xbacklight worked perfectly in Kubuntu 14.04 but now in Kubuntu 16.04, even when it it installed, I only get this message:
No outputs have backlight property
In my system there is a /sys/class/backlight folder already, so please note that this is not a duplicate of the completely different question in xbacklight: No outputs have backlight property - No /sys/class/backlight folder where the OP very clearly states in the title I do have a /sys/class/backlight folder, so this is not the same case, please read the title of that question where it says explicitly "no /sys/class/backlight folder"