root@vaio:/home/lily# cat /proc/acpi/video/GFX0/DD04/brightness
levels:  100 100 4 16 28 40 52 64 76 88 100
current: 0
root@vaio:/home/lily# echo 76 > /proc/acpi/video/GFX0/DD04/brightness
root@vaio:/home/lily# cat /proc/acpi/video/GFX0/DD04/brightness
levels:  100 100 4 16 28 40 52 64 76 88 100
current: 76
root@vaio:/home/lily# echo 16 > /proc/acpi/video/GFX0/DD04/brightness
root@vaio:/home/lily# cat /proc/acpi/video/GFX0/DD04/brightness
levels:  100 100 4 16 28 40 52 64 76 88 100
current: 16
root@vaio:/home/lily# echo 100 > /proc/acpi/video/GFX0/DD04/brightness
bash: echo: write error: Invalid argument
100
root@vaio:/home/lily# echo 88 > /proc/acpi/video/GFX0/DD04/brightness
root@vaio:/home/lily# cat /proc/acpi/video/GFX0/DD04/brightness
levels:  100 100 4 16 28 40 52 64 76 88 100
current: 88