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I have a late-2011 15" MacBook Pro running Mavericks. I normally don't reboot my computer and can leave it logged in for days on end. I decided to reboot my computer and when it was booting, the screen backlight would not turn on, although I could faintly see the login screen where I could type my password.

I tried resetting the SMC, but that didn't do anything.

I also tried resetting the PRAM, but I'm guessing because I have a firmware password and the computer is FileVault-encrypted, instead of actually resetting the PRAM, I have the prompt to type in my firmware password (also really faint since the backlight isn't on). If I type in my password, it boots into the recovery partition and the display backlight finally turns on. However upon reboot, the backlight will stop working again.

I tried using Disk Utility to check for any permissions/disk errors but didn't find any issues.

I haven't tried logging in with the faint login screen, only because I can't find my mouse cursor to select my account to login. I've tried rebooting with both the power cable connected and disconnected.

How can I get my screen backlight to turn back on again?

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    After clicking around a ton in the dimmed login screen I was able to finally click on my user account and login. After boot the screen backlight did turn on. When I tried rebooting, the backlight finally did turn on without any issues. I also tried a full shutdown and poweron and the backlight still turned on. I guess the successful login fixed the issue, but perhaps someone has some idea as to the cause? – reedog117 Jan 14 '14 at 14:27
  • Typically the PRAM reset will resolve this odd issue, though in your case you're correct in that your firmware password would prevent that. If it were to happen again I would boot to the recovery partition, disable the password, reset the PRAM and see if the issue is resolved. I wish I could give you a definitive answer but in my experience as a technician it's usually felt like an odd software bug that gets reset when the PRAM is reset. – Mr Rabbit Jan 14 '14 at 15:39
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I had the same problem. The dimmed screen happened during the reboot after turning on file vault. I was able to solve the problem by going into a darkroom. This allowed me to see the cursor and to log in to an account. Once I logged in the back light came on and everything was fine.

I had first tried to solve the problem by zapping the pram. This had no effect.

  • I am so surprised that no one agree with this solution! I hit this issue today when updating 10.10.3 and use the same solution it works. – asksw0rder Apr 10 '15 at 1:36
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If you put some light on back through apple logo you can see the logging screen more clearly!

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System Preferences > Displays : Uncheck Automatically adjust brightness ..that's what fixed it for me :)

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