This tip came from the current issue #59 of Full Circle Magazine. There are no brightness controls in Gnome GTK3.x I'm running Ubuntu 11.10 under the Gnome Classic desktop. It fixed an aging CRT monitor I have and use in one of my rigs. Many thanks ! Enjoy.
Q: When I try to reduce the brightness on my laptop using System Settings, it doesn't change.
A: Open a Terminal, and enter this command:
xgamma -gamma .5
You can try different values than .5, to see what works for you. ( .8 works great for my monitor. )
The other available values are:
usage: xgamma [-options]
where the available options are:
-display host:dpy or -d
-quiet or -q
-screen or -s
-gamma f.f Gamma Value
-rgamma f.f Red Gamma Value
-ggamma f.f Green Gamma Value
-bgamma f.f Blue Gamma Value
If no gamma is specified, returns the current setting