PX284 - J1 - blackbody radiation

an ideal absorber and emitter of radiation that absorbs all incident radiation and has an emissivity of $1$ , ie. emits isotopically
for a blackbody in an enclosed space, the energy density of emitted light:

U = \int_{0}^{\infty} U_{λ} d λ = \int_{0}^{\infty} U_{U} d U = \int_{0}^{\infty} U_{ω} d ω

where, $U_{U}$ is the spectral energy density, and $U_{λ} d λ$ is the energy density due to radiation between $λ$ and $λ + d λ$

U_{λ} = \frac{8 π h c}{λ^{5}} \frac{1}{\exp (\frac{h c}{λ k_{B} T}) - 1}