WO2008102300A1

WO2008102300A1 - High-pressure discharge lamp for use in a headlamp for automotive applications and headlamp for automotive application

Info

Publication number: WO2008102300A1
Application number: PCT/IB2008/050586
Authority: WO
Inventors: Johannes P. M. Ansems; Teunis W. Tukker; Benno Spinger; Lingli Wang
Original assignee: Koninklijke Philips Electronics N.V.; Philips Intellectual Property & Standards Gmbh
Priority date: 2007-02-23
Filing date: 2008-02-19
Publication date: 2008-08-28

Abstract

The invention provides a high-pressure discharge lamp comprising a first mirror and/or a second mirror, wherein, relative to a perpendicular to the longitudinal axis, the first mirror is located between angles γ2 and γ3 to said perpendicular and wherein the second mirror is located between angles δ2 and δ3 to said perpendicular, with γ3>γ2, γ2≥25°, γ3≤65°, δ3>δ2, δ2>125°, and δ3≤165°, and wherein the mirrors are arranged to reflect at least part of the light generated by the lamp back into at least part of the discharge arc. An advantage of such a high-pressure discharge lamp is that the lamp can have an improved luminance in the direction in which the light is used to illuminate the spot or area defined by 50V, 75R and 5OR in automotive applications, such as in a headlamp. Furthermore, such a lamp can be operated at a lower power than prior art lamps, but with substantially the same luminance in the direction in which the light is used to illuminate the spot or area defined by 50V, 75R and 5OR, i.e. such a lamp has an improved efficiency in illuminating the spot area.

Description

High-pressure discharge lamp for use in a headlamp for automotive applications and headlamp for automotive application

FIELD OF THE INVENTION

The present invention relates to a high-pressure discharge lamp for use in a headlamp in automotive applications, as well to such a headlamp.

BACKGROUND OF THE INVENTION

High-pressure discharge lamps for automotive applications, such as for headlamps, are known in the art. The construction, dimensions, and photometric properties are regulated by the United Nations in uniform provisions concerning the approval of motor vehicle headlamps equipped with gas-discharge light sources. An example of a prior art lamp is described in WO95/31001. WO95/31001 discloses a capped high-pressure discharge lamp suitable for use in a vehicle headlamp and having a discharge vessel which is surrounded by an outer envelope. The lamp has current conductors extending from electrodes to contacts at a cap in which a first neck-shaped portion of the discharge vessel is secured. A return portion of one current conductor extends along an outer surface of the outer envelope. The outer envelope has a light-absorbing coating in a region near the first neck-shaped portion, at a side which is remote from the return portion. The outer envelope may have band-shaped coatings at either side, aside from the discharge path between the electrodes, at its side which faces the return portion. Stray light in the beam formed by the reflector and the lens of a headlamp in which the lamp is used is obviated. The bands provide a rectilinear light/dark transition in said beam.

SUMMARY OF THE INVENTION

Such prior art lamps have one or more of the drawbacks that part of the light of the lamp is not suitable for use at the spot area, the area defined by 50V, 75R and 5OR, but is used to illuminate the roadside where it is used less effectively, while the area defined by 50V, 75R and 5OR would benefit from more light. Furthermore, the luminance of such prior art lamps can be increased, especially in the direction in which the light from the lamp is used to illuminate said spot area. Another disadvantage may be that prior art lamps tend to have a relatively short lifetime.

It is an object of the invention to provide an alternative high-pressure discharge lamp for use in a headlamp for automotive applications, which preferably obviates one or more of above-described drawbacks to an even larger degree. Preferably, such a lamp has an improved luminance especially in the direction in which the light from the lamp is used to illuminate the desired area defined by 50V, 75R and 5OR or, due to the increased performance, the power of such a lamp can be decreased while substantially the same luminance is maintained, especially in the direction in which the light is used to illuminate the spot area. The flux to the spot area is preferably also improved. A reduced power advantageously prolongs lamp life and in general reduces the cost of the ballast.

According to a first aspect of the invention, there is provided a high-pressure discharge lamp arranged to generate light, the lamp comprising: a. an outer envelope having an inner surface and an outer surface; b. a discharge vessel enclosed by the outer envelope, the discharge vessel having a vessel wall enclosing a discharge space with an ionizable filling, which discharge space further encloses electrodes arranged opposite each other and arranged to define a discharge arc between them during operation of the lamp, wherein the vessel has a longitudinal axis and the wall has an inner surface and an outer surface; and c. at least one mirror selected from the group consisting of a first mirror and a second mirror such that, relative to a perpendicular to the longitudinal axis, the first mirror is located between angles γ2 and γ3 to this perpendicular and wherein, relative to the perpendicular to the longitudinal axis, the second mirror is located between angles 52 and 53 to this perpendicular, with γ3>γ2, γ2>25°, γ3<65°, 53>52, 52>125° and 53<165°, and wherein the mirrors are arranged to reflect at least part of the light generated by the lamp back into at least part of the discharge arc.

An advantage of such a high pressure discharge lamp is that, in automotive applications such as in a headlamp, the lamp can have an improved luminance in the direction in which the light is used to illuminate the spot or area defined by 50V, 75R and 5OR. Furthermore, such lamp may be operated at a lower power than prior art lamps, but with substantially the same luminance in the direction in which the light is used to illuminate the spot or area defined by 50V, 75R and 5OR, i.e. such a lamp has an improved efficiency in illuminating the spot area. In this way, the lamp can have a higher luminous flux in the spot area. The invention thus provides a lamp that may consume less energy, may (therefore) have a longer life, and may have a cheaper ballast. The fact that the mirror or mirrors reflects or reflect at least part of the light generated by the lamp back into at least part of the discharge arc implies that at least part of the light reflected back is reflected to the source, i.e. the discharge arc, which is in a position offset from the longitudinal, for the discharge forms an arc offset from the longitudinal.

In a specific embodiment, the invention provides a lamp wherein the outer surface of the discharge wall or the outer surface of the outer envelope, or both the outer surface of the discharge wall and the outer surface of the outer envelope, comprises or comprise at least one protrusion selected from the group consisting of a first protrusion and a second protrusion, and wherein the first mirror is attached to the first protrusion and the second mirror is attached to the second protrusion. An advantage of this embodiment is that the mirror or mirrors is or are attached to the discharge vessel or to the outer envelope, which renders any complicated alignment of the mirrors to reflect at least part of the light generated by the lamp back into at least part of the discharge arc unnecessary. In another preferred embodiment, the invention provides a lamp as defined above, wherein the outer surface of the discharge vessel wall comprises at least one protrusion selected from the group consisting of the first protrusion and the second protrusion, wherein the inner surface of the discharge vessel wall is located at a radius rl from the longitudinal axis and the outer surface of the vessel wall is located at a radius r2 from the longitudinal axis, with r2>rl, and wherein independently: a. the first mirror, having a mirror surface, has a curvature with radius r3, with preferably r3>r2, and wherein at γl, with γ2<γl<γ3, a tangent to the outer surface of the wall and a tangent to the mirror surface of the first mirror enclose an angle β3, with β3> 0°, and b. the second mirror, having a mirror surface, has a curvature with radius r4, with preferably r4>r2, and wherein at δl, with 52<δl<δ3, a tangent to the outer surface of the wall and a tangent to the mirror surface of the second mirror enclose an angle β4, with β4> 0°.

An advantage of this embodiment is that the mirrors are attached to the discharge vessel. This renders any complicated alignment of the mirrors to reflect at least part of the light generated by the lamp back into at least part of the discharge arc unnecessary. In yet another specific embodiment, the invention provides a lamp as defined above wherein the outer surface of the outer envelope comprises at least one protrusion selected from the group consisting of the first protrusion and the second protrusion, wherein the inner surface of the outer envelope is located at a radius r5 from the longitudinal axis and the outer surface of the outer envelope is located at a radius r6 from the longitudinal axis, with r6>r5, and wherein independently: a. the first mirror, having a mirror surface, has a curvature with a radius r8, with preferably r8>r6, and wherein at γl, with γ2<γl<γ3, a tangent to the outer surface of the outer envelope and a tangent to the mirror surface of the first mirror enclose an angle β3, with β3> 0°, and b. the second mirror, having a mirror surface, has a curvature with a radius r9, with preferably r9>r6, and wherein at δl, with 52<δl<δ3, a tangent to the outer surface of the outer envelope and a tangent to the mirror surface of the second mirror enclose an angle β4, with β4> 0°.

In a preferred embodiment, r3/r2 and r4/r2 are preferably mutually independently in the range of 0.9-1.2. Likewise, in the embodiment in which the mirrors are arranged on the outer envelope, r8/r6 and r9/r6 are preferably mutually independently in the range of 0.9-1.2. As mentioned above, r3/r2, r4/r2, r8/r6 and r9/r6, are each independently preferably greater than 1.0.

Especially if the mirrors are attached to the protrusions to the outer surface of the outer envelope and more preferably to the outer surface of the discharge vessel, light which otherwise might be used for less important regions is sent back into the discharge arc, thereby increasing the luminance in the direction in which the light is used to illuminate the area defined by 50V, 75R and 5OR.

The principal features of the lamp of the invention, except for the specific additional mirror(s) as described herein, are described in WO95/31001, which is incorporated herein by reference. Furthermore, the lamp of the invention, except for the specific additional mirror(s) as described herein, is described in: - Regulation 98 - Rev. 1 "Motor vehicle headlamps equipped with gas- discharge light sources", Regulation 98 - Rev. 1 - Amend.1, Regulation 98 - Rev. 1 - Amend.2, which are all indicated as regulation 98 for the sake of simplicity; and especially Regulation 99 - Rev.l "Gas-discharge light sources for use in approved gas- discharge lamp units of power-driven vehicles", Regulation 99 - Rev.l - Corr.l, Regulation 99 - Rev.l - Amend.1, Regulation 99 - Rev.l - Amend.1 - Corr.l and Regulation 99 - Rev.l - Amend.2, which are all indicated as regulation 99 for the sake of simplicity.

These regulations are also incorporated herein by reference. Especially the types DlR, D2R, D3R and D4R described in Regulation 99 relate to preferred embodiments of the high-pressure discharge lamp of the invention, except for the specific mirrors described herein.

These Regulations are part of the "Agreement concerning the adoption of uniform technical prescriptions for wheeled vehicles, equipment and parts which can be fitted and/or be used on wheeled vehicles and the conditions for reciprocal recognition of approvals granted on the basis of these prescriptions", addendum 97, regulation No 98 Revision 1 (and amendments and addendums thereto, see above) "Uniform provisions concerning the approval of motor vehicle headlamps equipped with gas-discharge light sources" of 8 July 2005 and addendum 98, regulation No. 99 Revision 1 "Uniform provisions concerning the approval of gas-discharge light sources for use in approved gas-discharge lamp units of power-driven vehicles" (and amendments and addendums thereto, see above) of 10 August 2001 of the United Nations Economic Commission for Europe (UNECE), also known as E/ECE/324 E/ECE/TRANS/505 Rev.l/Add.97/Rev.l and Rev.l/Add.98/Rev.l, respectively, which are known to those skilled in the art and which can be found at http://www.unece.org/.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts:

Figures la-c schematically depict the main features of an embodiment of the high-pressure discharge lamp and headlamp of the invention, as known from the prior art, and without indicating the specific mirrors according to the invention. These mirrors are described below after the general description of the lamp. Fig. Ia shows a headlamp in side elevation, including a circumferential reflector; Fig. Ib is a cross-section, with the contours of the lamp cap; and Fig. Ic is another cross-section of the lamp in Fig. Ia;

Figures 2a-2c schematically depict an embodiment of the discharge vessel of the invention in more detail in rear elevation (2a), in plan view (2b), and in a perspective front view (2c), wherein the mirror or mirrors according to the invention is or are attached to protrusions on the outer surface of the discharge vessel; and

Figure 3 schematically depicts another embodiment of the discharge vessel and the outer envelope of the invention in more detail in back view, wherein the mirror or mirrors according to the invention is or are attached to protrusions on the outer surface of the outer envelope. DETAILED DESCRIPTION OF THE EMBODIMENTS

A general description of the high pressure discharge lamp according to the invention will first be given below with reference to figures Ia-Ic. Then, the specific mirrors of the invention will be described with reference to figures 2a-2c and 3.

Figures Ia-Ic show a preferred embodiment of the lamp of the invention, without going into detail about the specific mirrors according to the invention. Note that figures Ia-Ic herein refer to lamps DlR, D2R, D3R and D4R according to the abovementioned regulation No. 99 (including its revisions and amendments), which are preferred embodiments of the invention except for the fact that the invention advantageously adds at least one (additional) mirror for reflecting at least part of the light generated by the lamp back into at least part of the discharge arc (see below).

High pressure discharge lamp in general Fig. Ia shows a high pressure discharge lamp 10 of the invention in the form of a capped high-pressure discharge lamp 10 which has a light-transmitting lamp vessel or discharge vessel 1 , made of quartz glass, which is closed in a vacuumtight manner and encloses a discharge space 2 with an ionizable filling in which electrodes 3, 4 are arranged in mutual opposition so as to define a discharge path between them (see also Regulation 99). The filling comprises, for example, mercury, a mixture of metal halides such as sodium and scandium iodide, and a rare gas such as, for example, xenon or argon, for example with a filling pressure of several bar. As mentioned above, such lamps are known in the art.

The lamp vessel has an longitudinal axis 100, as depicted in figure Ia (and figure 2b; in figures Ib, Ic, 2a, 2c and 3 the longitudinal axis 100 is perpendicular to the plane of drawing) and a first 206 and a second neck-shaped portion 207 with pinches 208. The longitudinal axis 100 is parallel to the y-axis here. The longitudinal axis 100 is the axis through the electrodes 3, 4, which are arranged in mutual opposition, as is known in the art. The longitudinal axis is denoted the reference axis in the above mentioned regulation 99 (see Rev. l/Add.987/rev. I/Amend.1, regulation 99, page 10: the reference axis at A). The discharge vessel 1 is drawn as oval or spheroidal in shape here, but the discharge vessel 1 may alternatively be tubular or spherical. Hence, the discharge vessel 1 may have a substantially spherical shape, a substantially spheroidal shape, or a substantially cylindrical (tubular) shape, which are all rotationally symmetrical with respect to the axis 100 (also denoted the longitudinal axis), with an outer length L (see figure 2b for a substantially cylindrical shape) along axis 100. Spheroids are known in the art and are obtained by rotating an ellipse about one of its principal axes. The discharge vessel 1 of the invention may have a spheroidal shape, more especially a prolate spheroidal shape (i.e. a shape like a rugby ball as depicted in figure Ia). The discharge vessel is essentially rotationally symmetrical about the axis 100. The radii r2-r9 are radii perpendicular to the axis 100. As will be clear to those skilled in the art, the values of these radii may vary along the axis 100. This can be seen in figures Ia and 2b, where the radii are smaller close to the extremities of the discharge vessel 1, i.e. the extremities of the discharge vessel 1 at the first and second neck-shaped portions 206, 207 in the depicted embodiments, increasing in the direction of the center of the discharge vessel 1. The values of the radii may be constant along part of the discharge vessel 1 in the case of a substantially cylindrical discharge vessel, (see figure 2b). Hence, the discharge vessel 1, i.e. the vessel wall 11, has a longitudinal axis 100 and is substantially rotationally symmetrical about the longitudinal axis 100. Preferably, the discharge vessel 1 has a spheroidal or cylindrical shape as schematically depicted herein and in the above- mentioned regulation 99.

The discharge vessel further comprises first and second neck-shaped portion 206, 207, which are substantially cylindrically shaped and which have the same longitudinal axis 100. However, the invention is not limited to discharge vessels 1 having such neck- shaped portions. A tubular glass, for example quartz-glass, outer envelope 210 is present around the discharge space 2, surrounding the discharge vessel 1 with clearance, is connected to the lamp vessel 1 , and is under vacuum or filled with a gas, for example with a noble gas or air. The outer envelope encloses discharge vessel 1.

The lamp 10 further has a lamp cap 220 provided with contacts 221, 222, in which cap 220 the first neck-shaped portion 206 is fixed. A first 223 and a second current conductor 224, each connected to an electrode 3, 4, extend through the first 206 and the second neck shaped portion 207 to respective contacts 221, 222 at the lamp cap 220. The second current conductor 224 has a return portion 225 which extends along an outer side of the outer envelope 10. The outer envelope 210 may have a light-absorbing coating 311, see also Figs.

Ib and Ic, in a zone situated near the first neck- shaped portion 206 at the side thereof facing away from the return portion 225 of the second current conductor 24. The zone extends at least from a location which encloses an angle α of 50°, in Figure Ia of 40°, with a perpendicular to the outer envelope 210 at the center between the electrodes 3, 4, and parallel to the z-axis, at least up to a location which encloses an angle β of approximately 65° with said perpendicular. The vertices of α and β lie on the longitudinal axis 100 of the lamp vessel 1. The angles α and β are denoted angles αl and α3, respectively, in the above-mentioned regulation 99 (see Rev. l/Add.987/rev. I/Amend.1, regulation 99, page 10). A ceramic pipe 226 is present around the return portion 225 in Fig. Ia, which pipe is accommodated in the lamp cap 220 at one end and is fixed with cement in a ceramic cap 227 at another end. The lamp 10 is electrically safe to touch when powered via a connector on the lamp cap 220.

The outer envelope 10 may have a band-shaped light-absorbing coating 312, 313 on either side laterally of the discharge path at the side thereof facing the return portion 225 of the second current conductor 224. These band-shaped coatings 312, 313 have edges 312', 313' facing away from one another and enclosing an angle γ of substantially 165°, and mutually facing edges 312", 313" which enclose an angle δ of 85° to 145°. The vertices of γ and α lie on the longitudinal axis 100 of the lamp vessel 1. The discharge vessel 1 preferably has a circumferential clearance of at most 2 mm inside the outer envelope surrounding the discharge space 2. Stray light is effectively counteracted in the lamp.

Hence, an embodiment of the lamp can generally be described as a capped high-pressure discharge lamp 10 comprising (a) the light-transmitting lamp vessel or discharge vessel 1 which is closed in a vacuumtight manner and which encloses discharge space 2 with an ionizable filling, wherein the electrodes 3, 4 are arranged in mutual opposition so as to define a discharge path between them, which lamp vessel has an axis 100 and a first 206 and a second neck-shaped portion 207 (with pinches 208); (b) the glass tubular outer envelope 210 around the discharge space 2, surrounding the discharge vessel 1 with clearance, which envelope is connected to the lamp vessel 1 and is filled with gas; (c) the lamp cap 20 which is provided with contacts 21, 22 and in which the first neck-shaped portion 206 is secured; (d) the first 223 and the second current conductor 224, each connected to a respective electrode 3, 4 and extending through the respective first 206 and second neck- shaped portion 207 to respective contacts 221, 222 at the lamp cap 220, the second current conductor 224 having the return portion 25 which extends along an outer side of the outer envelope 210, wherein the outer envelope 210 has the light-absorbing coating 311 in a zone situated near the first neck-shaped portion 206 at the side thereof facing away from the return portion 225 of the second current conductor 224, which zone extends from a location enclosing an angle α of 50° with the perpendicular to the outer envelope 210 at the area of the center between the electrodes 3, 4 at least up to a location which encloses an angle β of approximately 65° with said perpendicular, wherein the vertices of α and β lie on the axis 100 of the lamp vessel 1.

In a specific embodiment, the outer envelope 210 has the band-shaped, light- absorbing coating 312, 313 on either side laterally of the discharge path at the side thereof facing the return portion 225 of the second current conductor 224, which band-shaped coatings 312, 313 have edges 312', 313' facing away from one another and enclosing an angle γ of substantially 165°, and edges 312", 313" facing towards one another and enclosing an angle δ of 85° to 145° with one another, the vertices of γ and δ lying on the axis 100 of the lamp vessel 1. The coatings 312, 313 of the outer envelope may be realized with conventional materials used for incandescent lamps in headlamps, for example a suspension of carbonyl iron and silicon. The coatings may be provided with a brush, by a printing technique, or by spraying, for example with an ink jet.

Hence, the main details of the lamp, without the specific mirrors of the invention, and without the above coatings 312, 313, can be summarized as a high-pressure discharge lamp 10 arranged to generate light, the lamp 10 comprising an outer envelope 210, having an inner surface 212 and an outer surface 213; a discharge vessel 1 enclosed by the outer envelope 210 and having a vessel wall 11 enclosing the discharge space 2 with an ionizable filling, wherein the discharge space 2 further encloses electrodes 3, 4 arranged opposite each other so as to define a discharge arc between them during operation of the lamp 10, wherein the vessel 1 (or vessel wall 11) is substantially rotationally symmetrical with respect to the longitudinal axis 100, the vessel wall 11 having an inner surface 12 and an outer surface 13.

Embodiments of the high pressure discharge lamp of the invention

After the discussion of the lamp 10 in general, the specific features of the invention will now be described with reference to figures Ia and 2a, 2b, 2c and 3. Note that figures 2a, 2c and 3 are views taken along the longitudinal axis 100 (in the Regulation this axis is indicated as "Reference axis", see also above). The perpendicular 101, as indicated in these figures, is perpendicular to this longitudinal axis and would, for example, be horizontal in a headlamp of a continental European automobile standing on a substantially horizontal surface. Figures of the lamp 10 or discharge vessel 1 seen from the first neck-shaped portion 206 are indicated as rear elevation figures; seen from the second neck-shaped portion 207 are indicated as front elevation figures. A view taken from A is a front elevation in the figure on page 10 of Rev.1/Add.98/Rev. I/Amend.1 and a rear elevation from the opposite direction. For instance, lamp 1 in figure Ia seen along the longitudinal axis 100 from the right would provide a front elevation and from the left along the longitudinal axis 100 a rear elevation. The lamp 10 of the invention further comprises at least one mirror selected from the group consisting of a first mirror 35 and a second mirror 45. The mirrors 35, 36 are arranged to reflect at least part of the light generated by the lamp 10 back into at least part of the discharge arc. This means that at least part of the visible light of the lamp 10 is reflected back into the discharge arc by mirror 35, mirror 45, or both.

Herein, the term mirror may also comprise a plurality of mirrors. The mirrors may be placed anywhere in the lamp 10, or in principle also outside lamp 10, but somewhere within reflector 130, assuming a headlamp 110 (see also below). Preferably, however, the mirror or mirrors is or are arranged on the outer envelope 210 or even more preferably on the wall 11 of the discharge vessel 1. The mirrors may be of reflective material known in the art, such as multilayer mirrors or aluminum-based mirrors. As was described above, the mirrors are arranged to reflect at least part of the light back into the arc. This implies that the mirrors are arranged to reflect light of the arc not back to the longitudinal axis 100, but part of the (visible) light is to be reflected to areas substantially offset from the longitudinal axis, since the arc is also offset therefrom. State of the art reflectors, such as the reflector 130, do not substantially reflect the light of the lamp 10 back into the arc. As known in the art, and as also shown in Regulation 99, the arc is substantially offset from the longitudinal axis 100.

To achieve the above, the mirrors 35, 45 preferably have a curved shape and have radii that are offset from the longitudinal. Assuming a lamp discharge vessel 1 arranged in a system of coordinates, wherein the longitudinal 100 is along the y-axis, a first perpendicular 101 is along the x-axis, and a second perpendicular is along the z-axis (see also the figures on pages 4- 10 of Rev. I/Amend.1 of Regulation No. 99), the radii from the mirrors will intersect the second perpendicular (z-axis) above the longitudinal axis 100, i.e. offset from the vertex of the axes x, y, z.

Preferably, the first mirror 35 is located between angles γ2 and γ3 to the perpendicular 101 to the longitudinal axis 100, and the second mirror 45 is located between angles 52 and 53 relative to this perpendicular 101, with γ3>γ2, γ2>25°, γ3<65°, 53>52, 52>125°, and 53<165°. If the mirrors 35,45 are arranged within these angles, light can be efficiently used for increasing the luminance directed to the desired area.

The phrases "wherein mirror 35/45 is located between angles γ2/52 and γ3/53" do not imply that the mirror(s) have to extend from the smallest angle to the largest angle as depicted herein; the mirror(s) may also be found within the range defined by γ2>25° and γ3<65° and δ2>125° and δ3<165°. Especially good results are obtained in a discharge lamp 10 in which γ2>30°, γ3<60° and in which δ2>130° and δ3<160°.

Figures 2a-2c schematically depict specific embodiments of the gas discharge vessel 1 in more detail, in rear elevation (2a), in plan view (2b), and in a perspective front view (2c), wherein the mirror(s) 35, 45 according to the invention are attached to protrusions on the outer surface 13 of the discharge vessel 1.

Such mirrors may be obtained by attaching the protrusions 30 and 40 to the discharge vessel's outer surface 13 and providing the mirrors 35 and 45, to the respective protrusions 30 and 40 before or after attaching the protrusions 30 and 40 to the outer surface 13 of the discharge vessel 1. Preferably, however, the protrusions 30 and 40 are created during the production of the discharge vessel 1, by molding the hot discharge vessel into the desired shape, i.e. the protrusions are quartz protrusions. Then the mirrors 35, 45 may be attached to or coated on at least part of the respective protrusions 30, 40, for example in a coating process.

Figures 2a-2c schematically depict preferred embodiments of the lamp 10 according to the invention, wherein the outer surface 13 of the discharge vessel wall 11 comprises at least one protrusion selected from the group consisting of the first protrusion 30 and the second protrusion 40, the inner surface 12 of the vessel wall 11 being located at a radius rl from the longitudinal axis 100 and the outer surface 13 of the vessel wall 11 being located at a radius r2 from the longitudinal axis 100, with r2>rl, wherein independently: a. the first mirror 35 has a mirror surface 33 which has a curvature with a radius r3, with preferably r3>r2, and wherein at γl, with γ2<γl<γ3, a tangent to the outer surface 13 of the wall 11 and a tangent to the mirror surface 33 of the first mirror 35 enclose an angle β3, with β3> 0°; and b. the second mirror 45 has a mirror surface 43 which has a curvature with a radius r4, with preferably r4>r2, and wherein at δl, with δ2<δl<δ3, a tangent to the outer surface 13 of the wall 11 and a tangent to the mirror surface 43 of the second mirror 45 enclose an angle β4, with β4> 0°. The mirror surfaces 33 and 43 are arranged to reflect at least part of the light generated by the lamp 10 back into at least part of the discharge arc. The specific position and curvature of the mirrors 35 and 45 (or mirror surfaces 33, 43), respectively, lead to the reflection of at least part of the light back into the arc, offset from the longitudinal axis 100. These mirrors 35, 45 (or in fact their respective mirror surfaces 33, 43) have a radius that is greater than the radius r2. The mirror surfaces 33 and 43 have an onset, relative to the outer surface 13 at at least γ2 and 52, respectively, and then curve away from the outer surface 13 to γ3 and 53, respectively, with γ3>γ2, γ2>25°, γ3<65°, 53>52, 52>125°, and 53<165°. At γ3 and 53, respective edges of the mirrors 35, 45 are reached, and the protrusions 30 and 40, have respective edges 34 and 44 which are preferably substantially at right angles to the outer surface 13. The edges 34 and 44 are preferably arranged to have a maximum slope relative to the outer surface 13, thereby minimizing any undesired optical effects or undesired losses or reflections of light (beyond γ3 and 53).

The angles β3 and β4 are the angles between the tangents at γl and 51, respectively, between the respective tangents at surface 13 (at γl and 51, respectively) and the respective tangents at mirror surfaces 33 and 43 (at γl and 51, respectively). Thus, for any γl between γ 2 and γ 3 as defined above and for any 51 between 52 and 53 as defined above, the angles β3 and β4 between the respective tangents to the surface 13 and the respective tangents to the mirror surfaces 33 and 43 are preferably greater than zero. Preferably, β3 and β4 are selected so as to have a maximum reflectance of the light of the lamp 10 back into the arc. For this reason, β3 and β4 are preferably in the range of 3-12° mutually independently, more preferably in the range of 6-9°. Note that the lamp 10 of the present invention may have one single mirror, either first mirror 35 or second mirror 45, or may have both mirrors 35 and 45. Likewise, the curvatures of the mirror surfaces 33 and 43, may be selected independently. Preferably, γ2>30°, γ3<60°, 52>130°, 53<160°, while β3 and β4 are independently chosen in the range of 6-9°. Preferably, the lamp 10 according to the invention comprises both the first and the second mirror 35, 45.

Figure 2b is a schematic plan view of an embodiment of the discharge vessel with mirror surfaces 33 and 43. Note that the mirror surfaces 33, 43 are directed to the arc; only the top of mirrors 35 and 45 (i.e. the back of mirror surfaces 33 and 43) is shown here. These mirrors 35, 45, i.e. mirror surfaces 33 and 43, and thus also the protrusions 30 and 40 in this embodiment, may extend over a certain length 1 of the total length L of the discharge space enclosed by discharge vessel 1. Preferably, the length over which the mirrors 35, 45, i.e. the mirror surfaces 33, 43, extend over the external surface 13 of the discharge vessel is independently chosen in the range of 50-95% of length L. As will be clear to those skilled in the art, the mirrors 35, 45 are preferably arranged symmetrically relative to the xz-plane. As mentioned above, the discharge vessel 1 may also have a spherical or spheroidal shape. Figure 2c is a schematic perspective front view of an embodiment of the discharge vessel 1 of the invention. Here, the mirrors 35, 45 extend over part of the external surface 13 of the discharge vessel, and are found between γ2 and γ3 and 52 and 53, respectively.

Instead of the preferred embodiments described above, in which the mirrors 35, 45 are located on respective protrusions 30, 40 on the outer surface 13 of the discharge vessel, these mirrors may alternatively be located on respective protrusions 30, 40 on the outer surface 213 of the outer envelope 210. Figure 3 schematically depicts another embodiment of the invention of the discharge vessel 1 and outer envelope 210 in rear elevation in more detail, wherein the mirror or mirrors 35, 45 according to the invention is or are attached to respective protrusions 30, 40 on the outer surface 213 of the outer envelope 210.

Hence, the invention also provides a lamp 10 in which the outer surface 213 of the outer envelope 210 comprises at least one protrusion selected from the group consisting of the first protrusion 30 and the second protrusion 40, the inner surface 212 of the outer envelope 210 being located at a radius r5 from the longitudinal axis 100 and the outer surface 213 of the outer envelope 210 being located at a radius r6 from the longitudinal axis 100, with r6>r5, and wherein independently: a. the first mirror 35 has a mirror surface 33 having a curvature with radius r8, with preferably r8>r6, wherein at γl, with γ2<γl<γ3, a tangent to the outer surface 213 of the outer envelope 210 and a tangent to the mirror surface 33 of the first mirror 35 enclose an angle β3, with β3> 0°; and b. the second mirror 45 has a mirror surface 43 having a curvature with a radius r9, with preferably r9>r6, wherein at 51, with 52<δl<53, a tangent to the outer surface 213 of the outer envelope 210 and a tangent to the mirror surface 43 of the second mirror 45 enclose an angle β4, with β4> 0°. Again, the mirror surfaces 33 and 43 are arranged to reflect at least part of the light generated by the lamp 10 back into at least part of the discharge arc. The specific position and curvature of the mirrors 35 and 45 (or mirror surfaces 33, 43, respectively) lead to the reflection of at least part of the light back into the arc, offset from the longitudinal axis 100. These mirrors 35, 45 (or in fact their respective mirror surfaces 33, 43) have a radius greater than the radius r6. The mirror surfaces 33 and 43 have an onset, relative to the outer surface 213 at at least γ2 and 52, respectively, and then curve away from the outer surface 213 up to γ3 and 53, respectively, with γ3>γ2, γ2>25°, γ3<65°, 53>52, 52>125°, and 53<165°. At γ3 and 53, respective edges of the mirrors 35, 45 are reached, and the protrusions 30 and 40 have edges 34 and 44, respectively, which are preferably substantially at right angles to the outer surface 213. The edges 34 and 44 are preferably arranged to have a maximum slope relative to the outer surface 213, thereby minimizing any undesired optical effects or undesired losses or reflections of light (beyond γ3 and 53).

The angles β3 and β4 are the angles between the tangents at γl and δl, respectively, between the tangents to surface 213 (at γl and δl, respectively) and the tangents to mirror surfaces 33 and 43 (at γl and δl, respectively). Thus, for any γl between γ 2 and γ3 as defined above and for any δl between δ2 and δ3 as defined above, the angles β3 and β4 between the respective tangents to surface 213 at γl and δl and the respective tangents to mirror surfaces 33 and 43 are preferably greater than zero. The same conditions as described above apply here. Hence, β3 and β4 are selected to have a maximum reflectance of the light of the lamp 10 back into the arc. For this reason, β3 and β4, are preferably independently chosen in the range of 3-12°, more preferably in the range of 6-9°. Note that the lamp 10 of the present invention may have one single mirror, either first mirror 35 or second mirror 45, or may have both mirrors 35 and 45. Likewise, the curvatures of the mirror surfaces 33 and 43, may be selected independently. Preferably, γ2>30°, γ3<60°, δ2>130°, δ3<160°, and β3 and β4 are independently chosen in the range of 6-9°. Preferably, the lamp 10 according to the invention comprises both the first and the second mirror 35, 45.

Likewise, these mirrors 35, 45, i.e. mirror surfaces 33 and 43, and thus also the respective protrusions 35 and 45 in this embodiment, may extend over a certain length of the total length of the outer envelope 210 that encloses the discharge vessel 1. Preferably, the length over which the mirrors 35, 45, i.e. the mirror surfaces 33, 43, extend over the external surface 213 of the outer envelope 210 is independently chosen in the range of 50-95% of the length. As will be clear to those skilled in the art, the mirrors 35, 45 are preferably arranged symmetrically relative to the xz-plane. As was mentioned above, the lamp 10 of the invention may preferably have one or two of the mirrors 35, 45 arranged to the outer surface 213 of the outer envelope 210 or may have one or two of the mirrors 35, 45 arranged to the outer surface 13 of the discharge vessel 1, or may alternatively have one of the mirrors 35, 45 arranged to the outer surface 13 of the discharge vessel 1 and the other one of the mirrors 35, 45 arranged to the outer surface 213 of the outer envelope 210. Preferably however, the lamp 10 has both mirrors 35, 45, and more preferably, these mirrors 35, 45 are attached (for example coated) to respective protrusions 30, 40 located on the outer surface 13 of the discharge vessel 1 (as schematically depicted in figures 2a-2c). Preferably, r3/r2, r4/r2, r8/r6 and r9/r6, are all mutually independently greater than 1.0, more preferably, r3/r2, r4/r2, r8/r6 and r9/r6, are all mutually independently in the range of 1.02-1.1.

In a further embodiment, the invention provides a head lamp 110 for a wheeled vehicle, wherein the head lamp 110 comprises the lamp 10 of the invention and a reflector 130 as herein described. The reflector has a reflector or mirror surface 131 directed towards the lamp 10. The reflector 130 circumferentially surrounds the lamp and is arranged to project the light of the lamp 10 onto the road. Preferably, the lamp 110 has an improved luminance especially in the direction in which the light from the lamp 10 is thrown by the reflector 130 so as to illuminate the spot area. Such a head lamp 110 may be arranged to direct more than about 20 % of the total luminous flux of the lamp in the area defined by 50V, 75R and 5OR of. Prior art lamps may have a luminous flux in this area of up to about 20%, but the luminous flux can be increased to above about 25 % of the total flux with the mirrors 35, 45 according to the invention. An increase in the area defined by 50V, 75R and 5OR to at least 30 % of the total luminous flux is possible. Preferably, the total luminous flux in this area is about 25-35 % of the total luminous flux, more especially in the range of about 30-35 %.

It should be noted that the above embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The use of the verb "to comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The invention may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In the device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

CLAIMS:

1. A high-pressure discharge lamp (10) arranged to generate light, the lamp (10) comprising: a. an outer envelope (210) having an inner surface (212) and an outer surface

(213); b. a discharge vessel (1) enclosed by the outer envelope (210), the discharge vessel (1) having a vessel wall (11) enclosing a discharge space (2) containing an ionizable filling, which discharge space (2) further encloses electrodes (3, 4) arranged opposite each other and arranged to define a discharge arc between the electrodes (3, 4) during operation of the lamp (10), wherein the vessel (1) has a longitudinal axis (100) and the wall (11) has an inner surface (12) and an outer surface (13); and c. at least one mirror selected from the group consisting of a first mirror (35) and a second mirror (45) such that, relative to a perpendicular (101) to the longitudinal axis (100), the first mirror (35) is located between angles γ2 and γ3 to this perpendicular (101) and wherein, relative to the perpendicular (101) to the longitudinal axis (100), the second mirror (45) is located between angles 52 and 53 to this perpendicular (101), with γ3>γ2, γ2>25°, γ3<65°, 53>52, 52>125°, and 53<165°, and wherein the mirrors (35, 43) are arranged to reflect at least part of the light generated by the lamp (10) back into at least part of the discharge arc.

2. The lamp (10) according to claim 1, wherein γ2>30° and γ3<60°, and wherein

52>130° and 53<160°.

3. The lamp (10) according to any one of the preceding claims, wherein the outer surface (13) of the discharge vessel wall (11) or the outer surface (213) of the outer envelope (210) or both the outer surface (13) of the discharge wall (11) and the outer surface (213) of the outer envelope (210) comprise at least one protrusion selected from the group consisting of a first protrusion (30) and a second protrusion (40), and wherein the first mirror (35) is attached to the first protrusion (30) and the second mirror (45) is attached to the second protrusion (40).

4. The lamp (10) according to claim 3, wherein the outer surface (13) of the discharge vessel wall (11) comprises at least one protrusion selected from the group consisting of the first protrusion (30) and the second protrusion (40), wherein the inner surface (12) of the vessel wall (11) is located at a radius rl from the longitudinal axis (100) and the outer surface (13) of the vessel wall (11) is located at a radius r2 from the longitudinal axis (100), with r2>rl, and wherein independently: a. the first mirror (35), having a mirror surface (33), has a curvature with a radius r3, with preferably r3>r2, and wherein at γl, with γ2<γl<γ3, a tangent to the outer surface (13) of the wall (11) and a tangent to the mirror surface (33) of the first mirror (35) enclose an angle β3, with β3> 0°; and b. the second mirror (45), having a mirror surface (43), has a curvature with a radius r4, with preferably r4>r2, and wherein at δl, with 52<δl<δ3, a tangent to the outer surface (13) of the wall (11) and a tangent to the mirror surface (43) of the second mirror (45) enclose an angle β4, with β4> 0°.

5. The lamp (10) according to claim 4, comprising both the first and the second mirror (35, 45).

6. The lamp (10) according to claims 4 or 5, wherein r3/r2 and r4/r2 are mutually independently in the range of 0.9-1.2.

7. The lamp (10) according to claim 3, wherein the outer surface (213) of the outer envelope (210) comprises at least one protrusion selected from the group consisting of the first protrusion (30) and the second protrusion (40), wherein the inner surface (212) of the outer envelope (210) is located at a radius r5 from the longitudinal axis (100) and the outer surface (213) of the outer envelope (210) is located at a radius r6 from the longitudinal axis (100), with r6>r5, and wherein independently: a. the first mirror (35), having a mirror surface (33), has a curvature with radius r8, with preferably r8>r6, and wherein at γl, with γ2<γl<γ3, a tangent to the outer surface

(213) of the outer envelope (210) and a tangent to the mirror surface (33) of the first mirror (35) enclose an angle β3, with β3> 0°, and b. the second mirror (45), having a mirror surface (43), has a curvature with a radius r9, with preferably r9>r6, and wherein at δl, with δ2<δl<δ3, a tangent to the outer surface (213) of the outer envelope (210) and a tangent to the mirror surface (43) of the second mirror (45) enclose an angle β4, with β4> 0°.

8. The lamp (10) according to claim 7, comprising both the first and the second mirror (35, 45).

9. The lamp (10) according to claims 6 or 7, wherein r8/r6 and r9/r6 are mutually independently in the range of 0.9-1.2.

10. The lamp (10) according to any one of claims 4-9, wherein β3 and β4, are mutually independently in the range of 3-12°, preferably in the range of 6-9°.

11. A headlamp (110) for a wheeled vehicle, comprising the lamp (10) according to any of the preceding claims and a reflector (130).

12. The head lamp (110) according to claim 11, arranged to have a luminous flux in the area defined by 50V, 75R and 5OR of at least 30 % of the total luminous flux.