Look at this problem logically. Practically sealed lamp housing, with a drain hole at bottom. Lamp on: air in enclosed space heats and expands, escapes through the hole.
Lamp off: air inside cools down and shrinks in volume, drawing fresh (damp) air into the enclosure. During the early hours, the air cools further and reaches it's dew point. Condensation forms, starts corroding susceptible parts. A continuous cycle of damp air in /condensation/corrosion, then dry air expelled, damp air drawn in...etc.
The corrosion will be due to the electrolytic action of carbonic-acid (CO2)in the condensation, on dissimilar metals, due to the electochemical series; some common metals in order, (more corroded first);
Magnesium, Aluminum, Chromium, Zinc, Cadmium, Iron, Nickel, Tin, Lead, Copper, Silver, Platinum, Gold.
If the bulb base is aluminum/ or aluminised steel, the aluminum corrodes. Unless the condensation is affecting the contacts or wiring, any overheating must be due to the bulb being overwattage for the fitting, since the cap is only a mechanical fastning device*. Voltage? No, unless it's dc, (which can drive electrochemical reactions the other way). Solution? One of the sprays described above, preventing the electrolyte wetting the metal.
Alan
*Bayonet, not the screw fitting type!
Time for a quick name change!
regards,
Neddy Seagoon.
[This message has been edited by Alan Belson (edited 06-08-2005).]
