ABSTRACT Growing phototrophic microorganisms consume the light energy. These microorganisms most often suffer from light deficiency because of exponential decrease in the energy of light passing through an absorbing medium. Therefore, effective distribution of light within the cultures is needed for their intensive cultivation. This is possible in special devices called photobioreactors. The photobioreactors described in the literature are classified into several types according to their geometric features. Their advantages and drawbacks are analyzed. Criteria currently used for comparing various photobioreactors are specified.