Successful design of photochemical processes hinges on two key factors: identifying the number of absorbed photons and deciphering its correlation to the production of the desired compound. The former encompasses the irradiation profile within the reactor, where the average path length of photons emerges as a pivotal element. The latter revolves around the quantum yield, a metric that enumerates reactive events per absorbed photon. Traditionally, chemical actinometry studies have been the predominant strategy to generate this wealth of information. Yet, the experimental conditions demanded by actinometric measurements pose challenges. Further complicating matters, the inherent variability in light intensity over a light source's lifespan necessitates laborious recalibrations through actinometry.