Backlight

sysfs

By default, the backlight uses the sysfs backlight interface. This should work out of the box on most laptops.

ddc/ci

With DDC/CI, we can control the backlight on regular monitors. Though a lot of monitors have an incomplete implementation of DDC, usually omitting input switching, backlight control is usually implemented.

Enable i2c-dev

DDC/CI uses i2c, so you need to enable the i2c module. This can be done with modprobe i2c, or permanently on Arch with this file:

i2c-dev

User permissions

Unpriveleged users don’t have access to i2c by default, so you need to add your user to the i2c group:

sudo usermod -aG i2c "${USER}"

Log out/reboot

Adding your user to a group requires logging out of your user session, so either log out or reboot to load the i2c kernel module if you didn’t modprobe it.