The present authors have carried out study on the reduction of harmonic current at the power supply side, with taps providing on the way to a ballast in lag type operating circuit of high-pressure mercury arc lamp, and with a by-pass circuit connecting.
Based on the theorectical consideration of lag type operating circuit with by-pass circuit, experiments have been carried out applying sinusoidal voltage to its input terminal. With the difference of tap positions to the ballast and the change in the characteristics of the lamp due to the variation of input terminal voltage considering, optimal tap position was lead through in comparison with the peak factor of lamp current, the distortion factor of power supply current, lamp, power, etc.