and the hot air could have more space to go when leaving the fans.