U.S. Philips Corporation

Peter A Tielemans

Cornelis A Jacobs

Gijsbert H Kuus

Jan R De Bie

The invention relates to a high-pressure sodium vapor discharge lamp having a ceramic discharge vessel. In addition to sodium and possibly mercury the discharge vessel also comprises a rare gas. In the discharge vessel an electrode of a refractory metal is accommodated. In the operating condition of the lamp the discharge emanates from the tip of the electrode. According to the invention the electrode is free from alkaline earth metals and the electrode tip in the operating condition of the lamp has a temperature between 2400 K and 2700 K. Disappearance of sodium caused by the electrode material is prevented in this manner.

Emitterless SDN electrode

A high-pressure sodium vapor discharge lamp contains an electron-emitting material consisting of alkaline earth metals bound to oxygen and tungsten bound to oxygen. It has been found that such lamps of less than 400 W which have either a high Hg/Na ratio or use neon/argon as a starter gas fail prematurely when the alkaline earth metals and tungsten in the electron-emitting material are present in stoichiometric quantities. The free ends of electrodes of lamps according to the invention are wound with tungsten wire. Electron-emitting material comprising carium, strontium and calcium bound to oxygen and tungsten bound to oxygen is disposed in the cavities formed between the tungsten wire turns. The molar ration of the total barium, strontium and calcium bound to oxygen to the tungsten bound to oxygen is between 8 and 50.

High-pressure sodium vapor discharge lamp

High-pressure sodium vapor discharge lamps having a color temperature of 2250 to 2750 K. and a color rendition index Ra of 60-85 emit light of a strongly reduced Ra already after approximately 2000 hours in operation. As compared with the life of normal, yellow high-pressure sodium vapor discharge lamps, this period is very short. The discharge vessel contains sodium, mercury and a rare gas, the weight ratio Na/Hg being from 1/1 to 1/9 and the sodium pressure during operation of the lamp being from 4.times.10.sup.4 to 10.7.times.10.sup.4 Pa. The rare gas pressure in the discharge vessel at 300 K. is between 1333 and 1333.times.10.sup.2 Pa. By using an emitter which contains oxygen-bound strontium and oxygen-bound tungsten in a molar ratio from 3/1 to 50/1, the initial properties of such white-light-producing lamps are maintained for a long period of time.

High-pressure sodium vapor discharge lamps are used which contain an electron-emitting material consisting of alkaline earth metal bound to oxygen and tungsten bound to oxygen. It has been found that such lamps which have a high Hg/Na ratio, use neon/argon as a starter gas or have powers of less than 400 W fail prematurely when the alkaline earth metal and tungsten in the electron-emitting material are present in stoichiometric quantities (total alkaline earth metal oxide: WO.sub.3 =3). The free ends of electrodes of lamps according to the invention are wound with tungsten wire. Electron-emitting material consisting of strontium bound to oxygen and tungsten bound to oxygen is disposed in the cavities formed between the tungsten wire turns. The molar ratio of the strontium bound to oxygen to the tungsten bound to oxygen is between 3 and 50.

In high-pressure discharge lamps an electrode pin is provided with a closed cavity extending in the longitudinal direction and in which a hydrogen getter is present. The end of the electrode pin extending in the discharge vessel is formed by a metal part of a hydrogen-permeable metal which bounds the cavity. This construction provides a solution for the contradictory requirements which have to be imposed upon the arrangement of a getter with a hydrogen-permeable envelope. The construction furthermore provides a hydrogen getter with both a high reactivity and a great capacity.

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Eindhoven, Netherlands

Peter A Tielemans