Under analogous conditions, without the air turned on, our aircooled lamp holder fared slightly better. Although the maximum temperature stabilised marginally lower at 87 °C, it took longer to reach, >30 minutes. This was likely due to the deliberate inclusion of venting around the lamp and above the photo-CDR to allow the air to vent. Once the compressed air was applied from a supply at a pressure of 7 bar, the temperature stabilised at 56 °C after 13 minutes as shown (Figure ). The effect of air cooling resulted in remarkably stable temperature in the photo-CDR and lowered the temperature by >30 °C. Ideally any reaction study should be conducted with stability in the temperature and so we planned to switch on the cooling air and the lamp to allow the photo-CDR to stabilise temperature prior to the introduction of the reactants. We then turned our attention to the effect of light intensity as a function of distance from the photo-CDR. In a previous publication we demonstrated the correlation between distance of the lamp and conversion in a standard bromination reaction. Light intensity decreases as a function of distance according to the Beer-Lambert Law. Here we studied the temperature over time with the introduction of a spacer between the lamp and photo-CDR (see figure &). The air-cooled lamp holder design had already included 25 mm space between the surface of the photo-CDR. The spacers were designed at mm, 15 mm and 25 mm giving an overall distance of the lamp from the photo-CDR of 30 mm, 40 mm, and 50 mm respectively (see figure ). We observed excellent correlation between distance / light intensity and temperature (see figure &). The combination of spacer and the compressed air cooling allowed us to have stable and controlled temperature for a given flow reaction in the photo-CDR reactor. We also wanted to investigate light sources from a different vendor to check performance of the air cooler with a different type of LED lamp. A number of lamps are available, and we sourced various wavelength light sources from Hepatochem. For consistency with the data that we obtained from the Kessil lamp, we investigated the 450 nm 18 W lamp from Hepatochem. We needed to insert an adaptor to the lamp holder to hold the smaller Hepatochem lamp securely and the design of this insert is included in the supplementary section. Figure shows the air-cooled lamp holder with the 18 Hepatochem 450 nm lamp. Using the same conditions and temperature probe insert we studied the temperature profile over time with the Hepatochem lamp.