Control brightness from command line

Screen brightness can be viewed and controlled from /proc directory.

/proc/acpi/video/VGA/LCDD/brightness is the file.

First cat the content of the file with cat /proc/acpi/video/VGA/LCDD/brightness

It will show all the supported levels and current level. The current level is the current brightness of your screen.

To change the screen brightness just put any number on that file.
For eg:
echo 10 > /proc/acpi/video/VGA/LCDD/brightness
echo 5 > /proc/acpi/video/VGA/LCDD/brightness
echo 1 > /proc/acpi/video/VGA/LCDD/brightness