Subsequently, the performance of the WLE system was evaluated versus the external irradiation. This was done in the exact same reaction vessel, just using an external lamp instead of the WLE. The comparison was also done normalized to the photon flux density determined by actinometry as mentioned above. Figure shows the results of this comparison, expressed again as the initial aniline formation rate. As already mentioned, the reaction rate in the WLE system scales linearly with the light intensity over the whole light intensity range studied. The maximum observed reaction rate was 39.4 mM h -1 which equals a space-time-yield of almost 88.1 g L -1 d -1 . Considering the electrical power used in this case (57 W), this corresponds to a photochemical space time yield (PSTY) of 0.83 mmol day -1 W -1 . Despite the fact that this reaction requires 6 photons per turnover and the relatively low quantum yield, this is still a demonstrated PSTY orders of magnitude higher than many conventional photochemical reaction systems (Table ). of the photon flux density (qp). Reaction conditions: 365 nm, 10 mM nitrobenzene start concentration, photocatalyst 2 g L -1 TiO2, solvent: isopropanol, room temperature. The dotted lines represent a simulation using our kinetic model. The results obtained with external irradiation are different, even under otherwise identical conditions. Initially, up to a photon flux density of about 25 µM s -1 , comparable reaction rates to the WLE system were observed. However, at higher light intensities, the reaction rate no longer increases linearly with the photon flux but increasingly shows diminishing returns. As the WLE system does not show this limitation, there is an increasing divergence between both systems, at the highest light intensities studied for external irradiation this culminates in a doubled reaction rate in favor of the WLE system.