lenovo G580 brightness control not working in ubuntu 12.04
I recently purchased a lenovo G580 laptop. It does not have a separate graphics card.
I also installed ubuntu and windows 7 64 bit . Lenovo provided a driver cd for windows 7. I installed all the drivers. The lenovo FN+up and down brightness control works fine in windows 7. But it does not work in Ubuntu. When I press the key combination, the brightness control appears and it shows the brightness is decreasing or increasing, but actually nothing happens. As i am new to linux, I did some search in the forums and found out two solution.
1. changing the etc/default/grub file to modify the entry
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi_backlight=video"
2. changing the XOrg.conf file (which does not even exist in ubuntu 12.04)
None of these worked for me. If you experts have any known solution, please share it with me.