Chemical actinometry has long served as a cornerstone technique for determining quantum yield and photon flux in photochemical processes. While it has proven invaluable in many traditional settings, its applicability and accuracy come into question when we transition to photochemical reactor platforms with highly transmitting characteristics. These advanced reactor systems, designed for enhanced efficiency and throughput, introduce a set of complexities that can challenge the conventional actinometric methods. In this subsection, we discuss the specific limitations and constraints of employing chemical actinometry in such intensified settings, underscoring the need for innovative approaches to reactor characterization.