Display dims before sleep, no matter the setting

You might try resetting the PMU (power management unit). Here's a link for the instructions:

Resetting MacBook and MacBook Pro Power Management Unit (PMU)

I did the PMU reset and mine still dims no matter what setting also. 😟 Only started to do this recently.

I've had the same problem, twice within a few minutes. My MacBook went dim while I was writing an email, so I closed it, reopened it and hit the power button, then the screen lit up again and I saw I had launched the "Do you want to shut down?" dialog box. So I clicked CANCEL and continued writing. Both times I could tell that the computer was still on, and I could just barely see my desktop, only very dimly. Scary stuff!

i was having the same problem and i was able to fix it by:

- system prefs
- energy saver
- options then deselect "reduce the brightness of the built-in display when using this power source" (make sure you adjust this for both the settings for the battery and the power adapter")

hope that helps
~ Heidi

It remains unchecked and it still does dim.

J. Morris,

I have to ask, have you installed any screen savers? What other software has been installed? Have any other user accounts been created? Do you have the computer set to automatically log in when you turn it on?

I have not installed an screen savers. No one else has an account on the computer. It is set to automatically login, as is the default when I got the computer (and it did not dim before with this setting). Installed programs included: Adobe Photoshop CS2, FileMaker Pro, Microsoft Word, Excel and PowerPoint.

One option to try would be to change the login settings so that you are not automatically logged in when you start up to the computer. After you make this change, log out, log back in, toggle that display sleep setting on then back off and check the result.

Something else that might be worth a try...

First, I'm not sure what preferences, if any, will need to be reset after this. Also, I have not done this and do not know the result. As always, backup your stuff.

1. Go to the folder ./Library/Preferences/SystemConfiguration (not your Library folder but the one at the root level of your hard disk).

2. Drag the file named com.apple.PowerManagement.plist to the trash. You will be prompted to enter your admin password when you do this.

3. Restart.


MacBook/2.0/1GB/CTO (white); PowerBook G4 12/1.33 Mac OS X (10.4.6) Airport Express, iPod mini, iPod nano

Changing the login settings did not do the trick. But deleting com.apple.PowerManagment.plist has seemed to fix the problem. It was located in ./Library/Preferences/ and not SystemConfiguration on my machine however.

I went into Energy Saver and the defaults were now in place. So OS X must have recreated the perference file, maybe the other one was corrupt somehow?

Thank you for your help Jim R.

My very new bacbook circa 13 hours is doing this

energy saver profile is for 15 min, automatically adjust and dim turned off
deleted the preferences and had no luck, its keeping them but well just dims when it want (did it whilst typing)

as thr baclight turns off my only option is to use f1 and f2 to adjust to hope it activates backlight, or shut and open and wake from sleep

is there any more ideas what to do (ok its just done it agin) the mac looks nice when it works but i want to see for more than 2 minutes

Oh and here's my power settings:

System Power Settings:

AC Power:
System Sleep Timer (Minutes): 25
Disk Sleep Timer (Minutes): 180
Display Sleep Timer (Minutes): 15
Automatic Restart On Power Loss: No
Wake On AC Change: No
Wake On Clamshell Open: Yes
Wake On LAN: Yes
Display Sleep Uses Dim: No
Battery Power:
System Sleep Timer (Minutes): 25
Disk Sleep Timer (Minutes): 180
Display Sleep Timer (Minutes): 15
Automatic Restart On Power Loss: No
Wake On AC Change: No
Wake On Clamshell Open: Yes
Display Sleep Uses Dim: No
Reduce Brightness: No

No worries, i tried that too but my setting was already that.

For me it definately was a hardware issue, another one is being shipped out to me and they are collecting my dud!

They sorta realised it was bad when during everything i was like "nope sorry i can't see the screen"