Why Does My iMac Keep Setting the Screen Brightness to 'Full'?

Question

I have a 2 week old 24" iMac running Mac OS X 10.6. It is the primary monitor with the menu bar on the top of display. I have an external monitor as well, a 19" Viewsonic LCD. The LCD is set to the left side of the iMac, rotated 90 degrees CCW and has the Dock along the far left edge.

When I restart the screen brightness on the iMac reverts to Full brightness. The Viewsonic LCD retains the setting I have for it. I am using a Mini DVI to DVI cable for the external display.

I even tried setting my Huey Pro to do automatic screen adjustment based on ambient lighting but the iMac still goes to stun with a reboot.

I am sure it is something dumb I have overlooked.

Solution 1

For clarification, do you set the brightness to the lowest possible? It appears there is a bug in 10.6 that won't save your brightness if it is set to the lowest possible. Any other notch and it saves. My iMac has personally never exhibited the issue but I never use brightness down all the way - I'm normally at half.

Sources: Apple Discussions, ehMac

Solution 2

all macs (iMac, MacBook or MacBook Pro) have ambient light sensors which adjust monitor brightness to the environment.

If you dim the lights in your room or around your iMac - you should see that the screen brightness is reduced too. You can turn off "auto-brightness" settings in Display preferences.

Solution 3

I use darkadapted to set a brightness for my Cinema Display monitors. It lets me set a brightness and save the settings. I find the results better than using Apple's brightness settings. Darkadapted is trialware but I think there are free programs that perform the same functions.

Comments

[TomB]

That is true for all Mac Laptops but neither of the two iMacs I have seem to have an ambient light sensor. Nor is there an "auto-brightness" setting in the Display Preferences.

[TomB]

Never would have guessed that in a million years. But yes, that is exactly what I was doing. Mad props for digging that esoteric bug out of the Apple DB.

[Chealion]

That's what SuperUser should be for :-)

[aalaap]

Seems like this bug has crawled into 10.7 as well. I came here looking for just that.