The inward refraction of incoming light impacts more than just the elongation of the effective optical path length. It also modifies the photon flux received by the reaction mixture. This effect stems from an expanded surface area available for capturing irradiation (see Supplementary Figure and for details). To illustrate, when the light source's intensity was measured with radiometry, the sensor registered approximately 28 W m -2 (i.e., for 21 W input electrical power). However, when the simulated photon flux reaching the reaction mixture at the same distance is assessed over its flat projected irradiated area (as shown in equation ( ), 2𝑅𝑅𝐻𝐻), the value rises to 45 W m -2 . This discrepancy implies that the reactor absorbs far more energy than possible based on the emission of the light source, even after accounting for losses like reflection. This phenomenon arises because the light interacting with the tube's outer surface refracts inward. As a result, the photon collection area for the reactor is determined by the flat projected outer surface, not the inner one. In other words, the light received by the outer area is focused on a smaller reaction medium area, resulting in an inflated value of 45 W m -2 . When this adjusted area is used to compute intensity, the resulting effective collected light intensity aligns more accurately at 22 W m -2 .