cure for condensation

I've got a 10 inch mirror mounted in a wooden box outside. It's completely covered with aluminum flashing to keep the rain out. It has a door sealed with a foam window weatherstripping so it ought to be bone dry in any rain. So I was surprised to find some condensation on the mirror when I checked it recently. What's the problem here and how do I fix it?
Ed Jones

Hi Ed,

It's condensation of H2O from the air in and out of the box. Try a desicant or heat in the box.

Thanks,
John

If you want to spend a bit more (and avoid Hamster fur on your optics) ...

Use a 12-volt "garden light" setup (to avoid some of the "stray electrons" problems) with two 12-volt lamps wired in series. That will give you 1/4 the wattage for each bulb (or 1/2 wattage for the total) and since the bulbs are running at half voltage they should last almost forever.

The GFI is still a good idea, however. (BTW – in many areas that’s a requirement for new Bathroom or Garage construction so you may already have it).