Comment 82 for bug 872652

I'm new to Ubuntu, I switched from Windows a while ago. I had this problem as well, and I am using an Emachines E525 Laptop. I don't know if this will work for every computer, or if it's just a temp. fix, but I got a bright light to see the screen then did these steps.
1. Opened Terminal
2. Typed in sudo su
3. Entered my password
4. Typed in setpci -s 00:02.0 F4.B=00
5. Then I hit enter.
For me this set the back light to full brightness, but when the computer gos into sleep mode the back light is off again.
This is the URL in which I got the information. ubuntuforums.org/showthread.php?t=1742575
I hope this helps a little.