lily@vaio:~$ cat /proc/acpi/video/GFX0/DD04/brightness
levels:  100 100 4 16 28 40 52 64 76 88 100
current: 0
lily@vaio:~$ sudo sh -c "echo 76 > /proc/acpi/video/GFX0/DD02/brightness"
lily@vaio:~$ cat /proc/acpi/video/GFX0/DD04/brightness
levels:  100 100 4 16 28 40 52 64 76 88 100
current: 0