I just installed Lubuntu 13.04 on my Acer Aspire One 532h and can't get the screen to automatically dim when the computer is idle. Manual dim works via the keyboard. In the preferences for the Xfce Power Manager I set to reduce screen brightness to 20% after 12 seconds of idleness (in battery mode), but nothing happens, even after reboot. The 'Monitor power management control'-option in the General-tab is ticked. I already uninstalled Xscreensaver since I read this could be a solution but it didn't help..