1. A group's influence The power radiated by a body is equal to :P=εSσT4 with : ε : emissivity, σ = 5.67.10-8 W.m-2 K-4, : S : surface, T : temperature in Kelvin. Distinguishing Pm the power radiated by heavy walls and Pl the power radiated by light walls, and taking the same ε for all walls, we have (figure 1):