Or you may try this if the above doesnt work,
bindsym XF86MonBrightnessUp exec xbacklight -inc 10
bindsym XF86MonBrightnessDown exec xbacklight -dec 10
and if needed install xbacklight
sudo pacman -S xorg-xbacklight
Or you may try this if the above doesnt work,
bindsym XF86MonBrightnessUp exec xbacklight -inc 10
bindsym XF86MonBrightnessDown exec xbacklight -dec 10
and if needed install xbacklight
sudo pacman -S xorg-xbacklight