[en] The results of studying cathodophosphors on the base of oxysulphides of rare-earth elements and the energy efficiency of cathodoluminescence are given. Lighting and power characteristics of cathodophosphors are presented. As the reference emitters have been used phosphors of the Zh₂SiO₄-Mn type, whose energy efficiency is 7.6% of the ZnS-Ag type (K-75) with an energy efficiency of 21.3%, and of the YVO₄-Eu type with an energy efficiency of 6.4%. Also summarized are results enabling the energy efficiency of inorganic cathodophosphors to be determined by a thermodynamic approach, using such data as formation heat, molecular weight and density