Photoreactors are of great importance and their design is very difficult because of the multiphysics nature and the nonuniformity of light intensity inside it. The radiative transfer in the participating media is performed using the finite volume method (RIM) and the models of radiation are verified and discussed for a wide range of optical thickness in the absorption and scattering medium. An iterative method of solving the radiation transport equation, which is the same as the method of solving flow, heat and momentum transfer is presented. A revised model for the lamp and the quartz sleeve, which is simplified to be a boundary wall with reflection, is proposed. The predicted profiles of light intensity agree well with the experimental data in the photoreactors. The model and methods verified in this contribution can be used as a tool for the design and scaling-up of photoreactors. (C) 2011 Elsevier Ltd. All rights reserved.