Here is the command I use in order to change my laptop screen’s brightness:
$ sudo sh -c "echo -n 4 > /sys/class/backlight/acpi_video0/brightness"
If the value which comes after “-n” is small, this means that you get a darker screen, if you want a blazing screen that value should be bigger. You can see the max value of n in the following file:
/sys/devices/pci0000:00/0000:00:01.0/0000:01:00.0/backlight/acpi_video0/max_brightness
Depending on your system, “acpi_video0” can be different. Look at this directory: “/sys/class/backlight/”