Had some trouble getting xbacklight to work on openSUSE Tumbleweed, so I wrote this simple program that should work around it. Requires root, a workaround can be found at stackoverflow.
The value of the fname variable might need to be changed to the correct path
to your backlight brightness file.
g++ -std=c++11 twbl.cpp
bindsym XF86MonBrightnessUp exec sudo /home/dzejrou/bin/twbl +100 # increase screen brightness
bindsym XF86MonBrightnessDown exec sudo /home/dzejrou/bin/twbl -100 # decrease screen brightness