The Beer-Lambert law (eq. 1) states that light penetration decreases exponentially over distance (𝑙) for a given molar extinction coefficient (𝑒) at a certain concentration (𝑐), suggesting that reactions might only take place at the surface (of the reaction medium), leaving a significant area of "dark" zones inside the reaction medium that could lead to quenching of excited states or side reactions, especially if the reaction medium is limited by photon flux. Quantifying the influence of photon flux was demonstrated by Corcoran et al. when transferring optimal conditions to larger scale reactors. Comparing 10, 60 and 150 mL reactors, the authors found that reaction yield versus absorbed photon equivalents followed the same line for all three reactors, suggesting that reaction is driven by absorbed photon equivalents not residence time alone. A similar study was reported by Lévesque et al. over lamp choices. For lamp intensities of 30, 60 and 82.5 W, product yield versus equivalents of emitted photons followed the same trajectory for three different lamps. Both studies highlight the importance of operating under conditions that are not limited by photon flux.