Comment 3 for bug 773820

Look at bug 518002 for a workaround. And please also test whether it is (half) fixed with the newest kernel from http://kernel.ubuntu.com/~kernel-ppa/mainline/daily/current/ .

There are two issues here:
the brightness controls do not actually work
the initial brightness with some kerenels is zero

The initial brightness is not zero anymore on 5635Z, might be the case for you, too.