The spectral radiance of a black body per unit solid angle is given by:

$I(\lambda ,T)={\frac {2hc^{2}}{\lambda ^{5}}}\,{\frac {1}{e^{hc/\lambda kT}-1}}$

It can also be given as a function of frequency:

$I(\nu ,T)={\frac {2h\nu ^{3}}{c^{2}}}\,{\frac {1}{e^{hc/\lambda kT}-1}}$