WO2008029369A1

WO2008029369A1 - Automotive lamp

Info

Publication number: WO2008029369A1
Application number: PCT/IB2007/053592
Authority: WO
Inventors: Godfried C. G. M. Manders; Bram Visser; Chantal Sweegers
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2006-09-07
Filing date: 2007-09-06
Publication date: 2008-03-13

Abstract

The invention relates to a high- intensity discharge lamp (1) comprising a discharge vessel (2) and electrodes (4, 5) extending into said discharge vessel for emitting visible light. An electrically conductive screening (16), which is translucent to said emitted light, is provided on said discharge vessel. By applying the screening directly on the discharge vessel, the screening is brought closer to the source of EMI and, consequently, the EMI screening performance of the lamp is improved. The invention also relates to a headlight of a motorized vehicle provided with such a lamp, and a method of manufacturing such a lamp.

Description

AUTOMOTIVE LAMP

FIELD OF THE INVENTION

The invention generally relates to the field of lighting. More specifically, the invention relates to an automotive high- intensity discharge lamp.

BACKGROUND OF THE INVENTION

Typical gas discharge lamps currently used in motor vehicles are, for example, so-termed high-intensity discharge (HID) lamps. These lamps may e.g. operate with a filling of xenon gas. However, a problem of using such gas discharge lamps is that the physical properties of the respective inert gas, for example, the xenon gas, the electrode and the discharge phenomenon resulting therefrom cause the discharge lamp to not only emit the desired light but also a high proportion of electromagnetic interference (EMI) radiation in the high-frequency range. The emission of undesired high-frequency interference radiation is particularly observed during start-up of the lamp.

Interference radiation leads to electromagnetic interference with other electronic units of a vehicle such as, for example, an audio set, a television set, an ABS system and an airbag control and may consequently lead to malfunctioning of these devices. It is therefore greatly desirable to reduce or eliminate electromagnetic interference from HID lamps. However, the possibility of modifying the interference source itself (i.e. the electrodes and the gas) is rather limited because of the fundamental physical properties of the lamp that require specific shapes and orientation of the electrodes and specific gas properties to be capable of emitting light from the lamp in the first place. This is why measures to prevent EMI are usually taken in such a way that the electromagnetic interference emission is prevented from being radiated into its surroundings.

One method of reducing electromagnetic interference radiation is to shield the entire high-intensity discharge lamp with a closed metal casing as well as using shielded cabling. However, the head light of a car remains an open box, because this part cannot be shielded with metal that would otherwise block the light. Furthermore, this method is comparatively complicated and, consequently, expensive. An improved method of reducing electromagnetic interference is disclosed in WO 2004/084250. This publication discloses a gas discharge lamp with a discharge vessel and electrodes projecting into the discharge vessel that is surrounded by an outer bulb. A translucent, electrically conductive screening is provided on the outer bulb for screening the discharge vessel.

There is a need in the art for an improved high-intensity discharge lamp in terms of improved screening, robustness, ease and manufacturing costs.

OBJECT AND SUMMARY OF THE INVENTION. A high- intensity discharge lamp is proposed, which comprises a discharge vessel and electrodes extending into said discharge vessel for emitting visible light. An electrically conductive screening, which is translucent to said emitted light, is provided on said discharge vessel.

Moreover, a method of manufacturing a high- intensity discharge lamp is proposed, which method comprises the steps of: providing a discharge vessel and electrodes extending into said discharge vessel; applying a translucent and electrically conductive screening on said discharge vessel. Although the temperature of the discharge vessel in high- intensity discharge

(HID) lamps may reach values of 800 to HOO⁰C, the applicant has found that it is possible to apply a screening directly on the discharge vessel. In particular, it has been found that the presence of high-frequency interference radiation outside the lamp can be significantly reduced by applying a transparent or translucent screening directly on the discharge vessel. By applying the screening directly on the discharge vessel, the screening is brought closer to the source of EMI and, consequently, the EMI screening performance of the lamp is improved. Furthermore, by directly applying the screening on the discharge vessel, the screen cannot be damaged, because touching of the discharge vessel is generally prevented by an outer bulb surrounding the discharge vessel. Moreover, the area for applying the screening is reduced as compared with the application of a screening on the outer bulb, which reduces the costs of manufacturing these lamps. The screening can be applied easily on the discharge vessel, e.g. by means of wet-chemical application techniques.

The embodiment of the invention as defined in claim 2 provides the advantage of a further improved EMI screening performance. The embodiment of the invention as defined in claim 3 provides the advantage that the further screening on the outer bulb can neither be damaged by touching.

The embodiment of the invention as defined in claim 4 provides a further improvement of the EMI screening performance. The embodiment of the invention as defined in claim 5 provides an appropriate structure of the screening as a coating. ITO is a preferred material, because the characteristics of this material, which is environmentally harmless, are well known. ITO is transparent to the relevant portion of the light spectrum emitted from the discharge vessel and may resist high temperatures. The embodiment of the invention as defined in claim 6 provides further materials that have been found to be capable of performing the desired EMI screening when applied directly on the discharge vessel of the lamp.

Advantageously, the lamp is applied in the head light of a motorized vehicle, such as a car. The embodiment of the invention as defined in claim 10 is advantageous in that appropriate coatings for performing the EMI shielding can be obtained directly on the discharge vessel in an easy and cost-effective way.

It should be noted that the embodiments defined above, and aspects thereof, may be combined. EP 991 107 discloses a discharge lamp with a transparent electrically conductive layer extending throughout the lamp vessel enclosing the discharge space. The transparent conductive layer is provided on the lamp vessel and comprises a 300 nm thick ITO layer with a square resistance of less than 100 Ohms. It should be noted, however, that this prior-art discharge lamp is not a high-intensity discharge lamp and, consequently, has a lamp vessel temperature which is significantly lower than that of the lamp according to the invention. For high-pressure discharge lamps, EP 991 107 discloses the provision of an outer bulb surrounding the lamp vessel, as well as the application of a light-transparent and electrically conductive coating on this outer bulb.

The invention will be elucidated with reference to the attached drawing, which schematically shows preferred embodiments according to the invention. It will be understood that the invention is not in any way limited to these specific and preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 shows a first embodiment of a high- intensity discharge lamp according to the invention, and

FIG. 2 shows a second embodiment of a high- intensity discharge lamp according to the invention.

DESCRIPTION OF EMBODIMENTS

FIGS. 1 and 2 show a high- intensity discharge (HID) lamp 1 comprising a discharge vessel 2 (also known as burner), generally consisting of quartz glass, with an inner space 3 of only a few cubic millimeters. A first electrode 4 and a second electrode 5 extend in known manner into the discharge vessel 2, i. e. its inner space 3, from two mutually opposed ends. The electrodes 4, 5 pass to the exterior of the lamp through hermetically sealed cylindrical end portions 6, 7 of the gas discharge vessel 2, so that the inner space 3 is sealed off from its surroundings. The inert gas, e.g. xenon, is present at a high pressure in the inner space 3 of the discharge vessel 2. A high voltage is applied between the electrodes 4, 5 for igniting the gas discharge lamp 1 to emit visible light.

During subsequent operation, i.e. after ignition of the lamp 1, an AC voltage is applied to the electrodes 4, 5. Note that the temperature of the discharge vessel 2 may be as high as 800 to HOO⁰C during operation of the lamp 1.

The discharge vessel 2 is surrounded by an outer bulb 8 which may be filled with a gas, in particular air, and which is sealed from the surrounding atmosphere so as to absorb, inter alia, ultraviolet radiation arising in the discharge. The outer bulb also generally comprises quartz glass and is fixedly connected to the end portions 6, 7 of the discharge vessel 2.

The electrodes 4, 5 are connected to supply lines 9, 10 of a lamp holder 11. The supply lines 9, 10 may be connected to a suitable driver device (not shown) which supplies the high voltage for igniting the lamp 1 and the AC voltage for its operation.

In particular, the insertion of the lamp 1 in the lamp holder 11 provides a connection of the electrode 5 to the supply line 10 leading to the driver device. The other electrode 4 is connected to a central lead 12 of a coaxial line 13, which is passed into the lamp holder 11 next to the discharge lamp and is connected in situ to the supply line 9 leading to the driver device. The central lead 12 of the coaxial line 13 and the electrodes are contacted with the supply lines 9, 10 through conventional plug connections in each case. An outer lead 14 of the coaxial line 13 is connected to a cover cap 15 at the upper end portion 6 of the discharge vessel 2, i.e. the portion remote from the lamp holder 11. During the ignition phase of the lamp 1 (start-up), a considerable amount of electromagnetic interference (EMI) radiation is emitted from the lamp 1. This EMI radiation disturbs the operation of equipment in its surroundings, including audio equipment, television equipment, etc. in a vehicle as mentioned in the introduction. In order to reduce the amount of EMI radiation from the lamp 1, the applicant has provided an electrically conductive screening 16 (indicated by bold broken lines) that is translucent to the light emitted from the lamp 1 on the discharge vessel 2. It is advantageous to provide the screening 16 on the entire discharge vessel 2 so as to obtain an optimum EMI screening performance. It has been experimentally verified that the presence of an electrically conductive and translucent screening 16 on the discharge vessel significantly reduces the effect of EMI disturbance of audio equipment in the neighborhood of the lamp 1.

For the HID lamp 1 in the embodiment of FIG. 1, the electrically conductive screening 16 is connected to earth via the conductive end cap 15 and a contact ring 17 at the respective end portions 6, 7. In this way, an electric connection between the outer lead 14 of the coaxial line 13 and the screening 16 of the gas discharge lamp 1 is obtained. The outer lead 14 is connected to the conductive housing of the lamp holder 11 again via suitable contacts 18. However, it should be noted that a connection of the electrically conductive and translucent screening 16 on the discharge vessel 2 to mass potential is not an essential feature of the invention. In this respect, it should be noted that the coaxial line 13 in FIGS. 1 and 2 may be replaced by a normal lead. Automotive lamps usually have such a normal lead instead of a coaxial line. For such an embodiment, grounding of the conductive screening 16 may only be obtained via the contact ring 17, or may be omitted.

For the HID lamp 1 in the embodiment of FIG. 2, the lamp 1 has an electrically conductive and translucent screening 19 on the outer bulb 8 in addition to the electrically conductive and translucent screening 16 on the discharge vessel. Such an arrangement improves the EMI screening performance of the lamp 1. While in FIG. 2 the additional screening 19 is provided on the outer side of the outer bulb 8, it should be appreciated that, alternatively or in addition to the additional screening 19, a further additional screening may be provided on the inner side of the outer bulb 8. An embodiment of an outer bulb 8 provided with EMI screens on both the inner and outer side of the outer bulb 8 is shown in international patent application WO 2004/084250 in the name of the present applicant, which embodiment is herein incorporated by reference. Each of the electrically conductive screenings on the outer bulb 8 may be connected to ground potential. Although the screening 16 on the discharge vessel 2 is shown to be electrically floating in FIG. 2, it should be appreciated that it may also be connected to ground.

The electrically conductive and translucent screening 16 on the discharge vessel 2 may comprise a grid or one or more continuous layers of suitable materials. Since, in operation of the HID lamp 1, the temperature of the discharge vessel 2 may reach values of 800 to 1000⁰C, the material and layer thickness of the screening 16 should be suitable to withstand these temperatures. Layer thicknesses may vary between 10 and 300 μm but are typically in the range of 80 to 200 μm. The skilled person will appreciate that the layer thickness influences both the translucency characteristics and the electrical resistance per square of the screening 16, the latter determining the EMI screening performance of the screening 16. A square resistance of approximately 10⁵ Ohms is considered appropriate in this case.

The materials that have been found to be applicable for the screening 16 on the discharge vessel 2 of a HID lamp 1 fulfilling these conditions include: indium-tin oxide (In₂O₃, Sn), also referred to as ITO; In₂O₃ with Zn and Sn; SnO₂ with Sb and In; antimony-tin oxide, also referred to as ATO; fluoride-tin oxide, also referred to as FTO and aluminum-zinc oxide, also referred to as AZO. A coating 16 of ITO on the discharge vessel 2 with a thickness of approximately 100 μm transmits approximately 95% of the light generated within the discharge vessel 2 to the outside world. For coatings with smaller thicknesses, a transmission of 96 to 98% for visible light may be obtained.

The electrically conductive and translucent screening 16 may be applied on the discharge vessel 2 by means of wet-chemical application techniques. Examples of such application techniques include dipping and spraying of the discharge vessel 2 after the electrodes 4, 5 are pinched into the discharge vessel 2. However, more complicated techniques, such as chemical vapor deposition (CVD), may be applied as well.

The invention can be advantageously applied in HID lamps marketed under the brand name of XenEco for automotive purposes.

Claims

CLAIMS:

1. A high- intensity discharge lamp (1) comprising a discharge vessel (2) and electrodes (4, 5) extending into said discharge vessel for emitting visible light, wherein an electrically conductive screening (16), which is translucent to said emitted light, is provided on said discharge vessel.

2. The high- intensity discharge lamp (1) according to claim 1, wherein said discharge lamp comprises an outer bulb (8) surrounding said discharge vessel (2) and a further translucent and electrically conductive screening (19) is provided on said outer bulb.

3. The high- intensity discharge lamp (1) according to claim 2, wherein said further screening (19) is provided on an inner surface of said outer bulb (8).

4. The high- intensity discharge lamp (1) according to claim 1, wherein said screening (16) is connected to a fixed voltage, preferably to ground.

5. The high- intensity discharge lamp (1) according to claim 1, wherein said translucent and electrically conductive screening (16) comprises a coating of indium-tin oxide (ITO).

6. The high- intensity discharge lamp (1) according to claim 1, wherein said translucent and electrically conductive screening (16) comprises a coating selected from the group of indium oxide with zinc and tin, tin oxide with antimony and indium, tin oxide with antimony, tin oxide with fluorine and zinc oxide with aluminum.

7. The high- intensity discharge lamp (1) according to claim 1, wherein said lamp is an automotive high-intensity discharge lamp and said discharge vessel (2) comprises quartz glass.

8. A headlight for a motorized vehicle comprising the high- intensity discharge lamp (1) according to claim 1.

9. A method of manufacturing a high-intensity discharge lamp (1), the method comprising the steps of: providing a discharge vessel (2) and electrodes (4,5) extending into said discharge vessel; applying a translucent and electrically conductive screening (16) on said discharge vessel.

10. The method according to claim 9, wherein said step of applying said translucent and electrically conductive screening (16) on said discharge vessel (2) comprises a wet-chemical coating step, preferably comprising dipping or spraying.