WARNING: This project is considered orphaned since the 8th of March, 2023. Use is heavily discouraged until such a time that it is adopted by another developer.
May be it is worth consider alternatives like brightnessctl.
Moreover brightnessctl allows to control brightness of external monitor, not only laptop screen:
I'd like to configure the brightness of an external monitor
Use the ddcci-driver-linux kernel module to expose external monitor brightness controls to brightnessctl.
light is orphaned at the moment:
May be it is worth consider alternatives like brightnessctl.
Moreover brightnessctl allows to control brightness of external monitor, not only laptop screen: