Luminescent solar concentrator-based photomicroreactors (LSC-PMs) have been recently proposed for sustainable and energy-efficient photochemical reactions. Herein, a Monte Carlo ray tracing algorithm to simulate photon paths within LSC-PMs was developed and experimentally validated. The simulation results were then used to investigate the expected efficiency of scaled-up devices. A novel metric, defined as the 'Average Photon Path Traveled in the Device' (APPTD), was introduced to measure the impact of different channel design choices and to rationalize the LSC-PM improvement over traditional LSC. The simulation results suggest that the combination of luminescent solar concentrators and continuous-flow photochemistry has the potential to become the most photon-efficient application of LSCs reported to date.