WO2004102614A1 - Mercury-free high-pressure gas discharge lamp with a burner design for increasing the arc diffuseness and reducing the arc curvature - Google Patents

Mercury-free high-pressure gas discharge lamp with a burner design for increasing the arc diffuseness and reducing the arc curvature Download PDF

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Publication number
WO2004102614A1
WO2004102614A1 PCT/IB2004/001363 IB2004001363W WO2004102614A1 WO 2004102614 A1 WO2004102614 A1 WO 2004102614A1 IB 2004001363 W IB2004001363 W IB 2004001363W WO 2004102614 A1 WO2004102614 A1 WO 2004102614A1
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Prior art keywords
volume
mercury
electrode
pressure gas
gas discharge
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PCT/IB2004/001363
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French (fr)
Inventor
Hermann Giese
Folke NÖRTEMANN
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Philips Intellectual Property & Standards Gmbh
Koninklijke Philips Electronics N.V.
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Publication of WO2004102614A1 publication Critical patent/WO2004102614A1/en

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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
    • H01J61/12—Selection of substances for gas fillings; Specified operating pressure or temperature
    • H01J61/16—Selection of substances for gas fillings; Specified operating pressure or temperature having helium, argon, neon, krypton, or xenon as the principle constituent
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J61/00—Gas-discharge or vapour-discharge lamps
    • H01J61/02—Details
    • H01J61/30—Vessels; Containers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J61/00—Gas-discharge or vapour-discharge lamps
    • H01J61/82—Lamps with high-pressure unconstricted discharge having a cold pressure > 400 Torr

Definitions

  • the invention relates to a mercury- free high-pressure gas discharge lamp with a defined inner bulb volume of the burner space, suitable for increasing the discharge arc diffuseness and suitable for reducing the discharge arc curvature, as well as to its use for illumination purposes, in particular for motor vehicles.
  • High-pressure gas discharge lamps are generally known in the art.
  • Mercury- xenon high-pressure gas discharge lamps known under the designations D 1 and D2 xenon lamps, are generally used nowadays in headlight systems of many motor vehicles.
  • An essential disadvantage of mercury-free high-pressure gas discharge lamps is that the luminous discharge arc forming between the electrodes is substantially narrower than in mercury-containing high-pressure gas discharge lamps that are similar in other respects, which is caused by the absence of mercury. This leads to a clearly smaller discharge arc diffuseness in mercury-free high-pressure gas discharge lamps.
  • a luminous discharge arc of insufficient diffuseness may lead to a permanent inhomogeneous front field illumination in particular in reflection headlight systems, whose reflectors are often very accurately adapted to the discharge arc geometry.
  • mercury-free high-pressure gas discharge lamps in particular mercury-free xenon high-pressure gas discharge lamps, that these lamps have too strong an arc curvature of the discharge arc in the burner space between the two electrodes at a high xenon pressure, because the arc curvature increases with an increase in xenon pressure.
  • the operational life of the mercury-free high-pressure gas discharge lamp as compared with that of the mercury-containing high-pressure gas discharge lamps may be clearly reduced, because the difference in temperature load on the burner space wall of the inner bulb leads to a higher load on the material, especially on the highest location above the arc, for example leading to a shorter lamp life.
  • US 5,121,034 Al proposes to operate the lamp at a high frequency within certain frequency bands so as to reduce the arc curvature by means of acoustic resonance.
  • the discharge arc diffuseness can be clearly increased and the discharge arc curvature, in particular the discharge arc curvature arising from a high xenon gas pressure, can be clearly reduced when the inner bulb surrounding the burner space, also denoted burner, has a defined inner volume.
  • the mercury-free high-pressure gas discharge lamp comprises an inner bulb surrounding the burner space, a first electrode extending into the burner space, a second electrode extending into the burner space, and an outer bulb, wherein the inner bulb has a defined volume such that the total inner bulb volume of the burner space is composed of: a volume A, which is the region occupying the space between the first and the second electrode tip extending into the burner space, - a volume B, which is the region occupying the space in a direction away from the electrode tip of the first electrode along this electrode to the burner space wall of the inner bulb accommodating this electrode, and a volume C, which is the region occupying the space in a direction away from the electrode tip of the second electrode along this electrode to the burner space wall of the inner bulb accommodating this electrode, for which it holds that volume A / volume B > 10 and volume A / volume C > 10.
  • the expressions "inner bulb” and "outer bulb” used in the present description relate to all conceivable suitable vessel forms.
  • Hg-free high-pressure gas discharge lamps according to the invention may preferably be filled with xenon.
  • Hg-free high-pressure gas discharge lamps according to the invention comprise an ionizable filling. Suitable ionizable fillings are based on metal halides. Preferred ionizable fillings comprise at least one metal halide chosen from the group comprising Nal, Scl 3 , ScBr , NaBr, halides of rare earths such as Cel 3 , Prl 3 , CeBr 3 and/or PrBr 3 .
  • Halides of the groups Ilia such as Inl, Til, InBr, TlBr, IVa such as Snl 2 , SnBr 2 , and Illb such as Lal 3 , LaBr 3 , of the periodic system of chemical elements may be used, for example, as ionizable fillings.
  • the volume A is defined in a manner known to those skilled in the art by the linear distance L from the first electrode tip to the second electrode tip and the diameter B A of the inner bulb obtaining for this region, measured up to the inner wall of the inner bulb.
  • the volume B is defined by the linear distance L B from the first electrode tip horizontally along the electrode up to the inner wall of the inner bulb through which the electrode is passed.
  • the volume B is thus determined in a manner known to those skilled in the art from the respective diameter D ⁇ of the inner bulb for the region L B , measured up to the inner wall of the inner bulb.
  • the volume C is defined by the linear distance Lc from the first electrode tip horizontally along the electrode up to the inner wall of the inner bulb through which the electrode is passed.
  • the volume C is thus determined in a manner known to those skilled in the art from the respective diameter Dc of the inner bulb for the region Lc, measured up to the inner wall of the inner bulb.
  • the inner bulb is rotationally symmetrical, and the volumes B and C are equally large.
  • the inner bulb has identical shapes in the volumes in the regions L B and Lc- It is also particularly preferred in the invention, for example, that an inner bulb which is tubular in its center narrows strongly towards the two ends. Alternatively, however, an inner bulb that is not rotationally symmetrical and that surrounds the burner space may be used in the invention.
  • the inner bulb volume of the burner space may alternatively be indicated as follows, wherein it holds that: volume A / volume B > 1 1.0 and volume A / volume B ⁇ 30.0, and volume A / volume C > 11.0 and Volume A / volume C ⁇ 30.0; preferably, volume A / volume B > 13.0 and volume A / volume B ⁇ 25.0, and volume A / volume C > 13.0 and Volume A / volume C ⁇ 25.0; - more preferably, volume A / volume B > 15.0 and volume A / volume B ⁇
  • volume A / volume C > 15.0 and Volume A / volume C ⁇ 20.0.
  • the volume A preferably is a volume of 7.0 mm 3 to 30.0 mm 3 , preferably from 9.0 mm 3 to 23.0 mm 3 , and more preferably from 10.0 mm 3 to 17.0 mm 3 .
  • Volume B and/or volume C preferably is a volume of 0.1 mm to 3.0 mm , preferably from 0.2 mm to 2.3 mm , and more preferably from 0.25 mm to 1.7 mm .
  • a substantial improvement in the discharge arc diffuseness can be achieved by means of the defined volumes A, B, and C for the inner bulb of the burner.
  • the defined volumes A, B, and C render it possible to achieve that the arc curvature of mercury-free lamps comes closer to that of mercury-containing lamps.
  • the definition of the volumes A, B, and C of the burner according to the invention leads to a considerably reduced convection of the plasma inside the inner bulb volume defined in accordance with the invention. It is suspected that the downward flow is substantially suppressed, in particularly because of the smaller volumes B and C, whereby the convection of the plasma is influenced in a determining manner.
  • mercury-free high-pressure gas discharge lamps with the volumes A, B, and C of the inner bulb of the burner according to the invention can be operated with a higher xenon pressure without the otherwise usual strong increase in arc curvature being observed as a result of this.
  • the reduction in arc curvature may be more or less pronounced in dependence on the gas pressure and the geometry.
  • Preferred xenon pressures for mercury-free lamps formed in accordance with the invention, measured at 300 K, preferably lie in a range from 5 to 20 bar, more preferably in a range from 6 to 18 bar, and particularly preferably in a range from 7 to 16 bar.
  • Further suitable xenon pressures for mercury-free lamps formed in accordance to the invention, measured at 300 K lie in a range from 8 to 19 bar, preferably in a range from 9 to 17 bar, and more preferably in a range from 11 to 15 bar.
  • the increase in luminous efficacy of lamps according to the invention is caused by the higher temperature of the coldest spot on the inner wall of the inner bulb and is dependent on the ionizable filling.
  • the luminous flux of a mercury-free high-pressure gas discharge lamp according to the invention expressed in lumens for a given power in comparison with the same high-pressure gas discharge lamp, but not with a volume division according to the invention, may be higher by > 5 lumens and ⁇ 500 lumens, preferably > 10 lumens and ⁇ 300 lumens, and more preferably > 30 lumens and ⁇ 200 lumens.
  • the luminous flux of mercury-free high-pressure gas discharge lamps according to the invention at a given power may alternatively be higher than that of the same high-pressure gas discharge lamps, but not with a volume division according to the invention, by > 20 lumens and ⁇ 100 lumens, preferably > 40 lumens and ⁇ 150 lumens, and more preferably > 50 lumens and ⁇ 90 lumens.
  • the arc curvature increases with an increasing gas pressure in mercury-free high-pressure gas discharge lamps, for example with high xenon pressures.
  • the volumes A, B, and C defined in accordance with the invention achieve a change in the position or location of the discharge arc, i.e. of the brightest spot of the discharge arc, owing to the changed convection of the plasma, i.e. the arc curvature is changed.
  • the arc curvature K of mercury-free high-pressure gas discharge lamps according to the invention preferably has a value in a range of 0.10 to 0.90 mm, preferably 0.20 to 0.80 mm, and particularly preferably 0.25 to 0.75 mm.
  • the highest point in the discharge arc of the mercury- free high-pressure gas discharge lamp lies lower than in the identical, in particular rotationally symmetrical similar high-pressure gas discharge lamp not with a volume division according to the invention by at least 0.01 to 0.50 mm, preferably from 0.03 to 0.45 mm, more preferably 0.05 to 0.40 mm, even more preferably 0.07 mm to 0.35 mm, and particularly preferably 0.09 mm to 0.30 mm.
  • the discharge arc diffuseness D of a mercury-free high-pressure gas discharge lamp according to the invention may have values in a range from 0.70 to 1.50 mm, preferably 0.80 to 1.40 mm, and particularly 0.85 to 1.35 mm.
  • the increase ⁇ D in the discharge arc diffuseness of a mercury- free lamp formed in accordance with the invention may amount to 0.01 to 0.50 mm, preferably 0.03 to 0.45 mm, more preferably 0.05 to 0.40 mm, even more preferably 0.07 to 0.35 mm, and particularly preferably 0.09 to 0.30 mm in comparison with the same mercury-free, in particular rotationally symmetrical high-pressure gas discharge lamp, but not with a volume division in accordance with the invention.
  • the construction principle of a mercury-free high-pressure gas discharge lamp according to the invention comprises a burner space in its inner bulb into which two electrodes are introduced, between which a discharge arc is ignited, as well as possibly an outer bulb.
  • the inner bulb also denoted the burner space hereinafter, may be filled with xenon gas and further ionizable lighting means.
  • the two electrodes may be fused into the inner bulb.
  • the application of a voltage to the electrodes ignites and maintains a gas discharge between them.
  • the discharge arc lies above the connecting line of the electrodes because of the thermal rise.
  • the transitional regions between the electrodes and the discharge arc are denoted the cathode spots.
  • the cathode spots are the hottest and brightest spots of the discharge arc.
  • a further object of the present invention relates to a lighting installation which comprises at least one mercury-free high-pressure gas discharge lamp, which lighting installation is in particular a reflection headlight, projection headlight, projector, and/or lamp for general lighting purposes.
  • the mercury-free high-pressure gas discharge lamps according to the invention may be used for each and every illumination purpose.
  • the mercury-free high- pressure gas discharge lamp is preferably a mercury-free xenon high-pressure gas discharge lamp.
  • the inner bulb and/or outer bulb of a mercury-free high-pressure gas discharge lamp according to the invention may be made from a material chosen from the group comprising quartz, glass, and/or ceramic materials, the inner bulb and outer bulb being preferably made of quartz.
  • the distance L between the electrode tips of the first and the second electrode of a mercury-free lamp formed in accordance with the invention may be at least 3.5 mm and at most 6 mm, preferably from 3.6 mm to 5.8 mm, more preferably 3.8 mm to 5.5 mm, even more preferably 4.0 mm to 5.3 mm, still more preferably 4.2 mm to 5.2 mm, still more preferably 4.4 mm to 5.0 mm, and particularly preferably 4.6 mm to 4.8 mm.
  • the inner bulb of a mercury-free lamp formed in accordance with the invention may have a wall thickness in a range from at least 1.3 mm to at most 2.2 mm, preferably 1.5 mm to 2.0 mm, and more preferably 1.7 mm to 1.9 mm.
  • the change in wall thickness of the inner bulb from the thickest location of the wall of the inner bulb to the thinnest location of the wall of the inner bulb is ⁇ 0.5 mm and > 0 mm, preferably ⁇ 0.4 mm and more preferably ⁇ 0.3 mm.
  • the wall thickness of the inner bulb is substantially constant, i.e. the change in wall thickness of the inner bulb from the thickest location of the wall of the inner bulb to the thinnest location of the wall of the inner bulb may amount to ⁇ 0.2 mm, or even ⁇ 0.1 mm.
  • the electrodes are each embedded in the inner bulb over a length of > 1 mm and ⁇ 20 mm, preferably > 2 mm and ⁇ 15 mm, and more preferably > 3 mm and ⁇ 10 mm.
  • the electrodes may be directly embedded or they may be embedded while enveloped by an additional material layer.
  • the inner bulb may have a total inner bulb volume of at least 9 mm 3 and at most 31 mm 3 , preferably 11 mm 3 to 20 mm 3 , and more preferably 14 mm 3 to 17 mm 3 . Because of the higher discharge arc curvature of mercury-free xenon high- pressure gas discharge lamps with high xenon pressures, the temperature of the wall of the inner bulb in the region perpendicularly above the highest point of the discharge arc is substantially higher than the temperature of the wall of the inner bulb in the region perpendicularly below the highest point of the discharge arc.
  • the volume defined in accordance with the invention renders it possible to adapt the temperatures of the wall of the inner bulb in the region perpendicularly above the highest point of the discharge arc and perpendicularly below the highest point of the discharge arc such that a more homogenous heat distribution is obtained.
  • This is particularly advantageous at a high gas pressure within the inner bulb surrounding the burner of lamps formed in accordance with the invention, because otherwise a high gas pressure, in particular Xe gas pressure, would lead to an increase in the arc curvature in the case of mercury-free lamps not formed in accordance with the invention.
  • the temperature difference ⁇ T of the inner bulb of a mercury - free lamp with volumes A, B, and C defined in accordance with the invention, measured in K perpendicularly above and below the highest point of the discharge arc at the outer wall of the inner bulb is ⁇ 150 K and > 0 K, preferably ⁇ 130 K, in particular ⁇ 1 10 K, more preferably ⁇ 100 K, even more preferably ⁇ 80 K, still more preferably ⁇ 50 K.
  • the temperature difference ⁇ T of the inner bulb of a mercury-free lamp with volumes A, B, and C defined in accordance with the invention, measured in K perpendicularly above and below the highest point of the discharge arc at the outer wall of the inner bulb may even be ⁇ 30 K.
  • the temperature in K was measured after a period of operation of 30 minutes perpendicularly above and below the highest point of the discharge arc at the outer wall of the inner bulb of a lamp according to the invention without outer bulb, which lamp was operated horizontally (electrodes in horizontal position).
  • Fig. 1 shows a mercury-free high-pressure gas discharge lamp according to the invention.
  • Fig. 1 shows a mercury-free high-pressure gas discharge lamp according to the invention with an inner bulb (1), a first electrode (2), a second electrode (3), and the volumes A, B, and C.
  • the distance L is the distance between the electrode tips (4, 5) of the first electrode (2) and the second electrode (3).
  • the volume A follows from the diameter D and the distance L.
  • a linear distance L B is shown for the volume B, which distance extends from the first electrode tip horizontally along the electrode up to the inner wall (6) of the inner bulb, through which the first electrode is passed.
  • a linear distance Lc is shown for the volume C, which distance extends from the second electrode tip horizontally along the electrode up to the inner wall (7) of the inner bulb, through which the second electrode is passed.
  • the xenon high-pressure gas discharge lamp was filled with an ionizable filling comprising 300 ⁇ g Nal/Scl 3 in a 70/30 ratio in percents by weight. The xenon pressure in the inner bulb was 13.8 bar at 300 K.
  • the total volume of the inner bulb was 14.0 mm 3 .
  • the xenon high- pressure gas discharge lamp was provided with an ionizable filling comprising 300 ⁇ g Nal/Scl in a 70/30 ratio in percents by weight + 50 ⁇ g Znl 2 .
  • the xenon pressure in the inner bulb was 13.8 bar at 300 K.
  • Luminous flux (lumens) The luminous flux (in lumens) was measured in an Ulbricht photometer sphere.
  • An Ulbricht sphere is a hollow metal sphere with an ideally reflecting inner coating for an integrating measurement of the luminous flux of the lamp, which is fastened in the sphere center in a lampholder. The reflected light hits a photocell which is present behind an ideally reflecting screen protecting the photocell from directly radiated light.
  • the sphere used had a diameter of 0.8 m.
  • a wattmeter and a colorimeter were connected. All test results relate to the steady state, unless indicated to the contrary, i.e. to a measurement taking place after three minutes at rated power and after a constant temperature has been reached.
  • Discharge arc curvature (mm) The discharge arc curvature was determined in that the distance was determined between the brightest point in the central region between the two electrode tips and the lamp axis, i.e. the axis of symmetry or the connecting line between the two electrode tips.
  • the discharge arc diffuseness (mm) was measured in that the distance was determined in a mercury-free high-pressure gas discharge lamp between those points of the discharge arc that have 20% of the maximum relative luminous intensity at the upper and lower edges of the discharge arc centrally between the two electrodes.
  • the increase in discharge arc diffuseness (mm) is obtained in that the difference in discharge arc diffuseness is determined between a mercury-free high-pressure gas discharge lamp according to the invention and the comparison lamp.
  • Discharge arc diffuseness (inv. lamp) discharge arc diffuseness (mm) of a mercury-free gas discharge lamp according to the invention.
  • Discharge arc diffuseness (comp. lamp) discharge arc diffuseness (mm) of the mercury-free gas discharge comparison lamp.

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  • Discharge Lamps And Accessories Thereof (AREA)

Abstract

The invention relates to a mercury-free high-pressure gas discharge lamp with a defined inner bulb (1) volume of its burner space, suitable for increasing the discharge arc diffuseness and suitable for reducing the discharge arc curvature, in particular in the case of high xenon gas pressures, and to the use thereof for lighting purposes, in particular for motor vehicles, wherein the total inner bulb volume of the burner space is constituted by: - a volume A, which is the region occupying the space between the first (6) and the second (5) electrode tip extending into the burner space, - a volume B, which is the region occupying the space in a direction away from the electrode tip (6) of the first electrode along this electrode to the burner space wall (4) of the inner bulb accommodating this electrode, and - a volume C, which is the region occupying the space in a direction away from the electrode tip (5) of the second electrode along this electrode to the burner space wall (7) of the inner bulb accommodating this electrode, for which it holds that volume A / volume B ≥ 10 and volume A / volume C ≥ 10.

Description

MERCURY-FREE HIGH-PRESSURE GAS DISCHARGE LAMP WITH A BURNER DESIGN FOR INCREASING THE ARC DIFFUSENESS AND REDUCING THE ARC CURVATURE
The invention relates to a mercury- free high-pressure gas discharge lamp with a defined inner bulb volume of the burner space, suitable for increasing the discharge arc diffuseness and suitable for reducing the discharge arc curvature, as well as to its use for illumination purposes, in particular for motor vehicles.
High-pressure gas discharge lamps are generally known in the art. Mercury- xenon high-pressure gas discharge lamps, known under the designations D 1 and D2 xenon lamps, are generally used nowadays in headlight systems of many motor vehicles. An essential disadvantage of mercury-free high-pressure gas discharge lamps is that the luminous discharge arc forming between the electrodes is substantially narrower than in mercury-containing high-pressure gas discharge lamps that are similar in other respects, which is caused by the absence of mercury. This leads to a clearly smaller discharge arc diffuseness in mercury-free high-pressure gas discharge lamps. A luminous discharge arc of insufficient diffuseness may lead to a permanent inhomogeneous front field illumination in particular in reflection headlight systems, whose reflectors are often very accurately adapted to the discharge arc geometry.
It is furthermore observed in mercury-free high-pressure gas discharge lamps, in particular mercury-free xenon high-pressure gas discharge lamps, that these lamps have too strong an arc curvature of the discharge arc in the burner space between the two electrodes at a high xenon pressure, because the arc curvature increases with an increase in xenon pressure. This leads inter alia to a strongly inhomogeneous heat distribution in the burner space, such that the region at the inner burner space wall of the inner bulb above the highest point of the discharge arc curvature is considerably hotter than the opposed region of the inner burner space wall perpendicularly below the highest point of the discharge arc curvature.
This is disadvantageous on the one hand for the color stability of mercury-free high-pressure gas discharge lamps because the ionizable filling can deposit in colder regions of the inner burner space wall, which leads to a color shift of the visible light emitted by the mercury- free high-pressure gas discharge lamp in the long run. In practice, therefore, all mercury-free high-pressure gas discharge lamps are to be exchanged in motor vehicles in the case of failure of one mercury-free high-pressure gas discharge lamp so as to avoid visible color differences. On the other hand, the operational life of the mercury-free high-pressure gas discharge lamp as compared with that of the mercury-containing high-pressure gas discharge lamps may be clearly reduced, because the difference in temperature load on the burner space wall of the inner bulb leads to a higher load on the material, especially on the highest location above the arc, for example leading to a shorter lamp life. To reduce the arc curvature of a xenon high-pressure gas discharge lamp, and to avoid overheating of regions above the discharge arc in the burner space, US 5,121,034 Al proposes to operate the lamp at a high frequency within certain frequency bands so as to reduce the arc curvature by means of acoustic resonance.
It is an object of the present invention to increase the discharge arc diffuseness in mercury-free high-pressure gas discharge lamps, which diffuseness is insufficient owing to the absence of mercury as a halogen buffer, and to reduce the discharge arc curvature, which increases strongly, for example, with the use of high xenon pressures, for the purpose, for example, of rendering possible their use in motor vehicles with reflection or projection headlights designed for lamps that do contain mercury.
It was surprisingly found that the discharge arc diffuseness can be clearly increased and the discharge arc curvature, in particular the discharge arc curvature arising from a high xenon gas pressure, can be clearly reduced when the inner bulb surrounding the burner space, also denoted burner, has a defined inner volume.
It is possible in mercury-free high-pressure gas discharge lamps having a defined volume according to the invention to achieve a lesser arc curvature in spite of a high interior burner pressure, which leads to a reduction in the temperature difference between the hottest spot (= above the highest point of the discharge arc) of the wall of the inner bulb and the directly opposed location of the wall of the inner bulb (= below the highest point of the discharge arc). The coldest spot below the discharge arc in a lamp according to the invention has a higher temperature owing to the smaller arc curvature, which is favorable for the color stability on the one hand, and on the other hand is capable of improving lamp efficacy, because, for example, higher vapor pressures of the radiating metals of the ionizable filling can be achieved.
In a preferred embodiment of the invention, the mercury-free high-pressure gas discharge lamp comprises an inner bulb surrounding the burner space, a first electrode extending into the burner space, a second electrode extending into the burner space, and an outer bulb, wherein the inner bulb has a defined volume such that the total inner bulb volume of the burner space is composed of: a volume A, which is the region occupying the space between the first and the second electrode tip extending into the burner space, - a volume B, which is the region occupying the space in a direction away from the electrode tip of the first electrode along this electrode to the burner space wall of the inner bulb accommodating this electrode, and a volume C, which is the region occupying the space in a direction away from the electrode tip of the second electrode along this electrode to the burner space wall of the inner bulb accommodating this electrode, for which it holds that volume A / volume B > 10 and volume A / volume C > 10. The expressions "inner bulb" and "outer bulb" used in the present description relate to all conceivable suitable vessel forms.
The expressions "similar rotationally symmetrical high-pressure gas discharge lamp" and "similar high-pressure gas discharge lamp" relate to respective comparison lamps which are identical to the lamp according to the invention as regards its shape, i.e. has the same inner bulb volume, the same ionizable filling, gas pressure, etc., but which distinguishes itself exclusively by a volume division of the volumes A, B and C not according to the invention, wherein volume A / volume B = 7.0 and volume A / Volume C = 7.0. All test results relate to the steady state, unless indicated to the contrary, i.e. measurements were made after 3 minutes at rated power and after a constant temperature had been reached.
The Hg-free high-pressure gas discharge lamps according to the invention may preferably be filled with xenon. Hg-free high-pressure gas discharge lamps according to the invention comprise an ionizable filling. Suitable ionizable fillings are based on metal halides. Preferred ionizable fillings comprise at least one metal halide chosen from the group comprising Nal, Scl3, ScBr , NaBr, halides of rare earths such as Cel3, Prl3, CeBr3 and/or PrBr3. Halides of the groups Ilia such as Inl, Til, InBr, TlBr, IVa such as Snl2, SnBr2, and Illb such as Lal3, LaBr3, of the periodic system of chemical elements may be used, for example, as ionizable fillings.
The volume A is defined in a manner known to those skilled in the art by the linear distance L from the first electrode tip to the second electrode tip and the diameter BA of the inner bulb obtaining for this region, measured up to the inner wall of the inner bulb.
The volume B is defined by the linear distance LB from the first electrode tip horizontally along the electrode up to the inner wall of the inner bulb through which the electrode is passed. The volume B is thus determined in a manner known to those skilled in the art from the respective diameter Dβ of the inner bulb for the region LB, measured up to the inner wall of the inner bulb.
The volume C is defined by the linear distance Lc from the first electrode tip horizontally along the electrode up to the inner wall of the inner bulb through which the electrode is passed. The volume C is thus determined in a manner known to those skilled in the art from the respective diameter Dc of the inner bulb for the region Lc, measured up to the inner wall of the inner bulb.
In the simplest case, the inner bulb is rotationally symmetrical, and the volumes B and C are equally large.
It is particularly preferred that the inner bulb has identical shapes in the volumes in the regions LB and Lc- It is also particularly preferred in the invention, for example, that an inner bulb which is tubular in its center narrows strongly towards the two ends. Alternatively, however, an inner bulb that is not rotationally symmetrical and that surrounds the burner space may be used in the invention.
It is self-evident that all other manufacturing tolerances are to be observed, so that within the scope of the invention the expression "rotationally symmetrical inner bulb" is still used if the inner bulb is not ideally rotationally symmetrical because of manufacturing tolerances.
The inner bulb volume of the burner space may alternatively be indicated as follows, wherein it holds that: volume A / volume B > 1 1.0 and volume A / volume B < 30.0, and volume A / volume C > 11.0 and Volume A / volume C < 30.0; preferably, volume A / volume B > 13.0 and volume A / volume B < 25.0, and volume A / volume C > 13.0 and Volume A / volume C < 25.0; - more preferably, volume A / volume B > 15.0 and volume A / volume B <
20.0, and volume A / volume C > 15.0 and Volume A / volume C < 20.0.
Preferred volume values for the partial volumes A, B, and C will be given below.
The volume A preferably is a volume of 7.0 mm3 to 30.0 mm3, preferably from 9.0 mm3 to 23.0 mm3, and more preferably from 10.0 mm3 to 17.0 mm3.
Volume B and/or volume C preferably is a volume of 0.1 mm to 3.0 mm , preferably from 0.2 mm to 2.3 mm , and more preferably from 0.25 mm to 1.7 mm .
According to the invention, a substantial improvement in the discharge arc diffuseness can be achieved by means of the defined volumes A, B, and C for the inner bulb of the burner.
In addition, the defined volumes A, B, and C render it possible to achieve that the arc curvature of mercury-free lamps comes closer to that of mercury-containing lamps.
This renders it easier for the headlight manufacturer to provide adequate headlight systems, and at the same time renders possible an exchange of mercury-containing lamps in use at present with mercury-free lamps.
Without being bound to a certain theory, it is suspected that the definition of the volumes A, B, and C of the burner according to the invention leads to a considerably reduced convection of the plasma inside the inner bulb volume defined in accordance with the invention. It is suspected that the downward flow is substantially suppressed, in particularly because of the smaller volumes B and C, whereby the convection of the plasma is influenced in a determining manner.
As a result, a clear improvement in the discharge arc diffuseness and an adaptation of the arc curvature are observed for the mercury- free lamps formed in accordance with the invention, so that they can correspond to mercury-containing lamps. A further advantage of mercury-free high-pressure gas discharge lamps with the volumes A, B, and C of the inner bulb of the burner according to the invention is that such mercury-free lamps can be operated with a higher xenon pressure without the otherwise usual strong increase in arc curvature being observed as a result of this. The reduction in arc curvature may be more or less pronounced in dependence on the gas pressure and the geometry.
Mercury-free lamps according to the invention may accordingly be operated at high xenon gas pressures, during which a smaller arc curvature establishes itself than in similar rotationally symmetrical high-pressure gas discharge lamps with volume A / volume B = 7.0 and volume A / volume C = 7.0. Preferred xenon pressures for mercury-free lamps formed in accordance with the invention, measured at 300 K, preferably lie in a range from 5 to 20 bar, more preferably in a range from 6 to 18 bar, and particularly preferably in a range from 7 to 16 bar. Further suitable xenon pressures for mercury-free lamps formed in accordance to the invention, measured at 300 K, lie in a range from 8 to 19 bar, preferably in a range from 9 to 17 bar, and more preferably in a range from 11 to 15 bar.
It is furthermore advantageous that the mercury-free lamps formed in accordance to the invention have an increased luminous flux (lumens) for a given power (watts) in comparison with similar mercury- free lamps with the same total volume of the inner bulb of the burner, with the difference that it holds for the mercury-free comparison lamp that: volume A / volume B = 7.0 and volume A / volume C = 7.0.
The increase in luminous efficacy of lamps according to the invention is caused by the higher temperature of the coldest spot on the inner wall of the inner bulb and is dependent on the ionizable filling.
The luminous flux of a mercury-free high-pressure gas discharge lamp according to the invention expressed in lumens for a given power in comparison with the same high-pressure gas discharge lamp, but not with a volume division according to the invention, may be higher by > 5 lumens and < 500 lumens, preferably > 10 lumens and < 300 lumens, and more preferably > 30 lumens and < 200 lumens.
The luminous flux of mercury-free high-pressure gas discharge lamps according to the invention at a given power may alternatively be higher than that of the same high-pressure gas discharge lamps, but not with a volume division according to the invention, by > 20 lumens and < 100 lumens, preferably > 40 lumens and < 150 lumens, and more preferably > 50 lumens and < 90 lumens. The arc curvature increases with an increasing gas pressure in mercury-free high-pressure gas discharge lamps, for example with high xenon pressures. The volumes A, B, and C defined in accordance with the invention achieve a change in the position or location of the discharge arc, i.e. of the brightest spot of the discharge arc, owing to the changed convection of the plasma, i.e. the arc curvature is changed.
The arc curvature K of mercury-free high-pressure gas discharge lamps according to the invention preferably has a value in a range of 0.10 to 0.90 mm, preferably 0.20 to 0.80 mm, and particularly preferably 0.25 to 0.75 mm.
It may furthermore be provided in mercury-free high-pressure gas discharge lamps according to the invention that the highest point in the discharge arc of the mercury- free high-pressure gas discharge lamp lies lower than in the identical, in particular rotationally symmetrical similar high-pressure gas discharge lamp not with a volume division according to the invention by at least 0.01 to 0.50 mm, preferably from 0.03 to 0.45 mm, more preferably 0.05 to 0.40 mm, even more preferably 0.07 mm to 0.35 mm, and particularly preferably 0.09 mm to 0.30 mm.
The discharge arc diffuseness D of a mercury-free high-pressure gas discharge lamp according to the invention may have values in a range from 0.70 to 1.50 mm, preferably 0.80 to 1.40 mm, and particularly 0.85 to 1.35 mm.
The increase ΔD in the discharge arc diffuseness of a mercury- free lamp formed in accordance with the invention may amount to 0.01 to 0.50 mm, preferably 0.03 to 0.45 mm, more preferably 0.05 to 0.40 mm, even more preferably 0.07 to 0.35 mm, and particularly preferably 0.09 to 0.30 mm in comparison with the same mercury-free, in particular rotationally symmetrical high-pressure gas discharge lamp, but not with a volume division in accordance with the invention. The construction principle of a mercury-free high-pressure gas discharge lamp according to the invention comprises a burner space in its inner bulb into which two electrodes are introduced, between which a discharge arc is ignited, as well as possibly an outer bulb. The inner bulb, also denoted the burner space hereinafter, may be filled with xenon gas and further ionizable lighting means. The two electrodes may be fused into the inner bulb. The application of a voltage to the electrodes ignites and maintains a gas discharge between them. The discharge arc lies above the connecting line of the electrodes because of the thermal rise. The transitional regions between the electrodes and the discharge arc are denoted the cathode spots. The cathode spots are the hottest and brightest spots of the discharge arc. A further object of the present invention relates to a lighting installation which comprises at least one mercury-free high-pressure gas discharge lamp, which lighting installation is in particular a reflection headlight, projection headlight, projector, and/or lamp for general lighting purposes. In principle, the mercury-free high-pressure gas discharge lamps according to the invention may be used for each and every illumination purpose.
In a preferred embodiment of the present invention, the mercury-free high- pressure gas discharge lamp is preferably a mercury-free xenon high-pressure gas discharge lamp.
The inner bulb and/or outer bulb of a mercury-free high-pressure gas discharge lamp according to the invention may be made from a material chosen from the group comprising quartz, glass, and/or ceramic materials, the inner bulb and outer bulb being preferably made of quartz.
The distance L between the electrode tips of the first and the second electrode of a mercury-free lamp formed in accordance with the invention may be at least 3.5 mm and at most 6 mm, preferably from 3.6 mm to 5.8 mm, more preferably 3.8 mm to 5.5 mm, even more preferably 4.0 mm to 5.3 mm, still more preferably 4.2 mm to 5.2 mm, still more preferably 4.4 mm to 5.0 mm, and particularly preferably 4.6 mm to 4.8 mm.
The inner bulb of a mercury-free lamp formed in accordance with the invention may have a wall thickness in a range from at least 1.3 mm to at most 2.2 mm, preferably 1.5 mm to 2.0 mm, and more preferably 1.7 mm to 1.9 mm.
Preferably, the change in wall thickness of the inner bulb from the thickest location of the wall of the inner bulb to the thinnest location of the wall of the inner bulb is < 0.5 mm and > 0 mm, preferably < 0.4 mm and more preferably < 0.3 mm.
Preferably, the wall thickness of the inner bulb is substantially constant, i.e. the change in wall thickness of the inner bulb from the thickest location of the wall of the inner bulb to the thinnest location of the wall of the inner bulb may amount to < 0.2 mm, or even < 0.1 mm.
Preferably, the electrodes are each embedded in the inner bulb over a length of > 1 mm and < 20 mm, preferably > 2 mm and < 15 mm, and more preferably > 3 mm and < 10 mm. The electrodes may be directly embedded or they may be embedded while enveloped by an additional material layer.
In a preferred embodiment of the invention, the inner bulb may have a total inner bulb volume of at least 9 mm3 and at most 31 mm3, preferably 11 mm3 to 20 mm3, and more preferably 14 mm3 to 17 mm3. Because of the higher discharge arc curvature of mercury-free xenon high- pressure gas discharge lamps with high xenon pressures, the temperature of the wall of the inner bulb in the region perpendicularly above the highest point of the discharge arc is substantially higher than the temperature of the wall of the inner bulb in the region perpendicularly below the highest point of the discharge arc.
The volume defined in accordance with the invention renders it possible to adapt the temperatures of the wall of the inner bulb in the region perpendicularly above the highest point of the discharge arc and perpendicularly below the highest point of the discharge arc such that a more homogenous heat distribution is obtained. This is particularly advantageous at a high gas pressure within the inner bulb surrounding the burner of lamps formed in accordance with the invention, because otherwise a high gas pressure, in particular Xe gas pressure, would lead to an increase in the arc curvature in the case of mercury-free lamps not formed in accordance with the invention.
For example, the temperature difference ΔT of the inner bulb of a mercury - free lamp with volumes A, B, and C defined in accordance with the invention, measured in K perpendicularly above and below the highest point of the discharge arc at the outer wall of the inner bulb, is < 150 K and > 0 K, preferably < 130 K, in particular < 1 10 K, more preferably < 100 K, even more preferably < 80 K, still more preferably < 50 K. The temperature difference ΔT of the inner bulb of a mercury-free lamp with volumes A, B, and C defined in accordance with the invention, measured in K perpendicularly above and below the highest point of the discharge arc at the outer wall of the inner bulb, may even be < 30 K. The temperature in K was measured after a period of operation of 30 minutes perpendicularly above and below the highest point of the discharge arc at the outer wall of the inner bulb of a lamp according to the invention without outer bulb, which lamp was operated horizontally (electrodes in horizontal position).
The subject of the present invention will be explained in more detail below with reference to the appended Fig. 1 , where Fig. 1 shows a mercury-free high-pressure gas discharge lamp according to the invention. Fig. 1 shows a mercury-free high-pressure gas discharge lamp according to the invention with an inner bulb (1), a first electrode (2), a second electrode (3), and the volumes A, B, and C. The distance L is the distance between the electrode tips (4, 5) of the first electrode (2) and the second electrode (3). The volume A follows from the diameter D and the distance L. Furthermore, a linear distance LB is shown for the volume B, which distance extends from the first electrode tip horizontally along the electrode up to the inner wall (6) of the inner bulb, through which the first electrode is passed. In addition, a linear distance Lc is shown for the volume C, which distance extends from the second electrode tip horizontally along the electrode up to the inner wall (7) of the inner bulb, through which the second electrode is passed.
Mercury-free lamps according to the invention will be discussed by way of example below so as to clarify the invention in more detail.
Example 1 The discharge arc diffuseness and arc curvature of a mercury-free, rotationally symmetrical, tubular xenon high-pressure gas discharge lamp according to the invention was determined, which lamp had an inner bulb, a first electrode, a second electrode, the volumes A = 15.2 mm3, B = 0.9 mm3, and C = 0.9 mm , and with an electrode spacing L = 4.2 mm and the distances LB = 1.35 mm and Lc = 1.35 mm. The total volume of the inner bulb was 17.0 mm3. The xenon high-pressure gas discharge lamp was filled with an ionizable filling comprising 300 μg Nal/Scl3 in a 70/30 ratio in percents by weight. The xenon pressure in the inner bulb was 13.8 bar at 300 K.
The following values were measured: discharge arc diffuseness D = 0.9 discharge arc curvature = 0.6 luminous flux = 3000 lumens power = 35 W
Example 2
The discharge arc diffuseness and arc curvature of a mercury-free, rotationally symmetrical, tubular xenon high-pressure gas discharge lamp was determined, which lamp comprised an inner bulb, a first electrode, a second electrode, the volumes A = 13.5 mm3, B = 0.75 mm , and C = 0.75 mm , with an electrode spacing L = 4.1 mm and the distances LB = 1.4 mm and Lc = 1.4 mm. The total volume of the inner bulb was 14.0 mm3. The xenon high- pressure gas discharge lamp was provided with an ionizable filling comprising 300 μg Nal/Scl in a 70/30 ratio in percents by weight + 50 μg Znl2. The xenon pressure in the inner bulb was 13.8 bar at 300 K.
The following values were measured: discharge arc diffuseness D = 0.9 discharge arc curvature = 0.5 luminous flux = 2940 lumens power = 35 W
The measuring methods used will be described below.
Luminous flux (lumens) The luminous flux (in lumens) was measured in an Ulbricht photometer sphere. An Ulbricht sphere is a hollow metal sphere with an ideally reflecting inner coating for an integrating measurement of the luminous flux of the lamp, which is fastened in the sphere center in a lampholder. The reflected light hits a photocell which is present behind an ideally reflecting screen protecting the photocell from directly radiated light. The sphere used had a diameter of 0.8 m. A wattmeter and a colorimeter were connected. All test results relate to the steady state, unless indicated to the contrary, i.e. to a measurement taking place after three minutes at rated power and after a constant temperature has been reached.
Discharge arc curvature (mm) The discharge arc curvature was determined in that the distance was determined between the brightest point in the central region between the two electrode tips and the lamp axis, i.e. the axis of symmetry or the connecting line between the two electrode tips.
Discharge arc diffuseness (mm)
The discharge arc diffuseness (mm) was measured in that the distance was determined in a mercury-free high-pressure gas discharge lamp between those points of the discharge arc that have 20% of the maximum relative luminous intensity at the upper and lower edges of the discharge arc centrally between the two electrodes. The increase in discharge arc diffuseness (mm) is obtained in that the difference in discharge arc diffuseness is determined between a mercury-free high-pressure gas discharge lamp according to the invention and the comparison lamp.
ΔD = discharge arc diffuseness (inv. lamp) - discharge arc diffuseness (comp. lamp) ΔD = increase in discharge arc diffuseness.
Discharge arc diffuseness (inv. lamp) = discharge arc diffuseness (mm) of a mercury-free gas discharge lamp according to the invention. Discharge arc diffuseness (comp. lamp) = discharge arc diffuseness (mm) of the mercury-free gas discharge comparison lamp.

Claims

CLAIMS:
1. A mercury-free high-pressure gas discharge lamp with an inner bulb surrounding the burner space, a first electrode extending into the burner space, a second electrode extending into the burner space, and an outer bulb, wherein the inner bulb has a defined volume such that the total inner bulb volume of the burner space is composed of: - a volume A, which is the region occupying the space between the first and the second electrode tip extending into the burner space, a volume B, which is the region occupying the space in a direction away from the electrode tip of the first electrode along this electrode to the burner space wall of the inner bulb accommodating this electrode, and - a volume C, which is the region occupying the space in a direction away from the electrode tip of the second electrode along this electrode to the burner space wall of the inner bulb accommodating this electrode, for which it holds that volume A / volume B > 10 and volume A / volume C > 10.
2. A mercury-free high-pressure gas discharge lamp as claimed in claim 1, wherein the inner bulb volume of the burner is constituted by: volume A / volume B > 11.0 and volume A / volume B < 30.0, and volume A / volume C > 11.0 and Volume A / volume C < 30.0; preferably, volume A / volume B > 13.0 and volume A / volume B < 25.0, and volume A / volume C > 13.0 and Volume A / volume C < 25.0; more preferably, volume A / volume B > 15.0 and volume A / volume B < 20.0, and volume A / volume C > 15.0 and Volume A / volume C < 20.0.
3. A mercury-free high-pressure gas discharge lamp as claimed in claim 1 or 2, wherein the discharge arc diffuseness D of the mercury-free high-pressure gas discharge lamp has a value in a range from 0.70 to 1.50 mm, preferably 0.80 to 1.40 mm, and particularly 0.85 to 1.35 mm.
4. A mercury-free high-pressure gas discharge lamp as claimed in any one of the claims 1 to 3, wherein the arc curvature K has a value in a range of 0.10 to 0.90 mm, preferably 0.20 to 0.80 mm, and particularly preferably 0.25 to 0.75 mm.
5. A mercury-free high-pressure gas discharge lamp as claimed in any one of the claims 1 to 4, wherein the distance between the electrode tips of the first and second electrodes is at least 3.5 mm and at most 6 mm, preferably between 3.6 mm and 4.4 mm, more preferably between 3.8 mm and 4.2 mm.
6. A mercury- free high-pressure gas discharge lamp as claimed in any one of the claims 1 to 5, wherein the inner bulb has a wall thickness in a range from at least 1.3 mm to at most 2.2 mm, preferably 1.5 mm to 2.0 mm, and more preferably 1.7 mm to 1.9 mm.
7. A mercury-free high-pressure gas discharge lamp as claimed in any one of the claims 1 to 6, wherein the change in wall thickness of the inner bulb from the thickest location of the wall of the inner bulb to the thinnest location of the wall of the inner bulb is < 0.5 mm and > 0 mm, preferably < 0.4 mm, and more preferably < 0.3 mm.
8. A mercury-free high-pressure gas discharge lamp as claimed in any one of the claims 1 to 7, wherein the inner bulb has a total inner bulb volume of at least 9 mm3 and at most 31 mm3, preferably 11 mm to 20 mm3, and more preferably 14 mm3 to 17 mm3.
9. A mercury-free high-pressure gas discharge lamp as claimed in any one of the claims 1 to 8, wherein the gas pressure, in particular Xe gas pressure, inside the inner bulb surrounding the burner space is at least 5 bar up to 20 bar at 300 K, preferably lying in a range from 6 bar to 18 bar, and particularly preferably in a range from 7 bar to 16 bar.
10. A lighting arrangement comprising at least one mercury-free high-pressure gas discharge lamp as claimed in any one of the claims 1 to 9, which lighting arrangement is in particular a reflection headlight, a projection headlight, a projector, and/or a lamp for general lighting purposes.
PCT/IB2004/001363 2003-05-16 2004-05-04 Mercury-free high-pressure gas discharge lamp with a burner design for increasing the arc diffuseness and reducing the arc curvature WO2004102614A1 (en)

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