Several factors could account for the evident discrepancy between the anticipated and fitted path lengths. The light source's beam angle affects the angle of incidence and, in turn, the initial single-pass path length. Additionally, the rotor might reflect light diffusely back into the system, allowing for a second pass. Another factor to consider is the phenomenon of total internal reflection, stemming from the pronounced refractive index difference at the quartz-air interface, which can confine a portion of the photons within the system. Given the knowledge that the initial transmittance following the determined 5.3 mm effective optical path length is virtually negligible, categorizing this reactor as a photon-efficient system becomes unexpectedly justified (Figure ). This highlights that the significance of accurate path length determination is intimately tied to the dimensions, and the absorbing attributes of the medium.