BALLAST FOR GAS DISCHARGE LAMPS

A ballast or impedance unit 7 for gas discharge lamps, particularly high pressure gas discharge lamps containing a gas discharge vessel (4) arranged inside the hermetically sealed evacuated or gas-filled interior of a light-transmitting outer glass bulb (1) includes at least one current- limiting element. The impedance unit (7) is a rotationally symmetrical body, preferably annular or cup-shaped. It has an internal annular bore for embracing and closely fitting to the neck (6) of the bulb (1). The impedance unit (7) may be separate, or it may be an inseparable integral component of the gas discharge lamp and is therefore very advantageous for creating compact light sources, particularly high pressure sodium vapour lamps which can replace the general lighting service incandescent lamps of 40-100 W without changing the light fitting or lamp- holder in an easy and energy saving manner.