I installed Ubuntu and KDE too on my MacBook Air 4,2, but I realised I cannot change brightness in KDE. In Unity, it works without problem. Other keyboard keys works properly, sound, play, etc., but I cannot change brightness in KDE. I tried KDE4.8.4 and KDE4.9 beta. Thx
I have laptop brightness buttons working. If I wouldn't I'd play with
files (do You have them - or some similar files there?). See what is written there - some shell commands.
Also in the old days bright could have been controlled with:
but now the mechanism is changed.