If you do not have xenons it could be this:
From what I can make out, it increases or reduces the intensity of your headlights depending on what your are doing eg. stopped at lights - low intensity, driving at high speed - high intensity, it may even lower the intensity when you are passing cars, I'm yet to work it out. There's something you can try on the weekend.
P.S If you have "aussie compliance" mirrors they will not defog.