Electric lamp and discharge devices: systems – Combined load device or load device temperature modifying... – Plural circuit elements
Reexamination Certificate
1999-04-09
2001-09-11
Vu, David (Department: 2821)
Electric lamp and discharge devices: systems
Combined load device or load device temperature modifying...
Plural circuit elements
C315S053000, C315S059000, C315S060000
Reexamination Certificate
active
06288491
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to high pressure arc discharge lamps and is particularly applicable to lamps containing a metal halide fill and employing a tungsten electrode.
High pressure metal halide discharge lamps (MHL) are generally comprised of a fused silica or quartz arc tube containing an ionizable fill and having a pair of main thermionic electrodes at the ends. In most applications the electrodes include a relatively high percentage of tungsten. The electrodes are supported by inleads which include a thin molybdenum ribbon portion extending hermetically through a pinch or press seal in the end of the lamp. The purpose of the ribbon being to prevent seal failures because of thermal expansion of the lead in wire. Generally, a starter electrode is disposed in the arc tube adjacent one of the main electrodes to facilitate starting. In most lamps, a discharge can be ignited between the starter and the adjacent main electrode at a much lower voltage than between the two main electrodes, and ignition of the arc between the main electrodes is thereby facilitated.
Historically, the metal halide lamp has been available as an interchangeable line which will start and operate reliably on many kinds of conventional ballasts, including those used in high pressure mercury vapor lamps. This is a great advantage since it is often desirable to replace mercury lamps and older installations of metal halide lamps with newer metal halides which have a much higher lumen output and better color rendition.
Unfortunately, the maintenance of initial lumens in even the newer MHL lamps is a problem because of highly complex chemical reactions occurring in the atmosphere within the arc discharge chamber. More specifically, at the operating temperature of 5,500° K. at the center of the arc, to approximately 1,100° K. at the wall of the arc tube, which defines a boundary of the plasma, many and various reactions occur. One negative reaction is the transport of metallic and inorganic compounds of tungsten (the main electrode constituent) from the electrode to the walls of the discharge tube during operation of the lamp. The tungsten, in its various compound forms so transported, creates an opaque barrier on the inner wall of the arc tube, thus preventing discharge radiation from being effectively transmitted. In short, significant losses to the level of lumens can occur. This loss of light level from within the discharge is perceived externally as a reduction of light output of the lamp, and thereby reduction in the maintenance of initial lumens. It is believed that the transport of tungsten and tungsten compounds to the walls of the discharge tube occurs through sputtering, evaporation and other chemical mechanisms.
SUMMARY OF THE INVENTION
Accordingly, it is a primary advantage of the present invention to provide a new and improved metal halide lamp.
It is a further advantage of this invention to provide a new and improved metal halide lamp that reduces the rate at which tungsten is lost from the electrodes to the inner walls of the arc discharge tube.
Additional objects and advantages of the invention will be set forth in part in the description which follows and in part will be obvious from the description or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the foregoing objects and in accordance with the purpose of the invention, as embodied and broadly described herein, the metal halide lamp of this invention comprises an arc tube containing an ionizable medium and having electrodes, preferably tungsten, sealed into opposed ends of the arc tube. An outer envelope encloses the arc tube and includes one end accommodating inleads sealed therethrough. A base is attached to the outer envelope and includes input terminals, the input terminals being connected to the inleads which in turn are connected to the tungsten electrodes. The ionizable medium includes mercury, a metal halide, and an inert gas selected from the group consisting of argon, krypton, xenon and mixtures thereof. Importantly, the inert gas will be at a cold pressure of at least about 50 torr. In addition, a starting circuit having an open circuit voltage of at least 200 volts RMS is provided.
In a preferred form of the invention, the inert gas will be present at a level of about 70 torr and possibly at greater than about 110 torr. In a particularly preferred form of the invention, the inert gas will be argon. Typically, the inventive lamp will operate at between 250 and 1500 watts.
REFERENCES:
patent: 4173730 (1979-11-01), Young et al.
Brown Casey Autumn
Dever Timothy Peter
Ramaiah Raghu
Fay Sharpe Fagan Minnich & McKee LLP
General Electric Company
Vu David
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