Electroded selenium lamp

Details Electroded selenium lamp Electroded selenium lamp

1999-09-10

2001-11-13

Patel, Ashok (Department: 2879)

Electric lamp and discharge devices

With gas or vapor

Electrode composition

C313S631000, C313S634000, C313S570000, C313S574000

Reexamination Certificate

active

06316875

ABSTRACT:

BACKGROUND
1. Field of the Invention
The present invention pertains to selenium lamps. More particularly, the invention relates to electroded lamps containing a fill including selenium or selenium compounds.
2. Related Art
An example of an electroded lamp with a selenium fill is disclosed in U.S. Pat. No. 5,606,220, entitled VISIBLE LAMP INCLUDING SELENIUM OR SULFUR, and PCT Publication No. WO 92/08240, each of which is hereby incorporated by reference in its entirety.
The lifetime of an electroded lamp depends in substantial part on the useful life of its electrodes. During operation, the electrode material reacts with the fill material and may decompose. Also, due to high electrode temperatures, some electrode material may evaporate and become deposited on the lamp walls, thereby blackening the walls. If too much electrode material evaporates, the lamp may fail to operate at all.
These problems are particularly relevant to electroded lamps with a selenium fill because of the reactive nature of selenium at typical lamp operating conditions. An electroded selenium lamp using conventional electrode materials may have an extremely limited operating lifetime.
SUMMARY
It is an object of the invention to provide an electroded selenium lamp with an improved operating lifetime.
It is a further object of the invention to provide an electroded selenium lamp with an improved electrode material.
The above and other objects of the invention are achieved by an electroded selenium lamp having electrodes which use an electrode material that chemically participates in the discharge as it heats up. For example, the electrode material may include a metal which when combined with selenium exhibits a characteristic wherein any solid compound of the electrode material and selenium decomposes at suitable lamp operating temperatures to release the solid metal and a selenium gas. An exemplary electrode material meeting these requirements is molybdenum.
An electroded selenium lamp according to the invention includes a light transmissive discharge envelope enclosing a fill which produces light when excited, and two electrodes, each electrode having a portion thereof disposed inside the light transmissive discharge envelope, wherein the two electrodes each include molybdenum or a molybdenum compound. The light transmissive discharge envelope may be, for example, a quartz arc tube made from, for example, clear fused quartz. Other examples for the arc tube material include alumina or sapphire. The fill may include, for example, selenium or selenium compounds. The selenium may, for example, be initially deposited on the electrodes when the electrodes are cool, wherein the selenium is driven off the electrodes to join the light producing fill as the electrodes are heated during operation. The fill may further include cesium halide (e.g. CsBr or Csl), and may additionally include an amount of halide in excess of stoichiometry.
If cesium is present in the fill in a quartz arc tube, a halide must also be present to prevent the cesium from attacking the quartz. Alternatively, the arc tube may be made from alumina or sapphire because cesium does not attack these materials.
The electroded selenium lamp may further include a light transmissive outer envelope surrounding the light transmissive discharge envelope. The light transmissive outer envelope is preferably evacuated to provide a vacuum around the light transmissive discharge envelope.
Another aspect of the invention provides an additive to the fill which facilitates a halogen cycle for thermal redeposition on the electrodes.


REFERENCES:
patent: 3234421 (1966-02-01), Reiling
patent: 3621322 (1971-11-01), Rehmet et al.
patent: 4864191 (1989-09-01), Van De Weijer et al.
patent: 4950954 (1990-08-01), Passmore et al.
patent: 5212424 (1993-05-01), Russell et al.
patent: 5404076 (1995-04-01), Dolan et al.
patent: 5504392 (1996-04-01), Natour et al.
patent: 5757130 (1998-05-01), Dolan et al.
patent: 5773918 (1998-06-01), Dolan et al.
patent: 0732719 (1996-09-01), None
patent: 92/08240 (1992-05-01), None
Patent Abstracts of Japan: JP 58080260 dated May 14, 1983.

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