The human body radiates energy as infrared light. The net power radiated is the difference between the power emitted and the power absorbed: P net = P emit − − P absorb . Applying the Stefan–Boltzmann law, P net = A σ σ ε ε ( T 4 − − T 0 4 ) , where A and T are the body surface area and temperature, ε ε is the emissivity, and T 0 is the ambient temperature.