I'm trying the following:
The filament inside a 100 W lightbulb has an absorption coefficient of 0.25, and while operating, it is at a temperature of 2,573 K. What's the size of the surface of the filament? (done with Stefan-Boltzmann) At what wavelength does it emit the highest intensity? (done with Wien displacement law). Relative to all emitted radiation, how much power is emitted as visible light (400 nm - 800 nm)?
The last one is causing me trouble. I have been trying to integrate Planck's radiation law for quite some time now, but I can't manage to do it(and neither can Mathematica). Is there another way of doing this?