A gaseous discharge lamp in combination with a special electrical circuit is described with which a high‐efficiency conversion of 60‐cycle a.c. power into 1000‐cycle pulsating light is obtained. The efficiency of this device is 17 lumens per watt as compared to 6 lumens per watt for an incandescent lamp with a mechanical shutter. As the modulated light is designed for the use in beacons and for the detection by means of a photoelectric tube and tuned amplifier, the component of fundamental frequency is the only important one. In a mathematical analysis of different wave shapes, the fundamental component is calculated as a function of the average light output; also the efficiency of a modulated neon discharge.