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On Lenovo T520 combination Fn + Home/End for increasing/decreasing screen brightness works perfectly out-of-box but with the step = 3. It's too coarse (HW values are 0..15).

How to change the step to 1?

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One way to change the brightness to individual settings is to use your console. So open a terminal (e.g. gnome-terminal) and:

  1. Find where your system saves brightness settings: sudo find /sys /proc -name brightness. Usually they can be found in /proc/acpi/video/*/*/brightness, where * is some directory which depends on your graphics card. On my system I find the brightness settings at /sys/devices/virtual/backlight/acpi_video0/brightness.
  2. If the find command produces no output, check if the video kernel module was loaded: lsmod | grep video should output something like video 18612 0.
  3. Now check what is contained in the files the find command found: cat $DIR, where $DIR is the directory from find output. Sometimes you will only find a number and sometimes some numbers (levels) and the actual setting.
  4. Change brightness setting: echo $somenumber | sudo tee $DIR, where $somenumber is an integer and $DIR the directory from the output of find.
  5. When the command was successful executed, you will notice a changed brightness.
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on my T520i, Ubuntu 12.04, it's found in /sys/devices/pci0000:00/0000:00:02.0/backlight/acpi_video0/brightness, and it changes brightness but we still need the finer step on the keyboard shortcut :(

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ups, seems like i cannot edit that file even with sudo?! – pyc Apr 14 '12 at 14:53

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