Vibrofluidized- and multiple fixed-bed photoreactors were compared under identical operating conditions. The comparison was based on the quantum efficiency for the gas-phase photocatalytic oxidation of acetone using TiO2 (Hombikat UV 100). Multiple fixed-bed reactor configurations were used, along with a vibrofluidized-bed configuration. Quantum efficiency decreased in the following order: vibrofluidized bed (8.7%) > fixed-bed granules (6.9%) > fixed film bed (5.9%) similar to fixed powdered bed (5.8%). The increased activity of the vibrofluidized-bed could nut be attributed to enhanced external mass transport, as all reactor systems used in the present study demonstrated negligible external mass transfer resistances. Instead, the increased activity is most likely credited to the effect of periodic illumination phenomenon taking place because of the random motion of catalyst granules in the fluidized-bed and higher light absorption of scattered light. The enhanced activity observed for the granular fixed bed could be related to mechanical activation of TiO2 during the preparation of granules, as well as to increased light absorption. A maximum of acetone oxidation rate with respect to humidity level was observed. Even at high humidity levels, ultrasound did not affect the rare of gas-phase acetone oxidation. A model has been developed to quantify the absorption of light in a fluidized-bed photoreactor. The model takes into account absorption and single-light scattering and accurately describes the dependence of acetone oxidation rate on the quantity of TiO2 granules in the vibrofluidized bed.