Fig. 5.

(A) Example of black painted POM parts: The four sample holders were varnished black because the colorless filament, in its untreated form, acts as an effective optical fiber to disperse stray light and causes significant tube-to-tube bleeding. Next to them, the rolled filter foil inserts, which shield the photodiodes from the blue excitation light. (B) Housing of the electronic components (ESP32 development board, MOSFET circuits, and constant current power supply). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)