Ever since I've updated to Mountain Lion, the screen brightness keeps changing automatically. I don't have the setting enabled in Energy Saver.

I usually have my brightness set to 100%, and the system sometimes changes it to 80% (e.g. when I wake my Mac from sleep). If I live it at 80%, it changes it to 60% ... and so on. This is really annoying.

My pmset -g results are:

Active Profiles:
Battery Power       -1*
AC Power        -1
Currently in use:
 standbydelay         4200
 standby              0
 halfdim              0
 sms                  0
 hibernatefile        /var/vm/sleepimage
 disksleep            0
 sleep                0
 hibernatemode        0
 ttyskeepawake        0
 displaysleep         10
 acwake               0
 lidwake              1

1 Answer 1


I see that you don't have the "Slightly dim the display while on battery power" setting enabled in Energy Saver, but do you happen to have "Automatically adjust brightness" enabled in your Display preference pane?

Displays pane in System Preferences highlighting "Automatically adjust brightness"

That's the setting that adjusts your brightness based off of the light level detected by a Mac's ambient light sensor. (You may have already thought of this and or maybe it's too obvious but I wanted to suggest it just in case.) Good luck!

  • Thanks! I was sure it's a bug and not something obvious, so I missed it.
    – bogdansrc
    Commented Aug 17, 2012 at 17:21

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