N_{ν} = \frac{8π}{c^{3}} \frac{ν^{2}}{e^{x} − 1}

F_{ν} = \frac{2π}{c^{2}} \frac{hν^{3}}{e^{x} − 1}

N_{λ} = 8π \frac{λ^{−4}}{e^{x} − 1}

F_{λ} = 2πc \frac{hcλ^{−5}}{e^{x} − 1}