On the wikipeida page http://en.wikipedia.org/wiki/Planck's_law_of_black_body_radiation two formula's are given for spectral radiance, I(nu, T) and I(lamda,T). However, I(nu, T) seems to have units of J/m^2 and I(lamda, T) seems to have units of J/s/m^3. My homework question is to show that these expression are equivalent, however the fact that the units don't work boggles my mind. Does each expression represent something different? Can someone please shed some light on this?