Comment 37 for bug 429942

The above post helped me to set backlight dimmer on my Asus EEEPC 1101HA, running ubuntu 12.04.
But the commands have to be changed somewhat to actually change the file /sys/class/backlight/psb-bl/brightness

2) chmod 666 /sys/class/backlight/psb-bl/brightness
to give yourself permission to read/write (711 actually only gives execute permission)

3) Using a text editor (I use vi) gives Fsync errors (/sys is not a normal filesystem), so use the shell to write to the "file" instead:
First choose the number, for example 50. The command is:
echo 50 >| /sys/class/backlight/psb-bl/brightness

4) done.