An important characteristic of a photochemical reaction system is the so-called photochemical space time yield (PSTY) which expresses the amount of product produced per time and energy input and is thus a measure for both the productivity and efficiency. Many conventional photochemical reaction systems have been reported at PSTYs of 10 -6 to 10 mmol d -1 W -1 . For the WLE system, the low specific power consumption of only 21.3 W at 442.2 µM s -1 photon flux leads to an astonishing photochemical space time yield (PSTY) of up to 1.8 mol d -1 W -1 assuming unity quantum yield. This value exceeds conventional photochemical reaction systems by orders of magnitude and even outperforms wirelessly-powered µLED in fixed-bed, which have recently been reported (Table ). To compare this internal irradiation system with external irradiation, an external irradiation setup with the same reactor geometry and scale was used in combination with two different high-power LEDs (Thorlabs M365LP1 and SOLIS-365C) to cover a wide range of light intensities. Analysis of the driver power settings or applied current versus incident photon flux density in the reactor allowed to calculate the corresponding driver setting to achieve a given photon flux density (Figures ) to match the data points obtained with the WLE system. However, the highest value that could be achieved with the external irradiation setup was limited at 185 μM s -1 and is thus substantially lower than for the WLE system. The wall-plug efficiency of the external irradiation setup varied from 5.9 to 13.6% with higher values achieved at higher output (Tables ). This is interesting as the employed LED is nominally rated at an electrical efficiency of 22.2% (4 W light output using 18 W electrical input). However, external irradiation often suffers from additional inefficiency factors such as off-target irradiation and reflection losses on the reactor walls which may explain this low value. After characterizing the reaction setups using actinometry, the performance was also evaluated using a model photocatalytic reaction, the reduction of nitrobenzene to aniline in 2-propanol using TiO2 nanoparticles, Scheme 1. 34