Patrick and Pj,
The phenomenon you describe sounds similar to one that is relatively common in all the high-output Mag incandescent mods that I've handled. This is especially true of mods which use an aluminum reflector. This is in fact a clue to what's going on. It is condensation because when the light bulb is first fired, everything in the head is cold. Since the Mag replacement reflectors and the SF reflectors are solid aluminum, they remain significant sinks for heat. As the extremely cramped environment of the head heats up, the air temperature rapidly zooms out of the range that we are familiar with even in the hottest of climes. Bulbs typically attain 400-600F surface temperature and that heats things up fast. As the surface of the reflectors is, well, reflective, even radiational heating will take some time. In the mean time, the air gets superheated and the moisture holding capacity actually drops, not as relative humidity but in weird measures like grains per cubic foot or pound. This causes temporary condensation on the reflector. As I have done runtime tests from 18-70 minutes with high-power bulbs, you can see the condensation form then eventually disappear as the reflector gets hot enough to prevent condensation. At this point the reflectors are so hot they can burn the skin.
Another point to keep in mind is that besides air (and its component gases) and water vapor, there is nothing else in the headspace. Sure, there might be a few ppm of solvents or other moderate volatiles but not enough to cause what you are seeing. This implies that it must be either air or water that is depositing.
I have also run the test with the Mag facecap loose such that I can whip it off during a test and when I do this, the superheated air escapes and the condensation dissipates rapidly.
If you had the opportunity to purge the headspace with nitrogen, helium, argon or some other dried gas, you would not see this effect. In fact, this is why high-end binoculars and deep cold water dive watches are charged with one of these gases.
I tried looking for my college chemical engineering texts to see if I could find psychrometric charts for air/water vapor but my basement was a mess. Sorry.
Wilkey
