backlight control not working

I just did a clean re-install on my hp laptop. I had been running f18 + kde-4.10. Now I'm running f18 with stock kde. When I bring up powermon, there's a slider for brightness. I can move it, but nothing happens. Screen is too dim. I logged into gnome, and with it's powermonitor, I was able to change brightness. Any ideas? Maybe I should install kde-4.10?