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ISSUE: Backlight brightness does not change.

More Detail: Brightness will not change, using both 'System Settings->Screen', or Fn keys (Brightness bar shows and moves, but screen brightness does not change).

Noticed a post about having multiple folders in Sys->Class->Backlight. I HAVE TWO FOLDERS TOO: intel_backlight and acpi_video0.

Using the function keys, alters the value in the acpi_video0's 'Brightness' file - But doesn't actually alter the brightness of the screen.

If I add backlight=vendor in Grub, my function keys then edit the value in the Intel_Backlight brightness file. - But again doesn't actually change the brightness of the screen.

Computer: Fujitsu Siemans Pi2515, Intel Integrated Graphics, No HDD partition.

Already Tried:

Many thanks for reading, I understand this problem may need a bit of a Linux pro to sort. If anyone up for the challenge I'll spend any amount of time being walked through this, posting results. Don't want to give up here!

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I have a very similar problem with a Toshiba Portege R935 in 12.04. I can't change the brightness after suspending and resuming.

The Grub line didn't help either (actually with that line, it stopped working even before suspending).

In the meantime, I discovered this workaround:

  • as root, change the value in sys/class/backlight/intel_backlight/brightness. for instance:

    echo 2937 | sudo tee /sys/class/backlight/intel_backlight/brightness
    

Warning: these values are not between 0 and 7 (as the ones in the other directory), but between 284 and 4539, or something like that.

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1  
One-liner that doesn't require su root? Yep, here you go: echo 2937 | sudo tee /sys/class/backlight/intel_backlight/brightness – Nathan J. Brauer Mar 18 '15 at 15:28

If you tried everything else and your system's backlight non-responsive and if you are using an Intel 915 or descendent thereof ("945GSE", etc.) then your issue may be backlight inversion confusion on gen4.

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-1 The link went offline. It's essential content should have been cited here in the first place. – David Foerster Dec 31 '15 at 8:42

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