## 2 Materials and Methods
### LED Power Supply and Controller  
The in-house-built controller unit powers and regulates two groups of LEDs separately. This enables the illumination of reactors to be turned on or off in groups of eight as well as dimmed. The built-in constant current source (MeanWell LDD 300 H, Mean Well Enterprises, New Taipei City, Taiwan) supplies 300 mA at a maximum voltage of 32 V. Groups of six parallel LEDs were connected in series. The constant current source (LDD-300H, Mean Well, New-Taipeh City, Taiwan) was dimmed by a pulse-width modulation (PWM) interface connected to the microcontroller (Raspberry Pi Pico, Raspberry Pi Foundation, Cambridge, UK). The emitted light intensity was measured over the distance from LED to reactor bottom (15 mm) and is shown in Figure 12. Incident light intensities between 0 and 1817 umol m\({}^{-2}\) s\({}^{-1}\) had a linear correlation and could be adjusted precisely. The duty cycle of the PWM was selectable between 0 and 100% with a theoretical accuracy of 65,535 steps. Three controller units and three illumination modules were required for the parallel photoautotrophic cultivation of microalgae in 48 stirred-tank bioreactors. An electronic schematic diagram of the controller unit is presented in Figure 13. A separate power connection was needed for each illumination module due to the use of a step-down transformer (TSR 1-2433-, Traco Electronic, Baar, Switzerland), which supplies 3.3 V to the microcontroller. A haptic power switch was used to turn the microcontroller on and off. The microcontroller (Raspberry Pi Pico with RP2040, Raspberry Pi Foundation,  
Figure 11: (**a**) Photograph showing three illumination modules on the deck of the LHS. LED illumination is switched on. (**b**) Photograph showing the bioreaction unit (bioREACTOR48, 2 mag AG, Munich, Germany) with 48 single-use bioreactors positioned above the three illumination modules. Headspace cooling and cooling for the magnetic inductive drive and parallel stirred-tank bioreactors are connected. LED illumination is switched on. (**c**) Gas supply cover with 48 openings for the LHS needles is mounted on top of the bioreaction unit during operation with LED illumination of a microalgae suspension (_Microchloropsis salina_). Cambridge, UK) transmitted PWM signals to both of the 300 mA constant current sources. Each current source powered the LEDs for eight reactor positions. The controller unit could be set either using tactile buttons for easy control or remotely via a USB port. The OLED display was powered by the microcontroller and showed the selected mode, the time, and the light intensity in % or \(\upmu\)mol m\({}^{-2}\) s\({}^{-1}\). All components of the controller unit were mounted inside 3D-printed housing (Figure A7). The LED control software v1 (see Supplementary Materials for details) was written in MicroPython and saved as a main.py file on the microcontroller ROM. After the microcontroller was supplied with power, the script was executed and the display and other devices initialized. The software controlled two rows of LEDs at once and adjusted their light intensities. Three different modes could be selected, and the active mode was shown on the display. The start mode was the home screen, where LEDs were turned off and the program was waiting for input. The input from the buttons could be detected and executed in all three modes. In constant mode, the LEDs turned on at the selected value. The internal real-time clock of the microcontroller was used to display the time from the start of illumination in constant mode. Although the timer was of millisecond accuracy, it displayed only the day, hour, minute, and second while running. A CSV file containing weather data from Almeria, Spain was saved on the ROM to enable execution of the day/night mode. The file had two columns: the date and time, and the respective radiation given as the light intensity W m\({}^{-2}\), with values recorded for each minute.