We have found out a phenomenon that the large fluctuation in the repetitive frequency of emission from a free-running, nanosecond-pulsed, Xe lamp can be reduced markedly by illuminating the lamp electrodes with a light flux from a blue light-emitting diode. There was a wavelength dependency in the stabilization effect. The upper limit of the effective wavelength of the illumination light was around 750 nm, but no power dependency was observed between 0.5 and 3.0 mW. The reduction in the fluctuation was observed only for a Xe lamp manufactured by a specific maker, where materials with low work function elements were mixed in its cathode electrode for the purpose of improving standard direct current arc operation. In order to evaluate the fluctuation quantitatively, we have constructed a system for measuring time intervals between every pulsed emissions. Our conclusion is that the reduction in the fluctuation is due to photoelectrons emitted from the surface of the cathode electrode and thereby the breakdown voltage for discharge in the lamp was maintained at a fixed value. © 2000 American Institute of Physics.