Jan changed bug 109178
What Removed Added
Resolution NOTOURBUG FIXED

Comment # 11 on bug 109178 from
Just for the sake of record I found the solution:

The (UEFI based) kernel creates /sys/firmware/efi/efivars with the variable:
KBDBacklitLvl-5af56f53-985c-47d5-920c-f1c531d06852

The set immutable flag can be disabled with:
chattr -i
/sys/firmware/efi/efivars/KBDBacklitLvl-5af56f53-985c-47d5-920c-f1c531d06852

After that the variable can be altered from 00 - 03:
echo 0700000002 | xxd -p -r >
/sys/firmware/efi/efivars/KBDBacklitLvl-5af56f53-985c-47d5-920c-f1c531d06852
(GUID dependent on the manufacturer)

00 - Backlight off (always)
01 - Backlight on DIM level (by low ambient light; detected by light sensor)
02 - Backlight on NORM level (by low ambient light)
03 - Backlight on FULL level (by low ambient light)

Inspired by: 
https://bugs.launchpad.net/ubuntu/+source/gnome-settings-daemon/+bug/1203592


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