Radiative heat transfer ($P_{\mathrm{net}}=ϵ\sigma A(T_s^4-T_e^4)$)

Transfer of energy by thermal radiation. A diffuse grey surface of area $A$ and emissivity $ϵ$ completely enclosed by isothermal black surroundings has net outward power $ϵ\sigma A(T_s^4-T_e^4)$. This subtracts absorbed environmental radiation from emitted radiation. Other geometries require exchange factors; a gross emitted power is not a net cooling rate.