The Stephan–Boltzmann law can be expressed as M ∘ ∘ = σ σ T 4 = N p h o t ⟨ ⟨ E p h o t ⟩ ⟩ where the flux of photons, N p h o t , is given by N p h o t = π π ∫ ∫ 0 ∞ ∞ B ν ν h ν ν d ν ν N p h o t = ( 1.5205 × × 10 15 photons ⋅ ⋅ s − − 1 ⋅ ⋅ m − − 2 ⋅ ⋅ K − − 3 ) ⋅ ⋅ T 3 and the average energy per photon, ⟨ ⟨ E phot ⟩ ⟩ , is given by ⟨ ⟨ E phot ⟩ ⟩ = π π 4 30 ζ ζ ( 3 ) k T = ( 3.7294 × × 10 − − 23 J ⋅ ⋅ K − − 1 ) ⋅ ⋅ T .