It has been recently suggested by several investigators that the accelerated charged particles provide the energy of the optical flare by the ionization loss process. We have examined this mechanism assuming different forms of the spectrum of the accelerated protons at lower chromosphere. The flux and the energy spectrum of protons of energy 0.1–100 MeV have been calculated at successive heights, from 103 to 40 × 103 km from the solar surface taking into account the ionization loss, pitch angle distribution and density distribution of the neutral and ionized hydrogen in the chromosphere and lower corona. Hence the energy spectrum of the protons escaping from the Sun and the amount of energy dissipated in the solar chromosphere are computed. Comparing the calculated results with the observational data on the solar event of September 28, 1961 it is found that the ionization loss of the accelerated protons and heavier nuclei in the solar atmosphere may supply a significant part of the energy of the optical flare assuming that the fraction, f, of magnetic tubes of force extending out of the solar atmosphere is about 1 %. The accelerated proton spectrum in the form of power law in kinetic energy seems to be the most appropriate form. In the event of September 28, 1961 best estimates are made on this basis of the total number and the energy spectrum of protons at injection, the flux and energy spectrum of escaping protons and the energy dissipated in the solar atmosphere by the accelerated ions. It is found that the possible range of variation of the height of injection level hardly affects the total energy dissipated. The high variability of the intensity of protons released by the Sun is interpreted in terms of the variations of the parameter, f, determined by the configurations of the magnetic field lines.