After updating to Ubuntu 13.04 Raring with the latest updates, adding "vendor=backlight" does no longer resolve the problem.
I did however see entries in /sys/class/backlight/ and echoing numbers to /sys/class/backlight/intel_backlight/brightness affects the brightness.
After adding also "acpi_osi=Linux" to the boot options I can now controll the brightness lever with the keys.
After updating to Ubuntu 13.04 Raring with the latest updates, adding "vendor=backlight" does no longer resolve the problem.
I did however see entries in /sys/class/ backlight/ and echoing numbers to /sys/class/ backlight/ intel_backlight /brightness affects the brightness.
After adding also "acpi_osi=Linux" to the boot options I can now controll the brightness lever with the keys.