1. The problem statement, all variables and given/known data Assume that the tungsten filament of an incandescent [tex]100 W[/tex] light bulb can be considered as a black body. Estimate the percentage of the irradiated energy in the visible spectra. The effective area of the filament is [tex]100 mm^2[/tex]. There are 3 more questions in the exercise that I'll try to do on my own. 2. Relevant equations Not even sure. 3. The attempt at a solution What I really think I need is the expression of the function [tex]u(\lambda )[/tex] that we can see in the picture http://en.wikipedia.org/wiki/File:Wiens_law.svg. Otherwise than this, I've attempted to use Wien's displacement law to see what wavelength of light is most created by the filament. But it's not a good idea, I couldn't even make a percentage guess. For instance if I get a wavelength of the kilometer order (I know I should get infrared which is somehow shorter), I'd have no idea about what would be the percentage of energy irradiated in the visible spectra. I'm just out of ideas. I'd like to listen to you guys, what would you do?