The quantum yield of fluorescence and triplet state of the primary electron donor (P) in reaction centers of the photosynthetic bacteria under reduction conditions (quinon - Fe complex is reduced) are discussed. The kinetics of the reversible electron transfer in ion radical pair [P+ primary acceptor -.] are considered by means of the ordinary kinetic equations and of the nonequilibrium spin-density operator method. It is shown, that present experimental data is not sufficient to find the value of energy (delta E) dissipated in the process of primary charge separation. The range of admissible values delta E can be defined on the base of the temperature dependence of the P fluorescence under reduction conditions.