Thanks. I am trying the acpi commands atm. Had to install udev. My main user is member of the following groups:
video storage optical audio wheel.
I added this line from the wiki to backlight.rules:
ACTION=="add", SUBSYSTEM=="backlight", KERNEL=="acpi_video0", GROUP="video", MODE="0664"
but...
I run arch with bspwm on a Lenovo a275 using amdgpu drivers and i am very new to linux. I can adjust screen brightness with the xrandr --output MONITORNAME --brightness VALUE command.
This works fine on battery and with the charger connected. But when I plug/unplug the charger the screen dims...