The article presents a simple model for immobilized photocatalytic microreactors following a first order reaction rate with either light independency or light dependency described by photon absorption carrier generation semiconductor physics. Experimental data obtained for various residence times, catalyst thicknesses and photon flux densities proved that the model is capable of describing the reactor performance. The extracted reaction rate constant reveals the intrinsic kinetics as both external and internal mass transport are accounted for. The effect of light is also considered by defining a criterion for neglecting light intensity based on film thickness and absorption coefficient. For the first time k values on the order of magnitude of 101 s−1 are reported. In the end, performance parameters are also derived for the light dependent model for which the internal effectiveness factor reveals both mass transfer and light limitations.