Abstract: An object recognition system for detecting visible light of a predetermined wavelength emitted by a fluorescent material illuminated with modulated ultraviolet light produced by a self-modulated high pressure mercury vapor lamp. The lamp forms part of a resonant LC circuit which produces oscillations in the lamp intensity at a frequency higher than line frequency. The resulting visible light is detected, demodulated, and compared with a predetermined threshold to sense when the fluorescent material is present. Self-modulation of the UV lamp source eliminates external triggering, excitation or switching of the lamp power supply.