We initiated our study with radiometric measurements, utilizing a calibrated light sensor strategically positioned within a pre-established grid. This setup facilitated the precise mapping of light intensity across an irradiated plane. Using the physical dimensions of the light source, we crafted a 3D model and simulated the radiometric conditions using ray-tracing within the COMSOL Optics Module (detailed in the Supplementary Information). This virtual model of the light source was complemented by an accurate digital replica of our experimental batch configuration, with a focus on maintaining authentic system dimensions. Our simulation, leveraging ray-tracing, took into account the Fresnel reflection and refraction occurring at the juncture of media with varying refractive indices. This allowed us to ascertain the power incident on the reaction mixture (illustrated in Figure ). By integrating this data over the entirety of the receiving surface, the photon flux (𝑞𝑞 𝑛𝑛,𝑝𝑝 ) could be determined for all 4 power settings of the light source (Figure ). Next, chemical actinometry experiments were carried out for the batch system (see Figure and the Methods section) and the results are presented in Figure and, which demonstrate excellent agreement between the simulated and actual photon fluxes. To determine the absorbance of the polychromatic light, we employed a modified version of Equation ( ), factoring in the lamp's spectral distribution and the wavelength-specific attenuation coefficients. This information facilitated our modeling of the reaction progression over irradiation time, as detailed in the Supplementary Information, resulting in the kinetic curves displayed in Figure . In examining the unreacted reaction mixture, the initial spectrum-average transmittance through the reaction tube is estimated at approximately 0.1% when the inner diameter alone is assumed as the effective optical path length. However, it is crucial to note that not all light will enter the reactor tube through its center, thereby not all light will perceive the inner diameter as the effective path length. Given that the tube is irradiated from a single side, a popular approach for a cylinder is the employment of a geometric average path length. This average can be deduced through integration, or more straightforwardly by visualizing the cylinder as a flat plate, where the total volume is divided by its projected irradiated area (Supplementary Figure ):