Aqui está um link abordando especificamente o brilho da tela de configuração abaixo do mínimo :
Diminuir o Backlight abaixo do mínimo - Ask Ubuntu
Open Terminal
Enter the following command:
cat /sys/class/backlight/intel_backlight/brightness
Write down the resulting value (12421 in my case)
Divide value by 6 and write it down (2070 in my case)
Enter the following in the terminal, replacing 2070 with your value:
sudo su -c "echo 2070 >/sys/class/backlight/intel_backlight/brightness"
Close Terminal
For future usage of the last command, open Terminal, press Ctrl and R together, start typing
brightness
. When the last command appears, just press Enter.It works for me on a Samsung NC110 with Ubuntu 12.04.