Comment 12 for bug 863038

I ran gnome-control-center from terminal and activated screen-cc-panel (I am running desktop system without battery)
Got this warining:

(gnome-control-center:5897): screen-cc-panel-WARNING **: Error getting brightness: GDBus.Error:org.gtk.GDBus.UnmappedGError.Quark._gsd_5fpower_5fmanager_5ferror.Code0: gsd-backlight-helper failed: No backlights were found on your system

From http://bazaar.launchpad.net/~ubuntu-branches/ubuntu/oneiric/gnome-control-center/oneiric/view/head:/panels/screen/cc-screen-panel.c, it seems like

set_brightness_cb (GObject *source_object, GAsyncResult *res, gpointer user_data) is called. Is it necessary to call this method on a system with only ac-power?