Sodium vapour discharge lamp - has auxiliary conductor lying along outer surface of tube to assist in starting

摘要

The high pressure sodium vapour discharge lamp includes an outer envelope enclosing a discharge tube in a vacuum. The discharge tube itself comprises a clear envelope of chemically stable material enclosing sodium, xenon and a buffer gas which is one of the group including mercury and cadmium. Two electrodes are sealed into the two ends of the tube. One of the discharge electrodes (4) includes a projecting conductor (9) which extends from the electrode towards the inner surface of the side wall of the tube, with a set gap separating it from the wall. A conductor (8) intended to assist starting is placed longitudinally on the outside surface of the wall, with one end being opposite the conductor inside the wall. This conductor is connected to a voltage equal to that on the other discharge electrode. The conductor is arranged to be disconnected when the temperature of the lamp reaches a chosen level by a bimetal switch.