Determination of a radiation field in a multilamp photoreactor is rather difficult due to the blockage of light by the neighbouring lamps in the reactor. Shadow zones in the photoreactor caused by the lamp blockage vary according to the different lamp arrangements. In addition, the reactor shape also has an effect on the average light intensity, since light is absorbed by the reactor wall if it reaches the wall. In this study, selected aspects of reactor configuration and lamp arrangement were investigated in order to achieve the maximum average light intensity. A line source with a diffused emission (LSDE) model, which shows sufficient accuracy and simplicity, was selected to simulate the light field in the, test reactor. Simulation indicates that the square and cylindrical reactors with two and four lamps installed symmetrically exhibited superior performance to elliptical and rectangular reactors. For a multilamp reactor, a triangular pitch of lamp arrangement with 33 degrees is recommended for maximum average light intensity.