Electric lamp and discharge devices – With gas or vapor – With particular gas or vapor
Patent
1996-06-20
1998-03-17
Patel, Nimeshkumar
Electric lamp and discharge devices
With gas or vapor
With particular gas or vapor
313 25, 313626, 313637, H01J 6182
Patent
active
057290911
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to metal halide discharge lamps having a discharge vessel enclosed within an outer bulb, and especially to low power lamps with minimum halide fill.
BACKGROUND
Metal halide, or halogenide, discharge lamps, especially of low power, in particular about 50 to 250 W, are described, for example, in German Patent Disclosure Document DE-A 36 19 068. A discharge vessel pinched on both ends is located in a bulb pinched on both ends. To increase the safety of operation, especially toward the end of the service life, the current supply leads are surrounded by an electrically insulating jacket. Sheaths of ceramic, glass or quartz glass are especially suitable for this. At the same time, it is noted that the development of photoelectrons (see German Utility Model DE-U 900 29 59, for instance) can be precluded by disposing the discharge vessel and outer bulb in such a way that frame parts extending parallel to the discharge vessel are not needed.
In metal halide lamps with a fill containing alkali metal and in which a conductor is extended along the discharge vessel, as is the case for a discharge vessel pinched on both ends in an outer bulb pinched on one end, it is known for the portion of the current supply lead extending along the discharge vessel to be provided with an electrically insulated, UV-impermeable shield, and especially a small tube of glass, ceramic or quartz glass (German Patent Disclosure DE-A 16 39 084).
THE INVENTION
It is the object of the invention to improve the operating performance of metal halogenide discharge lamps.
Briefly, an ultraviolet (UV) shielding jacket surrounds the leads from the discharge vessel which extend within the outer bulb, and the content of metals subject o diffusion in the discharge vessel is less than 6 .mu.mols/cm.sup.3 of the discharge volume.
Surprisingly, it has been found that the targeted use of a jacket that is impermeable to UV radiation, for current supply leads located in the outer bulb, also has advantages under certain circumstances in metal halogenide discharge lamps that have a discharge vessel pinched on both ends in an outer bulb pinched on both ends. In the previously prevailing opinion, such lamps were thought not to have any problems of photoionization. This means metal halogenide discharge lamps primarily of low power (typically 50 to 250 W) with a fill containing sodium. It has been found that here the use of a UV-shielding jacket that covers the current supply leads in the outer bulb as completely as possible makes it possible to keep the fill quantities of metal halides, and especially the sodium-containing component (such as NaI), quite low yet nevertheless very long service lives can be attained (about 6000 hours of operation). As a rough guideline it can be said that the total fill quantity (in mg) of metal halides can be limited to a maximum of three times the volume of the discharge vessel (in cm.sup.3 ).
It is advantageous to consider the lower limit to be a total fill quantity (in mg) of metal halides that is 1 (one) times the discharge volume (in cm.sup.3). The reason is that--especially in fill systems of sodium and rare earth--the residual oxygen is reliably absorbed in this way, because of the gettering effect of the fill components.
Previous experiments with lamps with this kind of small dose have demonstrated comparatively poor maintenance, because of a failure to recognize that even with this type of lamp, a slight but certainly notable photoionization occurs over the service life, which leads to depletion of fill components and especially of the sodium in the discharge vessel. The consequence was a drop in the partial pressure of this fill component, especially of the sodium, and an increase in the operating voltage along with an undesired drift toward higher color temperatures. Lamps according to the invention, however, exhibit very good maintenance of their light flux over the service life. The performance is similar for the color temperature as well.
The actual cause of poor maint
REFERENCES:
patent: 3484637 (1969-12-01), van Boort et al.
patent: 5064395 (1991-11-01), Kling et al.
patent: 5248913 (1993-09-01), Heider
patent: 5352952 (1994-10-01), Juengst
patent: 5432300 (1995-07-01), Nagaswa et al.
Barthelmes Clemens
Fromm Dietrich
Hohlfeld Andreas
Vom Scheidt Jurgen
Patel Nimeshkumar
Patent-Treuhand-Gesellschaft F. Electrische Gluehlampen mbH
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