Abstract:
An end of life quenching device for a vapor lamp preventing damage to the lamp and socket structure. Mica is attached to a lead wire of a filament. As an emission material on the filament is consumed and the vapor lamp reaches the end of its life, the resulting increase in voltage causes an arc. The arc may extend down the lead wire. The hydrated OH group in the mica releases hydrogen, which extinguishes the arc within the vapor lamp. Damage is thereby prevented. The mica withstands the high pressing temperatures required in the manufacture of vapor lamps with quartz envelopes and used to generate ultraviolet radiation in germicidal applications.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to vapor or gaseous discharge lamps, and more particularly to germicidal lamps. 
     BACKGROUND OF THE INVENTION 
     All vapor lamps have a limited life. One type of vapor lamp, a low pressure mercury lamp, uses an electrode having emission material thereon. A quartz envelope is used to contain the low pressure mercury within the lamp. Often, the emission material on the electrode is a factor in the life of the lamp and its failure. The emission material is slowly consumed during the operation of the lamp. When the emission material on the electrode is totally consumed, the lamp will reach the end of its life. When the emission material is consumed, there is a sudden increase in cathode fall voltage resulting in a sharp raise in lamp voltage, typically over 100 volts. For lamps having a rapid start or preheat ballast, this voltage increase rises the lamp voltage to a level that approximates the open circuit voltage, and the lamp will shut down. However, in applications where an instant start operation is used, this open circuit voltage is typically three or four times the lamp&#39;s operating voltage and the lamp will continue to operate despite the voltage increase. The continued operation of the lamp is not desirable, since the voltage increase will cause a great increase in wattage consumed at the lamp&#39;s end. Also, the resulting arc consumes the electrode and support structure. The temperatures at the base will rise to a level sufficient to melt the socket and burn the housing components. The lamp and related structures can be severely damaged if the lamp does not shut down. 
     There have been several solutions proposed in efforts to solve the uncontrolled operation of a vapor lamp at the end of its life to prevent this destructive and dangerous condition. In the past, thermal fuses have been used in the lamp base. Additionally, electronic shut down circuits that sense increased voltage or rectification have been used. While many of these solutions have been useful, they are often expensive and sometimes do not work properly. One solution that is promising is to utilize an arc quenching device within the lamp itself. As the lamp arcs back to the support structure, the temperature rise may be used to activate a material that raises the voltage by hundreds of volts to effectively shut down the lamp. A hydrogen containing gas may be liberated to cause a great voltage increase and cause the lamp to shut down. 
     An example of an arc quenching material is disclosed in U.S. Pat. No. 5,705,887 entitled “Fluorescent Lamp With End of Life Arc Quenching Structure” issuing to Schaffer on Jan. 6, 1998. Therein disclosed is a metal hydride material applied to the top of a lamp stem. Upon an increase in temperature at the end of life of the lamp, hydrogen gas is released by the disassociation of the hydride and the lamp is caused to shut down. However, for this solution to be effective, it is important that the hydride not decompose in normal lamp operation and that the temperatures experienced in lamp manufacture not decompose the hydride. Therefore, for many lamps, there is no metal hydride available which can be used. 
     For example, germicidal lamps or other vapor lamps using a quartz envelope that require sealing temperatures of approximately 1600° C. have special problems. There is no metal hydride which is stable at the sealing temperatures required for the manufacture of lamps having quartz envelopes. Additionally, there is essentially no room or site on the mount structure to apply a coating. 
     In germicidal lamps, it is particularly important to have a reliable shut down mechanism at the end of life of the lamp. Many germicidal lamps are operated in pressurized sealed vessels for water treatment. The lamp end and sleeves are sealed to the vessels with o-rings or gaskets clamped with compression fittings. If this seal integrity is compromised due to damage as the result of arcing of the vapor lamp at the end of its life, the damage may result in the lamp and sleeve being violently expelled from the vessel, causing injuries, flooding and total system failure. Therefore, there is a need for a safe, reliable and easy to implement arc quenching device for use with germicidal lamps or other lamps utilizing a quartz envelope and requiring high temperatures during manufacture. 
     SUMMARY OF THE INVENTION 
     The present invention comprises a vapor lamp or gaseous discharge lamp having a quartz envelope containing a filament and lead wire. The lead wire is held in a stem and coupled to an exterior contact pin. Mica or hydrous aluminum silicate mineral is placed on the lead wire between the filament and the stem. The mica releases hydrogen when subjected to high temperatures, effectively quenching the arc formed at the end of the lamps life. 
     Accordingly, it is an object of the present invention to prevent damage to a vapor lamp and fixture when the vapor lamp reaches its end of life. 
     It is a further object of the present invention to provide a simple, inexpensive solution to end of life arcing within a vapor lamp. 
     It is an advantage of the present invention that it may be used with high sealing temperatures that occur in the manufacture of vapor lamps having quartz envelopes. 
     It is an advantage of the present invention that it does not affect the normal operation of the vapor lamp. 
     It is another advantage of the present invention that it can withstand high sealing temperatures required during manufacture of lamps with quartz envelopes. 
     It is a feature of the present invention that mica is attached to a lead wire below the filament. 
     It is another feature of the present invention that the mica is held on a lead wire with a ferrule. 
     These and other objects, advantages, and features will become readily apparent in view of the following more detailed description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a vapor lamp incorporating the present invention. 
     FIG. 2 is a perspective view illustrating a single lead vapor lamp embodiment of the present invention. 
     FIG. 2A is a perspective view illustrating a single ended vapor lamp embodiment of the present invention 
     FIG. 3 is an enlarged view of one end of a single lead vapor lamp. 
     FIG. 4 is a plan view of the mica assembly of the present invention. 
     FIG. 5 is a cross section of FIG. 4 along line  5 — 5 . 
     FIG. 6 is a perspective view of the mica assembly of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 is a perspective view illustrating a vapor lamp, such as a fluorescent lamp, which uses a low-pressure mercury arc to produce ultraviolet radiation. The ultraviolet radiation is often utilized in germicidal applications for the disinfecting and treatment of water. The vapor lamp  10  comprises an envelope  12 , which is generally made of quartz, with end caps  14  and  16 . Contact pins  18  and  20  extend from the end caps  14  and  16  so as to provide an electrical contact. Press sealed ends may be used to seal the envelope  12  forming a pressurized container. Sealed within a portion of the press sealed ends are lead wires  26  and  28 . The lead wires are often made of molybdenum or moly. Between each lead wire  26  is a filament  30  coated with an emission material. 
     Similarly, between the lead wires  28  is another filament  32 . Filament  32  is also coated with an emission material. Between the stem  24  and the filament  32  is mica  34 . The mica  34  may be made of any of a group of hydrous aluminum silicate minerals. For example, the mica may be muscovite, paragonite, phlogopite, biotite or lepidolite. All of these micas contain an OH group. 
     FIG. 2 illustrates a single ended vapor lamp. In this embodiment, the vapor lamp  110  has an envelope  112  and end caps  114  and  116  on each end. Contact pins  118  and  120  extend from the end caps  114  and  116 . In this embodiment, only a single contact pin for each end of the lamp is used. A press seals  122  and  124  seal each end of the envelope  112 . Pressed within the press seal  122  are ribbon wires  123 . The ribbon wires  123  are used to facilitate sealing and prevent the possibility of leakage. A lead wire  126 A and a lead wire  126 B are connected to a respective ribbon wire  123 . Lead wire  126 A is coupled to the contact pin  118  through contact wire  119 . Between the lead wires  126 A and  126 B is a filament  130 . The filament  130  is coated with an emission material. Mica  134  is attached to the lead wire  126 A coupled to the pin  118 . The lead wire  126 B is dead ended within the press seal  122 . The mica  134  is positioned between the filament  130  and the press seal  122 . 
     Similarly, at the other end of the vapor lamp  110  are lead wires  128 A and  128 B. Lead wire  128 A is coupled to pin  120  through contact wire  121  and lead wire  128 B is dead ended within the press seal  124 . Ribbon wires  125  are used to facilitate sealing. Filament  132  is connected between the lead wires  128 A and  128 B. Mica  136  is attached to the lead wire  128 A coupled to the contact pin  120 . The mica  136  is placed between the filament  132  and the press seal  124 . The filament  132  has an emission material thereon. 
     The lamp illustrated in FIG. 2A has a construction such that the contact pins only come out of one end of the lamp. A wire extends from one end of the lamp to the other to provide an electrical coupling for the other filament. A similar construction is illustrated in U.S. Pat. No. 4,701,101 entitled “Elongated Tubular Lamp Construction” issuing to Ellner et al on Oct. 13, 1987, which is herein incorporated by reference in its entirety. This embodiment permits the lamp to be electrically connected to a socket or fixture at one end only. 
     In FIG. 2A the vapor lamp  210  has an envelope  212  and end caps  214  and  216  on each end. Contact pins  218  and  220  extend from end cap  214 . Wire  226 C connects lead wire  226 A to pin  218 . Only a single contact pin for each end of the lamp is used, with both contact pins  218  and  220  at a single end of the vapor lamp  210 . Press seals  222  and  224  seal each end of the envelope  212 . Pressed within the press seal  222  are ribbon wires  223  coupled to a lead wire  226 A and a lead wire  226 B. Lead wire  226 A is coupled to the contact pin  218  through wire  226 C. A shunt wire  226 D couples the lead wires  226 A and  226 B together. Between the lead wires  226 A and  226 B is a filament  230 . The filament  230  is coated with an emission material. Mica need not be placed at this end since an end of life failure at this end will not destroy seals on the system. However, if desired and for added protection, mica may be placed at this end also. 
     Similarly, at the other end of the vapor lamp  210  are lead wires  228 A and  228 B. Lead wire  228 A is coupled to pin  220  and lead wire  228 B is dead ended within the press seal  224 . Pressed within the press seal  224  are ribbon wires  225 . Lead wire  228 A is coupled to a contact wire  219  through a ribbon wire  225 . Filament  232  is connected between the lead wires  228 A and  228 B. Mica  236  is attached to the lead wire  228 A coupled to the contact pin  220 . The mica  236  is placed between the filament  232  and the press seal  224 . The filament  232  has an emission material thereon. 
     FIG. 3 is an enlarged view of one end of the electrode assemblies illustrated in FIG.  2 . The lead wires  126 A and  126 B are pressed within the press seal  122 . Between the lead wires  126 A and  126 B is placed filament  130 . On filament  130  is an emission material  131 . Attached to or placed on the stem  126 A is mica  134 . The mica  134  has an opening therein through which a split ferrule  138  is placed. The ferrule  138  holds the mica  134 . The ferrule  138  is then spot welded to the lead wire  126 A with weld  140 . The ferrule  138  may be made of a metal. Other materials or equivalent techniques may be used to hold mica  134  on the lead wire  126 A. The mica  134  may also be directly attached to the lead wire  126 A by any suitable adhesive or other equivalent material. 
     FIG. 4 is a plan view illustrating the attachment of the mica  134 . In this view, a slot  139  in the mica  134  is more clearly illustrated. The slot  139  facilitates placement of the mica  134  on the lead wire  126 A. Additionally, the split in the split ferrule  138  is better illustrated. The split in the ferrule  138  also facilitates placement of the mica assembly on the lead wire  126 A. 
     FIG. 5 is a cross section taken along line  5 — 5  in FIG.  4 . Ferrule  138  extends through an opening within the mica  134 . The ferrule  138  is attached to the mica  134  by a press fit or by crimping and the ferrule  138  is attached to the lead wire  126 A with a spot weld  140 . It should be appreciated that the mica  134  may be attached to the lead wire  126 A by any suitable means or equivalent techniques well known to those skilled in the art. The ferrule  138  may be made from any suitable material. 
     FIG. 6 is a perspective view illustrating the mica assembly. The mica assembly comprises mica  134  and attached split ferrule  138 . Mica  134  has a slot  139  therein. While the shape of the mica  134  is illustrated as generally rectangular with a curved edge, the mica  134  may have other shapes, for example round or square. The curved edge of the mica  134  conforms to the tubular lamp envelope. 
     In operation, when the emission material  131  contained on filament  130  is consumed, the lamp has reached its end of life. At the end of life of the vapor lamp, the cathode fall voltage increases suddenly. This causes an arc to extend down the support structure. As the arc extends down the lead wire  126 A, made of molybdenum, the arc hits the mica  134 . The high temperatures generated liberate the water from the mica  134 , which extinguishes the arc. The mica  134  is substantially unaffected by the high temperatures needed in the manufacture of quartz lamps. During pressing of the lamp and sealed ends, the entire mount becomes red hot, but the mica remains intact. While some of the hydrated water is liberated during pressing, enough remains to quench the arc at the end of life of the vapor lamp. 
     The present invention has been subjected to severe testing. In one test, lamps were made with only a small amount of emission material, less than 0.1% of normal, giving a life of approximately 10 hours, to simulate an end of life event. The mica was then mounted on a lead wire and the lamp press sealed. During pressing, the mica was subjected to very high temperatures to which previously used metal hydride materials would not have withstood. The lamp was operated with an instant start ballast with an open circuit voltage of 800 volts. A 50 volt lamp operating with this open circuit voltage of 800 volts resulted in the arc to be extinguished as the arc burned back to the mica. Accordingly, the lamp voltage can be increased substantially without a catastrophic failure, breakage or damage to the lamp or socket structure. The present invention utilizes mica in a vapor lamp in a new and unique way without affecting the electrical output characteristics of the vapor lamp. The mica, when subjected to high temperatures, results in the liberation of hydrogen from the hydrated OH group in the mica that successfully extinguishes an arc and shuts down the vapor lamp at its end of life. The mica is able to withstand the very high temperatures needed in the manufacture of germicidal lamps having quartz envelopes, or other materials needing high temperatures for manufacture. 
     While the present invention has been illustrated with respect to several embodiments, it should readily be appreciated by those skilled in the art that various modifications may be made without departing from the spirit and scope of this invention.