Various methods have been proposed to sustain high absorbance (meaning low actinometer conversion) and prevent product precipitation -these include shortening irradiation times or introducing pulsation. Yet, inaccuracies in path length can still profoundly skew the photon flux measurements in intensified systems. Deriving the path length purely based on geometry, such as using reactor diameter or other geometrical approximations, is not always reliable. This is because light sources come with unique emission distribution patterns, and factors like refraction, back reflection, and total internal reflection can alter the effective optical path length. While spectro-radiometric measurements offer a way to delineate the system's path length, their precision can be compromised in scenarios with uneven irradiation fields or when bulky light sensors are paired with micro-scaled (or intensified) reactors. Furthermore, achieving accuracy becomes more challenging when interfaces of materials, each having distinct refractive indices, affect the local irradiation profile.