This contribution aims at developing engineering approaches to characterize radiative transfer and kinetics of a catalyst to be activated by electromagnetic radiation, one of the main bottlenecks when evaluating materials in heterogeneous photocatalytic processes. A specialized LED‐based photoreactor is engineered to obtain reliable information on the aforementioned mechanisms. The radiative transfer approach serves as a criterion to elucidate the capability of a catalyst to be activated or not by visible light or UV‐A light. When the catalyst favours the absorption of photons rather than their scattering or transmission, the experimental methodology allows the determination of intrinsic optical information being independent of fluid dynamics, and catalyst concentration. Radiative characterization, along with a mass transfer analysis, guides the proposal of the operational design of the photoreactor to carry out intrinsic kinetic studies. Thus, the operation of the photoreactor under pseudo‐isoactinic and differential reaction conditions leads to the determination of intrinsic initial reaction rates, enabling the understanding of the complex interaction among the optical properties of the catalyst, the reaction rate for the production of hydroxyl radicals (•OH), and the oxidation of a recalcitrant organic pollutant. The procedures assessed are worthy of being used for evaluating other materials, activated at different wavelength ranges or designed for different photocatalytic applications, paving the way for the scale‐up of the reactor, another of the main challenges in photocatalysis.