EP0713608A1 - A gas discharge lamp - Google Patents
A gas discharge lampInfo
- Publication number
- EP0713608A1 EP0713608A1 EP94923017A EP94923017A EP0713608A1 EP 0713608 A1 EP0713608 A1 EP 0713608A1 EP 94923017 A EP94923017 A EP 94923017A EP 94923017 A EP94923017 A EP 94923017A EP 0713608 A1 EP0713608 A1 EP 0713608A1
- Authority
- EP
- European Patent Office
- Prior art keywords
- gas discharge
- inner tube
- discharge lamp
- gas
- 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.)
- Granted
Links
- 230000003287 optical effect Effects 0.000 claims description 7
- 239000007789 gas Substances 0.000 description 71
- 239000011521 glass Substances 0.000 description 25
- 238000000034 method Methods 0.000 description 5
- 229910052754 neon Inorganic materials 0.000 description 4
- GKAOGPIIYCISHV-UHFFFAOYSA-N neon atom Chemical compound [Ne] GKAOGPIIYCISHV-UHFFFAOYSA-N 0.000 description 4
- 238000007789 sealing Methods 0.000 description 3
- 239000011248 coating agent Substances 0.000 description 2
- 238000000576 coating method Methods 0.000 description 2
- 230000003247 decreasing effect Effects 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 150000002500 ions Chemical class 0.000 description 2
- 239000004033 plastic Substances 0.000 description 2
- 229920003023 plastic Polymers 0.000 description 2
- 230000001419 dependent effect Effects 0.000 description 1
- 239000011261 inert gas Substances 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 230000000737 periodic effect Effects 0.000 description 1
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
- H01J61/10—Shields, screens, or guides for influencing the discharge
- H01J61/103—Shields, screens or guides arranged to extend the discharge path
-
- 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
- H01J61/045—Thermic screens or reflectors
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J61/00—Gas-discharge or vapour-discharge lamps
- H01J61/92—Lamps with more than one main discharge path
Definitions
- the present invention relates to a gas discharge lamp and more particularly to a gas discharge lamp capable of being operated over a range of brightnesses.
- a gas discharge lamp comprises a sealed elongate glass tube formed at opposite ends with electrodes which comprise a cathode and an anode.
- the glass tube is filled with an inert gas such as neon at low pressure, typically at iooth of atmospheric pressure.
- an inert gas such as neon at low pressure, typically at iooth of atmospheric pressure.
- the first method is to vary the operating current of the gas discharge lamp such that by increasing the current a greater brightness is obtained and by decreasing the current a lower brightness is obtained.
- the second method is to pulse width modulate the power supply to the gas discharge lamp thus turning the lamp on and off very rapidly. This varies the ratio of on-time to off-time thereby causing the lamp to appear bright for a high ratio of on-time to off-time and dim for a low ratio of on-time to off-time.
- the brightness or efficacy (lumens per watt) of a lamp under certain conditions can be increased by using a thin or narrow tube.
- a thin tube the current density between the electrodes is increased, as compared with a wider tube of the same length.
- a similar effect may also be achieved under certain conditions by lowering the gas pressure within the tube. Accordingly, it is desirable to use a thin tube to provide a bright light source.
- the negative resistance characteristics of a thin gas discharge lamp are labelled K/A and the power supply unit requirements to operate at a low brightness and at a high brightness are labelled PSU L and PSU H respectively.
- a thin lamp operates satisfactorily at a high current I H , low voltage V H to produce high brightnesses.
- the operating current of the lamp must be decreased.
- the Voltage- Current (VI) characteristics of a thin tube are such that the negative resistance of the gas discharge lamp increases dramatically at low current levels (I L ) . Accordingly, when a thin tube is operated at the lower current I L which is necessary to dim the lamp to a suitable level, the voltage requirement V L of such a lamp becomes very high.
- the power supply unit required to operate a thin gas discharge tube over a wide range of brightnesses must be capable of providing both a high voltage, low current condition (V L ,I L ) and a low voltage, high current condition (V H ,I H ).
- the cost of such a high performance power supply unit is higher than that of a standard power supply unit and the size of such a unit is large.
- the lifetime of a gas discharge lamp is proportional to the volume of the gas within the tube and, because of the reduced amount of volume present in a thin gas discharge tube, the lifetime of a thin gas discharge lamp is reduced. Further, thin gas discharge lamps become very hot in use due to the relatively small surface area of thin lamps.
- the present invention provides a gas discharge lamp comprising an outer envelope housing an inner tube, the gas in the inner tube sharing a common atmosphere with the gas in the outer envelope, first and second electrodes between which a discharge path is defined, the first electrode being located within the inner tube and the second electrode being located outside the inner tube, the inner tube bounding at least part of the discharge path.
- a third electrode is provided outside the inner tube such that a second discharge path is defined between the second electrode and the third electrode.
- the operating voltage of the discharge path between the first and second electrodes is substantially equivalent to the operating voltage of the discharge path between the second and third electrodes.
- the current density in the discharge path between the first and second electrodes is greater than the current density in the discharge path between the second and third electrodes.
- the discharge path between the first and second electrodes produces a light source between five and forty times brighter than the light source produced by the discharge path between the second and third electrodes.
- the inner tube bounds the majority of the discharge path between the first and second electrodes.
- the inner tube is surrounded by gas contained with the outer envelope.
- the outer envelope is of elongate, tubular form, the inner tube being concentrically mounted within the outer envelope.
- the second electrode is mounted in the outer envelope at a position substantially opposite an open end of the inner tube.
- the inner tube is of circular cross-section.
- the internal diameter of the inner tube is 3mm (0.12 inches).
- the internal diameter of the inner tube is 2mm (0.08 inches .
- the internal diameter of the inner tube is lmm (0.04 inches).
- the length of the lamp is less than 381mm (15 inches) .
- the outer envelope is provided with one or more optical elements to focus or diffuse light produced by the lamp, the or each optical element forming an integral part of the outer envelope.
- Figure 1 is a schematic graph showing the voltage- current characteristics of a conventional thin gas discharge lamp and the current-voltage requirements of a power supply suitable for operating such a gas discharge lamp over a range of brightnesses;
- Figure 2 is a schematic side elevation of a gas discharge lamp embodying the present invention
- Figure 3 is a cross-section through the gas discharge lamp of Figure 2 taken along the line III - III;
- Figure 4 is a schematic side elevation of a gas discharge lamp embodying another aspect of the present invention.
- Figure 5 is a schematic graph of the voltage- current characteristics of the gas discharge lamp of Figure 4, and;
- Figure 6 is a cross-section through a gas discharge lamp embodying the present invention and incorporating a reflective optical component.
- a gas discharge lamp 1 embodying the present invention comprises an outer sealed elongate glass sleeve 2 provided at one end with a cold cathode K and at the other end with an anode Al.
- the cathode K is sealed in the glass of the sleeve 2 and is provided with a portion 3 which projects into the sleeve 2.
- the anode Al is centrally located in a cylindrical sealing plug 4 and projects into the sleeve 2.
- the plug 4 is also provided with an open ended thin glass tube 5 which surrounds the anode Al and which extends within the glass sleeve 2 towards the cathode K at the other end of the gas discharge lamp.
- the glass tube 5 has an open end 6 adjacent the cathode K so that the gas in the tube 5 shares a common atmosphere with the gas in the sleeve 2.
- the sealing plug 4 is pinch sealed with the glass sleeve 2 at the end containing the anode Al.
- the glass sleeve 2 is filled with neon gas under low pressure (typically 1 / 100 th of atmospheric pressure) .
- a cross-section through the gas discharge lamp 1 is shown in Figure 3.
- the configuration of a gas discharge lamp embodying the present invention provides an ionisation path from the anode Al to the cold cathode K via the neon gas located in the thin glass tube 5.
- the thin glass tube 5 serves to define or limit the gas ionisation or discharge path such that in use only the gas contained within the tube 5 and between the end 6 of the tube and the cathode K is ionised. The remainder of the gas held in the glass sleeve 2 is not ionised during discharge. Because of the high current density in the thin central glass tubes, the brightness or efficacy (lumens per watt) of the gas discharge lamp 1 is greater for given operating conditions than that of a conventional gas discharge lamp having the same cross- sectional area as the glass sleeve 2.
- the power dissipated during discharge is a function of two primary factors: the current carried by the discharge and the voltage drop across the discharge.
- the general result is more light per unit length.
- the lifetime of a gas discharge lamp is proportional to the volume of ionising gas present in the lamp and so the lifetime of the gas discharge lamp 1 embodying the present invention is increased because the total volume of gas within the glass sleeve 2 is large compared to that contained within a conventional thin gas discharge lamp of the same length, where the thin conventional lamp would normally have a cross-sectional area of the same order of magnitude as the tube 5.
- the ionisation path from the anode Al to the cathode K is thermally insulated by the volume of gas held in the glass sleeve 2 surrounding the tube 5.
- the temperature of the outer surface of the glass sleeve 2 lags behind that of the thin tube 5.
- the resultant steady state temperature of the sleeve 2 will be dependent upon the ratio of the surface areas of the thin tube 5 and the sleeve 2.
- the gas discharge lamp 1 is provided with a second anode A2 at the same end of the glass sleeve 2 as the first anode Al but outside the central thin glass tube 5.
- the second anode A2 is held in the sealing plug 4 and is located in the volume of gas outside the thin tube 5 but within the sleeve 2.
- the second anode A2 provides the gas discharge lamp 1 with a second discharge path in the glass sleeve 2 from the anode A2 to the cathode K but not within the central glass tube 5 which remains the discharge path for anode Al.
- Figure 5 shows the negative resistance characteristics of the discharge path between the anode Al and the cathode K (the curve labelled K/Al) and of the discharge path between the anode A2 and the cathode K (the curve labelled K/A2) .
- the two discharge paths have different characteristics, the "broader" discharge path K/A2 having a lower characteristic voltage drop and a less pronounced negative resistance and the thin discharge path K/Al being similar to that shown in Figure 1 for a conventional thin gas discharge lamp having a dramatically increasing negative resistance at low current levels.
- the lamp of Figure 4 can be operated to provide differing levels of brightness of this order of magnitude.
- the light source created by the gas discharge path between the anode Al and the cathode K is some twenty times brighter than the light source created by the discharge path between the anode A2 and the cathode K.
- the discharge path ie. the appropriate anode Al or A2
- the desired level of brightness can be achieved. This may be effected by powering either anode Al or anode A2 independently of the other or, for example, by powering anode A2 constantly and simultaneously powering anode Al when greater brightness is required.
- the lamp of Figure 4 will be used in a motor vehicle as the light source in a combined side light and brake light unit where the brake light must be visibly brighter than the side light.
- the running side light of a car would be operated at the lower brightness level via the gas discharge path from the anode A2 to the cathode K whilst the braking light of a vehicle would be operated at the high brightness level created by the gas discharge path between anode Al and cathode K.
- anode Al is operated at a high current level I H but to obtain the lower brightness light source anode A2 is operated at a low current level I .
- Both anodes Al and A2 are operated at substantially equal voltages V H and V L respectively or at least at a voltage well within the capabilities of a conventional and economic power supply unit.
- the power supply unit requirement of the gas discharge lamp l shown in Figure 4 is therefore less demanding than for a conventional thin gas discharge lamp operating over the same range of brightnesses.
- the discharge path from anode Al to cathode K through the thin central glass tube 5 provides a high current density ionisation or discharge path which thereby provides a high brightness light source when the lamp is discharged at high current levels I H .
- the light source from the thin central glass tube 5 is a line source which can be efficiently focused thereby reducing the power requirement of the gas discharge lamp.
- the glass sleeve 2 can incorporate a focusing means such as a reflective coating 10 to focus the line light source in a particular direction.
- a reflective coating may be made of plastics material.
- the cross-section of the gas discharge lamp may be of a "rounded" triangular form having a substantially parabolic reflecting surface as shown in Figure 6 rather than the circular cross-section shown in Figure 3.
- the gas discharge lamp of Figure 4 can be operated by either a DC or an AC supply. When using a DC supply, the anodes Al and A2 can be made very small because they will not be bombarded by ions. Because of the small size of the anodes, the anodes Al can be readily inserted within the thin central glass tube 5 and the size of the anode Al does not limit the thinness of the thin central tube 5.
- the size of the electrodes Al, A2 must be increased because the electrodes Al, A2 must act both as cathodes and anodes and will be bombarded by ions. Accordingly, the size of the thin central tube 5 is constrained by the size of the electrode Al.
- optical reflector 10 shown in the embodiment of Figure 6 in such a way as to minimise any discharge current leakage from the gas discharge lamp 1.
- the thin tube 5 has an internal diameter of 3mm (0.12 inches) and the internal diameter of the sleeve is 13mm (0.51 inches).
- the gas discharge lamp is configured as a centre high mounted stop light (CHMSL) for use on a compact or sub- compact vehicle.
- CHMSL requires high efficacy as well as a short discharge length, i.e. less than 281mm (15 inches).
- Such a CHMSL would typically have an illuminated area of 3871mm 2 (6 square inches, 25.4mm (1 inch) by 152mm (6 inches) in length.
- the minimum light output of the CHMSL is not less than 32 Candelas and the lifespan is greater than 2000 hours and preferably greater than 7500 hours.
- a gas discharge lamp having such a high efficacy with such a short tube 152mm (6 inches) is possible because of the provision of the narrow tube within the outer envelope.
- Such a narrow tube having an internal diameter of the order of 3mm (0.12 inches) produces a much higher voltage per unit length and, as such, operates at a higher power than a conventional single envelope gas discharge lamp.
- the general result is more light per unit length allowing CHMSLs to be manufactured having a length of 152mm (6 inches). Tubes having a diameter of 2%mm (0.1 inches), 2mm (0.08 inches) and 1mm (0.04 inches) are possible and provide suitable increases in light per unit length.
Abstract
Description
Claims
Applications Claiming Priority (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB9316505 | 1993-08-09 | ||
GB939316505A GB9316505D0 (en) | 1993-08-09 | 1993-08-09 | A gas discharge lamp |
PCT/GB1994/001733 WO1995005001A1 (en) | 1993-08-09 | 1994-08-08 | A gas discharge lamp |
Publications (2)
Publication Number | Publication Date |
---|---|
EP0713608A1 true EP0713608A1 (en) | 1996-05-29 |
EP0713608B1 EP0713608B1 (en) | 1999-10-27 |
Family
ID=10740191
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP94923017A Expired - Lifetime EP0713608B1 (en) | 1993-08-09 | 1994-08-08 | A gas discharge lamp |
Country Status (4)
Country | Link |
---|---|
EP (1) | EP0713608B1 (en) |
DE (1) | DE69421401D1 (en) |
GB (1) | GB9316505D0 (en) |
WO (1) | WO1995005001A1 (en) |
Families Citing this family (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
SE9704764L (en) | 1997-12-19 | 1999-06-20 | Ericsson Telefon Ab L M | Method and device in a communication network |
FR2882489B1 (en) * | 2005-02-22 | 2007-03-30 | Saint Gobain | LUMINOUS STRUCTURE PLANE OR SIGNIFICANTLY PLANE |
Family Cites Families (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
DE2862125D1 (en) * | 1977-08-10 | 1983-01-20 | Hitachi Ltd | Low pressure metal vapour discharge lamp |
US4598229A (en) * | 1984-07-23 | 1986-07-01 | Lightmasters, Ltd. | Luminous tube color generator |
-
1993
- 1993-08-09 GB GB939316505A patent/GB9316505D0/en active Pending
-
1994
- 1994-08-08 DE DE69421401T patent/DE69421401D1/en not_active Expired - Lifetime
- 1994-08-08 EP EP94923017A patent/EP0713608B1/en not_active Expired - Lifetime
- 1994-08-08 WO PCT/GB1994/001733 patent/WO1995005001A1/en active IP Right Grant
Non-Patent Citations (1)
Title |
---|
See references of WO9505001A1 * |
Also Published As
Publication number | Publication date |
---|---|
DE69421401D1 (en) | 1999-12-02 |
GB9316505D0 (en) | 1993-09-22 |
EP0713608B1 (en) | 1999-10-27 |
WO1995005001A1 (en) | 1995-02-16 |
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