Xbacklight

Adjust the screen backlight from the commandline.

Documentation

man xbacklight

https://man.archlinux.org/man/extra/xorg-xbacklight/xbacklight.1.en

Install

pacman -S xorg-xbacklight

Usage

xbacklight -set 40

Troubleshooting

Wrong Display

If xbacklight is unable to determine the display (or chooses the wrong one), you can configure the correct one in your Xorg.conf

# /etc/X11/xorg.conf

Section "Device"
    Identifier  "Card0"
    Driver      "intel"
    Option      "Backlight"  "intel_backlight"  # <-- /sys/class/backlight/${DIRNAME}
EndSection