Hi and welcome to the forum 
There is/was a post with your specific problem and hardware here on this forum suggesting that adding the option below to /etc/grub/default and running sudo update-grub is a partial solution.
GRUB_CMDLINE_LINUX_DEFAULT="video.use_native_backlight=1"
The same thread has some links to posts on the arch-linux forums where users have experienced the same problem and have varied success in solving it.