Abstract
A retrofit high pressure sodium lamp initiates discharge with the aid of surge voltage generated in a choke ballast at the moment of operation of Bl-metallic switch. The large dispersion of the surge voltage has been imposing restriction on operation of the lamp on the mercury lamp ballast so as to avoid destruction of insulation of operating circuits. The dispersion and the value of the surge voltage could be decreased by introducting gas into an outer bulb. It is this reason that the surge voltage could not go over a certain value, because the conductivity of the gas would be increased by the discharge when the generated voltage exceeded a certain value. The authors applied this new method to a practical retrofit HPS lamp and confirmed that the dispersion and the value of the surge voltage could be decreased without any sacrifice on the starting and other performance of the lamp.
