Computational fluid dynamics coupled with the radiant transport equation was used to simulate oxalic acid photodegradation in a TiO2-coated glass-bead photoreactor irradiated by end-emitting optical fibre (EEOF) or side-emitting optical fibre (SEOF) bundles. Light irradiance distributions in the photoreactor were modelled for specular. partially specular and diffusive reactor wall reflectivities with specularly reflective reactor walls best representing the experimental data. The light irradiance distribution for the SEOF bundle was found to be more uniform along the fibre length than for the EEOF bundle. Under the experimental radiant power input (108 mW) the EEOF and SEOF bundles exhibited similar oxalic acid photodegradation rates. However, the developed model demonstrated that at incident radiant power more than ten times greater than the experimental power used, a uniform light distribution gave faster oxalic acid photodegradation with the relative improvement of the SEOF bundle over the EEOF bundle increasing with increasing radiant power. This was attributed to increased electron-hole recombination in photocatalytic surfaces close to the EEOF tip, induced by the increased light irradiance in this region. The model also demonstrated a constant light irradiance profile along the length of a SEOF bundle giving an improved photocatalytic performance when compared to linear or exponentially decaying light profiles. (C) 2009 Elsevier Ltd. All rights reserved.