I use xbacklight to change brightness. Although, I thought it would be fun to write an applet to change brightness.

I wrote it and works fine for me.

At first, "./autogen.sh -> ./configure -> make -> make install" hasn't worked fine yet so you need to install manually :( I'll fix it.
Anyway, it requires lxpanel and libXrandr development libraries. If you are using Fedora you need to install libXrandr-devel and lxpanel-devel packages. I tested it on Fedora 16.

1. Build
$ ./autogen.sh
$ ./configure
$ make
$ make DESTDIR=/path/to/temporary install

2. Install
Check where lxpanel applets and icons are installed. For example, Fedora(x86_64) installs plugins are in /usr/lib64/lxpanel/plugins/ and icons are in /usr/share/lxpanel/images/
Then copy files
# cp /path/to/temporary/usr/usr/lib/lxpanel/plugins/backlight.so /usr/lib64/lxpanel/plugins/.
# cp /path/to/source code directroy/data/bklight.png /usr/share/lxpanel/images/.

3. Add applet
Add "Backlight Control" to your lxde panel

It source code is in my github repogitory.

btw, quick look xbacklight. It is a simple tool but is useful. There is some options to change brightness. The "set" option to set brightness given percentage. The "inc" and "dec" options to increment/decrement given percentage from current setting.

[masami@rune]~% xbacklight -h
usage: xbacklight [options]
  where options are:
  -display <display> or -d <display>
  -set <percentage> or = <percentage>
  -inc <percentage> or + <percentage>
  -dec <percentage> or - <percentage>
  -time <fade time in milliseconds>
  -steps <number of steps in fade>

Ok, let's see how it works. It's really easy, isn't it?

[masami@rune]~% xbacklight   
[masami@rune]~% xbacklight -set 50
[masami@rune]~% xbacklight -get   
[masami@rune]~% xbacklight +20 
[masami@rune]~% xbacklight        
[masami@rune]~% xbacklight -dec 50  
[masami@rune]~% xbacklight