Comment 19 for bug 415023

About you two solutions, but first... thanks

- gnome-power-manager also change the brightness after couple of minutes of inactivity. So it's not only the keys I think

-the xrandr --output LVDS --set BACKLIGHT_CONTROL combination is not working for me because there is no such option as BACKLIGHT_CONTROL (check with xrandr -v --verbose)

You get an error like
  X Error of failed request: BadName (named color or font does not exist)
  Major opcode of failed request: 149 (RANDR)
  Minor opcode of failed request: 11 (RRQueryOutputProperty)
  Serial number of failed request: 25
  Current serial number in output stream: 25