The coefficient of transformation of the kinetic energy flow of air particles into the luminous flow is obtained from fireball observational data. The coefficient is dependent only on the fireball velocity over a wide range of fireball parameters. The coefficient values cannot explain the observed ablation of fireball-generating bodies for velocities under 20 km/s. The flow of air particles is probably the main source of the heating of the body in this case. For velocities over 40 km/s the fireball radiation flow to the body is substantially less than the flow to the outside space. The evaluation of the classical fireball luminous efficiency is still largely an indefinite procedure on account of the body fragmentation.