[en] The physical conditions in flares of the UV Ceti type stars are analyzed and the nature of their optical emission is determined. It is assumed that the optical flare takes place in the transition layer between chromosphere and photosphere where the atomic concentration is in the range of 10¹⁵ to 10¹⁷ cm^-3, and that hydrogen radiation plays an important role in the flare luminescence. Hydrogen gas of this concentration is considered at temperatures between 5.000 and 20.000. Radiation of this gas at T<10.000 is composed of hydrogen atom radiation and negative hydrogen ion radiation. For T>10.000 the flare zone is partially opaque to continuous spectrum. Various gas radiation parameters, such as color indices U-B, B-V and energy distribution in spectrum, have been calculated. The calculated values are generally consistent with the observed data. It is concluded that the optical flare is in essence a secondary phenomenon caused by an ''explosion'' in the upper atmospheric layers. Radiation generated directly by the ''explosion'' can appear during the first flane stage. The flare energy problem and question of analogy between the stellar and solar flares are briefly discussed