Backlight

check if X can set backlight

xbacklight -set 10

if it can, then inability to change backlight from keyboard or gui may be Scan Code or desktop environment problem.

Else creating /usr/share/X11/xorg.conf.d/20-intel.conf file with following content has worked.

Section "Device"
        Identifier  "card0"
        Driver      "intel"
        Option      "Backlight"  "intel_backlight"
        BusID       "PCI:0:2:0"
EndSection