  The fermion spin-flip conversion f_L -> f_R + gamma is considered, caused by
the difference of the additional energies of the electroweak origin, acquired
by left- and right-handed fermions (neutrino, electron) in medium. An accurate
taking account of the fermion and photon dispersion in medium is performed. It
is shown that the threshold arises in the process, caused by the photon
(plasmon) effective mass. This threshold leaves no room for the so-called
``spin light of neutrino'' and ``spin light of electron'' in the real
astrophysical situations.
