I made this working code:

def lightdemo():
    dark = 0
    orig_light_level = float(tux.status.requestOne('light_level')[0])
    speak("Autonomous mode activated")
    while dark == 0:
        current_light_level = float(tux.status.requestOne('light_level')[0])
        if current_light_level <= (orig_light_level-4):
            speak("Hey! Who turned out the lights?")
            dark = 1
    while dark == 1:
        current_light_level = float(tux.status.requestOne('light_level')[0])
        if current_light_level >= (orig_light_level-1):
            speak("Ah, That is much better!")
            dark = 0

And i want to trigger it with the head botton. Can someone show me how? I think you use...

self.tux.button.head.registerEventOnPressed

Yep,

that's it. You should register a function to be called when the button is pressed. In your case something like

    tux.button.head.registerEventOnPressed(lightdemo)

you should also keep your script running with a loop like

    while(not tux.button.remote.waitPressed(10.0, K_STANDBY)):

        pass

which wait until the stand by key the remote is pressed.

See http://gist.github.com/40256 for a complete script that use the remote. I cannot test it right now, but I believe that using the head and flippers buttons is the same (but there is no second argument in registerEventOnPressed and waitPressed).