Hello, My question is in regards to Planck's Law and a blackbody: For the single lambda case I can readily find the spectral exitance. Alternately, if I substitute to create an integral in the form of x^3 / (e^x - 1) and integrate over all lambda, I reach Stefan-Boltzmann. No problems there, but I am really interested in finding the (average?) spectral exitance over a small, finite spectral band. Any tips on how to go about this? Thanks in advance.