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Title:
DISCHARGE LAMP WITH DISTORTION REDUCED DISCHARGE VESSEL
Document Type and Number:
WIPO Patent Application WO/2011/045696
Kind Code:
A2
Abstract:
A discharge lamp (1) is provided with a discharge vessel (2) comprising a discharge vessel wall made at least partly of a transparent ceramic material, said dis¬ charge vessel wall enclosing a discharge chamber (3) with opposing first (11) and second ends (12), a filling, provided in said discharge chamber (3), a first electrode (7) comprising a first projecting end (8) and a second electrode (5) comprising a second projecting end (6). The first electrode (7) is arranged to project into the chamber (3) from the first end (11) and the second electrode (5) is arranged to project into the chamber (3) from the second end (12). The discharge chamber wall comprises at least one joining seam (4), resulting from a joining of at least two parts (2a, 2b) of ceramic material. The joining seam (4) is located in the discharge chamber wall at a position closer to the first end (11) of the discharge chamber (3) than the first projecting end (8), so that the output beam of the lamp (1) is not impaired by the joining seam (4).

Inventors:
KUEPPER LUKAS (DE)
VOS THEODORUS P C M (NL)
Application Number:
PCT/IB2010/054336
Publication Date:
April 21, 2011
Filing Date:
September 27, 2010
Export Citation:
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Assignee:
KONINKL PHILIPS ELECTRONICS NV (NL)
PHILIPS INTELLECTUAL PROPERTY (DE)
KUEPPER LUKAS (DE)
VOS THEODORUS P C M (NL)
International Classes:
H01J61/36
Domestic Patent References:
WO2004049391A22004-06-10
WO2009067289A12009-05-28
WO2008095771A22008-08-14
WO2007078574A12007-07-12
Foreign References:
US6620272B22003-09-16
Attorney, Agent or Firm:
BEKKERS, Joost et al. (AE Eindhoven, NL)
Download PDF:
Claims:
CLAIMS:

1. A discharge lamp with

a discharge vessel (2) comprising a discharge vessel wall made at least partly of a transparent ceramic material, said discharge vessel wall enclosing a discharge chamber (3) with opposing first (11) and second ends (12),

a filling, provided in said discharge chamber (3),

- a first electrode (7) comprising a first projecting end (8) and

a second electrode (5) comprising a second projecting end (6), where

said first electrode (7) is arranged to project into said chamber (3) from said first end (11) and

said second electrode (5) is arranged to project into said chamber (3) from said second end (12), where

said discharge chamber wall comprises at least one joining seam (4), resulting from a joining of at least two parts (2a, 2b) of ceramic material

where said at least one joining seam (4) is located in said discharge chamber wall at a position closer to said first end (11) of said discharge chamber (3) than said first projecting end (8).

2. Discharge lamp according to claim 1, where

said joining seam (4) is located at a position distant from said first projecting end (8) by at most 70% of the free projecting length of the first electrode (7).

3. Discharge lamp according to one of the preceding claims, where said dis- charge vessel wall comprises an inhomogeneity (14) resulting from a closed filling opening and where said inhomogeneity (14) is located at a position closer to said first end (11) of said discharge chamber (3) than said first projecting end (8) or at a position closer to said second end (12) of said discharge chamber (3) than said second projecting end (6).

4. Discharge lamp according to one of the preceding claims, where said discharge vessel (2) is fixed to a lamp cap (9) such that said first end (11) of said discharge chamber (3) is arranged closer to said lamp cap (9) than said second end (12).

5. Discharge lamp according to one of the preceding claims, where said discharge lamp (1) is an automotive discharge lamp. 6. Headlight comprising

a reflector (21) with a lamp socket (22) and

a discharge lamp (1) according to one of the above claims, mounted to said lamp socket (22). 7. Headlight according to claim 6, where

said discharge lamp (1) is mounted such that light from said discharge lamp (1) is reflected by said reflector (21) into a direction of an optical axis (23), where

said lamp (1) is arranged with a longitudinal axis, defined by the electrodes (5, 7) of said lamp (1), substantially parallel to said optical axis (23).

8. Method of manufacturing a discharge lamp (1), where

at least a first (2a) and a second (2b) part of a transparent ceramic material are joined at at least one joining seam (4) to form a discharge vessel (2) with a discharge vessel wall enclosing a discharge chamber (3) with opposing first (11) and second ends (12),

said first part (2a) comprising a first electrode (7), a first projecting end (8) and said second part (2b) comprising a second electrode (5) with a second projecting end (6).

where said at least one joining seam (4) is located in said discharge chamber wall at a position closer to said first end (11) of said discharge chamber (3) than said first projecting end (8).

Description:
DISCHARGE LAMP WITH DISTORTION REDUCED DISCHARGE VESSEL

FIELD OF THE INVENTION

The present invention relates to a discharge lamp. More particularly, the invention relates to a gas discharge lamp with a ceramic discharge vessel.

BACKGROUND OF THE INVENTION

Discharge lamps and in particular high-pressure discharge lamps are used in a large variety of applications, such as general room or office lighting, architectural lighting or, more recently, also in mobile applications, e.g. in automotive headlamps.

Conventional discharge lamps comprise a sealed discharge vessel, forming an inner discharge space into which two electrodes extend.

Recent developments enabled the use of ceramic discharge vessels, which allow higher temperatures, thus enabling smaller dimensions and an increase in the vapor pressures and a consequent gain in luminous efficacy and color rendering properties.

Document US 6,620,272 Bl discloses a method of manufacturing an axially symmetric, two-piece ceramic arc tube.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a discharge lamp that enables a high beam quality, while allowing a cost efficient manufacture.

The object is solved by a discharge lamp according to claim 1, a headlight according to claim 6 and a method of manufacturing a discharge lamp according to claim 8. The dependent claims refer to preferred embodiments of the invention.

The basic idea of the present invention is to provide a discharge lamp with a discharge vessel manufactured from a ceramic material, where the position of inhomogeneities in the ceramic material, such as a joining seam or a filling tube, is chosen such that the beam of light emitted by the lamp is not impaired.

According to the invention, the discharge lamp comprises at least a dis- charge vessel with a discharge vessel wall made at least partly of a transparent ceramic material. Preferably, the discharge lamp is a ceramic metal halide (CDM) lamp.

The discharge vessel wall may be made of any suitable ceramic material, providing that at least a fraction of light is transmitted though the material. Therefore, the term "transparent material" is understood to include any type of transparent or at least translucent material. Certainly, the ceramic material should preferably provide that the generated light at the wavelengths of interest is transmitted without substantial attenuation.

The ceramic material may preferably be an alumina (AI 2 O 3 ) ceramic ma- terial, especially preferred poly crystalline alumina ceramic.

According to the invention, the discharge vessel wall encloses a discharge chamber with opposing first and second ends. A suitable filling is provided in said discharge chamber and a first and a second electrode, each comprising a corresponding projecting end, are arranged so that the first electrode projects into said chamber from said first end and the second electrode projects into said chamber from said second end. The projecting ends of the electrodes are thus arranged in said discharge chamber opposing each other, so that an electric arc may be formed in the discharge chamber in an arc area, i.e. between the projecting ends.

The distance between said projecting ends should be chosen according to specific application and the corresponding lamp design parameters, e.g. voltage, current and the composition of the filling in said chamber. Preferably, the distance is chosen between 3 - 5 mm. The electrodes may be made of any suitable material; preferably, the electrodes are at least partly made of tungsten.

The filling may be of any suitable type and typically includes a rare gas such as xenon as well as metal halides. Preferably, the filling comprises xenon gas at a cold fill gas pressure of at least 4 bar. Most preferably, the filling further comprises a metal halide composition, resulting in a CDM-type discharge lamp. Suitable metal halides include especially Nal and other rare earth halides.

The discharge chamber certainly should be sufficiently sealed, so that the filling is safely kept in the chamber. The chamber may exhibit any suitable geometry and dimensions; however the discharge chamber preferably has a cylindrical shape with a longitudinal axis extending said first and second ends. Most preferably, the chamber has a volume of 5-15 mm 3 , particularly 9-13 mm 3 .

The inventive discharge vessel comprises at least one joining seam, result- ing of a joining of at least two parts of said ceramic material, i.e. the discharge vessel is manufactured from at least two parts of ceramic material. According to the invention, the at least one joining seam is located in said discharge vessel wall at a position closer to said first end of said discharge chamber than said first projecting end of the first electrode. The discharge lamp is thus manufactured, so that said at least one joining seam is - regarding its position on the longitudinal axis - advantageously not in the arc area of the discharge vessel, i.e. between the electrodes, so that the output beam of light, emitted by the arc discharge, is not impaired by the joining seam.

The inventive discharge lamp thus provides a very homogeneous beam distribution, which is especially advantageous in applications requiring a directed beam, such as automotive applications.

The term "closer to" in this connection refers to the distance between the first end of the discharge chamber and the at least one joining seam in relation to the distance of said first end of said chamber to the projecting end of the first electrode, i.e. the tip of the electrode, defined in the direction of an axis, parallel to the first electrode.

The discharge vessel may certainly be made of more than two parts of ceramic material. In this case, all resulting joining seams should be arranged outside of said arc area, i.e. at a position closer to the end of the discharge chamber than said projecting end of the respective electrode.

During manufacture of a discharge vessel in accordance with the present invention, the discharge vessel is manufactured by joining at least two parts of ceramic material at the joining seam, as discussed above. The joining may be conducted by any suitable method, such as bonding or preferably by sintering said at least two parts of ceramic material. The electrodes are preferably inserted into openings in the respective part prior to the joining to form a gas tight connection between the electrode and the respec- tive ceramic part.

As discussed above, the at least one joining seam is located closer to the first end of the discharge chamber than said first projecting end of the first electrode. To facilitate manufacture while obtaining a high beam quality of the output light, the joining seam is preferably located at a position spaced from the first projecting end (electrode tip) by at most 70% of the free projecting electrode length, i. e. the distance from said first projecting end to said first end of the chamber. More preferred, the distance between the electrode tip and the joining seam is 50% or less, most preferred 30%> or less of the free projecting electrode length. While acceptable optical properties are already achieved with the joining seam located directly behind the electrode tip, it may be pre- ferred to arrange the joining seam at a small distance behind the electrode tip, e. g. at least 3% or at least 5% of the free electrode length.

The optical properties of the inventive discharge lamp may be further improved in case not only the joining seams are arranged outside of the arc area, but also further imperfections, such as an inhomogeneity resulting from a closed filling opening. Therefore, according to a development of the invention, the discharge vessel wall com- prises at least one inhomogeneity resulting from a closed filling opening and where said inhomogeneity is located at a position closer to said first end of said discharge chamber than said first projecting end of said first electrode or at a position closer to said second end of said discharge chamber than said second projecting end of said second electrode.

This enhances the optical properties of the discharge lamp, especially because the inhomogeneity resulting from a closed filling opening may substantially distort the output beam. In many cases, at least a part of a filling tube may still remain at the closed filling opening, which substantially impairs light emitted if positioned within the arc area. During manufacture, the filling gas is typically introduced using said filling opening or filling tube after the discharge chamber has been evacuated. The filling opening is then closed and sealed so that said inhomogeneity remains. Although it is sufficient that the inhomogeneity is located closer to an end of the discharge chamber than the projecting end of the respective electrode, i.e. outside of said arc area, it is preferred, that the inhomogeneity is located at a distance from the electrode tip of 3-70% of the free projecting length.

While it would be beneficial for the optical properties to have both inho- mogeneities, resulting from the filling tube and from the joining seam, at one end of the lamp, it has proven to be better for manufacturing reasons to arrange the joining seam and the filling tube on opposite ends of the lamp.

According to a further embodiment of the invention, the discharge vessel is fixed to a lamp cap, so that the first end of the discharge chamber is arranged closer to the lamp cap than the first end to the discharge chamber. Thus, the joining seam is provided at the end of the discharge vessel closer to the lamp cap, and preferably the filling inhomogeneity is arranged at the lamp tip, distant from the lamp cap.

The lamp cap connects the discharge lamp with an electric power supply and further allows the discharge lamp to be mounted to a lighting unit, e. g. a headlight, comprising a corresponding lamp socket. According to the present embodiment, the lamp cap is provided on the side of the first end of the chamber, so that the at least one joining seam is arranged on the side of the closer end of said chamber, which may be referred to as the bottom area of the lamp. In this case it is particularly preferred that an inhomogeneity resulting from the closed filling tube is located at the opposite end of the lamp, i. e. at a position closer to said second end of said discharge chamber than said second projecting end, i.e. that the inhomogeneity is located in the top area of the lamp, distant from said lamp cap. The present embodiment is particularly advantageous in case the discharge lamp is used in a reflector lighting unit, providing a further enhanced beam quality, because here the portions of the light used by the reflector cover a broader angular range on the bottom end of the lamp than at the top.

As discussed above, the discharge lamp may be of any suitable type, depending on the application. Preferably, the discharge lamp is an automotive discharge lamp.

According to a further aspect of the invention, a headlight, e.g. for automotive applications, comprises a reflector with a lamp socket and the inventive discharge lamp, mounted to said lamp socket. As discussed above, the inventive lamp is particularly useful in applications, where a directed beam of light is needed. The present embodi- ment thus advantageously provides a directed beam with an outstanding beam quality.

The reflector may be of any suitable type, depending on the application. Preferably, the reflector is asymmetrical, e.g. adapted for vehicle low and high beam profiles. The lamp socket provides at least a mechanical support for the lamp and may further be adapted to connect the lamp to a power supply line. Preferably, the lamp socket is adapted for a removable connection to said lamp, so that the lamp may easily be exchanged in case of a failure.

The headlight may certainly comprise further components, such as further lamp sockets, a power supply unit, electrical or electronic control circuitry or any type of mounting device for a connection to a vehicle body.

According to a further preferred embodiment, the discharge lamp is mounted such that light from said discharge lamp is reflected by said reflector into a direction of an optical axis, where said lamp is arranged with a longitudinal axis, defined by the electrodes of said lamp, substantially parallel to said optical axis. In the context of the present invention, the term "substantially parallel" is understood to include slight deviations of ± 10°.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the present invention will become apparent from the following description of preferred embodiments, in which

Fig. 1 shows an embodiment of a discharge lamp according to the invention and

Fig. 2 shows an embodiment of a headlamp comprising the discharge lamp of fig. 1. DETAILED DESCRIPTION OF EMBODIMENTS

Fig. 1 shows an embodiment of a discharge lamp 1 in a cross-sectional view. The discharge lamp comprises a discharge vessel 2, which forms a cylindrical dis- charge chamber 3. A first electrode 7 with a first projecting end 8 is arranged to project into the discharge chamber 3 from a first end 11 of the discharge chamber 3. A second electrode 5 with a second projecting end 6 is arranged to correspondingly project into the chamber 3 from a second end 12 of the discharge chamber 3.

As can be seen from fig. 1, the first and the second end 11, 12 of the dis- charge chamber 3 are arranged opposing each other along a longitudinal axis of the cylindrical discharge chamber 3. In the present example, the discharge chamber 3 has a volume of about 11 mm 3 . The internal diameter is 1.2 mm, the wall thickness is 0.5 mm.

The projecting ends 6, 8 of the electrodes 5, 7 are arranged parallel to the longitudinal axis of the chamber 3. The electrodes thus form an arc area, as indicated by the dotted lines 13 in Fig. 1, in which light is generated in the operational state of the lamp. In the present example, the electrode distance is 4 mm. The electrodes 5, 7 project by approx. 2 mm into the discharge chamber 3.

The two electrodes 5, 7 are made of three sections. A tip section is made of Tungsten doped with Rhenium. A center section, embedded in the material of the dis- charge chamber 3, is made of Iridium to form a tight seal there. A further distant portion is again made of Tungsten.

The electrodes 5, 7 are connected to a lamp cap 9 by electrical supply lines 10. The lamp cap 9 is adapted for removable engagement with a corresponding lamp socket (not shown) to connect the supply lines 10 to a power supply unit for opera- tion.

The discharge vessel 2 is made of a first part 2a and a second part 2b of ceramic alumina material, co-sintered at a joining seam 4. As can be seen from fig. 1, the joining seam 4 is located at a position, closer to the first end 11 of the chamber 3 than the first projecting end 8 of the first electrode 7, i.e. the corresponding electrode tip. Accordingly, the joining seam 4 is located outside of the arc area and thus the output beam of light is not impaired by the joining seam 4. The present discharge lamp 1 thus enables a homogeneous beam distribution of the output beam of light. The discharge vessel 2 is arranged within a transparent outer bulb 16 which is fixed to the electrical supply lines 10 and sealed to the outside. According to the present embodiment, the distance between the joining seam 4 and the projecting tip 8 of the first electrode 7 is approx. 20% of the free projecting length of the electrode 7.

The discharge vessel 2 is made of two parts 2a, 2b of ceramic material, as discussed above. The parts 2a, 2b are made by injection molding of alumina material. The first part 2a is molded with a filling tube including a filling opening (from which in the lamp only an inhomogeneity 14 remains) to allow a filling mixture to be inserted in the chamber 3. After molding, the electrodes 5, 7 are inserted into openings of the respective parts 2a, 2b together forming a gas tight jacket. Then, the two parts 2a, 2b are co-sintered at the seam 4 to form the discharge chamber 3.

Once the vessel 2 is formed, the chamber 3 is evacuated using the filling opening. Then, a filling comprising Xenon gas at 12 bar and a mixture of metal halides is introduced. The filling opening is then laser sealed, so that an inhomogeneity 14 remains. The inhomogeneity 14 is located at a position closer to the second end 12 than the second projecting end 6 of the second electrode 5, so that the output beam is not impaired by said inhomogeneity.

Fig. 2 shows an embodiment of a vehicle headlight 20 comprising an asymmetrical reflector 21 and a lamp socket 22. The discharge lamp 1 according to fig. 1 is mounted in said lamp socket 22, so that light, emitted from the lamp 1 is reflected by the reflector 21 to form a directed beam of light in the direction of an optical axis 23. A lens 24 is provided for further beam-shaping, e. g. for forming a typical automotive low- beam profile. Alternatively to a projector-type headlight shown in fig. 2 including the lens 24, the lamp 1 may also be used in a reflector-type headlight (not shown), which does not have a lens. The lamp 1 is arranged in the reflector 21 so that the longitudinal axis of the discharge chamber 3 and the electrodes 5, 7 are parallel to the optical axis 23.

As can be seen from fig. 2, the arrangement of the joining seam 4 and the inhomogeneity 14 provides that the beam of light, emitted by the lamp 1 and reflected by the reflector 21 is not impaired, so that an advantageously homogeneous beam distribution is given.

While the invention has been illustrated and described in detail in the drawings and the foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention from a study of the drawings, the disclosure and the appended claims.

In the claims, the word "comprising" does not exclude other elements and the indefinite article "a" or "an" does not exclude a plurality. The mere face that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.