Abstract: In a ballast for operating one of a high-pressure sodium-vapor and a mercury-vapor lamp from a source of electric power, the ballast has a first one of a condenser and an inductor connected to be in series between the lamp and the source of electric power. A second of the one of the condenser and inductor is connected in a path that is connected in parallel with the first one of the condenser and inductor. A timer is connected to the source of electric power and a relay is in path for closing the path, the timer providing a predetermined time only to the relay for opening the path, whereby the electric power consumed by the ballast for operating the lamp is reduced when the relay has opened the path.