EP0378338B1 - Discharge tube - Google Patents

Discharge tube Download PDF

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Publication number
EP0378338B1
EP0378338B1 EP90300190A EP90300190A EP0378338B1 EP 0378338 B1 EP0378338 B1 EP 0378338B1 EP 90300190 A EP90300190 A EP 90300190A EP 90300190 A EP90300190 A EP 90300190A EP 0378338 B1 EP0378338 B1 EP 0378338B1
Authority
EP
European Patent Office
Prior art keywords
electrode
discharge
cup
shaped
tube
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 - Lifetime
Application number
EP90300190A
Other languages
German (de)
English (en)
French (fr)
Other versions
EP0378338A2 (en
EP0378338A3 (en
Inventor
Yoriyuki Nieda
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
TOKYO DENSOKU KK
Original Assignee
TOKYO DENSOKU KK
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by TOKYO DENSOKU KK filed Critical TOKYO DENSOKU KK
Publication of EP0378338A2 publication Critical patent/EP0378338A2/en
Publication of EP0378338A3 publication Critical patent/EP0378338A3/en
Application granted granted Critical
Publication of EP0378338B1 publication Critical patent/EP0378338B1/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J61/00—Gas-discharge or vapour-discharge lamps
    • H01J61/02—Details
    • H01J61/04—Electrodes; Screens; Shields
    • H01J61/06—Main electrodes
    • H01J61/067—Main electrodes for low-pressure discharge lamps

Definitions

  • the present invention relates to a discharge tube having a positive glow discharge characteristic in which the tube voltage increases as the discharge current increases and a negative arc discharge characteristics in which the tube voltage decreases as the discharge current increases due to an increase in emission of thermoelectrons.
  • Cold-cathode tubes have positive discharge characteristics and have the advantages of long life, low power consumption, low heat dissipation, and the ability to be easily lit and quenched.
  • the disadvantage of cold-cathode tubes is their low intensity.
  • Hot-cathode tubes which are known as fluorescent lamps, have negative thermionic discharge characteristics and the advantage of high intensity. Hot-cathode tubes, however, have the disadvantages of short life, high power consumption, high heat dissipation, and cannot be lit and quenched in themselves.
  • Semi-hot-cathode tubes are arranged such that no filament electrode is energized by external circuits and have the disadvantage that a relatively long time is required to reach the desired intensity after energization. Also, semi-hot-cathode tubes are impractical in terms of life and intensity.
  • the present inventor proposes a discharge tube of the type having a discharge characteristic in which the negative discharge characteristic of a cold-cathode tube is combined with the positive discharge characteristic of a hot-cathode tube. More specifically, the proposed discharge tube comprises a pair of electrode assemblies which are disposed opposite each other in a discharge space. Each of the electrode assemblies includes a cup-shaped electrode for glow discharge and, a filament electrode for arc discharge which is disposed in the cup-shaped electrode. This arrangement is intended to achieve long life with glow discharges and very high brightness with arc discharges. However, it is necessary that such discharge tube be provided with an automatic control circuit for controlling discharge current in order to stably maintain the state of discharge.
  • US-A-2 314 134 discloses an electric discharge device of the luminescent tube type used in luminous signs. It comprises a sealed tube of glass or other suitable transparent material, the inside surface of which is coated with fluorescent powder for light generation.
  • the tube contains an inert gas at a low pressure and also mercury.
  • a respective electrode is provided at each end of the tube.
  • An illustrated electrode is supported by a current-carrying lead sealed in the glass tube and extending inwardly to a larger diameter portion of nickel or iron. About the end of the larger diameter portion there is wrapped, and welded thereon, one end of a filamentary electrode member composed of a tungsten wire.
  • the tungsten filament is in the form of a coiled coil and is coated with an emittive material comprising a mixture of barium and strontium oxides.
  • a tubular quartz insulating member On the outside of the larger diameter portion, a tubular quartz insulating member is secured and has an exterior annular recess in which is secured the lower end of a second electrode member in the form of a frusto-conical shell of nickel which may, if desired, be coated interiorly with emittive material.
  • a metal for instance thorium, having comparatively high emission characteristics when cold is deposited.
  • the filament is connected at its inward end to the shell by means of a connector wire.
  • an electrode arrangement in a second embodiment for operation at relatively low currents, includes a tungsten filament, a thin frusto-conical metallic shell interiorly coated with emittive material, and an outer, generally cylindrical, shell of non-conductive material, a plate connecting the lead wire with the interior of the shell to form part of a supplementary electrode.
  • the present invention provides a discharge tube comprising: a tubular member, including a tubular wall having opposite closed ends defining a gas charged space; first and second electrode assemblies respectively disposed at said closed ends in said gas charged space; and means for applying an a.c. voltage to said first and second electrode assemblies; wherein: each electrode assembly comprises a first, cup-shaped, electrode having a closed end, an open end and a central axis, and a second electrode extending along said axis, the second electrode of each electrode assembly of each electrode assembly including a coating of a thermoelectron emitting material, said electrode assemblies producing, in use, an arc discharge therebetween; each cup-shaped electrode has an outer surface directly facing and open to said tubular wall; and each cup-shaped electrode has an inner surface directly facing the associated second electrode; characterized in that: each cup-shaped electrode is a glow discharge electrode; voltage is applied to the cup-shaped electrodes at their closed ends; each cup-shaped electrode is electrically connected in parallel with the associated second electrode; and said electrode assemblies produce, in use, glow
  • a high intensity arc discharge and a glow discharge are stably formed in the discharge space at the same time, whereby a very high intensity of 35,000 nit or more can be obtained by the synergistic effect of the arc discharge and the glow discharge.
  • metal such as nickel
  • stable glow discharge will be obtained up to a current level of about 3 mmA.
  • the discharge characteristic of the electrodes for glow discharge enters an arc-discharge region where glow discharge does not stabilize.
  • the above-described arrangement according to the present invention makes it possible to provide stable glow discharge even when the current increases, and an intensity of 10,000 nit can be achieved with glow discharge alone.
  • Fig. 1 shows a discharge tube to be described as a background to the present invention.
  • a rod-like sintered electrode 2 and a filament coil electrode 3 are disposed at each end of a transparent glass tube 1 which has a diameter of approximately 6 mm and a length of approximately 260 mm.
  • the rod-like sintered electrode 2 and the filament coil electrode 3 are arranged in parallel and close to each other, i.e., in a non-contact state.
  • Each of the rod-like electrodes 2 has a diameter of 2 mm and a length of 6 mm and is prepared by mixing tungsten powder, zirconium, nickel and barium carbonate, forming the mixture with a press, and sintering the formed mixture.
  • Each of the filament coil electrodes 3 has a good electron emission characteristic and is prepared by coating a solution of barium hydroxide over the peripheral surface of a tungsten wire, sintering the tungsten wire to form a coat of barium carbonate, and forming it into a coil.
  • each of these electrodes 2 and 3 is supported by a tungsten wire or rod-like member 7 and connected to one end of a lead wire 8 via the tungsten rod-like member 7.
  • One end of each of the lead wires 8 extends into the glass tube 1 through a glass end wall thereof.
  • the inner surface of the glass tube 1 is coated with a fluorescent film 4 and the interior of the glass tube 1 is charged with argon gas pressurized at a pressure of 4000 Pa (30 torr) and 5 mmg of mercury 6.
  • a strip or trigger coating 9 is formed on the outer surface of the glass tube 1 to extend along the length thereof.
  • a lead wire 10 is led from the trigger coating 9 and connected to the lead wire 8 which is led from one end of the glass tube 1.
  • the other ends of the respective lead wires 8 are connected to an A.C. power source 11.
  • Fig. 2 shows a discharge tube (not, however, embodying the invetnion) according to a modification of the discharge tube shown in Fig. 1.
  • Fig. 2 the same reference numerals are used to denote the same elements as those shown in Fig. 1.
  • This modification differs from the first embodiment in that each filament coil electrode 3a is arranged to surround a corresponding rod-like sintered electrode 2a in a non-contact state.
  • a highly stable discharge can be achieved with a discharge current of 20 mA and an intensity of 35,000 nit.
  • the temperature of the tube wall of the portion of the discharge tube which is adjacent to each electrode assembly is approximately 15 degrees higher than room temperature and the amount of heat generated can be reduced compared to conventional arrangements. Accordingly, it is possible to reduce power consumption.
  • the discharge-tube driving circuit can be made compact.
  • Fig. 3 shows another modification (not, however, embodying the invention) of the discharge tube of Fig. 1 and only the electrode assembly which differs from that shown in Fig. 2 is illustrated.
  • This modification is similar to the modification of Fig. 2 in that a rod-like sintered electrode 2b is surrounded by a filament coil electrode 3b, but the filament coil electrode 3b is densely coiled in cup-like form with each of its ring segments held in close contact with the adjacent ring segment.
  • Fig. 4 shows an embodiment of the invention constituted by yet another modification of the discharge tube of Fig. 1 and an electrode assembly which differs from that shown in Fig. 3 is illustrated.
  • a sintered metallic electrode 2c for glow discharge is formed into a cup-like shape, and a filament coil electrode 3c for arc discharge extends straight along the axis of the assembly.
  • the cup-like electrode 2c may be formed into the shape of a hollow cylinder with a bottom.
  • the discharge tubes have a glass-tube diameter of about 4 mm to about 10 mm.
  • the sintered electrode shown in Fig. 4 there can be used an electrode formed in such a way that a nickel or tungsten wire is densely coiled in a shape similar to that of the electrode 3b shown in Fig. 3 while coating a nickel or tungsten powder over the peripheral surface of the coiled wire. Further, then the filament coil electrode 3c is set at the center of the thus-formed electrode.
  • a sine-wave oscillating voltage was applied across the discharge tube shown in Fig. 2 under the following conditions:
  • glow discharge was started between the opposite sintered electrodes at 400 rmsV, and the filament coil electrodes started discharges at approximately 500 rmsV. Even if the voltage was raised to 500 rmsV or more, a positive discharge characteristic was maintained between the sintered electrodes. In other words, it was proved that the glow discharge could be maintained even at a voltage level of 500 rmsV or more. In addition, it was proved that, at a voltage level of 500 rmsV or more, a negative discharge characteristic could be obtained between the filament coil electrodes, whereby arc discharge could be maintained.
  • the two kinds of discharge, glow discharge and arc discharge are realized within a single discharge tube, very high intensity of illumination can be achieved. Also, since the filament coil electrodes are heated by glow discharge, arc discharge can be generated by using a relatively low voltage. In addition, since the two kinds of electrodes are arranged in a non-contact state, the sintered metallic electrodes are not heated by the heat generated in the adjacent filament coil electrodes. Accordingly, since no thermorunway takes place in the sintered metallic electrodes, glow discharge does not proceed with arc discharge and the glow discharge can be kept highly stable between the sintered metallic electrodes.
  • Each of the filament coil electrodes is coated with an active oxide such as barium, strontium or the like in order to accelerate emission of thermoelectrons. Accordingly, particles may be scattered due to evaporation or peeling caused by ion bombardment or heating and fall on the inner tube wall of the discharge tube, thereby causing the shading phenomenon in which dark shades are formed on the inner tube wall of the discharge tube.
  • the cup-shaped sintered metallic electrode shown in Fig. 4 when the cup-shaped sintered metallic electrode shown in Fig. 4 is employed, scattered particles stick to the inner wall of the cup-shaped sintered metallic electrode and the stuck particles or active oxide can be reused.
  • the lifetime of the discharge tube can be improved.
  • the present inventor conducted a lifetime test with a discharge tube having such electrode assemblies, and the shading phenomenon was not substantially observed even after running of 10,000 hours or thereabouts.
  • Fig. 6 shows another embodiment of the discharge tube of the present invention.
  • This embodiment is like the discharge tube of Fig. 2 but a top glass plate 1c and a bottom glass plate 1d have ribs 12a and 12b formed on their facing surface, respectively.
  • a postcard-size surface light source made from a glass plate with a plate thickness of approximately 4 mm.
  • the thickness of the glass plate also increases to an impractical extent.
  • the strength of each of the top and bottom glass plates 1c and 1d can be increased to a considerable extent. Accordingly, a surface light source having a light weight and a considerably large size can be obtained.
  • Electrode assemblies E are respectively arranged at the opposite ends of each of the small discharge spaces X, Y and Z, whereby a discharge plate is obtained which is constructed as if a plurality of discharge tubes were arranged side by side.
  • sintered metal is used for the electrodes for glow discharge. Although intensity is somewhat low, nickel may also be used.
  • thermoelectrons is accelerated and rapid lighting (several tens of seconds) is enabled.
  • the electrodes for arc discharge can be heated by the respective electrode assemblies themselves, no external preheating device is needed and power consumption can be reduced to a considerable extent. In addition, the amount of heat generated can be reduced.
  • the electrodes for glow discharge are not forced to the state of arc discharge and stable discharge can therefore be achieved.

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  • Discharge Lamp (AREA)
  • Lasers (AREA)
EP90300190A 1989-01-12 1990-01-08 Discharge tube Expired - Lifetime EP0378338B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP5753/89 1989-01-12
JP1005753A JPH02186551A (ja) 1989-01-12 1989-01-12 放電管

Publications (3)

Publication Number Publication Date
EP0378338A2 EP0378338A2 (en) 1990-07-18
EP0378338A3 EP0378338A3 (en) 1991-06-12
EP0378338B1 true EP0378338B1 (en) 1997-04-02

Family

ID=11619881

Family Applications (1)

Application Number Title Priority Date Filing Date
EP90300190A Expired - Lifetime EP0378338B1 (en) 1989-01-12 1990-01-08 Discharge tube

Country Status (4)

Country Link
EP (1) EP0378338B1 (ja)
JP (1) JPH02186551A (ja)
KR (1) KR920010057B1 (ja)
DE (1) DE69030333D1 (ja)

Families Citing this family (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2599192Y2 (ja) * 1990-07-19 1999-08-30 東京電測 株式会社 放電管
JPH04174951A (ja) * 1990-07-19 1992-06-23 Tokyo Densoku Kk 放電管
US5585694A (en) * 1990-12-04 1996-12-17 North American Philips Corporation Low pressure discharge lamp having sintered "cold cathode" discharge electrodes
DE9202638U1 (de) * 1992-02-28 1992-04-16 Patent-Treuhand-Gesellschaft für elektrische Glühlampen mbH, 8000 München Niederdruckentladungslampe
JP3498072B2 (ja) * 2001-06-25 2004-02-16 炳霖 ▲楊▼ 放電ランプ用発光体
KR101206681B1 (ko) * 2011-07-13 2012-12-03 (주) 상일시스템 조명용 냉음극 형광 램프

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0343625A2 (en) * 1988-05-27 1989-11-29 Toshiba Lighting & Technology Corporation Single end-sealed metal halide lamp

Family Cites Families (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
NL41599C (ja) * 1934-10-27
US2314134A (en) * 1942-01-08 1943-03-16 Colonial Lighting Co Inc Gaseous discharge device
CH319769A (de) * 1953-03-06 1957-02-28 Mueller Felix Ing Dr Elektrode für Entladungsgefässe
JPS5750760A (en) * 1980-09-13 1982-03-25 Matsushita Electric Works Ltd Electrode for discharge lamp
AU6841387A (en) * 1986-01-17 1987-08-14 Sidefact Ltd. Flat light source

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0343625A2 (en) * 1988-05-27 1989-11-29 Toshiba Lighting & Technology Corporation Single end-sealed metal halide lamp

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
Philips: Het Internationale Eenhedensystem (SI-eenheden) volgens UN-D 21 voor straling en licht. Philips (November 1976). *

Also Published As

Publication number Publication date
KR920010057B1 (ko) 1992-11-13
JPH02186551A (ja) 1990-07-20
DE69030333D1 (de) 1997-05-07
KR900012321A (ko) 1990-08-03
JPH0546048B2 (ja) 1993-07-12
EP0378338A2 (en) 1990-07-18
EP0378338A3 (en) 1991-06-12

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