KLcdDimmer
A KDE Panel applet to set brightness of LCD screen
http://klcddimmer.sourceforge.net

Copyright (C) 2006, Lorenzo Bettini, http://www.lorenzobettini.it

Notice that this relies on an external program to get/set the
brightness.

For instance, I've used

SmartDimmer http://www.acc.umu.se/~erikw/program/
NVclock http://www.linuxhardware.org/nvclock/

but it is supposed to work also with others, since you can
configure the applet.

When you run configure, you should pass the KDE root directory
as --prefix (in my system it is /usr).