Comment 33 for bug 779166

I have same problem..
Mine is Acer Aspire 4736 with Intel GMA 4500M.
Linux - 2.6.38-8-generic #42-Ubuntu SMP Mon Apr 11 03:31:50 UTC 2011 i686 i686 i386 GNU/Linux

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.