This photoreactor with double-capacity leverages the same patented concept (US Patent #10,906,022) as the original PhotoRedOx Box™. A flexible design allows interchangeable LEDs from 365 nm to 808 nm and a wide variety of vials. PhotoRedOx Duo™ increases the reaction vials capacity to 16 vials (2, 4 or 8 ml) using 2 of the same vial holders as the PhotoRedOx Box™. Using the 2 LED light setup allows to increase reaction rate of difficult reaction conditions.