The P-1 model which allows to numerically solve the radiation transport equation (RTE) was used to predict the light intensity in an annular photocatalytic reactor. Experimental results on light intensity distribution in a photoreactor were used to validate the P-1 model and a good agreement was obtained. The effect of absorption coefficient, scattering coefficient, wall reflectivity and phase function parameter was investigated on the relative local light intensity. The light intensity decreased rather sharply with the increase in the absorption coefficient, but slightly decreased with the increase in the scattering coefficient. The local volumetric rate of energy absorption (LVREA) increased with the catalyst loading in the region r < 0.06m and the opposite trend was obtained beyond this region. However, the wall reflectivity had very little effect on the light intensity at high catalyst loading. Furthermore, the light intensity is not much influenced by the phase function parameter. (c) 2008 Elsevier Ltd. All rights reserved.