Photocatalytic purification of indoor air requires devices that are compact and ensure good contact between the air flow and the photocatalyst-coated material with a minimal pressure drop. These three conditions lead to materials-destined to be coated by a photocatalyst-having complex shapes. Accordingly, modeling becomes essential in optimizing the irradiance of the photocatalytic support, which obviously is a factor of paramount importance. We present here a methodical strategy to optimize irradiance on a regularly folded and a honeycomb-shaped material. The first step was to calculate the irradiance on a planar material. The surface of the UV lamp tubes was modeled as an ensemble of elemental lighting sources emitting according to a Lambert law. After the validity was verified by irradiance measurements, similar calculations were performed for a folded and a honeycomb-shaped material, using appropriate geometrical parameters. Using an experimental design (Doehlert matrix), the effects of the interval between the lamps, the distance between the lamps and the material, and the geometrical characteristics of the folds or the honeycomb cells upon the homogeneity and value of the irradiance were calculated. Finally, a multicriterion analysis was employed to determine the configuration producing optimal irradiance. The methodology can easily be applied to UV lamps and reactors having dimensions different from those used in our calculations. (c) 2007 Elsevier B.V. All rights reserved.