xorg-xbacklight or brightnessctl don't work for this imac. on the laptop that was my goto fix before.
on the 2008 imac you gotta use sysfs interface
- check the available interfaces
ls ~/sys/class/backlight/
in my case it was radeon_bl0
sudo vim ~/sys/class/backlight/brightness
it says 255 jeez. im going to lower it to 70
chmod and chown the brightness file so you don't need sudo to edit the file then:
# Increase brightness
bindsym XF86MonBrightnessUp exec --no-startup-id sh -c 'echo $(($(cat /sys/class/backlight/radeon_bl0/brightness) + 10)) > /sys/class/backlight/radeon_bl0/brightness'
# Decrease brightness
bindsym XF86MonBrightnessDown exec --no-startup-id sh -c 'echo $(($(cat /sys/class/backlight/radeon_bl0/brightness) - 10)) > /sys/class/backlight/radeon_bl0/brightness'