  A critical review of the obscure nature of the contribution of spin energy to
the energy of the electromagnetic field is presented. It is proposed that the
total energy of photon h\nu comprises of kinetic and spin parts each equal to
h\nu/2. Classical magnetic field is reinterpreted as angular momentum flux of
photon fluid. The black-body radiation law is revisited in the light of new
significance of the zero-point energy proposed here.
