Gas-discharge lamp

Abstract

The invention describes a gas-discharge lamp (1) comprising a vessel (5), which vessel (5) is partially coated with at least one longitudinal stripe (S.sub.H, S.sub.H) arranged on the surface of the vessel (5) below a horizontal plane (P) through a longitudinal axis (X) through the centre of the lamp (1) such that, on each side of the lamp, an angle (.sub.H1, .sub.H2) subtended at the lamp centre by the horizontal plane (P) and an upper edge (16, 17) of the longitudinal stripe (S.sub.H, S.sub.H) on that side of the lamp comprises at least 10, more preferably at least 13, most preferably at least 15. The invention also describes a reflector (8) for a lamp (1), comprising a reflective interior surface realized to deflect light (L.sub.20A, L.sub.20B, L.sub.21A, L.sub.21B) originating from the lamp (1) outward to give a specific beam profile (3) with a bright/dark cut-off line (31) and a shoulder (32), and wherein the lamp (1), in particular a lamp (1) according to any of claims 1 to 12, is positioned horizontally in the reflector (8), and wherein the reflective interior surface comprises at least one beam-shaping region (81 A, 81B) realised to deflect a portion (L.sub.21A, L.sub.21B) of the light (L.sub.20A, L.sub.20B, L.sub.21A, L.sub.21B), emitted from the lamp (1) between 7.5 and 15 below a horizontal plane (P), at a specific region (21A, 21B) within the beam profile (3). The invention further describes a lighting assembly (9) comprising such a reflector (8) and a lamp (1), in particular a lamp (1) according to the invention.

Claims

1. A lighting assembly for a reflection-type automotive headlamp, comprising: a reflector, and a gas-discharge lamp mounted horizontally in the reflector such that a longitudinal axis (X) through a lamp center is horizontal, the lamp comprising: a vessel will a partial coaling comprising first and second longitudinal opaque stripes (S.sub.H) arranged on a surface of the vessel, wherein, as seen in the lamp's horizontal mounting position: the first longitudinal opaque stripe is located on a first side of the lamp below a horizontal plane (P) through the longitudinal axis (X); the second longitudinal opaque stripe is located on a second side of the lamp below the horizontal plane (P); a first angle (.sub.H1) subtended at the lamp center by the horizontal plane (P) and a first upper edge of the first longitudinal opaque stripe (S.sub.H) is essentially the same as a second angle (.sub.H2) subtended at the lamp center by the horizontal plane (P) and a second upper edge of the second longitudinal opaque stripe (S.sub.H); and the first and the second angles comprise 10 to 15; and the reflector comprising a reflective interior surface with beam shaping regions to deflect light originating from the lamp outward to give a beam profile with a bright/dark cut-off line and a shoulder, wherein the reflection interior surface comprises at least one beam-shaping region realized to deflect a portion (L.sub.21A, L.sub.21B) of the light, emitted from the lamp in an angular range between 7.5 and 15 below the horizontal plane (P), to form an image within the beam profile having a greater tilt than another image formed by another beam-shaping region that deflects another portion of the light, emitted from the lamp in another angular range above the angular range between 7.5 and 15 below the horizontal plane.

2. The lighting assembly according to claim 1, wherein the partial coating further comprises a circumferential opaque stripe (S.sub.V) arranged circumferentially on the surface of the vessel.

3. The lamp lighting assembly according to claim 2, wherein the length of the circumferential stripe (S.sub.V) is shorter than the circumference of the vessel.

4. The lighting assembly according to claim 2, wherein a width (w.sub.V) of the circumferential stripe (S.sub.V) comprises 3.5 to 4.5 mm.

5. The lighting assembly according to claim 1, wherein the reflector comprises at least one first beam-shaping region on one side of the lamp for deflecting a light portion (L.sub.21A) into a region close to a cut-off boundary of the beam profile, and at least one second beam-shaping region on the other side of the lamp for deflecting a light portion (L.sub.21B) close to a cut-off boundary of a shoulder region of the beam profile.

6. The lighting assembly according to claim 1 with the lamp with a nominal power of 25 W, which lamp comprises an inner discharge vessel enclosed in an outer vessel, and for which lamp the capacity of the inner discharge vessel is greater than or equal to 15 l and less than or equal to 23 l ; the inner diameter of the inner discharge vessel comprises at least 2.0 mm and at most 2.4 mm; and the outer diameter of the inner discharge vessel comprises at least 5.2 mm and at most 5.8 mm.

7. The lighting assembly according to claim 1, wherein the first and the second longitudinal opaque stripes (S.sub.H) are arranged on an outer surface of an outer vessel of the lamp.

8. The lighting assembly according to claim 1, wherein the first and the second longitudinal opaque stripes (S.sub.H) are essentially rectangular and each having a width (w.sub.H) comprising 1.5 to 1.9 mm.

9. A lighting assembly for a reflector-type automotive headlight, comprising: a reflector; and a gas-discharge lamp mounted horizontally in the reflector such that a longitudinal axis (X) through a lamp center is horizontal, the lamp comprising: a vessel with a partial coating comprising a single longitudinal opaque stripe (S.sub.H) arranged on a surface of the vessel, wherein, as seen in the lamp's horizontal mounting position: the longitudinal opaque stripe is located below a horizontal plane (P) through the longitudinal axis (X); a first angle (.sub.H1) subtended at the lamp center by the horizontal plane (P) and a first upper edge of the longitudinal opaque stripe (S.sub.H) on a first side of the lamp is essentially the same as a second angle (.sub.H2) subtended at the lamp center by the horizontal plane (P) and a second upper edge of the longitudinal opaque stripe (S.sub.H) on a second side of the lamp; and the first and the second angles comprise 10 to 15 ; and the reflector comprising a reflective interior surface with beam-shaping regions to deflect light originating from the lamp outward to give a beam profile with a bright/dark cut-off line and a shoulder, wherein the reflective interior surface comprises at least one beam-shaping region that deflects a portion of the light, emitted from the lamp in an angular range between 7.5 and 15 below the horizontal plane, to form an image within the beam profile having a greater tilt than another image formed by another beam-shaping region that deflects another portion of the light, emitted from the lamp in another angular range above the angular range between 7.5 and 15 below the horizontal plane.

10. The lighting assembly according to claim 9, wherein the partial coating further comprises a circumferential opaque stripe (S.sub.V) arranged circumferentially on the surface of the vessel.

11. The lighting assembly according to claim 10, wherein the circumferential stripe (S.sub.V) entirely surrounds the vessel.

12. The lighting assembly according to claim 10, wherein a width (w.sub.V) of the circumferential stripe (S.sub.V) comprises 3.5 to 4.5 mm.

13. The lighting assembly according to claim 9 with the lamp with a nominal power of 25 W, which lamp comprises an inner discharge vessel enclosed in an outer vessel, and for which lamp the capacity of the inner discharge vessel is greater than or equal to 15 l and less than or equal to 23 l; the inner diameter of the inner discharge vessel comprises at least 2.0 mm and at most 2.4 mm; and the outer diameter of the inner discharge vessel comprises at least 5.2 mm and at most 5.8 mm.

14. The lighting assembly according to claim 9, wherein the longitudinal opaque stripe (S.sub.H) is arranged on an outer surface of an outer vessel of the lamp.

15. The lighting assembly according to claim 9, wherein the reflector comprises at least one first beam-shaping region on one side of the lamp for deflecting a light portion (L.sub.21A) into a region close to a cut-off boundary of the beam profile, and at least one second beam-shaping region on the other side of the lamp for deflecting a light portion (L.sub.21s) close to a cut-off boundary of a shoulder region of the beam profile.

16. A gas-discharge lamp comprising a vessel with a partial coating comprising at least one longitudinal opaque stripe (S.sub.H, S.sub.H) arranged on a surface of the vessel below a horizontal plane (P) through a longitudinal axis (X) through the center of the lamp such that, on each side of the lamp, an angle (.sub.H1, .sub.H2) subtended at the lamp center by the horizontal plane (P) and an upper edge of the longitudinal opaque stripe (.sub.H, S.sub.H) on that side of the lamp comprises 10 to 15, wherein: the partial coating further comprises a circumferential opaque stripe (S.sub.V, S.sub.V) arranged circumferentially on the surface of the vessel; and the circumferential stripe (S.sub.V, S.sub.V) is arranged such that a first long side of the circumferential stripe (S.sub.V, S.sub.V) is situated close to a base (6) of the lamp, and the width of the circumferential stripe (S.sub.V, S.sub.V) is such that a first angle (v.sub.1) subtended at the lamp center between a radius (r) and a point on the first long side of the circumferential stripe (S.sub.V, S.sub.V) comprises at most 55, and a second angle (v.sub.2) subtended at the lamp center between another radius (r) and a point on a second long side of the circumferential stripe (S.sub.V, S.sub.V) comprises approximately 50.

17. The lamp according to claim 16, wherein the circumferential stripe (S.sub.V) entirely surrounds the vessel or the length of the circumferential stripe (S.sub.V) is shorter than the circumference of the vessel.

18. The lamp assembly according to claim 17, wherein a width (w.sub.V) of the circumferential stripe comprises 3.5 to 4.5 mm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a schematic representation of a prior art gas-discharge lamp;

(2) FIG. 2 shows a schematic representation of a gas-discharge lamp according to a first embodiment of the invention;

(3) FIG. 3 shows a schematic representation of a gas-discharge lamp according to a second embodiment of the invention;

(4) FIG. 4 shows a lighting assembly according to an embodiment of the invention;

(5) FIG. 5 shows a cross section through a lighting assembly according to the invention and a corresponding beam profile;

(6) FIG. 6 shows a schematic representation of a reflector according to the invention;

(7) FIG. 7 shows a bar chart of initial lumen output;

(8) FIG. 8 shows graphs of lumen maintenance;

(9) FIG. 9 shows graphs of lamp voltage.

(10) In the drawings, like numbers refer to like objects throughout. Objects in the diagrams are not necessarily drawn to scale.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(11) FIG. 1 shows a cross section of a prior art gas-discharge lamp 10, with a partial coating 11, 12 comprising a circumferentially arranged stripe 11 and a pair of longitudinally arranged stripes 12, 13. The lamp 10 shown corresponds to a D4R lamp, with a ballast 6 or base 6, for use in an automotive headlight assembly. The width of the circumferential stripe 11 is defined in the appropriate regulation, in this case ECE R99, by the angles .sub.1, .sub.2 subtended at the lamp centre between a radius r and points on the outer edges of the circumferential stripe 11. The regulation ECE R99 requires that the smaller angle .sub.1 be 455, and that the larger angle .sub.2 be at least 70. On a D4R lamp, such a circumferential stripe 11 can therefore have a width of about 8.3 mm, and usually covers a substantial part of the underlying pinch region. A pair of longitudinal stripes 12, 13 is arranged one of each side of the lamp 10. This is illustrated in the cross-section A-A shown on the left of the diagram. According to the regulation ECE R99, these longitudinal stripes 12, 13 are arranged asymmetrically on the lamp outer vessel 5 such that one stripe 13 is lower than the other stripe 12. The higher stripe 12 is positioned to lie just below the horizontal plane P, while the upper edge of the lower stripe 13 is positioned at most 15 below the horizontal plane P. The reason for this arrangement is the older reflector designs, which required an asymmetric light source in order to produce the required asymmetric front beam. However, this known prior art arrangement of stripes 11, 12, 13 leads to the problems mentioned above, namely a shorter lamp lifespan (owing to the excessive heat that develops in the pinch region under the circumferential stripe 11), an uneven light intensity distribution in the beam profile (owing to the pronounced temperature gradient between the upper and lower regions of the lamp 1), and a lower light output (owing to the light lost in the areas blocked by the longitudinal stripes 12, 13).

(12) FIG. 2 shows a gas-discharge lamp 1 according to a first embodiment of the invention. The construction of the lamp 1 is essentially the same as in the above FIG. 1, in order to comply with regulations regarding lamp size, ballast, etc. The relative sizes of the inner and outer vessels 4, 5 will depend on whether the lamp is realised as a 25 W lamp or a 35 W lamp. In this embodiment, two horizontal stripes S.sub.H are arranged symmetrically on the outer vessel 5. In contrast to the horizontal stripes 12, 13 of FIG. 1, the horizontal stripes S.sub.H are arranged symmetrically on either side of the lamp 1, are positioned lower down, and are narrower than the prior art stripes 12, 13. This is illustrated in the cross-section A-A shown on the left of the diagram. In this embodiment, the longitudinal stripes S.sub.H are arranged symmetrically on the lamp outer vessel 5 such that an angle .sub.H1, .sub.H2 subtended at the lamp centre between the horizontal plane P and a point on an upper edge 16, 17 of a longitudinal stripe S.sub.H comprises 15. The angular region .sub.H between the upper edges 16, 17 of the horizontal stripes S.sub.H and below the horizontal plane P comprises only 150. As a result, the light output of the lamp 1 is increased, since less light is blocked by the lower and narrower longitudinal stripes S.sub.H, and more useful arc images can be collected by a surrounding reflector and used to form a brighter front beam, as will be shown below.

(13) The diagram also shows a rectangular vertical stripe S.sub.V arranged about the circumference of the outer vessel 5 of the lamp 1, such that the short ends of the vertical stripe S.sub.V do not meet on the underside of the lamp 1. The width w.sub.V of the vertical stripe S.sub.V is defined by the angles .sub.V1, .sub.V2 subtended between a radius r through the lamp centre and points on the outer edges 14, 15 of the circumferential stripe S.sub.V. In this embodiment of the invention, the smaller angle .sub.V1 to the inner edge 15 closer to the burner 4 is about 50, and the larger angle .sub.V2 to the outer edge 14 closer to the base 6 is only about 55. Therefore, the vertical stripe S.sub.V has a width w.sub.V of about 3.5 mm, so that it only covers a small section of the underlying pinch region. During operation of the lamp, then, superfluous light L.sub.S (light that would not be used in any case to contribute to the front beam) can leave the lamp 1 without being absorbed or reflected back into the lamp 1, and therefore the temperature in the lamp is not unnecessarily increased.

(14) FIG. 3 shows a further embodiment of a lamp 1 according to the invention. Here, a vertical stripe S.sub.V and a horizontal stripe S.sub.H are arranged as shown on the outer surface of the outer vessel 5. In this realisation, the vertical stripe S.sub.V extends all the way around the outer vessel 5, and the horizontal stripe S.sub.H comprises a single stripe S.sub.H. The position and width of the vertical stripe S.sub.V can be the same as in FIG. 2 above. In this embodiment, the defining angle .sub.H1, .sub.H2 of the horizontal stripe S.sub.H can be smaller, for example 10, as shown in the cross-section A-A on the left of the diagram. In this case, the angular region .sub.H between the upper edges 16, 17 of the horizontal stripes S.sub.H comprises 160.

(15) In prior art lamps, the stripes were required to provide an asymmetric light source, and the prior art reflectors were largely symmetrical. The lamp 1 according to the invention makes use of the fact that the reflectors available at present can be favourably designed to form lighteven light originating from a symmetrical light sourceinto an asymmetric front beam. Since the reflector can achieve the required asymmetry largely on its own, the width and placement of the stripes can be favourably adjusted as described above to optimise the light output and to prolong the lamp lifetime.

(16) FIG. 4 shows a lighting assembly 9 with a lamp 1 according to the invention and a reflector 8. As can be seen clearly in the diagram, the circumferential stripe S.sub.V is narrow, so that light L.sub.S, which is in any case superfluous, can pass through the outer vessel 5 into the base region of the lamp 1. This light can, for example, be absorbed in the rear of the reflector 8 or can pass through an opening 83 in the rear of the reflector 8. Wasting the superfluous light L.sub.S in this way does not detract from the beam quality. Instead, the lamp 1 is protected from overheating by the narrow width of the vertical stripe S.sub.V.

(17) FIG. 5 illustrates the beneficial effect of the inventive arrangement of horizontal stripes S.sub.H on a lamp 1 in a reflector 8 for an automotive headlamp arrangement. On the right-hand side of the diagram, a cross-section through the lamp 1 and reflector 8 is shown, and regions 80A, 80B, 81A, 81B are indicated on the inside surface of the reflector 8. Images 20A, 20B, 21A, 21B of the discharge arc 2 originating from light L.sub.20A, L.sub.20B, L.sub.21A, L.sub.21B collected at these regions 80A, 80B, 81A, 81B, are projected onto the beam profile 3 according to the relevant regulation, for example R98, as shown in the left-hand side of the diagram. Images 20A, 20B (dotted lines) show the region close to the cut-off 31 and in the shoulder 32 that can be illuminated with a prior art lamp having higher horizontal stripes. Because these arc images 20A, 20B are collected relatively high up in the reflector 8, near to or above the horizontal plane P, they are not tilted to any significant extent, and lie more or less along the cut-off line of the beam profile 3. The additional images 21A, 21B (solid lines) that are projected into the beam profile 3 ensure a better illumination by the front beam owing to the greater light flux and the longer reach of the front beam. These additional images 21A, 21B are collected on account of the inventive lower arrangement of longitudinal stripes S.sub.H on the outer vessel 5. Because these images 21A, 21B are collected lower down in the reflector 8, they are tilted noticeably compared to the other arc images 20A, 20B, and make a favourable contribution to the overall brightness of the beam profile.

(18) FIG. 6 shows a view of a reflector 8 according to the invention. Here, a lamp 1 with a stripe arrangement S.sub.V, S.sub.V, S.sub.H, S.sub.H according to the invention is mounted horizontally in the reflector. Images of the discharge arc 2, collected in the interior of the reflector 8, are deflected outward to give a beam profile 3 with a desired cut-off line 31 and a shoulder 32 relative to axes H, V. The diagram shows the regions 81A, 81B for collecting additional light L.sub.21A, L.sub.21B allowed by the lower placement of horizontal stripes S.sub.H, S.sub.H . This additional light is deflected onto the beam profile as the arc images 21A, 21B. The positions and orientations of these additional arc images 21A, 21B in the diagram is exemplary. The position of the horizontal stripe(s) S.sub.H, S.sub.H and the actual realisation of the reflector regions 81A, 81B will influence the orientation and positioning of the arc images 21A, 21B. For example, a lower placement of the horizontal stripe(s) S.sub.H, S.sub.H will result in a more tilted arc image 21A, 21B. Using this reflector 8 with the inventive lamp 1 allows a better illumination of the region in front of the vehicle between 25 m and 60 m owing to the improved reach of the beam and to the better illumination in the cut-off 31 and shoulder 32 regions of the beam profile 3.

(19) FIGS. 7-9 show experimental results obtained for 35 W and 25 W D4R lamp batches A35, A25 according to the invention, for D4R 35 W and 25 W lamp batches B35, B25 with a prior art pinstripe arrangements, and for D4R 35 W and 25 W lamp batches C35, C25 with no pinstripes.

(20) FIG. 7 shows a bar chart of initial lumen output in percent (%) for different batches of automotive gas-discharge lamps measured 15 hours after burning in. Batch B35 comprised prior art 35 W lamps with pinstripes arranged according to the R99 regulation, while batch B25 comprised prior art 25 W lamps with such pinstripes.

(21) Batches C35, C25 comprised 35 W and 25 W D4R lamps respectively, without any stripes. To satisfy the regulation, an automotive lamp 25 W or 35 W lamp must deliver 3200450 lumens at 15 hours after burning in. The light output that can be achieved initially is given as 100%. Batch A35 comprised 35 W lamps and batch A25 comprised 25 W lamps, in each case with horizontal stripes arranged according to the invention, i.e. lower down and narrower, and a narrow vertical stripe. For these batches, improvements in light output of 5% and 3% respectively were obtained. Evidently, since the absence of any stripes means no light is blocked, the light output for batches C35, C25 are highest, and these are only given as a reference against which the favourable improvements of batches A35 and A25 can be compared. As the chart shows, the lamp according to the invention, while having stripes to assist in obtaining a desired beam shape, can still provide an initial lumen output favourably close to that of a lamp without any stripes.

(22) FIG. 8 shows graphs of lumen maintenance measured for the lamp type batches A25, B25, C25 of FIG. 1 after 1500 hours of burning. An initial value of 100% corresponds to the lumen output of each lamp batch type after burning in. Lamp type batch B25 showed relatively poor lumen maintenance, dropping to only about 89% of its initial value after 1500 hours. Batch A25 showed quite favourable lumen maintenance, dropping only to about 92%. The lamp batch C25, without any partial coating, dropped to about 95%, so that the lumen maintenance of lamp type batch A25 compares quite well to a lamp type without any stripes. In the 25 W lamp, the burner is small, but the outer vessel is of the same size as for a 35 W lamp. Therefore, the clearance between burner and outer vessel is greater, and the coefficient of thermal conductivity is lower. The burner is therefore to some extent thermally insulated from the outer vessel, so that heat generated because of the stripe regions does not affect the temperature in the burner to the same extent as in a prior art 35 W lamps. This explains the very favourable lumen maintenance of the 25 W lamps according to the invention. Measurements taken for the lamp batches A35, B35, C35 showed a drop in lumen maintenance to 82%, 72% and 87% respectively after 2000 hours of burning, so that the 35 W lamp A35 with the inventive pinstripe arrangement exhibited a favourable lumen maintenance compared to a prior art lamp B35 with pinstripes.

(23) FIG. 9 shows graphs of lamp voltage measured for batches A25, B25, C25 of FIG. 7 and FIG. 8 after 1500 hours of burning. An initial value of 100% corresponds to the lamp voltage of each lamp batch type after burning in. Lamp batch B25 showed a marked increase in lamp voltage after 1500 hours, rising to about 114%. The lamp voltage of lamp batch C25, without any stripes, increased to about 113%. Lamp batch A25 showed a very favourably low increase in lamp voltage, which rose to only about 109%. Positive effects of the low increase in lamp voltage are a reduced tendency to flicker and a prolonged lamp lifetime. Owing to the better thermal insulation of the inner vessel, the temperature in the 25 W lamp according to the invention can be maintained at a favourably low level, which explains the slower increase in lamp voltage even compared to a 35 W lamp with inventive stripe arrangement. Measurements taken for the lamp batches A35, B35, C35 showed an increase in lamp voltage of 127%, 131% and 135% respectively after 2000 hours of burning, so that the 35 W lamp with the inventive pinstripe arrangement exhibited the lowest percent increase in lamp voltage over lamp lifetime.

(24) Although the present invention has been disclosed in the form of preferred embodiments and variations thereon, it will be understood that numerous additional modifications and variations could be made thereto without departing from the scope of the invention. For the sake of clarity, it is also to be understood that the use of a or an throughout this application does not exclude a plurality, and comprising does not exclude other steps or elements.