The photocatalytic aerobic oxidation of thiols to disulfides was investigated in a photomicroreactor. The base in this protocol allows to activate the photocatalyst and to facilitate a proton-coupled electron transfer. On this basis, a mechanism was postulated for the photocatalytic aerobic oxidation. The photon/energy efficiency of the photomicroreactor is described. By varying the power supply, the effect of the photon flux on the yield of the photocatalytic process could be demonstrated. The effective photoelectric transformation efficiency was rather low, which indicated that sufficient cooling is required to dissipate non-productive energy. Under optimal reaction conditions, the photonic efficiency substantially increased compared to batch reactors and other photomicroreactors. This could be attributed to the similar dimensions of the capillary photomicroreactor and the light-emitting diode light source, which minimizes energy losses due to unfocused light irradiation.