Backlight brightness

1. Backlight name (of the directory) depends on the graphics card model:

   ls /sys/class/backlight/

2. Brightness setting is set by writing a number to brightness. Attempting to set a brightness greater than the maximum results in an error:

   echo 5 > /sys/class/backlight/radeon_bl0/brightness

   Maximum brightness can be displayed by reading from max_brightness (often 15):

   cat /sys/class/backlight/radeon_bl0/max_brightness

Adapted from: Arch wiki