first of all I hope this is the right place to post this...

When it gets darker my screen (of a desktop computer) is too bright and hurts the eyes. I'm looking for a way to reduce the brightness of the screen temporarily. When searching for possible ways I mainly found solutions which are about special laptops or to change the gamma-setting, but this seems to be a permanent change (also it wouldn't include played videos(?)). Some simply way to change the the brightness would be wonderful, is it possible?

I don't know which details might be needed, I use openSUSE 11.2 with KDE 4.3.1 and nVidia GeFroce 9400GT (driver from the nVidia repo) and my screen is a ViewSonic 703b.

Help is appreciated!