New iMac brightness level keeps changing (auto adjust NOT checked)

I have the same issue on a new 21.5" iMac. Auto brightness is turned off, but everytime we start up it's back to full brightness even though the slider shows its in the middle in system preferences. My other iMac is fine and doesn't do it. I did buy it in 2010 though. Did you find a solution?

I'd try a Pram reset first.

http://support.apple.com/kb/ht1379

Captfred

It apply's to both. There are several video settings stored there. If it doesn't work than I'd try an SMC reset next.

http://support.apple.com/kb/HT3964

I have the exact same thing on my newest iMac that purchased in November and have tried all of the reset "pram" and other stuff and nothing changes it. I can manually change it each time it reboots, but it never saves itself.

Okay, I just figured something out on my 2011 iMac. I was trying to put it right in the center for brightness (50%), but at every reboot it would change back to 70% (approx) brightness. If I put it at 100% it would stay there. Next I tried putting it at 30% just to see what would happen and it stayed there on reboot.

So....it looks like there is only 4 settings on my new iMac that can be saved: lowest, approx 30%, approx 70%, and full. Full it just way to bright and so is 70% so it looks like I'm to keep it at 30%. It's much easier on the eyes after 8 hours. My 2010 iMac would save at any increment (or at least the change wasn't noticeable) upon reboot.

I rebooted again and now it went from 30% to just over 50%. I'm not sure where it's getting it's numbers from. I rebooted again and now it's around 70% again. Another time...it's even higher. I can't tell you what is going on....

UPDATE: I set it clear down to the lowest and after several reboots it had climbed, I'd guess, 25% each time (maybe more.)

Same started here today on 27"iMac

Brightness backs down slowly to 'dim'.

Wondered if anything to do with Time Capsule restoring some settings.

I have same problem, of autobrightness being unchecked and my brightness going from full to about 3/4 bright

all by itself. I had that problem, then flickering of my screen also was taking place. I didn't bring my unit into Apple

because this autobrightness thing plus flickering would not happen on command,, and I wouldn't be able to show them properly. Well , finally my left side of the screen dimmed,, and that was the go ahead to bring it in to them

to show the left side of screen. I also told them about the flickering,, and the autobrightness, which I figured played a role into the final left side dimming. They replaced the backlight and the display LCD on warranty.

I have had it for about 5 days. The screen is equally lit (as should be), however, I discovered that my same old

problem of autobrightness, is slipping back to 3/4. So most of you have autobrightness problem in a sort of different way. I set mine to "torch" because my downstairs bedroom is dim (with one overhead light), but sometimes, just plain dark,, so I want to sometimes keep it at torch,, however, it still slips back. You would

almost think that if my surronding was dim or dark, that it would stay on torch if the autobrightness was really working properly. Go figure. I just tried SMC a short while ago,, I had tried, before my repair doing PRAM and the other one (I think VRAM). I also will unhook my second monitor to see if that is having an impact on things.

Do any of you in this post have a second monitor attached,, and have you tried unhooking it to see if the problem

is resolved?

Same problem here, no 2nd monitor. Did PRAM and SMC resets fix the issue?

Thanks,

Adam