US2342806A - High pressure mercury vapor lamp - Google Patents

High pressure mercury vapor lamp Download PDF

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Publication number
US2342806A
US2342806A US278742A US27874239A US2342806A US 2342806 A US2342806 A US 2342806A US 278742 A US278742 A US 278742A US 27874239 A US27874239 A US 27874239A US 2342806 A US2342806 A US 2342806A
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electrodes
arc
lamp
cathode
voltage
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US278742A
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English (en)
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Hofmann Josef
Schreiber Felix
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J61/00—Gas-discharge or vapour-discharge lamps
    • H01J61/02—Details
    • H01J61/04—Electrodes; Screens; Shields
    • H01J61/06—Main electrodes
    • H01J61/073—Main electrodes for high-pressure discharge lamps
    • H01J61/0732—Main electrodes for high-pressure discharge lamps characterised by the construction of the electrode
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J61/00—Gas-discharge or vapour-discharge lamps
    • H01J61/02—Details
    • H01J61/04—Electrodes; Screens; Shields
    • H01J61/06—Main electrodes
    • H01J61/073—Main electrodes for high-pressure discharge lamps
    • H01J61/0735—Main electrodes for high-pressure discharge lamps characterised by the material of the electrode

Definitions

  • This invention relates to high pressure mercury vapor lamps, such for example as are -used for illumination and/or irradiation.
  • Such lamps are habitually provided with selfheating incandescent cathodes and a basic filling of a suitable gas, such as neon, argon, etc.
  • a suitable gas such as neon, argon, etc.
  • One of the objects of the present invention is to eliminate this objectionable feature characteristic of self-heating cathodes without intensied electron emission, used in high pressure mercury vapor lamps, by a special forming of the cathode body and a relative adjustment or adaptation of said body and the current load, thus providing a newbasis for the simple and commercial construction of high pressure mer- CllIy Vapor lamps.
  • the present invention is based upon the discovery that in high pressurev mercury vapor lamps using self-heating incandescent cathodes without intensified electron emission, volatilization or evaporation of the electrodes can be vreduced practically to zero, providing care be electron emission is'delivered from a 'surface area of about 0.01 cm?, an arc of a current strength of 4 a. could'obviously only be maintained by a purely thermal ⁇ electron emission on condition that said surface area be heated to a temperature of 2750 C. or ⁇ thereabout (emission ⁇ 400 a./cm.2).f At that temperature, however,
  • tantalum of which the meltingwpointis 2900 C., evaporates or volatilizes appreciably.
  • said surface area from which the electrons are emitted 0.5 cm?
  • said surface area fromv the time i-t reaches a temperature of 23506 C. would l emit a purely thermic electron emission of 4 a. (emissionv 8 a./cm.2) which would enable the arc to be maintained at a much lower temperature 'of the cathode and with negligibly slight volatilization-of the latter.
  • the desired increase in the area of that part of thecathode surface from which the arc emanates can be secured simply by making the Cathode of a sheet metal having a high melting point', such as tantalum for example, and reducing the heat losses of said thin cathode as -much as possible.
  • Such'reduction of heat losses may be effected by any suitable means, a very simple means consisting of an envelope surrounding the cathode and acting as a reiiector to reduce the'heat losses due to radiation.
  • the cathode is made of thin sheet metal having a high melting point and may be given different shapes as hereinafter described.
  • Another object of the invention therefore is to provide a high pressure mercury Vapor lamp, in which the thickness of the incandescent elec trodes without intensified electron emission, and the load of the lamp, ⁇ are relatively adjusted or adjustable to reduce the voltage drop at the electrodes to less than 50 volts.
  • Fig, l shows dia-grammatically a longitudinal section of a tube embodying an illustrative embodiment of the invention comprising sheet-metal electrodes;
  • Figs. 2, and 3 each show one end portion of a tube similar to that of Fig. l, having sheet-metal electrodes of different shapes;
  • Figs. 4 and 5 are diagrams illustrating the advantage of using thin sheet-metal electrodes
  • Fig. 6 is a graph showing how, for a given strength of current, the drop in voltage is dependent upon the thickness of the electrode;
  • Fig. 7 is a graph showing how, for a given thickness of electrode, the drop in voltage is dependent upon the strength of current
  • Fig. 8 shows diagrammatically a longitudinal section of a tube embodying an illustrative embodiment of the invention comprising pencil or wire shaped electrodes;
  • Fig. 9 is a graph which shows the Vlimits of the propitious zone to be selected in accordance with the present invention, for electrodes of given thicknesses;
  • Fig. l0 shows one end of a tube similar to that of Fig. 8, in which the thin wire electrodes are provided, somewhat back from their free ends, with a lateral, thin sheet-metal extension.
  • a tube of suitable material herein quartz, is shown at I.
  • two supply Wires 2a, 2b and 3a, 3b, respectively, are sealed in the molten glass.
  • These wires carry the actual electrodes, which in this illustrative embodiment of the invention consist of thin U-shaped sheet-metal bands 4 and 5 of a thickness of approximately 0.08 mm.
  • suitable reflecting means herein conveniently consisting of silver plated sheetcopper sleeves or bands 6 and 1.
  • Said tube I will be provided With a filling of suitable gas and contains a small amount of mercury, a few milligrams, the quantity of mercury being such that it will be completely vaporized when the tube is in high pressure operation.
  • argon gas is used as a filling with a pressure of about 20 to 30 mm.
  • the mercury is indicated by the small globule 8 in Fig. 1.
  • the lamp will preferably be connected in series with suitable means for controlling or regulating the strength of the current, such as a 0.1 to 0.2 henry choking coil (not shown).
  • cylindrical electrodes Eb as shown in Fig. 3, ⁇ of thin sheet metal, may be used.
  • the electrodes may be recessed as shown at a in Fig. 2, for example, to diminish the carrying off of heat from the emitting head. Whatis of capital importance in each case, however, is not only that the electrodes be made of material having a high melting point, but also that they be quite thin, of very thin sheet-metal, for example, as above.
  • FIG. 4 A reference to Figs. 4 and 5, will clearly demonstrate the importance of making the electrodes of quite thin material. If as shown in Fig. 4 a quite thick metal sheet be used, isothermal lines such as a to d will be formed about the highly heated arc emission zone.y But if a quite thin electrode, one made of very thin sheet metal, for example, be used, the isothermal picture will be somewhat as shown in Fig. 5, from which it will be clearly seen that in this case there will be a far less abrupt drop in temperature as between the highly heated arc emission zone x-y and the cooler side zones heated mainly by the fall at anode when operating with an alternating current. In this case, therefore, the temperature necessary for thermal electron emission will be produced over a relatively greater area.
  • the total drop in voltage in the case of an arc discharge is obviously composed of the voltage drop at the cathode, the voltage' drop at the anode and the voltage drop in the ionized gas column.
  • the voltage drop at the cathode and that at the anode cannot be accurately determined separately in the case of an alternating current lamp, as they are both dependent on the distribution of the temperature over the electrodes and are-therefore bound together functionally.
  • they will be referred to by the single term voltage drop at the electrodes which includes both and is designated by Ue.
  • the voltage drop in the ionized gas column, designated by Us can, on the other hand, be determined by comparing the total voltage drop, designated by Uy, which occurs in lamps of different lengths of arc, al1 other yconditions being equal.
  • volatilization or evaporation of the cathode can always be kept at a sufficiently low level for the production of lamps having a suiiiciently long life to render them commercial, providing the electrodes be so thin relatively to the operating load of the lamp that the voltage drop at the electrodes, Ue, falls below 50 volts.
  • This operating condition can be attained either by using an electrode of predetermined thickness and varying the current load, or inversely by using a predetermined current load and choosing a suitable electrode thickness.
  • Thickness of electrode Ue are graphically shown in Fig. 6.
  • the lamp provided with an electrode of sheet tantalum of 0.5 mm. in thickness could not be made to burn quietly with a current of less than 5 a. With that load there was still a very marked volatilization of its electrodes.
  • this lamp was operated with a current load of l0 a., the value of Ue dropped to 25 to 30 volts, and notwithstanding the increased load, the lamp could be operated with greatly diminished volatilization, that is to say, under more favorable conditions for long life.
  • Thickness of electrode A Uy Us Ue 0.25 mm 1.6 ce. 21 s4 2.75 91 ea. 21 ⁇ 70 5.0 0l ca. 2l 40 0.o 55 ea. 21 34 0.08 mm 0.75 93 ea. 21 72 1.0 s1 011.21 00 1. 25 7s es. 21 52 1.8 58 ca. 2l 37 2.5 4s es. 21 27 3.5 42 ce. 21 2i 4. 0 40 ca. 2l 19 4, 25 39 ce. 21 is These values are graphically illustrated in Fig.
  • a lamp 100 mm. in length with an argon filling (25 mm.) and electrodes of the shape shown in Fig. 3, made of commercial sheet tantalum of 0.08 mm. thickness could be operated for more than 1000 hours on a 220 volt alternating current network through a choking means of 0.134 henry, and a mean current strength of 4 a., without objectionable blackening of the tube.
  • the mean voltage of the lamp in 'this case rose to a round 130 volts and could have been raised to volts without extinction of the lamp, that is to say, without its failing to relight within a single period.
  • the quartz tube I of the lamp has walls of about 1 mm. in thickness and is about 12 to 14 cm. long.
  • Two pencil-shaped electrodes 9 and l0 are sealed in the opposite ends respectively of said tube. These electrodes are about 0.5 mm. in thickness and their length from the end wall of said tube to their free end is about 15 mm.
  • Said tube has a filling of a suitable gas, such as argon, for example, with'a pressure of about 20 to 30 mm. and contains a small quantity of mercury, no more than will completely vaporize when the prescribed operating temperature of 300 to 500 C. is reached.
  • Saidelectrodes are in circuit with a resistance I'I of about 50 ohms and an alternating voltage ⁇ of about 220 volts. A choking coil of about 0.1 to 0.3 henry can be substituted for said resistance.
  • Conventional ignition means not shown (ignition strip, high frequency ignition), for the rst starting of the discharge may be used.
  • the graph of Fig. 9 also enables the particular electrode dimensions, which would be suitable for any predetermined load, to be readily determined.
  • the present invention teaches how to determine the correct load for any given lamp, by first taking from the known tables the voltage drop attributable to the arcy at a given temperature, and then calculating therefrom the voltage, which, at said temperature, must exist at the terminals, if l5 to 20 volts, for example, be taken as the voltage drop at the electrodes. Then, as soon as the arc is struck, one adjusts said resistance, or said choking coil of the lamp so as to produce said voltage at the terminals.
  • said lamp can at once be connected up and allowed to operate in the high pressure Zone of the mercury vapor discharge, without fear of any inadmissible volatilization occurring.
  • the pencil electrode 9 of Fig. l1 may advantageously .be provided with a very thin sheet-metal lateral extension l0, which is suitably secured at one edge to said electrode 9 at a suitable distance from the latters free end.
  • Said extension will preferably be curved spirally as shown to facilitate its introduction into the tube l.
  • Said pencil and said extension may be of any suitable thickness; the thickness of the former, for example, may be 0.4 and that of the latter 0.05 mm.
  • tantalum and tungsten have 'been more particularly mentioned in the illustrative embodiments of the invention herein described, it will be understood that other suitable materials, such as molybdenum and niobium, having a sumciently high melting point, could also ⁇ be used for electrodes without departing from the spirit of our invention. Tantalum lamps have proven to be best suited for general commercial use. Thus, for lamps with a current consumption usual in the trade, sheet tantalum electrodes of a thickness of only 0.08 mm. to 0.04 mm. have proven especially advantageous.
  • High pressure mercury vapor arc lamp with gas filling and a long drawn out arc designed for inclusion in an arc energizing circuit and comprising a discharge tube; non-intensified selfheating incandescent pencil-shaped electrodes of material having a high melting point; and means for starting the arc comprising a non-intensied selfheating incandescent extension member, of thin sheet-metal having a high melting point carried by and extending laterally of each electrode and spaced somewhat back from the free end thereof, said free ends being directed toward the center of said tube; the potential of said circuit being regulated relatively to the thickness of said electrodes to limit the voltage drop lamp is in operation.
  • an arc energizing circuit andl comprising a discharge tube; non-intensified self-heating incandescent pencil-shaped tungsten electrodes; and means for starting the yarc comprising a non-intensiiied selfheating incan-l descent eXtension member, of thin sheet-tungsten carried by and extending laterally of each electrode and spaced somewhat back from the free end thereof, said free ends lbeing directed toward the center of said tube; the potential of said circuit being regulated relatively to the thickness of said electrodes to reduce the voltage dropvat saidelectrodes to less than 50 volts when the lamp is in operation.

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  • Vessels And Coating Films For Discharge Lamps (AREA)
  • Discharge Lamp (AREA)
US278742A 1938-06-22 1939-06-12 High pressure mercury vapor lamp Expired - Lifetime US2342806A (en)

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DE530405X 1938-06-22

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FR (1) FR856699A (fr)
GB (1) GB530405A (fr)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2497496A (en) * 1943-01-15 1950-02-14 Gen Electric Electrode structure for electric discharge devices or lamps
US2499506A (en) * 1944-09-11 1950-03-07 Gen Electric Electric discharge device and electrode therefor
FR2507385A1 (fr) * 1981-06-05 1982-12-10 Commissariat Energie Atomique Tube a eclairs a connexions electriques radiales avec alimentation en gaz

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3444922A1 (de) * 1984-12-08 1986-06-12 Philips Patentverwaltung Gmbh, 2000 Hamburg Hochdruck-gasentladungslampe mit einer aus wolframblech bestehenden elektrode

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2497496A (en) * 1943-01-15 1950-02-14 Gen Electric Electrode structure for electric discharge devices or lamps
US2499506A (en) * 1944-09-11 1950-03-07 Gen Electric Electric discharge device and electrode therefor
FR2507385A1 (fr) * 1981-06-05 1982-12-10 Commissariat Energie Atomique Tube a eclairs a connexions electriques radiales avec alimentation en gaz
EP0067758A3 (en) * 1981-06-05 1983-04-06 Commissariat A L'energie Atomique Etablissement De Caractere Scientifique Technique Et Industriel Flash lamp with radial electric connections and gaseous supply
US4496873A (en) * 1981-06-05 1985-01-29 Commissariat A L'energie Atomique Flash tube having coax cable connector

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GB530405A (en) 1940-12-11

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