Various embodiments may relate to a power supply unit including an output for outputting a current, a communications line, a current-measuring device and a microcontroller including an analog-to-digital converter. The current-measuring device generates a current on the communications line which is proportional to the conductance of a current-setting resistance, the current is convertable into a digital value by the analog-to-digital converter, the power supply unit assumes various operating states based on the digital value of the measured current, and at least one light source module is connectable to the output, wherein the at least one light source module has the current-setting resistance, which is connectable to the communications line. Various embodiments may further relate to a light source module including an input, a communications line and a current-setting resistance for setting the current applied to the light source module.