I recently started using a window manager (XMonad) and am enjoying it. The only issue is I have to reconfigure a lot of the the function keys (volume, brightness, etc) to do what they're supposed to do. I've been able to figure out everything except for the brightness.
All the solutions using xbacklight or xrandr I've found online seem to do absolutely nothing. For instance,
xbacklight -get gives no output.
I'm running Ubuntu 16.04 on a Dell xps 13.