Electric lamps and their production

DETAILED DESCRIPTION I claim: 1.
An electrical discharge lamp comprising a lamp envelope, electrodes and leads therefor and a vapour fill including metal halide and a quantity of phosphorus in the form of a metal phosphide sufficient to effectively getter water vapour inside the envelope but insufficient to affect the luminous efficacy of light from said lamp.
2.
A lamp according to claim 1 wherein the quantity of phosphorus is less than 0.
1 mg per c.
c.
3.
A lamp according to claim 1, wherein said metal phosphide comprises the same metal as said metal halide.
4.
A lamp according to claim 1, wherein said metal phosphide is gallium phosphide.
5.
A lamp according to claim 4 wherein the quantity of said phosphorus is less than 0.
1 mg.
per cc.
6.
In the manufacture of an electrical discharge lamp comprising a lamp envelope, electrodes and leads therefor and a vapour fill including metal halide the improvement which comprises eliminating traces of water vapour from the finished lamp by the steps of: introducing into the lamp envelope a quantity of phosphorus in the form of a metal phosphide sufficient to effectively getter said residual water vapour but insufficient to affect the luminous efficacy of light from said lamp; sealing said envelope; and operating said lamp and thereby causing said phosphorus to getter said water vapour.




Description:
The present invention relates to electric lamps containing metal halides, and more especially to metal halide discharge lamps.
Metal halide lamps are more difficult to exhaust in the course of production than the corresponding plain mercury discharge lamps, mainly because the metal halides are hygroscopic.
Traces of water vapour are consequently difficult to eliminate from the finished lamp and, because of the well known "water cycle", even a small trace of water has a serious effect on lamp life.
The "water cycle" is described in the "Collected Works of Irving Langmuir", Volume 2, page 185 (Pergamon Press 1960).
The use of dry boxes in storing and weighing the metal halide doses and the heating and recondensing of the metal halides within the lamp envelope during the exhaust procedure are methods which have been used in attempts to eliminate traces of water vapour from the filling of the lamp