lily@vaio:~$ sudo find /proc -iname "*brightness*"
/proc/acpi/video/GFX0/DD05/brightness
/proc/acpi/video/GFX0/DD04/brightness
/proc/acpi/video/GFX0/DD03/brightness
/proc/acpi/video/GFX0/DD02/brightness
/proc/acpi/video/GFX0/DD01/brightness