On the other hand, while lowering the catalyst concentration, yields predictably decreased due to the now imposed kinetic limitations, it seemed to slightly improve selectivity; especially apparent at the higher rotation speeds for 0.25 mol%. This is mostly likely due to the lower catalyst concentration having better light transmittance throughout the reactor, therefore preventing "dark reactions" (Fig ) from proceeding. Nonetheless, it seems that further optimization of the catalyst concentration for a given light source, is an important strategy to further improve the achieved yields and selectivity . As ratio of substrate decreased relative to the oxygen flowrate, we observed an increase in yield and conversion. Therefore, by imposing a higher relative oxygen concentration we have effectively improved the availability of oxygen. The rotation speed still influences the conversion; however, by around 1000 RPM, the effect is much less pronounced for 0.05M. This implies that due to the relative excess of oxygen, the mass transfer is of less importance. Interestingly, the selectivity does not seem to be influenced by the decrease in substrate concentration once mass transfer limitations are overcome.