alt.sci.physics

"eric h" wrote in message
news: @ ...
> Hi,
>
> Trying to find this out for a project (not a school one).
>
> I've been looking all over the place for this information and it just
> doesn't seem to exist.
>
> We all know that incandescent lightbulbs get very hot. Most of us
> know that the Easy-bake oven used to use lightbulbs to cook food.
>
> But how hot does a 100 Watt lightbulb actually get, if you assume
> perfect insulation around it?
>
> I've read that the filament "burns" at 1722 F, but that doesn't sound
> right.
>
> Any ideas?
>
If you assume a perfectly insulated space, you limitation to the temperature
will be only when the bulb burns out.

The bulb cools itself by warming gasses, which then travel to the sides of
the bulb and release the heat to the glass, hence to the atmosphere. As the
insulated room warms up, the glass will also warm, reducing the cooling
capacity of the bulb. This will eventually increase the temperature of the
filament, which will increase its resistance. The resistance increase will
mean that more heat is released by it, further increasing its temperature,
until it finally burns out.

The bulb temperature probably doesn't have to reach the normal filament
temperature to make the cooling cycle break down sufficiently to overheat
the filament. I'm not sure just how hot it would get.

I would expect that if you had perfect insulation, that the bulb would last
a lot less than the 1000 hours it was designed to do.

I don't know what temperature that happens at. It will vary a bit from bulb
style and manufacturing process and the age of the bulb.

Michael