The final design of the photoreactor is shown in Fig. . Two axial cooling fans are installed on both sides of the photoreactor to ensure good air cooling. The self-developed Python code enables the fans usually work at 80% power, once the sensor detects the system temperature is above the setting value (in our setup, the value is set at 30 degrees Celsius), the fan will accelerate and work at full power. When the circulating cooling bath is working, the system temperature can even reach lower values. Therefore, the photoreactor can work at a broad operating temperature range. The distance between the test tube and the LEDs is fixed at around 2.5 cm, and the symmetrical design standardizes the operation conditions because the same position of the tube is used for each independent experiment. The proposed photoreactor setup is able to run 4 reactions in parallel with each test tube illuminated by two LEDs (total irradiation power, 20 W per tube), thereby increasing the efficiency of reaction screening. Of course, one can combine more light sources to increase the total number of reactions that can be run. In the current design, three wavelengths of LEDs are installed for different purposes of reaction screening and can be easily replaced with other wavelengths of interest by inserting new aluminum rods and gluing the LEDs to them. In addition, with the controllable Arduino Board, the research can manually change the output power of the LEDs and monitor the output of the parameters from the digital display screens. Therefore, the corresponding light intensity is tunable. The flexibility of the photoreactor can be achieved by printing different sizes of test tube guide and holder. In addition, the built-in stirring system endows the photoreactor with portability, which can easily transfer from one lab to another lab. Another advantage is that there is no need to include an external magnetic stirring system, as is the case with many batch photoreactors. The total price (without LEDs) of the photoreactor is very cheap (roughly below €400) and the majority of research groups will afford it.