A Light Emitting Diode (LED) is added to a weed control system for calibrating the weed control system. A detector generates an electrical signal based on receiving light emitted by the LED. An electronically-tunable capacitor of a bandpass filter is adjusted based the signal received from the detector to adjust a center frequency of the bandpass filter so that light from an optical source, different from the LED, can more efficiently be detected by the weed control system.