Comment 8 for bug 752165

I run this command under no-backlight condition on terminal (I still can read my screen under flashlight):
sudo setpci -s 00:02.0 F4.B=00
and my back light is back!
but back light is off again after reboot, need to run that command again :(

All I did was add the setpci command into sudoers file (sudo visudo) so i don't need to type password when running setpci,
and make a new executable file contains that command, then make new startup entry to run that executable file every startup.

Now i have my back light function normally every startup..
Try this guys, who knows it can help you.