Re: What is the temperature inside a 100 watt lightbulb?

Your calculations are about right. What you calculated is called the color 
temperature. It's defined as the temperature of a blackbody that has the 
same spectrum as the body itself. A blackbody is a perfect radiator. A 
star comes pretty close to being a perfect radiator, I guess that's why 
you are doing this in astronomy class. The color temperature of a frosted 
100 watt tungsten filament light bulb is at least 2100K, depending on 
manufacturer, operating voltage, frosting, etc. That means that a ball of 
gas in outer space, like a star, would have to be at a temperature of 
2700K in order to radiate light similar to that of a 100 watt lightbulb. 
The temperature inside the lightbulb is tricky because we usually think of 
temperature as air temperature and light bulbs are evacuated to remove 
air. The tiny tungsten (actually, not pure tungsten) filament in the 
evacuated light bulb gets extremely hot, but doesn't burn up because there 
is no air. The filament is at least 2100K, but their is no transfer of 
heat until some of the radiation from the tungsten filament is absorbed by 
the glass of the light bulb as light passes through. Heating a filament by 
passing an electric current through in order to produce light is called 
incandescence. The color temperature of an electric stovetop as it glows 
orange-red, is about 675K, also due to incandescence. I love astronomy, I 
hope you continue learning about it!