US3906275A

US3906275A - Electric lamp with electrolysis preventing apparatus

Info

Publication number: US3906275A
Application number: US463738A
Authority: US
Inventors: Raymond Francois Spiessens; Rop Walter Jan Roza Adolf De
Original assignee: US Philips Corp
Current assignee: US Philips Corp
Priority date: 1973-05-04
Filing date: 1974-04-24
Publication date: 1975-09-16
Anticipated expiration: 1992-09-16
Also published as: JPS5027357A; NL7306208A; FR2228295A1; BE814480A; FR2228295B3; DE2418890A1

Abstract

An electric lamp having a lamp envelope transmitting radiation which is sealed in a vacuum-tight manner at least one end by means of a pinch in which at least two current lead-through conductors are sealed. An electric voltage comprising a direct voltage component is present between these conductors during operation of the lamp. A metal scrreming element is placed in the pinch between the two current lead-through conductors. The screening element is connected to the current lead-through conductor which has as an average a negative potential relative to the other current lead-through conductor during operation so that the drawbacks of electrolysis phenomena in the pinch are eliminated.

Description

United States Patent Spiessens et al.

[ 1 Sept. 16, 1975 Walter Jan Roza Adolf De Rop, both of Eindhoven, Netherlands Assignee: U.S. Philips Corporation, New

York, NY.

Filed: Apr. 24, 1974 Appl. No.: 463,738

[30] Foreign Application Priority Data A May 4, 1973 Netherlands 7306208 [52] US. Cl. 313/318; 174/5059; 313/225; 313/229; 313/315; 315/60 [51] Int. Cl. H01J 5/50; H01J 61/36; H01J 61/54; HOIK H38 [58] Field of Search 313/332, 318, 315, 184, 313/219, 222, 197, 198, 315, 225, 229; 174/5059, 50.64

[56] References Cited UNITED STATES PATENTS 1,985,028 12/1934 Gehrts 174/5059 X 2,329,019 9/1943 Wagencr 174/5059 X 2,454,384 11/1948 Henry 174/5059 X 2,569,848 10/1951 Eitel et a1. 174/5059 X 3,275,885 9/1966 Pomfrett.... 313/197 X 3,668,456 6/1972 Anderson 313/318 Primary ExaminerPalmer C. Demeo Attorney, Agent, or FirmFrank R. Trifari 5 7 1 ABSTRACT An electric lamp having a lamp envelope transmitting radiation which is sealed in a vacuum-tight manner at least one end by means of a pinch in which at least two current lead-through conductors are sealed. An electric voltage comprising a direct voltage component is present between these conductors during operation of the lamp. A metal scrreming element is placed in the pinch between the two current leadthrough conductors. The screening element is connected to the current lead-through conductor which has as an average a negative potential relative to the other current 1ead-through conductor during operation so that the drawbacks of electrolysis phenomena in the pinch are eliminated.

10 Claims, 3 Drawing Figures PATENTEU SEP 1 6 I975 sum 2 0 2 ELECTRIC LAMP WITH ELECTROLYSIS PREVENTING APPARATUS The invention relates to an electric lamp having a lamp envelope transmitting radiation and being sealed in a vacuum-tight manner at at least one end by means of a pinch in which at least two current lead-through conductors are sealed. Particularly the invention relates to a dischargelamp provided with a first and a second main electrode between which the discharge isieffected during operation and an auxiliary electrode arianged in the vicinity of the first main electrode, the current lead-through conductors for the first main electrode and for the auxiliary electrode being sealed in a pinch.

ln lamps of the above-mentioned kind a very disturbing electrolysis phenomenon may occur between the current lead-through conductors sealed in the pinch when during operation of the lamp a direct voltage is present as an average in time between these conductors. The material of the pinch consisting of glass or quartz glass then serves as the electrolyte. It is assumed that the charge transport in this electrolysis phenome non is effected by alkali metal ions which occur in the glass or quartz and which are displaced towards the negative conductor. A result of the said electrolysis in the pinch of a lamp is a discolouration and attack of the quartz or glass around the negative current leadthrough conductor and possibly an attack of this conductor itself. The said attack may proceed after a large number of operating hours to such an extent that the lamp drops out due to leakage, cracking of the pinch or even explosion. I

The above-mentioned drawbacks are particularly manifest in gas discharge lamps, for example, in highpressuremercury vapour discharge lamps which in addition to mercury comprise one or more metal halides. These lamps generally have a hard glass or quartz glass discharge tube as a lamp envelope which is closed at both ends by a pinch. A main electrode is placed within the discharge tube at each end which electrode is passed to the exterior by means of a current lead through conductor sealed in the adjacent pinch. In order to obtain a vacuum-tight seal these lead-through conductors are at least partly formed as thin molybdenum foils. An auxiliary electrode may be arranged in the vicinity of one of the main electrodes in such lamps, which auxiliary electrode is passed to the exterior by means' of a current lead-through conductor sealed in the adjacent pinch and comprising a molybdenum foil and which outside the lamp is connected through a resistor to the other main electrode. This auxiliary electrode serves to facilitate the ignition of the lamp. During operation of these lamps which are fed by an alternating voltage an electric voltage is present between the auxiliary electrode and the adjacent rnain electrode, which voltage contains such a direct voltage component that the auxiliary electrode has an average negative potential relative to the main electrode. The said direct voltage component is a result of the fact that the main electrode more easily emits electrons than the auxiliary electrode.

To prevent electrolysis in the pinch of a discharge lamp different steps are known (see for example German Patent Application No. 2,052,060). These known steps include all relatively complicated circuits such as rectifiers and or temperature-dependent mechanical switches, such as bimetals which prevents the occurrence of the phenomenon of electrolysis. The known steps are, however, comparatively expensive and are found to be not always reliable in practice.

Electrolysis in the pinch of a lamp and the attendant difficulties are found to occur also in electric incandescent lamps, for example, halogen lamps which are intended for direct voltage operation and in which the two current lead-through conductors are sealed in one pinch.

The invention provides electric lamps provided with simple means with which the drawback of the abovedescribed phenomenon of electrolysis can at least largely be obviated. The invention is based on the recognition of the fact that it is not necessary to entirely prevent the occurrence of electrolysis in the pinch of a lamp so as to avoid the above-mentioned drawbacks of this electrolysis. v

An electric lamp according to the invention has alamp envelope transmitting radiation and is sealed in a vacuum-tight manner at at least one end by means of a pinch in which at least two current lead-through conductors are sealed between which conductors an electric voltage is present during operation of the lamp which voltage comprises a direct voltage component and is characterized in that a metal screening element is placed in the pinch between the two current leadthrough conductors, the screening element not intersecting the internal surface of the lamp envelope and being connected to the current lead-through conductor which at an average has a negative potential relative to the other current lead-through conductor.

In a lamp according to the invention a metal screening element is incorporated in the pinch between the two current lead-through conductors. The screening element is connected to the current lead-through conductor which during operation, possibly as an average in time, has a negative potential relative to the other current leadthrough conductor. As a result the screening element will have the same negative potential relative to the other current lead-through conductor. In this manner the electrical field resulting from the direct voltage component between the two current leadthrough conductors will be displaced for the greater part to the region in the pinch between the positive current lead-through conductor and the screening element. Consequently in a lamp according to the invention the negative current lead-through conductor is screened in an effective manner from the electrical field resulting in electrolysis by the screening element located between this conductor and the positive current lead-through conductor. As a result the consequences of electrolysis (discolouration and attack) on this negative current lead-through conductor are substantially completely prevented. Only at a very late in stant of the lifetime of the lamp may these electrolysis consequences occur (and then generally in an undisturbing manner) on the negative current lead-through conductor.

It is evident from the foregoing that in a lamp according to the invention the electrolysis phenomenon is not prevented but is displaced to another part of the pinch. It has been surprisingly found that electrolysis between positive current lead-through conductor and negative screening element in a lamp according to the invention can be noticed to a lesser extent on the screening element and does not lead to any harmful consequences for the lamp for a very long time. A condition is, however, that the screening element does not intersect the internal surface of the lamp envelope. In fact, it has been found that the lamp quickly becomes defective when the screening element extends as far as the space within the lamp envelope.

The invention is used very advantageously in electric lamps formed as gas discharge lamps because in such discharge lamps the electrolysis phenomenon may often occur to a very disturbing extent. Such a gas discharge lamp according to the invention has a discharge space enclosed by the lamp envelope, which space comprises a gas filling and is provided with a first and a second main electrode between which the discharge takes place during operation and furthermore with an auxiliary electrode arranged in the vicinity of the first main electrode in which the current lead-through conductor for the first main electrode and the current leadthrough conductor for the auxiliary electrode are sealed in a pinch, which conductors are substantially co-planar and comprise a foil mainly consisting of molybdenum and is characterized in that the metal screening element is placed in the pinch between the foils and substantially in the plane determined by the foils and that the screening element has the same potential as the auxiliary electrode during operation.

Likewise as the known gas discharge lamps, the gas discharge lamps according to the invention have an auxiliary electrode which, as described in the preamble, may be connected outside the lamp through a resistor to a main electrode and which serves to ignite the lamp easily. As a result of the difference in electron emission power between auxiliary electrode and the adjacent main electrode the auxiliary electrode has a negative potential during operation relative to the main electrode. The phenomena of electrolysis which conse quently might occur on the auxiliary electrode are prevented according to the invention by a metal screening element located between the current lead throughconductors in the pinch. These conductors are substantially co-planar and the screening element is in the same plane. The screening element is connected to the current lead-through conductor for the auxiliary electrode in such a manner that this screening element assumes the same potential as the auxiliary electrode. This construction according to the invention provides a very satisfactory screening of the current lead through conductor for the auxiliary electrode because the said conductor for the auxiliary electrode is substantially entirely screened by the screening element as viewed from the current lead-through conductor for the main electrode.

It has been found that optimum results in gas discharge lamps according to the invention are obtained when the screening element extends as far as the vicinwithin the discharge space and in which the screening element extends in said elevation beyond the part of the current lead-through conductor of the auxiliary electrode located in the pinch. A screening which is as complete as possible is obtained with this construction while the risk of electrolysis along paths around the part of the screening element facing the discharge space is excluded as much as possible.

It is possible to connect the screening element within the pinch to the current lead-through conductor for the auxiliary electrode in order to bring the two components at the same potential. However, discharge lamps according to the invention are preferred in which the screening element is passed to the exterior through the pinch and is connected outside the lamp to a conductor secured to the current lead-through conductor for the auxiliary electrode. In fact, a reliable pinch seal can be manufactured more easily in this manner.

The screening element may be, for example, a foil mainly consisting of molybdenum. However, a wire of high melting point metal is preferably used, for example, tungsten, molybdenum or tantalum as a screening element. Such a wire-shaped screening element yields optimum results.

The invention is preferably used in high-pressure mercury vapour discharge lamps which in addition to mercury also comprise a rare gas as a starter gas. In such lamps the phenomenon of electrolysis may be very disturbing especially when the lamps are intended for the horizontal operating condition where the auxiliary electrode is located below the main electrode.

Such high-pressure mercury vapour discharge lamps according to the invention are especially preferred which in addition to mercury and a rare gas comprise at least one metal halide. Notably when such a halidecontaining lamps is provided with an alkali metal halide the phenomena of electrolysis may be very serious because alkali metal may penetrate the material of the pinch from the discharge space and may cause an increase of a number of charge carriers and consequently an increase of the electrolysis current.

The invention may likewise be used to great advantage in electric incandescent lamps, for example, in halogen lamps which are intended for direct voltage operation and are provided with a filament body located within the lamp envelope which body can be connected to a direct voltage source by means of two current lead-through conductors sealed in one pinch. The said current lead-through conductors are then substantially co-planar and comprise a foil mainly consistin g'of molybdenum. According to theinvention electrolysis in the pinch of such an incandescent lamp is prevented by a metal screening element placed in the pinch between the foils and substantially in the plane determined by the foils. The screening element is then connected to the negative terminal of the voltage source during operation of the lamp.

The invention will now be described in greater detail with reference to a drawing in which FIG. 1 shows a metal halide-containing high-pressure mercury vapour discharge lamp according to the invention and in which FIG. 2 is a cross-sectional of an embodiment of a pinch construction and screening element for use in a lamp according to the invention.

FIG. 3 shows an incandescent lamp according to the invention.

In FIG. 1, l is the quartz glass discharge tube of a high-pressure mercury vapour discharge lamp according to the invention. The main electrodes 2 and 3 con sisting of tungsten spirals secured to tungsten current lead-through conductors 4 and 5 are present at the ends of the tube 1. These conductors 4 and 5 are passed in a vacuum-tight manner through the

pinches

6 and 7, respectively. The vacuum-tight seal is obtained by forming part of the conductors 4 and 5 as molybdenum foils 8 and 9, respectively. An auxiliary electrode 10 consisting of a tungsten pin is placed in the vicinity of the main electrode 2. The auxiliary electrode 10 is passed in a vacuum-tight manner through the pinch 6 by means of a current lead-through conductor 1 1 comprising a molybdenum foil 12. The tube 1 is suspended in a glass outer envelope 13 by means of metal strips 14 and .15 which clamp about the

pinches

6 and 7 and are secured to the supporting terminals or

current supply members

16 and 17, respectively. These supporting

terminals

16 and 17 also serve as current supply members for the electrodes 2 and 3 and are passed in a vacuumtight manner through the outer envelope 13 and are connected to the contacts of the lamp cap 18. The auxiliary electrode 10 facing the main electrode 2 is connected outside the discharge tube 1 through a resistor 19 to the current supply conductor 17 for the main electrode 3. A screening element 20 is sealed in the pinch between the current lead-through conductors 1 1, l2 and 4, 8 of auxiliary electrode 10 and main electrode 2. This element 20 consists of a tungsten wire and is located in the plane of the molybdenum foils 8 and 12. The wire 20 extends in the pinch 6 up to a distance of approximately 2 mm from the internal surface of the discharge tube 1 and is connected outside the lamp to the current supply conductor 21 for the auxiliary electrode 10.

The discharge tube 1 is provided with a quantity of mercury completely evaporating during operation of the lamp and furthermore with the iodides of sodium, thallium and indium. Furthermore a quantity of rare gas is introduced as an ignition gas into the tube 1. The distance between the electrodes 2 and 3 is approximately 40 mm. The lamp has a power of 400 W during operation.

Known lamps having a construction identical to that of the lamp shown in FIG. 1 but having no screening element 20 become defective in many cases after an operating period of 1000 to 2000 hours as a result of attack of the quartz around the lead-through

conductor

11, 12, particularly around the part of the molybdenum foil 12. adjoining 11. In lamps according to the invention having the construction shown in FIG. 1 there is no discolouration or only a very slight discolouration around the lead-through

conductor

11, 12 after an operating period of several thousand hours. In the lamps according to the invention a discolouration of the quartz around the screening element 20 is found to occur. This discolouration does not have any detrimental results.

FIG. 2 shows a preferred embodiment in a crosssection of a pinch construction and a screening element for a lamp according to the invention. The reference numeral 120 denotes the quartz glass pinch body which changes over to the quartz glass wall 121 of the lamp. The pinch 120 has an elevation 22 projecting within the lamp. A screening element 23 which extends into the elevation 22 is sealed in the pinch. The element 23 consisting of a tungsten wire extends in the pinch in the direction of the inner surface 24 of the lamp wall up to beyond those parts of the

portions

25 and 26 of the current lead-through

conductors

25, 27, 29 and 26, 28, 30 which are located within the pinch. The screening element 23 is connected outside the lamp to the current lead-through

conductor

25, 27, 29 which assumes a negative potential during operation of the lamp relative to the lead-through

conductor

26, 28, 30.

In FIG. 3 the reference numeral 30 denotes the wall of a halogen incandescent lamp according to the invention. The lamp is sealed by a pinch 31 through which the current lead-through

conductors

32, 34, 36 and 33, 35, 37 are passed in a vacuum-tight manner. These conductors provide for the current supply of the filament body 38 consisting of a tungsten spiral. The lamp is intended for direct voltage operation and the conductor 33 is connected to the negative terminal and the conductor 32 is connected to the positive terminal of a voltage source. Electrolysis phenomena on the negative current lead-through

conductor

33, 35, 37 particularly on the molybdenum foil 35 are prevented by the tungsten wire screening element 39 sealed in the pinch 31. The element 39 is connected outside the pinch 31 to the negative current lead-through conductor 33.

What is claimed is:

1. An electric lamp for use with an associated electric power supply which comprises: a radiation transmitting lamp envelope, means for sealing in a vacuum-tight manner at one end of said envelope, said means including a pinch, at least two current lead-through conductors extending through said pinch in sealed relation said lead-through conductors having an electric voltage comprising a direct voltage component being present between said conductors during operation of the lamp from the associated electric power supply, a metal screening element disposed in the pinch between the two current lead-through conductors, said screening element not intersecting the internal surface of the lamp envelope and being connected to the current lead-through conductor which at an average has a negative pontential relative to the other current leadthrough conductor during operation.

2. A lamp asclaimed in claim 1 wherein said lamp is a gas discharge lamp having a gas-filled discharge space surrounded by said lamp envelope, said lamp including a first and a second main electrode between which a discharge is effected during operation, said lamp further including an auxiliary electrode arranged in the vicinity of said first main electrode, said lead-through conductors being connected to said first electrode and said auxiliary electrode respectively, said conductors being disposed in substantially co-planar relationship and comprising a foil primarily consisting of molybdenum, said metal screening element being disposed in the pinch between the foils and substantially in the plane determined by said foils, and means for maintaining said screening element at the same potential as said auxiliary electrode during lamp operation.

3. A gas discharge lamp as claimed in claim 2, wherein said screening element in said pinch extends up to at least a distance of 0.5 mm from the internal surface of the lamp envelope.

4. A gas discharge lamp as claimed in claim 2, wherein said pinch has an axial portion projecting within the discharge space intermediate said leadthrough conductors extending from said pinch into said lamp envelope, said screening element being disposed in said axial portion.

5. A gas discharge lamp as claimed in claim 2, wherein said screening element extends from said pinch and is connected outside said lamp to a conductor secured to said current lead-through conductor for said auxiliary electrode.

6. A gas discharge lamp as claimed in claim 2, wherein said screening element is a wire of high melting point metal.

7. A lamp as claimed in claim 6 wherein said lamp is a high-pressure mercury vapour discharge lamp in which mercury and a rare gas as an ignition gas are disposed in said discharge space.

8. A high-pressure mercury vapour discharge lamp as claimed in claim 7 in which at least one metal halide is disposed in said discharge space.

9. A lamp as claimed in claim 8 wherein said halide is an alkali metal halide.

10. A lamp as claimed in claim 1, said lamp being an incandescent lamp for use with an associated direct voltage supply, and having a filament body disposed within said lamp envelope, said current lead-through conductors sealed in one pinch and being substantially co-planar and comprising a foil primarily consisting of molybdenum, said metal screening element being disposed in the pinch between the foils and substantially in the plane determined by the foils, and said screening element being connected to the negative terminal of the associated direct voltage source during lamp operatlOl'l.

UNITED sTATEs PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENTNO.I 3,906,275 DATED September 16, 1975 INVENTORQ) RAYMOND FRANCOIS SPIESSENS ET AL it is certified that error appears in the above-identifiedpatent and that said Letters Patent are hereby corrected as shown below:

IN THE ABSTRACT line 7, "scrreming" should read -screening+ En'gncd and Scaled this twenty-third 1y 0f March 1976 [SEAL] Attest:

RUTH C. MASON C. MARSHALL DANN Arresting Officer Commissioner oj'Parents and Trademarks UNITED STATES PATENT AND TRADEMARK OFFICE CETTFTCATE 0F ECTTQN PATENT NO. 3,906,275 DATED September 16, 1975 INV ENTOR(S) RAYMOND FRANCOIS SPIESSENS ET AL It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

IN THE ABSTRACT line 7, "scrreming should read -screening- Signed an Sealed this twenty-third fly O March 1 976 {SEAL} Arrest:

C. MARSHALL DANN Commissioner ofParenrs and Trademarks RUTH C. MASON Arresting Officer

Claims

1. An electric lamp for use with an associated electric power supply which comprises: A radiation transmitting lamp envelope, means for sealing in a vacuum-tight manner at one end of said envelope, said means including a pinch, at least two current lead-through conductors extending through said pinch in sealed relation said lead-through conductors having an electric voltage comprising a direct voltage component being present between said conductors during operation of the lamp from the associated electric power supply, a metal screening element disposed in the pinch between the two current lead-through conductors, said screening element not intersecting the internal surface of the lamp envelope and being connected to the current lead-through conductor which at an average has a negative pontential relative to the other current lead-through conductor during operation.

2. A lamp as claimed in claim 1 wherein said lamp is a gas discharge lamp having a gas-filled discharge space surrounded by said lamp envelope, said lamp including a first and a second main electrode between which a discharge is effected during operation, said lamp further including an auxiliary electrode arranged in the vicinity of said first main electrode, said lead-through conductors being connected to said first electrode and said auxiliary electrode respectively, said conductors being disposed in substantially co-planar relationship and comprising a foil primarily consisting of molybdenum, said metal screening element being disposed in the pinch between the foils and substantially in the plane determined by said foils, and means for maintaining said screening element at the same potential as said auxiliary electrode during lamp operation.

4. A gas discharge lamp as claimed in claim 2, wherein said pinch has an axial portion projecting within the discharge space intermediate said lead-through conductors extending from said pinch into said lamp envelope, said screening element being disposed in said axial portion.

9. A lamp as claimed in claim 8 wherein said halide is an alkali metal halide.

10. A lamp as claimed in claim 1, said lamp being an incandescent lamp for use with an associated direct voltage supply, and having a filament body disposed within said lamp envelope, said current lead-through conductors sealed in one pinch and being substantially co-planar and comprising a foil primarily consisting of molybdenum, said metal screening element being disposed in the pinch between the foils and substantially in the plane determined by the foils, and said screening element being connected to the negative terminal of the associated direct voltage source during lamp operation.