CA1060533A - Metal halide discharge lamp starting electrode - Google Patents
Metal halide discharge lamp starting electrodeInfo
- Publication number
- CA1060533A CA1060533A CA230,745A CA230745A CA1060533A CA 1060533 A CA1060533 A CA 1060533A CA 230745 A CA230745 A CA 230745A CA 1060533 A CA1060533 A CA 1060533A
- Authority
- CA
- Canada
- Prior art keywords
- electrode
- arc tube
- envelope
- starting
- inleads
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J61/00—Gas-discharge or vapour-discharge lamps
- H01J61/02—Details
- H01J61/54—Igniting arrangements, e.g. promoting ionisation for starting
- H01J61/545—Igniting arrangements, e.g. promoting ionisation for starting using an auxiliary electrode inside the vessel
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- Discharge Lamps And Accessories Thereof (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
In metal halide arc lamps utilizing fused silica arc tubes, prevention of electrolysis between the inleads to the main and auxiliary starting electrodes has generally required a shorting thermal switch. Electrolysis can be prevented in a simpler way by using a stub starter, that is an auxiliary electrode having such a short projection into the arc chamber that there is substantially no conduction thereto on either half cycle when the lamp is operating.
In metal halide arc lamps utilizing fused silica arc tubes, prevention of electrolysis between the inleads to the main and auxiliary starting electrodes has generally required a shorting thermal switch. Electrolysis can be prevented in a simpler way by using a stub starter, that is an auxiliary electrode having such a short projection into the arc chamber that there is substantially no conduction thereto on either half cycle when the lamp is operating.
Description
- ' LD-6596 ` ` 1060533 The invention relates to high pressure arc lamp8 having a pair of main electrodes, and an auxiliary ~tarting lectrode sealod into an ~ velope of vitreous material such as fu~ed 8iliC~, and i8 more particularly concerned with the auxiliary electrode and probl m~ of electrolysis incident , thereto.
The electrodes of metal halide discharge lamps are gen-rally supported by inleads which includ a thin molybdenum , ., :.
... ribbon 80ction sealed through a pre~s seal at oach end of an longat-d fused ~ilica tub- which serves as the arc chamber To facilit-t- ~t~rting of the discharge, an auxiliary starting electrode i8 generally provided adjacent one of the main lectrodes An arc can be ignitod betweon the starter elec-trode and its adjacent main electrode at a much lower voltage j than i~ rguirod to ignite an arc between th- two main lec-trod ~ By this m an~, the lamp tarting voltag reguirement ~ii may be r-duc-d to a value r-asonably clo~e to that reguired for ~u~taining the arc in normal lamp operation During operation of metal halide lamps containing alkali or alkaline earth motal additiv-s, lectrolysis can occur within the pr-~s ~eal between the inleads of the starter and of the adjacent ~ain electrode if an electric potential sxists between them The lectrolysis occurs primarily as alkali-ion displacement through the silica, and c-n alway~
occur, irrespective of lamp fill, because high silica glass or fu~ed silica contains minute quantities of alkali metals as impurities Howevor it is much greater ~hen an alkali metal, such as sodium in the form of an iodide, i8 providod as part of the lamp fill, and is greatly aggravated when a net potential difference is allowed to exist between the starter and the adjacent main electrode Electrolysis causes the silicai to . . . ~ . ~ . - .
: .. - . , .
` ~ ~ LD-6596 ~060S33 ~:
devitrify and leads to ~racking of the hermatic ~eal, or alter-nately it deteriorates the molybdenum ribbon to the point of failure and either event end~ the Life of the lamp.
Several schemes have been proposed to overcome the el~ctrolysis pro~lem in metal halide lamps containing alkali metal in the fill. The most widely used i~ that of U.S. patent ~,226,597 issued December 28, 1965 - Green, which provides a thermal switch in the form of a bimetal element to electrically short-circuit the starter electrode to the adjacent main electrode when the lamp reaches normal operating temperature.
An alternative proposed by U.S. patent 3,619,711 i~sued November 9, 1971 - Freese, provides a semiconductor diode connected between the starter and the adjacent main electrode in such polarity that the Ytarter cannot develop a n~gative potential. ~hese schemes all require the addition of active components that add cost and derogate from reliability.
Bimetallic switches are difficult to de~ign for satisfactory operation under all lamp operating conditions. Under prolonged exposure of the switch to the heat emanating from the arc tube, the bimetal may take a "set" in the stre~sed position resulting in progressively longer time intervals for closure. While the switch is open, electrolysis can occur and in the extreme condition, the switch may fail to close altogether and the lamp will fail within a few hundred hours thereafter. As for s~mi-conductor device~, they are subject to a high rat~ of failure because the high temperature of the lamp environment both during processing and in subse~uent operation are hostile to it.
The object of the invention i~ to provide a metal halide arc discharge lamp having starting mean~ which sub~tantiaL~
eliminates lamp failures due to electrolysi~ and w~ich does not require the addition of co~ponents which are ~ubject to ' -~ ~ ~060533 LD-6596 ; failure such as thermal switches or ~emiconductor device In accordance with our invention we have found that 80 long as no discharge occurs between the auxiliary #tarting electrode and the adjacent main electrode on eith~r half cycle during normal la~p operation, there will be no net potential differonce between them, that i8, there will be no average or D C. potential extending over more than one full A C cycle Under these conditions, electrolysis i~ substantially liminated and no external circuit devico~ are needed to prevent eloctrolytic failure The condition is achieved by u~ing a ~hort starter electrodo, som times referred to as a stub starter, and~by di~posing the starter electrode tip as far from the tip of the main olectrode as po~sible within the practical limit- of extending the inlead~ for both el-ctrod 8 through the ~ame pinch or pres~ seal We have found that the starter electrode need hardly project out of the ~ilica of the pinch into the arc tube ~o long as a path is provided whereby the discharge can reach the tip of the starter The tarter electrode should not project into the envelop~ a distance greater than lOX of the inside diameter of the tubular envelope In addition to eliminating the co~t of the bimetallic switch, our invention sub~tantially improve~ lamp reliability Our starter configuration also works well with the starter end down and i~ not limited to having the starter at the upper end a8 i8 Dormally the ca~e with la~ps using a thermal switch In the drawings FIG. 1 is a side view of a ~etal halide lanp provided with a ~tub starter embodying the invention FIG 2 i8 an enlarged detail of the upper end of the arc tube ~howing the stub ~tarter 106~533 FIG. 3 ia a typical metal halide lamp ~chematic circuit showing the electrode connectionæ.
FIG. 4 ~hows voltag~ waveform~ obtained in the lamp under various operating oDnditions.
A metal halide vapor arc lamp 1 enbodying the ~ --inv~ntion comprises an outer vitreous envelope or jacket 2 having a neck portion 3 closed by a re-entrant ~tem 4. Stiff -~
inlead wires 5, 6 extending through the stem are connected at their outer end~ to the contacts of a screw base 7 and have conneGtions from their inner ends to the inner arc tube 8.
The arc tube is formed of fused ~ilica and ha~ sealed therein at opposite ends main arcing electrodes 9,10 plus an auxiliary ~tarting electrode 11. The arc tube i8 supported within the outer envelope by a divided or two-part mount, 12 at the base end and 13 at the dome end. Each part comprises a pair of longitudinally extending support rods bridged by me~al straps 14 which clamp about the pinched ends of the arc tube. The base end mount part i5 welded to inlead 5 and serve3 as a conductor to main electrode 9. Main electrode 10 i~ connected to inl~ad 6 by curving wire 15. Starter electrode 11 is conn~cted to inlead 6 through current limiting resistor 16.
The arc tube contains argon at a pressure of about 25 torr, a quantity of mercury #ubstantially vaporized during operation and exterting a partial pressure o~ 1 to lS atmo~pheres, and sodium iodide, scandium iodide and thorium iodide in excess of ~h quantity vaporized at the operating temperature. The outer envelope is filled with an inactive gas, suitably nitrogen at about one half atmo~phere pressure.
The invention is more particularly concerned with -auxiliary electrode 11 at the upper end of the arc tube and its physical relationship to main electrode 9, both shown ,, . -. , - . . . :
:, .~. ; , 1060S33 1,D-6596 to a larger scale in FIG. 2. The main electrode comprise~
a core portion which may be a prolongation of wire 18 consisting of suitable electrode metal ~uch a~ tungsten or molybdenum; the core portion is surrounded by a tungsten or molybdenum wire helix 19. The tip of electrode 9 i~ located `~
close to the center of the rounded end of the arc tube. The auxiliary ~tarting electrode 11 compri~es the inwardly projecting end or ~tub of wire 20 which may likewise be of tungsten or molybdenu~.~ The outer ends of wires 18 and 20 are welded to molybdenum ribbon or foil connector~ 21,22 which are completely embedded within the pinch or press ~eal end 23 of arc tube 8. Relatively short molybdenum wires 24,25 are wolded to the end~ of the molybdenum ribbon connectorQ and ~erve to convey current to electrodes 9 and 11, respectivoly.
FIG. 3 illustrates a typical circuit for operating a high pres~ure metal vapor discharge lamp. Tho commercial line voltage Em is sinowave alternating current at a frequency of 60 hz. or alternat~ly 50 hz. and at a voltage from 100 to 600 volts rms. Typically Zl is a linear inductor having an impedance from 20 to 100 ohms and serving to lLmit lamp current. Z2 i8 typically a resistor of 10,000 to 100,000 ohms impedance which serves to limit the starter electrode current and which corre~ponds to resistor 16 in FIG. 1. Starting is effected by breakdown of the gap between the ~tarter and adjacent main electrode into a glow discharge. The local ionization greatly reduces the voltage required to break down the gap between the main electrodes.
The common pract~ce up to now has been to locate the tip of the starter electrode as near to the tip of the main electrode as pos~ible while allowing for manufacturing tolerance and the need to avoid contact between them. When ', ' : -1060533 ~D-6596 ., such lamps are operated in a circuit such as illu~trated in FIG. 3 a discharge will occur between the main electrode and the starter electrode during normal lamp operation. Breakdown will normally occur on the positive half cycle of lamp voltage when the starter electrode acts as anode. The adjacent main electrode is already acting as cathode and providing thermionic electron emission to support the main discharge. During the negative half cycle when the starter electrode must act as cathode, it i8 usually too cold to provide thermionic emission.
Thus on the negative half cycle a discharge will generally not D
ignite, and in cases where ignition does occur the current remains low and the burning voltage is quite high.
Referring to FIG. 4, the applied sinusoidal line voltage i8 represented by solid line curve Em~ After ignition and during normal operation, the voltage acros~ the main electrodes of th~ lamp is represented by solid line curve Ee.
The voltage between the starter electrode and the adjacent main electrode is represented by dash line E8. When using the ~ prior art starting electrodes which projected into the ;~
nvelop- close to the tip of the main electrode, on the positive half cycle of the starter electrode, breakdown occurs after ,:.
the initial pèak indicated at 30 and current flow through impedance Z2 maintains the starter electrode voltage low for -th remainder of the half cycle as indicated at 31. On the negative half cycle there i8 no conduction to the starter electrode and the voltage i8 high as indicated at 32. The end r--ult is that a net or average potential difference exists between th main and starter electrode over a full cycle.
A n-gative net potential at the ~tarter electrode favors displacement of positive sodium ions through the silica from the region of the main electrode inlead to that of the 106~)533 starter electrode inlead. The hermetic seals of the inleads occur at the molybdenum foils and sodium iodide vapor may enter the crevices alongside the wires 18,19 leading up to the foils. The sodium attack on the inleads i8 generally most severe at the forward corner of ~tarter foil next to the main electrode ~oil, as indicated by arrow 33. At the usual operating temperatures of metal halide lamps, electrolysis within the seal area leading to cracXing of the seal results in la~p failure in a few hundred hours of operation.
The principle of operation of the thermal switch which has boen used up to now to prevent electroly~is has been to eliminate all potential between the starter and adjacent main electrode. our invention uses a different principle, namely to make the voltage between the starter and the main electrode equal and opposite on succes~ive half cycles. Thi~ condition is realized when no discharge occurs between the ~tart-r and main electrode on either half cycle.
This eliminates any average D.C. potential and ~ubstantially oliminates electrolysis without need for external circuit 20- devices. To in~ure no di~charge on either half cycle, a short starter electrode is usea and the starter electrode is di~posed as far from the tip of the main electrode as possible within the practical limits of extending the inleads for both electrode~ through the same pinch or pres~ seal. ~he starter electrode voltage E~ on the positive half cycle then follows dotted line curve 34 and is symmetrical on positive and negative half cycle~.
Referring to FIG. 2, wire portion 20 of the starter electrode is cut off to a short stube which barely projects into the arc cha~ber cavity. We ~have found that the ~tarter electrode need hardly project out of the silica of the pinch ~ - .
~0~533 LD-6595 . .
and may even be buried witllin the silica pinch as long as a path is provided whereby the discharge can reach the tip of the starter. In order to maintain congruent starter voltage waveforms on positive and negative half cycles, we have found ' '~
that the starter should project into the generally rounded end of the envelope a distance no greater than 10% of the arc tube diameter in order to insure the necessary minimurn spacing between its tip and the tip of the main electrode.
Any greater projection may result in breakdown on the negative '' 1~ half cycle. ;
As long as no discharge occurs between starter and ~i~
adjacent main electrode during normal lamp operation, thera ' will be no net potential difference between them and no external circuit devices are needed to prevent electrolytic failure. ' Our invention not only eIiminates the cost of the bimetallic ~j switch,' it also substantially improves lamp reliability. ~ ''' Furthermore our starter configuration works well with the ~ '' starter end of the lamp lowermost, and is not limited to having the starter at the upper end as is normally the case ~ith lamps , '' using a thermal switch.' The starter works weIl at either end ~''' of the lamp, particularly when using an arc tube having formed ~' end chambers as des'cribed and claimed in Canadian patent ~; ' 1,004,721 issued February L, 1977 to Wayne R. HeIlman, ; Klaus Gottschalk and Edward C. DeGeorge, titled "Discharge Lamp Having Blow-Molded Arc Tube Ends" and assigned to the present assignee.' The reason that bIow-molded lamps operate better .;
with a stub-starter may be that the'uniformity of the end "
chambers permits operation at a slightly higher temperature '' than ormerly possible. Thus a bIow-molded lamp using '~
the stub-starter of our invention permits a universal burning position lamp design capahle of replacing ~' ,~
the two la~p type~ formerly u~ed, namely the base-up and base-down versions.
We have found that the stub-startor configuration of our invention i8 a~ effective in reducing la~p voltago starting reguirements as was the prior art configuration not only at room temperature but also at low operating ten- -.
peraturos down to minus 20F. Thus our invention achieves elimination of olectrolysis, greater reliability, universal burning position of the la~pJ, and an appreciable co~t reduction by tb li ination d xternal circuit d vic -.
a, : S, ..
A
~, ' ~ ,"
_ g _ t '................................. . .
The electrodes of metal halide discharge lamps are gen-rally supported by inleads which includ a thin molybdenum , ., :.
... ribbon 80ction sealed through a pre~s seal at oach end of an longat-d fused ~ilica tub- which serves as the arc chamber To facilit-t- ~t~rting of the discharge, an auxiliary starting electrode i8 generally provided adjacent one of the main lectrodes An arc can be ignitod betweon the starter elec-trode and its adjacent main electrode at a much lower voltage j than i~ rguirod to ignite an arc between th- two main lec-trod ~ By this m an~, the lamp tarting voltag reguirement ~ii may be r-duc-d to a value r-asonably clo~e to that reguired for ~u~taining the arc in normal lamp operation During operation of metal halide lamps containing alkali or alkaline earth motal additiv-s, lectrolysis can occur within the pr-~s ~eal between the inleads of the starter and of the adjacent ~ain electrode if an electric potential sxists between them The lectrolysis occurs primarily as alkali-ion displacement through the silica, and c-n alway~
occur, irrespective of lamp fill, because high silica glass or fu~ed silica contains minute quantities of alkali metals as impurities Howevor it is much greater ~hen an alkali metal, such as sodium in the form of an iodide, i8 providod as part of the lamp fill, and is greatly aggravated when a net potential difference is allowed to exist between the starter and the adjacent main electrode Electrolysis causes the silicai to . . . ~ . ~ . - .
: .. - . , .
` ~ ~ LD-6596 ~060S33 ~:
devitrify and leads to ~racking of the hermatic ~eal, or alter-nately it deteriorates the molybdenum ribbon to the point of failure and either event end~ the Life of the lamp.
Several schemes have been proposed to overcome the el~ctrolysis pro~lem in metal halide lamps containing alkali metal in the fill. The most widely used i~ that of U.S. patent ~,226,597 issued December 28, 1965 - Green, which provides a thermal switch in the form of a bimetal element to electrically short-circuit the starter electrode to the adjacent main electrode when the lamp reaches normal operating temperature.
An alternative proposed by U.S. patent 3,619,711 i~sued November 9, 1971 - Freese, provides a semiconductor diode connected between the starter and the adjacent main electrode in such polarity that the Ytarter cannot develop a n~gative potential. ~hese schemes all require the addition of active components that add cost and derogate from reliability.
Bimetallic switches are difficult to de~ign for satisfactory operation under all lamp operating conditions. Under prolonged exposure of the switch to the heat emanating from the arc tube, the bimetal may take a "set" in the stre~sed position resulting in progressively longer time intervals for closure. While the switch is open, electrolysis can occur and in the extreme condition, the switch may fail to close altogether and the lamp will fail within a few hundred hours thereafter. As for s~mi-conductor device~, they are subject to a high rat~ of failure because the high temperature of the lamp environment both during processing and in subse~uent operation are hostile to it.
The object of the invention i~ to provide a metal halide arc discharge lamp having starting mean~ which sub~tantiaL~
eliminates lamp failures due to electrolysi~ and w~ich does not require the addition of co~ponents which are ~ubject to ' -~ ~ ~060533 LD-6596 ; failure such as thermal switches or ~emiconductor device In accordance with our invention we have found that 80 long as no discharge occurs between the auxiliary #tarting electrode and the adjacent main electrode on eith~r half cycle during normal la~p operation, there will be no net potential differonce between them, that i8, there will be no average or D C. potential extending over more than one full A C cycle Under these conditions, electrolysis i~ substantially liminated and no external circuit devico~ are needed to prevent eloctrolytic failure The condition is achieved by u~ing a ~hort starter electrodo, som times referred to as a stub starter, and~by di~posing the starter electrode tip as far from the tip of the main olectrode as po~sible within the practical limit- of extending the inlead~ for both el-ctrod 8 through the ~ame pinch or pres~ seal We have found that the starter electrode need hardly project out of the ~ilica of the pinch into the arc tube ~o long as a path is provided whereby the discharge can reach the tip of the starter The tarter electrode should not project into the envelop~ a distance greater than lOX of the inside diameter of the tubular envelope In addition to eliminating the co~t of the bimetallic switch, our invention sub~tantially improve~ lamp reliability Our starter configuration also works well with the starter end down and i~ not limited to having the starter at the upper end a8 i8 Dormally the ca~e with la~ps using a thermal switch In the drawings FIG. 1 is a side view of a ~etal halide lanp provided with a ~tub starter embodying the invention FIG 2 i8 an enlarged detail of the upper end of the arc tube ~howing the stub ~tarter 106~533 FIG. 3 ia a typical metal halide lamp ~chematic circuit showing the electrode connectionæ.
FIG. 4 ~hows voltag~ waveform~ obtained in the lamp under various operating oDnditions.
A metal halide vapor arc lamp 1 enbodying the ~ --inv~ntion comprises an outer vitreous envelope or jacket 2 having a neck portion 3 closed by a re-entrant ~tem 4. Stiff -~
inlead wires 5, 6 extending through the stem are connected at their outer end~ to the contacts of a screw base 7 and have conneGtions from their inner ends to the inner arc tube 8.
The arc tube is formed of fused ~ilica and ha~ sealed therein at opposite ends main arcing electrodes 9,10 plus an auxiliary ~tarting electrode 11. The arc tube i8 supported within the outer envelope by a divided or two-part mount, 12 at the base end and 13 at the dome end. Each part comprises a pair of longitudinally extending support rods bridged by me~al straps 14 which clamp about the pinched ends of the arc tube. The base end mount part i5 welded to inlead 5 and serve3 as a conductor to main electrode 9. Main electrode 10 i~ connected to inl~ad 6 by curving wire 15. Starter electrode 11 is conn~cted to inlead 6 through current limiting resistor 16.
The arc tube contains argon at a pressure of about 25 torr, a quantity of mercury #ubstantially vaporized during operation and exterting a partial pressure o~ 1 to lS atmo~pheres, and sodium iodide, scandium iodide and thorium iodide in excess of ~h quantity vaporized at the operating temperature. The outer envelope is filled with an inactive gas, suitably nitrogen at about one half atmo~phere pressure.
The invention is more particularly concerned with -auxiliary electrode 11 at the upper end of the arc tube and its physical relationship to main electrode 9, both shown ,, . -. , - . . . :
:, .~. ; , 1060S33 1,D-6596 to a larger scale in FIG. 2. The main electrode comprise~
a core portion which may be a prolongation of wire 18 consisting of suitable electrode metal ~uch a~ tungsten or molybdenum; the core portion is surrounded by a tungsten or molybdenum wire helix 19. The tip of electrode 9 i~ located `~
close to the center of the rounded end of the arc tube. The auxiliary ~tarting electrode 11 compri~es the inwardly projecting end or ~tub of wire 20 which may likewise be of tungsten or molybdenu~.~ The outer ends of wires 18 and 20 are welded to molybdenum ribbon or foil connector~ 21,22 which are completely embedded within the pinch or press ~eal end 23 of arc tube 8. Relatively short molybdenum wires 24,25 are wolded to the end~ of the molybdenum ribbon connectorQ and ~erve to convey current to electrodes 9 and 11, respectivoly.
FIG. 3 illustrates a typical circuit for operating a high pres~ure metal vapor discharge lamp. Tho commercial line voltage Em is sinowave alternating current at a frequency of 60 hz. or alternat~ly 50 hz. and at a voltage from 100 to 600 volts rms. Typically Zl is a linear inductor having an impedance from 20 to 100 ohms and serving to lLmit lamp current. Z2 i8 typically a resistor of 10,000 to 100,000 ohms impedance which serves to limit the starter electrode current and which corre~ponds to resistor 16 in FIG. 1. Starting is effected by breakdown of the gap between the ~tarter and adjacent main electrode into a glow discharge. The local ionization greatly reduces the voltage required to break down the gap between the main electrodes.
The common pract~ce up to now has been to locate the tip of the starter electrode as near to the tip of the main electrode as pos~ible while allowing for manufacturing tolerance and the need to avoid contact between them. When ', ' : -1060533 ~D-6596 ., such lamps are operated in a circuit such as illu~trated in FIG. 3 a discharge will occur between the main electrode and the starter electrode during normal lamp operation. Breakdown will normally occur on the positive half cycle of lamp voltage when the starter electrode acts as anode. The adjacent main electrode is already acting as cathode and providing thermionic electron emission to support the main discharge. During the negative half cycle when the starter electrode must act as cathode, it i8 usually too cold to provide thermionic emission.
Thus on the negative half cycle a discharge will generally not D
ignite, and in cases where ignition does occur the current remains low and the burning voltage is quite high.
Referring to FIG. 4, the applied sinusoidal line voltage i8 represented by solid line curve Em~ After ignition and during normal operation, the voltage acros~ the main electrodes of th~ lamp is represented by solid line curve Ee.
The voltage between the starter electrode and the adjacent main electrode is represented by dash line E8. When using the ~ prior art starting electrodes which projected into the ;~
nvelop- close to the tip of the main electrode, on the positive half cycle of the starter electrode, breakdown occurs after ,:.
the initial pèak indicated at 30 and current flow through impedance Z2 maintains the starter electrode voltage low for -th remainder of the half cycle as indicated at 31. On the negative half cycle there i8 no conduction to the starter electrode and the voltage i8 high as indicated at 32. The end r--ult is that a net or average potential difference exists between th main and starter electrode over a full cycle.
A n-gative net potential at the ~tarter electrode favors displacement of positive sodium ions through the silica from the region of the main electrode inlead to that of the 106~)533 starter electrode inlead. The hermetic seals of the inleads occur at the molybdenum foils and sodium iodide vapor may enter the crevices alongside the wires 18,19 leading up to the foils. The sodium attack on the inleads i8 generally most severe at the forward corner of ~tarter foil next to the main electrode ~oil, as indicated by arrow 33. At the usual operating temperatures of metal halide lamps, electrolysis within the seal area leading to cracXing of the seal results in la~p failure in a few hundred hours of operation.
The principle of operation of the thermal switch which has boen used up to now to prevent electroly~is has been to eliminate all potential between the starter and adjacent main electrode. our invention uses a different principle, namely to make the voltage between the starter and the main electrode equal and opposite on succes~ive half cycles. Thi~ condition is realized when no discharge occurs between the ~tart-r and main electrode on either half cycle.
This eliminates any average D.C. potential and ~ubstantially oliminates electrolysis without need for external circuit 20- devices. To in~ure no di~charge on either half cycle, a short starter electrode is usea and the starter electrode is di~posed as far from the tip of the main electrode as possible within the practical limits of extending the inleads for both electrode~ through the same pinch or pres~ seal. ~he starter electrode voltage E~ on the positive half cycle then follows dotted line curve 34 and is symmetrical on positive and negative half cycle~.
Referring to FIG. 2, wire portion 20 of the starter electrode is cut off to a short stube which barely projects into the arc cha~ber cavity. We ~have found that the ~tarter electrode need hardly project out of the silica of the pinch ~ - .
~0~533 LD-6595 . .
and may even be buried witllin the silica pinch as long as a path is provided whereby the discharge can reach the tip of the starter. In order to maintain congruent starter voltage waveforms on positive and negative half cycles, we have found ' '~
that the starter should project into the generally rounded end of the envelope a distance no greater than 10% of the arc tube diameter in order to insure the necessary minimurn spacing between its tip and the tip of the main electrode.
Any greater projection may result in breakdown on the negative '' 1~ half cycle. ;
As long as no discharge occurs between starter and ~i~
adjacent main electrode during normal lamp operation, thera ' will be no net potential difference between them and no external circuit devices are needed to prevent electrolytic failure. ' Our invention not only eIiminates the cost of the bimetallic ~j switch,' it also substantially improves lamp reliability. ~ ''' Furthermore our starter configuration works well with the ~ '' starter end of the lamp lowermost, and is not limited to having the starter at the upper end as is normally the case ~ith lamps , '' using a thermal switch.' The starter works weIl at either end ~''' of the lamp, particularly when using an arc tube having formed ~' end chambers as des'cribed and claimed in Canadian patent ~; ' 1,004,721 issued February L, 1977 to Wayne R. HeIlman, ; Klaus Gottschalk and Edward C. DeGeorge, titled "Discharge Lamp Having Blow-Molded Arc Tube Ends" and assigned to the present assignee.' The reason that bIow-molded lamps operate better .;
with a stub-starter may be that the'uniformity of the end "
chambers permits operation at a slightly higher temperature '' than ormerly possible. Thus a bIow-molded lamp using '~
the stub-starter of our invention permits a universal burning position lamp design capahle of replacing ~' ,~
the two la~p type~ formerly u~ed, namely the base-up and base-down versions.
We have found that the stub-startor configuration of our invention i8 a~ effective in reducing la~p voltago starting reguirements as was the prior art configuration not only at room temperature but also at low operating ten- -.
peraturos down to minus 20F. Thus our invention achieves elimination of olectrolysis, greater reliability, universal burning position of the la~pJ, and an appreciable co~t reduction by tb li ination d xternal circuit d vic -.
a, : S, ..
A
~, ' ~ ,"
_ g _ t '................................. . .
Claims (6)
1. An electric discharge arc tube for alternating current operation comprising:
a tubular envelope of vitreous material subject to electrolysis and deterioration under electrical stress at high temperatures;
an ionizable radiation-emitting filling within said envelope;
a pair of main thermionic arc-supporting electrodes mounted on inleads including foil portions extending through seals at the generally rounded ends of said envelope;
an auxiliary starting electrode adjacent one of said main electrodes and mounted on an inlead including a foil portion extending through an end seal generally side-by-side with and in close proximity to the foil portion of the adjacent main electrode at one end of said envalope; and a resistance permanently connecting said starting electrode to the opposite main electrode for starting purposes, said starting electrode projecting into said envelope a distance no greater than 10% of the inside diameter of said envelope, said starting electrode having its tip far enough from that of the adjacent main electrode that substantially no discharge occurs to said tip during normal operation, whereby there will be no net potential difference between said starting electrode and the adjacent main electrode and electrolysis in the seal region through which their inleads extend is sub-stantially eliminated.
a tubular envelope of vitreous material subject to electrolysis and deterioration under electrical stress at high temperatures;
an ionizable radiation-emitting filling within said envelope;
a pair of main thermionic arc-supporting electrodes mounted on inleads including foil portions extending through seals at the generally rounded ends of said envelope;
an auxiliary starting electrode adjacent one of said main electrodes and mounted on an inlead including a foil portion extending through an end seal generally side-by-side with and in close proximity to the foil portion of the adjacent main electrode at one end of said envalope; and a resistance permanently connecting said starting electrode to the opposite main electrode for starting purposes, said starting electrode projecting into said envelope a distance no greater than 10% of the inside diameter of said envelope, said starting electrode having its tip far enough from that of the adjacent main electrode that substantially no discharge occurs to said tip during normal operation, whereby there will be no net potential difference between said starting electrode and the adjacent main electrode and electrolysis in the seal region through which their inleads extend is sub-stantially eliminated.
2. An arc tube as in claim 1, wherein said envelope is fused silica.
3. An arc tube as in claim 1, wherein said envelope is fused silica, and the ionizable filling includes alkali metal halide.
4. An arc tube as in claim 3, wherein the inleads include molybdenum foils extending through press seals.
5. An alternating current metal halide electric discharge lamp comprising:
a tubular fused silica arc tube containing an inert gas with mercury and metal halide including a sodium halide;
a sealed outer envelope enclosing said arc tube but spaced therefrom;
a pair of main thermionic arc-supporting electrodes mounted on inleads including foil portions extending through seals at the generally rounded ends of said arc tube;
an auxiliary starting electrode adjacent one of said main electrodes and mounted on an inlead including a foil portion extending through an end seal generally side-by-side with and in close proximity to the foil portion of the adjacent main electrode at one end of said arc tube; and a resistance permanently connecting said starting electrode to the opposite main electrode for starting purposes;
said starting electrode being a wire projecting into said arc tube a distance no greater than 10% of the inside diameter of said arc tube, said starting electrode having its tip far enough from that of the adjacent main electrode that substantially no discharge occurs to said tip during normal operation, whereby there will be no net potential difference between said starting electrode and the adjacent main electrode and electrolysis in the seal region through which their inleads extend is substantially eliminated.
a tubular fused silica arc tube containing an inert gas with mercury and metal halide including a sodium halide;
a sealed outer envelope enclosing said arc tube but spaced therefrom;
a pair of main thermionic arc-supporting electrodes mounted on inleads including foil portions extending through seals at the generally rounded ends of said arc tube;
an auxiliary starting electrode adjacent one of said main electrodes and mounted on an inlead including a foil portion extending through an end seal generally side-by-side with and in close proximity to the foil portion of the adjacent main electrode at one end of said arc tube; and a resistance permanently connecting said starting electrode to the opposite main electrode for starting purposes;
said starting electrode being a wire projecting into said arc tube a distance no greater than 10% of the inside diameter of said arc tube, said starting electrode having its tip far enough from that of the adjacent main electrode that substantially no discharge occurs to said tip during normal operation, whereby there will be no net potential difference between said starting electrode and the adjacent main electrode and electrolysis in the seal region through which their inleads extend is substantially eliminated.
6. A lamp as in claim 5, wherein the inleads include molybdenum foils extending through press seals.
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US495638A US3909660A (en) | 1974-08-08 | 1974-08-08 | Metal halide discharge lamp starting electrode |
Publications (1)
Publication Number | Publication Date |
---|---|
CA1060533A true CA1060533A (en) | 1979-08-14 |
Family
ID=23969409
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
CA230,745A Expired CA1060533A (en) | 1974-08-08 | 1975-06-26 | Metal halide discharge lamp starting electrode |
Country Status (5)
Country | Link |
---|---|
US (1) | US3909660A (en) |
JP (1) | JPS5135580A (en) |
CA (1) | CA1060533A (en) |
DE (1) | DE2535031C3 (en) |
GB (1) | GB1512067A (en) |
Families Citing this family (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3993922A (en) * | 1976-01-05 | 1976-11-23 | Gte Sylvania Incorporated | Arc discharge lamp with integral trigger electrode |
US4413206A (en) * | 1981-06-04 | 1983-11-01 | Gte Products Corporation | Metal halide arc discharge lamp having electrolysis prevention means |
Family Cites Families (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US2660692A (en) * | 1950-03-30 | 1953-11-24 | Gen Electric | High-pressure discharge lamp |
US3234421A (en) * | 1961-01-23 | 1966-02-08 | Gen Electric | Metallic halide electric discharge lamps |
US3226597A (en) * | 1963-09-04 | 1965-12-28 | Gen Electric | High pressure metal vapor discharge lamp |
US3275885A (en) * | 1965-04-07 | 1966-09-27 | Gen Electric | High pressure discharge lamp with electrolysis preventing means |
US3619711A (en) * | 1969-10-27 | 1971-11-09 | Sylvania Electric Prod | High-pressure metal halide electric discharge lamp |
GB1343780A (en) * | 1970-06-26 | 1974-01-16 | Thorn Electrical Ind Ltd | Discharge lamps |
-
1974
- 1974-08-08 US US495638A patent/US3909660A/en not_active Expired - Lifetime
-
1975
- 1975-06-26 CA CA230,745A patent/CA1060533A/en not_active Expired
- 1975-07-09 GB GB28918/75A patent/GB1512067A/en not_active Expired
- 1975-07-22 JP JP50088947A patent/JPS5135580A/ja active Pending
- 1975-08-06 DE DE2535031A patent/DE2535031C3/en not_active Expired
Also Published As
Publication number | Publication date |
---|---|
DE2535031A1 (en) | 1976-02-26 |
DE2535031B2 (en) | 1978-07-27 |
JPS5135580A (en) | 1976-03-26 |
DE2535031C3 (en) | 1979-03-29 |
US3909660A (en) | 1975-09-30 |
GB1512067A (en) | 1978-05-24 |
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