Abstract: A circuit for supplying controlled direct current power to an electric discharge vapor lamp during ignition, warm-up and normal operation. A bridge rectifier and a capacitor voltage doubler convert standard alternating current line voltage into a direct current voltage of adequate magnitude to operate the lamp. The lamp is connected in series with a semiconductor control circuit across the DC supply. The semiconductor control circuit operates as a resistive ballast whose effective resistance decreases as vapor pressure within the lamp increases during warm-up, thereby limiting lamp current to a safe value immediately after ignition while reducing the amount of power dissipated in the ballast circuit during normal operation for improved efficiency. In a second embodiment, the conductivity of the resistive ballast circuit is controlled in response to variations in both lamp voltage and lamp current to control the amount of power delivered to the lamp.