The coils were connected to a capacitor with an appropriate capacitance to generate a series resonant circuit. This circuit is part of the amplifier. The resulting LC-circuit is tuned to a frequency of 178 kHz For external illumination, the coils were replaced by an external lamp (Thorlabs M365LP1 or SOLIS-365C) with a collimation lens and circular spot of 3 cm diameter as irradiated area on the outside of the reaction vessel.