A system includes multiple devices configured to emit and detect germicidal radiation. Each of the multiple devices operates in emitting mode when connected to a drive source in a forward bias configuration and operates in detecting mode when disconnected from the drive source or when connected to the drive source in a reverse bias configuration. Cycling circuitry generates a sequence of control signals that control switching circuitry to change the connections of the devices to the drive source in a cycle in which one or more of the multiple devices are switched to detecting mode and senses radiation emitted by one or more of the multiple devices simultaneously operating in emitting mode. Each device operating in detecting mode generates a signal in response to the sensed radiation. Detection circuitry detects signals of the devices operating in detecting mode and generates a detection output in response to the detected signals.