ρ ( ν ) = 8 π ν 2 c 3 {\displaystyle \rho (\nu )={\frac {8\pi \nu ^{2}}{c^{3}}}} [1] ρ ( ω ) = ω 2 2 π c 3 {\displaystyle \rho (\omega )={\frac {\omega ^{2}}{2\pi c^{3}}}} [2]
[1]
[2]