WO2009130639A2

WO2009130639A2 - Electric lamp and wire for use in the electric lamp

Info

Publication number: WO2009130639A2
Application number: PCT/IB2009/051585
Authority: WO
Inventors: Marc L. Verwillegen
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2008-04-24
Filing date: 2009-04-16
Publication date: 2009-10-29
Also published as: WO2009130639A3

Abstract

The invention relates to an electric lamp (100), a wire (12), an image projection system (200) and a headlight (300). The wire (12) connects a first feedthrough (115) of a lamp at a far end of the lamp with respect to a lampholder (150). The wire is arranged between the lampholder and the feedthrough and is arranged along an outer wall of a vessel (105) of the lamp for electrically connecting the feedthrough to the lampholder. A first part (20) of the wire comprises a first conductive material which is connected to a second part (30) of the wire which comprises a second conductive material having a different heat tolerance compared to the first conductive material. The effect of the measures according to the invention is that by using different parts in the wire, the conductive material which can withstand high temperatures is applied only where needed. As a result, the efficiency of the lamps is improved.

Description

Electric lamp and wire for use in the electric lamp

FIELD OF THE INVENTION:

The invention relates to an electric lamp.

The invention also relates to a wire for use in the electric lamp, to an image projection system and to a headlight.

BACKGROUND OF THE INVENTION:

Electric lamps, such as high pressure discharge lamps, are known per se. They are used, inter alia, in image projection systems such as beamers and projection televisions and in headlight illumination systems, for example, for use in cars and motorcycles. High pressure discharge lamps typically comprise a lampholder for holding the lamp and positioning the lamp inside collimating optics. The lampholder generally comprises supply pins connected to a power supply for providing electrical power to the high pressure discharge lamp.

The known high pressure discharge lamps generally have a vessel, also known as burner, and generally comprise two feedthroughs being electrodes which each extend from the discharge vessel to the exterior. By applying a potential difference between the two electrodes, a discharge arc is produced. The discharge arc ionizes the gas mixture inside the discharge vessel which subsequently emits light. The color of the light emitted by the high pressure discharge lamp depends, amongst others, on the gas mixture in the discharge vessel and on the pressure inside the discharge vessel.

Alternatively, the lamp may be a halogen lamp in which the light emitting element is a filament which glows when current flows through the filament to produce light. The filament is arranged inside a vessel between the two feedthroughs protruding through the vessel. Generally, the vessel of the lamp comprises a center part, also known as discharge vessel in high pressure discharge lamps, in which the light is produced, either, for example, via a discharge arc or via a glowing filament. Typically, the vessel comprises two seal extensions via which the feedthroughs extend from inside the vessel to the exterior. The extensions, also known as the neck of the burner in a high pressure discharge lamp, are generally arranged on opposite sides of the vessel and comprise means for introducing the feedthroughs into the vessel, while preventing a gas filling of the vessel to leak out. The lamp is often fixed to the lampholder, using one of the extensions, which has the benefit that the collimating optics may be arranged substantially symmetrically around the center part of the vessel for providing a good light distribution. In such an embodiment, one of the two extensions is connected to the lampholder and the other extension is arranged at a far end of the vessel with respect to the lampholder. To be able to connect the feedthrough issuing from the vessel at the opposite side of the center part to one of the supply pins of the lampholder, a wire is present. The wire is guided along an outer wall of the vessel at a distance from the vessel. As the temperature, during operation, of the center part containing the light emitting element is relatively high, the known wire is typically manufactured of conductive material which has a relatively high resistance against high temperatures, or, in other words, has a relatively high heat tolerance.

A disadvantage of the use of the known wires is that the efficiency of the lamp is relatively low.

SUMMARY OF THE INVENTION:

It is an object of the invention to provide an electric lamp having an improved efficiency. According to a first aspect of the invention, the object is achieved with the electric lamp comprising:

- a vessel enclosing a space comprising a light emitting element,

- a first feedthrough and a second feedthrough protruding into the vessel on opposite sides of the vessel for providing, during operation, power to the light emitting element generating a temperature gradient along an outer wall of the vessel,

- a first supply pin and a second supply pin, both arranged at a same side of the vessel, and arranged for connecting the lamp to a power supply, and

- a wire running at least partially along the outer wall of the vessel for connecting the first feedthrough to the first supply pin, the wire comprising a first part comprising a first conductive material and a second part comprising a second conductive material having an increased heat tolerance compared to the first conductive material, the first part being arranged in an first area and the second part being arranged in a second area, the maximum temperature, in operation, in the second area being higher than in the first area. A material having a specific heat tolerance is a material which substantially maintains its shape and functionality for normal use while being exposed to high temperatures up to a specific value. In operation, the outer wall of the vessel of the lamp, such as a high pressure discharge lamp or a halogen lamp, may reach temperatures ranging from 800 degrees Celsius to 1500 degrees Celsius. Especially near the light emitting element, such as the discharge arc or the filament, the temperature ranges between 1000 degrees Celsius and 1500 degrees Celsius, which is defined in this document as high temperature range. Materials which have, for example, a heat tolerance up to 1000 degrees Celsius may still function normally and substantially maintain their shape when used in an environment in which the temperature does not exceed 1000 degrees Celsius. Materials having a lower heat tolerance may alter shape and may not function normally in the environment in which the temperature reaches 1000 degrees Celsius and thus should preferably be used below their heat tolerance level. The effect of the measures according to the invention is that due to the use of the wire comprising the first part and the second part, each comprising conductive materials having different heat tolerances, the efficiency of the lamp is improved. The known wires are constituted of known materials which have a heat tolerance sufficient to withstand the harsh environment near the discharge vessel. Such known materials which have a relatively high heat tolerance also have a relatively high electrical resistance. Such a high electrical resistance is very unfavorable, as it increases the losses in the wire and thus reduces the efficiency of the lamp. The second part of the wire according to the invention comprises the conductive material which has a higher heat tolerance compared to the first part of the wire, and thus the second part of the wire has a relatively high electrical resistance compared to the first part of the wire. The second conductive material is, for example, only used at a part of the wire where the temperature is relatively high, for example, near the discharge arc or near the filament. The remainder of the wire may be constituted of the first conductive material having a lower electrical resistance. Due to the use of the second conductive material only at a location where it is required, the overall electrical resistance of the wire is limited, thus improving the efficiency of the lamp, such as the high pressure discharge lamp or the halogen lamp. During operation, the temperature of the outer wall of the vessel varies from the first feedthrough to the second feedthrough and typically is highest near the light producing element, for example, the discharge arc or the filament. In the known lamps, the wire is fully constituted of a single material which thus must have a heat tolerance such that it is able to function normally in the vicinity of the discharge arc or filament. Such a known wire contributes considerably to the electrical resistive losses of the lamp, thus limiting the efficiency of the known lamps. By choosing, for example, the first conductive material such that this first conductive material has, for example, a relatively low heat tolerance and thus a lower electrical resistance value, the overall electrical resistance of the wire may be reduced by using this first conductive material where possible and only using the second conductive material where necessary, thereby reducing the electrical resistive losses of the lamp and improving the efficiency. This first conductive material may, for example, be used in an area along the vessel where the temperature of the vessel is relatively low, for example, along the extensions of the vessel.

In an embodiment of the lamp, the lamp is a high pressure discharge lamp, the vessel being a discharge vessel, the first feedthrough being a first electrode and the second feedthrough being a second electrode and, during operation, the high pressure discharge lamp comprising a discharge arc between the first electrode and the second electrode for emitting light.

In an embodiment of the lamp, the first supply pin and the second supply pin are arranged at the same side of the discharge vessel as the second feedthrough. In this configuration, the wire runs from the first feedthrough substantially along the whole of the vessel to the first supply pin near the second feedthrough. In this embodiment, the wire is relatively long and passes the discharge arc or filament which typically constitutes the hottest part of the lamp. Due to the use of the wire comprising the first and second part, a high efficiency improvement is obtained.

In an embodiment of the lamp, the wire further comprises a third part comprising a third conductive material, the second part being arranged between the first part and the third part. Using the third conductive material having, for example, a different heat tolerance compared to the second conductive material, the first, second and third part along the lamp may be chosen such that each area comprises a conductive material having the required heat tolerance while the overall resistance of the wire can be chosen to be as low as possible, thus achieving a relatively high efficiency. The heat tolerance of the third conductive material may, for example, be the same as the heat tolerance of the first conductive material. In such an arrangement, the second conductive material having the highest heat tolerance may, for example, be arranged in the vicinity of the discharge arc of the high pressure discharge lamp or in the vicinity of the filament of the halogen lamp. Because the temperature in the vicinity of the discharge arc or filament is relatively high, the conductive material having the high heat tolerance is required for that part of the wire. Because the electrical resistance of this second conductive material is relatively high, the first conductive and third conductive materials are used where possible, being in areas near the lamp where the temperature near the vessel is lower, for example, near the feedthroughs. So, by sandwiching the second conductive material in-between the first conductive material and the third conductive material and by choosing the heat tolerance of the second conductive material to be relatively high and choosing the heat tolerance of the first and third conductive material to be relatively low, the heat tolerance of the whole wire may be sufficient to withstand the temperature gradient next to the vessel of the lamp, while further reducing the resistance value. As a result, the current embodiment of the wire according to the invention provides sufficient heat tolerance, while enabling to achieve the lowest resistance value, thus providing high efficiency of the high pressure discharge lamp or of the halogen lamp.

In an embodiment of the lamp, the lamp being a high pressure discharge lamp and the wire further comprising an antenna arranged outside the discharge vessel for reducing an ignition voltage of the high pressure discharge lamp, the antenna is electrically connected to the wire. The use of such an antenna for reducing the ignition voltage of the high pressure discharge lamps is known. These antennas are constituted of a further wire wound around the extension of the discharge vessel near the second electrode of the high pressure discharge lamp, while being electrically connected to the first electrode. So, preferably the antenna is located relatively near to the discharge arc. Due to this preferred arrangement of the antenna, the antenna is also located relatively close to the relatively high temperature area of the high pressure discharge lamp and thus is preferably also constituted of the second conductive material which comprises conductive material having a relatively high heat tolerance.

In an embodiment of the lamp, the antenna is integrated in the second part of the wire. A benefit of this embodiment is that the number of connections required to produce the wire is limited, thus reducing the manufacturing costs of the wire according to the invention. In the known wires which comprise an antenna, the antenna is connected to the wire, for example, welded to the wire. This connecting means an additional production step in the production of the high pressure discharge lamp, which increases the cost of the high pressure discharge lamp. Integrating the antenna in the second part of the wire which comprises high heat tolerance conductive material causes the number of welding steps to be limited. To produce the wire according to the invention, generally the first part is welded to the second part, which is welded to the third part. The use of the antenna generally adds an additional welding step. However, by integrating the antenna in the second part of the wire, the additional welding step to connect the antenna to the wire is omitted.

In an embodiment of the lamp, the second area is arranged between the protrusion points of the first feedthrough and the second feedthrough into the vessel. In a further embodiment of the lamp, the second area is arranged between the points where the first feedthrough and the second feedthrough enter the vessel. In an alternative embodiment, the second area is arranged between the first electrode and the second electrode of the high pressure discharge lamp.

In an embodiment of the lamp, the second conductive material is chosen from a list comprising: Nifethal70, Nifethal52, Nikrothal80, Nikrothal70, NikrothalβO,

NikrothaWO, Nikrothal20, Kanthal APM, Kanthal A-I, Kanthal A, Kanthal AF, Kanthal AE, Kanthal D, Alkrothal, and mixtures thereof. The listed conductive materials have a high heat tolerance and maintain their normal functionality when exposed to temperatures ranging from 900 degrees Celsius up to 1400 degrees Celsius. Consequently, the listed second conductive materials are able to withstand the heat conditions in the vicinity of the discharge arc of the high pressure discharge lamp or of the filament of the halogen lamp, while still maintaining their normal functionality. Kanthal is an alloy comprising, amongst other materials, Aluminum and has a melting point between 1400 degrees Celsius and 1500 degrees Celsius. These listed second conductive materials which have a relatively high heat tolerance also have a relatively high electric resistance because these second conductive materials are typically produced as heating wires. For heating wires, high resistance means that a considerable part of the conducted current is converted into heat, which is beneficial for heating. However, when using these second conductive materials as a wire for connecting the first electrode of the high pressure discharge lamps to the first supply pin connected to the power supply, or for connecting the first feedthrough of the halogen lamp to the first supply pin connected to the power supply, the relatively high electric resistance only reduces the efficiency of the lamp, because part of the power required to drive the lamp is "wasted" due to the conversion into heat by the second conductive material. In the wire according to the invention, the second conductive material is only used in part of the wire which is exposed to the harsh temperature conditions in the vicinity of the discharge arc or in the vicinity of the filament. The remainder of the wire is constituted of different material having improved conductivity, which reduces the losses of power in the wire.

In an embodiment of the lamp, the first and/or third conductive material is chosen from a list comprising: Nickel-Manganese, Molybdenum, Nickel, AISI 304, AISI 310, AISI 330, AISI 430, AISI 446, ASTM E230, ASTM 800HT, SUS 304, SUS 310, SUS 330, SUS 430, SUS 446, and mixtures thereof. A benefit when using the Nickel-Manganese alloy as the first and/or third conductive material is that this material can be connected relatively easily to the second conductive material. This connecting may be done using welding, for example, laser welding by a butt weld in which the wires are welded axially. Alternatively, the connection between the two different conductive materials may be generated via a tube covering both ends of the two connectable conductive materials in which the tube is squeezed together. These different ways of connecting the different conductive materials ensure a good electrical connection between the two parts and prevent the diameter of the wire at the connection point to increase too much due to the connection. A relatively large increase of the diameter of the wire would obstruct light emitted by the lamp, which would not be preferred. A further benefit of the listed materials is that they show a relatively long lifetime of the wire and produce a reliable connection between the first feedthrough and the first supply pin. The materials denoted by "AISI" represent grades in steel alloys defined by standardized AISI steel grades defined by the American Iron and Steel Institute. The materials denoted by "ASTM" represent grades in steel alloys defined by the American Society for Testing and Materials. The materials denoted by "SUS" represent similar steel grades as the AISI grades, but now defined by the Japanese government. Also other countries have similar steel grades, for example, Germany has comparable DIN grades (although coded differently), France has AFNOR grades (also coded differently), England has the BSI grades (coded differently), Spain has the UNE grades (coded similarly as the DIN grades), and, for example, Europe has the EURONORM grades (coded similarly as the DIN grades). It will be clear to the person skilled in the art that products similar to the ones listed above, although indicated in different standardized grades, will fall under the scope of this embodiment. In an embodiment of the lamp, a diameter of the wire is smaller than

1 millimeter. Because the wire runs at least partially along the outer wall of the vessel, the wire obstructs some of the light emitted by the lamp. This obstruction may be visible as a non-uniform distribution of the light across a surface which is to be illuminated by the lamp. Consequently, the diameter of the wire should be as small as possible. Preferably, the diameter of the wire may be smaller than 0.8 millimeter or even more preferably the diameter may be equal to or smaller than 0.6 millimeter. However, reducing the diameter of the wire also reduces the strength of the wire, which may cause the wire to loose its functionality more quickly when exposed to relatively high temperatures. For example, the relatively thin wire may easily deform when exposed to high temperatures and thus a wire having reduced thickness also has reduced heat tolerance. To still allow the thickness of the wire to be less than 1 millimeter, the second part of the wire is constituted of the second conductive material having increased heat tolerance compared to the first conductive material.

The invention also relates to a wire according to claim 13. The invention also relates to an image projection system as claimed in claim 14 and to a headlight as claimed in claim 15.

BRIEF DESCRIPTION OF THE DRAWINGS:

These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter. In the drawings:

Figs. IA and IB show an electric lamp according to the invention in which the lamp is a high pressure discharge lamp,

Fig. 2 shows an electric lamp according to the invention in which the lamp is a halogen lamp,

Figs. 3 A and 3B show a schematic overview of a first and second embodiment of the wire for use in the lamp according to the invention,

Figs. 4A and 4B shows a schematic overview of a third embodiment of the wire according to the invention which comprises an antenna, Fig. 5 shows the high pressure discharge lamp comprising a further lampholder comprising collimating optics, and

Figs. 6 A and 6B show an image projection system and a headlight, respectively.

The figures are purely diagrammatic and not drawn to scale. Particularly for clarity, some dimensions are exaggerated strongly. Similar components in the Figures are denoted by the same reference numerals as much as possible.

DETAILED DESCRIPTION OF EMBODIMENTS:

Figs. IA and IB show an electric lamp 100 according to the invention being a high pressure discharge lamp 100. In Fig. IA a schematic three-dimensional view of the high pressure discharge lamp 100 is shown while in Fig. IB a schematic cross-sectional view of the high pressure discharge lamp 100 is shown. The high pressure discharge lamp 100 according to the invention comprises a discharge vessel 105 enclosing a discharge space 130 and comprising the first feedthrough 115 arranged opposite a second feedthrough 125 between which, in operation, a discharge arc is produced. The first feedthrough 115 is a first electrode and the second feedthrough 125 is a second electrode of the high pressure discharge lamp 100. On opposite sides of the discharge vessel 105, two seal extensions 110, 120 are present via which the first electrode 115 and the second electrode 125 extend from the exterior into the discharge vessel 105 for generating, in operation, a discharge arc. The first electrode 115 and/or second electrode 125 may comprise further elements, for example, a UV-chamber (not shown) for generating UV radiation to allow easier ignition of the high pressure discharge lamp, or, for example, a connection foil connecting the inner first and/or second electrode 115, 125 with the exterior of the discharge vessel 105. The connectors which are connected to the inner electrodes and which emerge via the extensions 110, 120 to the outside of the discharge vessel 105 are often also indicated as connection pins, with the connection pin of the first electrode 115 often being indicated as back-pin 115 and the connection pin of the second electrode 125 often being indicated as the front-pin 125.

The high pressure discharge lamp 100 is placed in a lampholder 150 which comprises the first and second supply pins 140, 145 for connecting the high pressure discharge lamp 100 to a power supply (not shown). For light efficiency reasons it is preferred that the lampholder 150 connects to the discharge vessel 105 via one of the extensions 110, 120 of the high pressure discharge lamp 100. Therefore, there must be an electrical connection between the first supply pin 140 and the first electrode 115, possibly via the back- pin 115 (if present). The first electrode 115 (or the back-pin) emerges from the extension 110 on an opposite side of the discharge space 130 compared to the first supply pin 140. To enable the electrical connection between the first electrode 115 (or back-pin) and the first supply pin 140, the wire 12 according to the invention is used, which runs along the outer wall of the discharge vessel 105. This wire 12 preferably may be relatively thin to minimize the blocking of light emitted by the high pressure discharge lamp 100. However, to allow the wire to withstand the harsh temperatures in the vicinity of the discharge arc in the discharge vessel 105, the wire 12 comprises a first part 20 (see Fig. 3) and a second part 30, each comprising a different conductive material. The second conductive material of the second part 30 has a higher heat tolerance compared to the first conductive material of the first part 20. The wire 12 may also comprise a third part 40 having a third conductive material (see Fig. 3B). By choosing the heat tolerances of the first, second and third conductive materials, the heat tolerance of the wire 12 may be sufficient to withstand the temperature gradient along the high pressure discharge lamp 100, while limiting the electrical resistance of the wire 12. The first part 20, the second part 30 and/or the third part 40 may be connected 50 using welding 50 or using other means of connection, such as the squeeze tube indicated before.

In operation, a discharge arc between the first electrode 115 and the second electrode 125 ionizes a gas mixture inside the discharge vessel 105 of the high pressure discharge lamp 100, which subsequently emits light. The color of the light emitted by the high pressure discharge lamp 100 depends, amongst others, on the gas mixture in the discharge vessel 105 and on the pressure inside the discharge vessel 100. The discharge also increases the temperature around the lamp and generates a temperature gradient along the high pressure discharge lamp in which the highest temperature is near the discharge arc. Fig. 2 show a lamp 101 according to the invention being a halogen lamp 101.

Also the halogen lamp 101 according to the invention comprises a vessel 105 enclosing a space 130 and comprising the first feedthrough 115 which is arranged opposite a second feedthrough 125 between which a filament 102 is arranged which, in operation, emits light due to the passing current. On opposite sides of the vessel 105 two seal extensions 110, 120 are present via which the first feedthrough 115 and the second feedthrough 125 extend from the exterior into the vessel 105.

The halogen lamp 101 is placed in a lampholder 151 which in this embodiment is a quartz envelope 151 and which comprises the first and second supply pins 140, 145 for connecting the halogen lamp 100 to a power supply (not shown). For light efficiency reasons it is preferred that the lampholder 151 connects to the discharge vessel 105 via one of the extensions 110, 120 of the halogen lamp 101. Therefore, there must be an electrical connection between the first supply pin 140 and the first feedthrough 115. The first feedthrough 115 emerges from the extension 110 on an opposite side of the space 130 compared to the first supply pin 140. To enable the electrical connection between the first feedthrough 115 and the first supply pin 140, the wire 12 according to the invention is used which runs along the outer wall of the vessel 105. Again, this wire 12 preferably may be relatively thin to minimize the blocking of light emitted by the halogen lamp 101. However, to allow the wire to withstand the harsh temperatures in the vicinity of the filament 102 in the vessel 105 of the halogen lamp 101, the wire 12 comprises the first part 20 (see Fig. 3) and the second part 30, each comprising a different conductive material. The wire 12 may also comprise the third part 40 having a third conductive material (see Fig. 3B). By choosing the heat tolerances of the first, second and third conductive materials, the heat tolerance of the wire 12 may be sufficient to withstand the temperature gradient along the halogen lamp 101, while the electrical resistance of the wire 12 is limited. Figs. 3 A and 3B show a schematic overview of a first and second embodiment of the wire 10, 12 for use in the lamp 100, 101 according to the invention. The wire 10, 12 is arranged for connecting a first feedthrough 115 (see Fig. 1) of a lamp 100, 101 (see Figs. 1 and 2) at a far end of the lamp 100, 101 with respect to a lampholder 150, 151 (see Figs. 1 and 2) to a first supply pin 140 (see Figs. 1 and 2).

In the first embodiment of the wire 10 as shown in Fig. IA, the wire 10 is constituted of the first part 20 which is electrically connected 50 to a second part 30, for example, via welding or via a squeeze tube. The first part 20 of the wire 10 is arranged parallel to the extension 120 (see Fig. 1) via which the second feedthrough 125 is introduced into the vessel 105 (see Fig. 1). The second part 30 of the wire 10 which extends in the vicinity of the space 130 generally requires the second conductive material, which can withstand these high temperatures, or, in other words, which has a high heat tolerance. The only conductive materials currently available on the market which have a heat tolerance sufficiently high to be used in the vicinity of the space 130 are heating wires which are constituted of Nifethal70, Nifethal52, Nikrothal80, Nikrothal70, NikrothalβO, NikrothaWO, Nikrothal20, Kanthal APM, Kanthal A-I, Kanthal A, Kanthal AF, Kanthal AE, Kanthal D, Alkrothal, and mixtures thereof. The drawback of these known high heat tolerance materials is that their electrical resistance value is relatively high. The reason for this high electrical resistance value is that these high heat tolerance materials have been developed as heating wires in which a high resistive value means an efficient conversion of the flowing current into heat required for heating. However, when using these heating- wire materials as wire 10 for connecting the first electrode 115 to the first supply pin 140 in a lamp 100, 101, the resistance of the wire 10 preferably should be as low as possible, because electrical resistance only contributes to the losses of the lamp 100, 101 due to the (in this case unnecessary) heating of the wire 10. However, because there are no alternative conductive materials available which have sufficient heat tolerance to be suitably applied in the vicinity of the discharge arc or the filament 102, these listed materials have to be used in the wire 10 to connect the first feedthrough 115 to the first supply pin 140 (see Figs. 1 and 2). The wire 10 as shown in Fig. 3A is constituted of the first part 20 and the second part 30. The first part 20 is arranged near the lamp 100, 101, however at a location near the lamp 100, 101 where the temperature, during operation, is still relatively low - thus not too close to the space 130. Only near the space 130 of the lamp 100, 101 the wire 10 is constituted of the second part 30, which comprises the second conductive material which has high heat tolerance and thus can withstand the harsh conditions in the vicinity of the discharge arc or the filament 102. By splitting the wire 10 into the first part 20 and the second part 30, the high heat tolerance material is only used at the location near the lamp 100, 101 where it is needed, and thus the electronic resistance value of the wire 10 is reduced compared to the known wires, which are generally constituted of a single conductive material. In the second embodiment of the wire 12 as shown in Fig. 3B, the wire 12 is constituted of the first part 20 which is electrically connected 50 to the second part 30, which is electrically connected 50 to a third part 40. The third part 40 comprises a third conductive material which has a different heat tolerance compared to the second conductive material of the second part 30. Typically, the third part 40 is arranged near the extension 110 (see Figs. 1 and 2) via which the first feedthrough 115 is introduced into the vessel 105 (see Figs. 1 and X). Also this part of the lamp 100, 101 has a relatively low temperature during operation compared to the temperature in the vicinity of the discharge arc or the filament in the space 130. So, also the third part 40 of the wire 12 may be constituted of a conductive material have lower heat tolerance compared to the conductive material of the second part 30. Because such a conductive material having lower heat tolerance generally also has a reduced electrical resistance value, the replacing of a part of the second part 30 by the third part 40 further reduces the electrical resistance value of the wire 12 and thus further improves the efficiency of the lamp 100, 101 according to the invention.

In a preferred embodiment of the wire 12, the third part 40 and the first part 20 are constituted of the same conductive material.

Figs. 4 A and 4B shows a schematic overview of a third embodiment of the wire 14 according to the invention. In this third embodiment of the wire 14, the wire 14 comprises an antenna 35 for reducing an ignition voltage of the high pressure discharge lamp 100. The antenna 35 is electrically connected to the wire 14. The antenna 35 is constituted of a further wire wound around the extension 130 of the vessel 105 near the second electrode 125 of the high pressure discharge lamp 100. Preferably, the antenna 35 is integrated in the second part 30 of the wire 14. The integration of the antenna 35 into the second part 30 ensures that the antenna 35 is also constituted of the second conductive material, which can withstand the harsh conditions near the space 130. A further benefit of the integration of the antenna 35 into the second part 30 is that this reduces the number of electrical connections 50 required to produce the wire 14. Each electrical connection 50 which is required to produce the wire 14 means an additional process step in the production of the wire 14. So, reducing or limiting the number of electrical connections 50 to produce the wire 14 reduces the production cost of the high pressure discharge lamp 100. Fig. 4A shows the individual first part 20, second part 30 and third part 40 which constitute the wire 14 and in which the second part 30 comprises the antenna 35. Fig. 4B shows the wire 14 in which the first part 20, the second part 30 and the third part 40 are electrically connected 50. Fig. 5 shows the high pressure discharge lamp 100 comprising a further lampholder 154 comprising collimating optics 152. The further lampholder 154 comprises collimating optics 152 being a back reflector 152. The back reflector 152 is connected to the lampholder 150, which positions and fixes the high pressure discharge lamp 100 in the back reflector 152 and which typically provides the first and second supply pins 140, 145, also often indicated as leads 140, 145, which are electrically connected to the second electrode 125 (see Fig. 1) and via the wire 10, 12, 14 to the first electrode 115 for providing power to the electrodes of the high pressure discharge lamp 100.

As can be seen from Fig. 5, the extension 120 comprising the second electrode 125 is used to fix and position the high pressure discharge lamp 100 inside the lampholder 150. So, the second supply pin 145, which connects to the second electrode 125, may make electrical contact directly inside the lampholder 150. However, to allow electrical contact between the first supply pin 140 and the first electrode 115, the wire 10, 12, 14 is required. The wire 10, 12, 14 is electrically contacted to the first supply pin 140 and ensures the connection to the first electrode 115. Due to the wire 10, 12, 14 extending relatively close to the outer wall of the discharge vessel 105 of the high pressure discharge lamp 100, at least part of the wire 10, 12, 14 is constituted of high heat tolerance conductive material.

It is directly apparent to the person skilled in the art that the high pressure discharge lamp 100 in Fig. 5 may easily be replaced by a halogen lamp 101 without departing from the scope of the invention. Figs. 6 A and 6B show an image projection system 200 and a headlight 300 according to the invention, respectively.

The image projection system 200 shown in Fig. 6 A comprises the high pressure discharge lamp 100 comprising the lampholder 150 which comprises collimating optics 152. Again, the high pressure discharge lamp 100 may easily be replaced by the halogen lamp 101 according to the invention. The image projection system 200 comprises a shaping lens 212 for shaping the light emitted from the high pressure discharge lamp 100 or halogen lamp 101 to illuminate a digital light processor 220 via a beam splitting cube 214. The modulated reflected light from the digital light processor 220 is imaged via a projection lens 216 on to a screen 225. Alternatively, the image projection system may use a liquid crystal display module (not shown), for example, which is used as a light valve in transmission.

The image projection system 200 may, for example, be a beamer or a projection television. Alternatively, the image projection system 200 may be a rapid prototyping system (3D printers) or a lithography system.

The headlight 300 shown in Fig. 6B also comprises the high pressure discharge lamp 100 comprising the further lampholder 154 according to the invention. The headlight 300 may comprise light shaping elements, such as a lens 312 and light blocking arrangements (not shown) to ensure that the distribution of the light emitted by the headlight 300 is according to the automotive requirements. Especially in automotive applications, the efficiency of the high pressure discharge lamps 100 is essential as they determine the visibility of the driver of the vehicle. Using the high pressure discharge lamp 100 having the wire 10, 12, 14 according to the invention improves the visibility of the driver of the vehicle and thus improves the safety of the vehicle. Again, the high pressure discharge lamp 100 may easily be replaced by the halogen lamp 101 according to the invention.

It should be noted that the above-mentioned 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. Use of the verb "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. 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. Electric lamp (100, 101) comprising: a vessel (105) enclosing a space (130) comprising a light emitting element, a first feedthrough (115) and a second feedthrough (125) protruding into the vessel (105) on opposite sides of the vessel (105) for providing, during operation, power to the light emitting element generating a temperature gradient along an outer wall of the vessel (105), a first supply pin (140) and a second supply pin (145) both arranged at a same side of the vessel (105), and arranged for connecting the lamp (100, 101) to a power supply, and - a wire (10, 12, 14) running at least partially along the outer wall of the vessel

(105) for connecting the first feedthrough (115) to the first supply pin (140), the wire (10, 12, 14) comprising a first part (20) comprising a first conductive material and a second part (30) comprising a second conductive material having an increased heat tolerance compared to the first conductive material, the first part (20) being arranged in a first area and the second part (30) being arranged in a second area, the maximum temperature, in operation, in the second area being higher than in the first area.

2. Electric lamp (100, 101) as claimed in claim 1, wherein the lamp (100, 101) is a high pressure discharge lamp (100), the vessel (105) being a discharge vessel (105), the first feedthrough (115) being a first electrode (115) and the second feedthrough (125) being a second electrode (125) and, during operation, the high pressure discharge lamp comprising a discharge arc between the first electrode (115) and the second electrode (125) for emitting light.

3. Electric lamp (100, 101) as claimed in claim 1 or 2, wherein the first supply pin (140) and the second supply pin (145) are arranged at the same side of the discharge vessel (105) as the second feedthrough (125).

4. Electric lamp (100, 101) as claimed in claim 1, 2 or 3, wherein the wire (10,

12, 14) further comprises a third part (40) comprising a third conductive material, the second part (30) being arranged between the first part (20) and the third part (40).

5. Electric lamp (100, 101) as claimed in claim 2, 3 or 4, wherein the wire (10,

12, 14) further comprises an antenna (35) arranged outside the vessel (105) for reducing an ignition voltage of the high pressure discharge lamp (100, 101), the antenna (35) being electrically connected (50) to the wire (10, 12, 14).

6. Electric lamp (100, 101) as claimed in claim 5, wherein the antenna (35) is integrated in the second part (30) of the wire (10, 12, 14).

7. Electric lamp (100, 101) as claimed in any of the previous claims, wherein the second area is arranged between the protrusion points of the first feedthrough (115) and the second feedthrough (125) into the vessel (105).

8. Electric lamp (100, 101) as claimed in claims 1 to 6, wherein the second area is arranged between the points where the first feedthrough (115) and the second feedthrough (125) enter the vessel (105).

9. Electric lamp (100, 101) as claimed in claims 2 to 6, wherein the second area is arranged between the first electrode (115) and the second electrode (125) of the high pressure discharge lamp (100, 101).

10. Electric lamp (100, 101) as claimed in any of the previous claims, wherein the second conductive material is chosen from a list comprising: Nifethal70, Nifethal52, Nikrothal80, Nikrothal70, NikrothalβO, NikrothaWO, Nikrothal20, Kanthal APM, Kanthal A- 1, Kanthal A, Kanthal AF, Kanthal AE, Kanthal D, Alkrothal, and mixtures thereof.

11. Electric lamp (100, 101) as claimed in any of the previous claims, wherein the first and/or third conductive material is chosen from a list comprising: Nickel-Manganese, Molybdenum, Nickel, AISI 304, AISI 310, AISI 330, AISI 430, AISI 446, ASTM E230, and ASTM 800HT, and mixtures thereof.

12. Electric lamp (100, 101) as claimed in any of the previous claims, wherein a diameter of the wire (10, 12, 14) is smaller than 1 millimeter.

13. Wire (10, 12, 14) for use in an electric lamp (100, 101) as claimed in any of the claims 1 to 12.

14. Image projection system (200) comprising the electric lamp (100, 101) as claimed in any of the claims 1 to 12.

15. Headlight (300) for a vehicle comprising the electric lamp (100, 101) as claimed in any of the claims 1 to 12.