Doryman":31y5v00p said:
C-Hawk":31y5v00p said:
The metal shade transmits heat from the light bulb.
I'm no physicist, but isn't the total amount of heat generated by the light bulb going to be the same with or without a shade? Joe, care to elucidate?
Warren
Warren-
You're absolutely right, the same amount of energy is emitted by the light bulb with or without the shade.
Some of the energy is in the form of radiant energy, the rest in hot air transfered from the inner bulb gasses through the glass and to the air at the surface of the bulb.
This later hot air creates convection currents of warm air starting at the bulb's surface, which rise up from the bottom of the hull where the bulb rests in it's fixture, and where the most dampness accumulates or condenses because it's colder there at the bottom. Moisture is carried up to the top of the cabin where it is vented or lost to incidental air circulation.
As for the radiant part of the energy, much is invisible infra-red heat rays
that move out in all directions from the bulb filament, and the rest is visible light that does the same.
The shade functions to partially absorb these forms of radiant energy and turn them into hot air at the surface of the shade, which then joins the rest of the hot air circulation.
The shade will also reflect some of the radiation down to the hull itself, warming it and making sure no water condenses there in the lowest and coldest part of the boat.
The thinking may also include some reasoning that the shade protects any nearby flammable objects from being heated too much by radiant energy, but prudence would demand a good safe zone around the bulb anyway.
What kind of bulb does the lamp have? A half or hemi-sphere like metal shell that half surrounds the bulb?
Hope this makes sense and is correct to the best of my knowledge and intuition.
Joe. :teeth :thup