After installing Ubuntu on my ThinkPad T510, the GDM screen and GNOME session would always start at 100% brightness.
I quickly found out, that this can be controlled via gnome-power-preferences, but I'd like to have GDM and the GNOME session follow the global backlight setting (ie., when I set it during POST, GRUB, GDM, a GNOME session, or on a TTY, I expect it not to automatically change).
So, how can I make gnome-power-manager stop automatically changing my backlight level?
It seems this can only be disabled by editing a gconf setting using gconf-editor or the command line tool gconftool-2 (easier). As GDM is run by a special user (gdm), you got to disable it for the desktop user and that special user:
Run the following from a gnome-terminal:
gconftool-2 --set --type boolean "/apps/gnome-power-manager/backlight/enable" false
This will deactivate the backlight control for your user. Now type:
sudo -u gdm gconftool-2 --set --type boolean "/apps/gnome-power-manager/backlight/enable" false
This will deactivate the backlight control for the user that controls the GDM screen.
You should now no longer see automatic backlight level changes.
In Ubuntu 11.10 Oneiric Ocelot this changed to:
gsettings set org.gnome.settings-daemon.plugins.power idle-dim-ac false
gsettings set org.gnome.settings-daemon.plugins.power idle-dim-battery false
Still not sure how to disable it for the login screen.