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

Question

Just got a new 27 inch iMac and keep on having to change the brightness level back to the brightness I prefer.
I do not have auto adjust checked, I put the brightness slider up to the level I like and after a while the brightness dims to what seems like the default level as its always down to the same spot on the slider...what gives? i just want it to stay where I want it...
Help.

Answer 1

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?