Different designs for photocatalytic wastewater treatment were compared with a new benchmark measure, photocatalytic space-time yield. This benchmark is the ratio of the reactor space-time yield to the standardized lamp power, defined as the volume of water treated for each kW lamp power per volume of reactor per unit of time. This benchmark gives a clearer view of the reactor performance than the current benchmarks such as pseudo first order rate constant or photonic efficiency. Using the benchmark, 14 reactors with 12 different designs were compared. Comparison showed that the photocatalytic membrane reactors scored the highest. It is also shown that with efficient light distribution, the microreactor technology can prove to be the new generation wastewater treatment reactor conditional to effective scale out strategies. The proposed benchmark measure indicates a new direction to the research on photocatalytic wastewater treatment, which is lighting design instead of new geometries. (C) 2015 Elsevier B.V. All rights reserved.