WO2006043191A1

WO2006043191A1 - High intensity discharge lamp

Info

Publication number: WO2006043191A1
Application number: PCT/IB2005/053311
Authority: WO
Inventors: Pieter Postma; Gerhard Hebbinghaus
Original assignee: Philips Intellectual Property & Standards Gmbh; Koninklijke Philips Electronics N. V.
Priority date: 2004-10-20
Filing date: 2005-10-10
Publication date: 2006-04-27
Also published as: TW200631053A

Abstract

The invention relates to a high intensity discharge lamp (1), at least - comprising a bulb (2) which has a discharge chamber, - comprising two electrodes which extend into the discharge chamber, - comprising an ionizing gas filling in the discharge chamber, which contains at least one noble gas and a suitable metal halide mixture, and - comprising an outer tube (3) which is fixed to the bulb (2), wherein the metal halide mixture contains at least 0.01 to 0.07 jig/mm 3 of InI.

Description

High intensity discharge lamp

The present invention relates to a high intensity discharge lamp, at least

- comprising a bulb which has a discharge chamber,

- comprising two electrodes which extend into the discharge chamber,

- comprising an ionizing gas filling in the discharge chamber, which contains at least one noble gas and a suitable metal halide mixture, and

- comprising an outer tube which is fixed to the bulb.

On account of their optical properties, high intensity discharge lamps (HID lamps) and in particular xenon HID lamps are preferably used inter alia as a light source for headlamps for vehicles, in particular front headlamps. Within the context of the invention, the term xenon HID lamp (Philips) also comprises xenon HID-type lamps made by other manufacturers.

For these applications, an optical light source is required wherein the arc which forms between the electrode tips has dimensions which are defined and specified in a regulation, said dimensions relating to arc length, arc curvature and arc diffusity. Such high intensity discharge lamps are used as a light source for headlamps of vehicles.

Within the context of the invention, headlamps for vehicles, for example with a low-beam function, are all headlamps which produce a cut-off, such as for example pure low-beam headlamps, combined main-beam and low-beam headlamps, pure fog lamps, combined low-beam and fog lamps, and bending light headlamps.

Usually, headlamps are equipped with lamps which emit light with a virtually uniform color which is visible in all spatial directions, so that a traffic space which is illuminated with a homogeneous color is then usually produced.

It is known that blue light is reflected better on obstacles in the traffic space, for example traffic signs, and thus can be perceived better or more quickly in particular by the driver of the vehicle which in this respect illuminates the traffic space, but on the other hand dazzles in particular the oncoming traffic in an undesirable manner.

By contrast, yellow-colored light is less likely to dazzle the driver of the oncoming vehicle. Lamps which are to be used for vehicle headlamps are subject to international standards with respect to their most important parameters, such as for example the SAE or ECE standards which relate specifically to the European or US market. By way of example, the color properties which are to be observed in each case are precisely defined. One of these parameters is the so-called color point of the emitted light, which can be shown for example by a conventional CIE 1931 diagram.

It has been known for many years that indium in the metal halide mixture of the ionizing gas filling serves to influence the color point in the desired sense, and this is moreover used in commercially available lamps. The color point is usually shifted to a value from 380 to 390 of the y-value in the CIE 1931 diagram.

To date, this could be achieved only once stable lamp operation had been established. During the time from when the lamp was cold-started until stable lamp operation was reached (known as the run-up), no stabilization of the color point by indium in the metal halide mixture could be achieved. The considerable shifts in this respect from red to violet (y « 300), particularly during the first 5 to 8 seconds of run-up, represent a particular problem.

With this aforementioned light color during the run-up phase, the illumination of the traffic space in front of the vehicle is not optimal for the driver. The traffic safety of the oncoming vehicles is also adversely affected by this light color. In order to eliminate this problem, the market requires values for y > 310 during the run-up, which usually ends after more than 12 to 15 seconds.

By way of example, EP 1037258 A discloses a mercury-free high intensity discharge lamp as a light source for headlamps, which is said to correspond to the Japanese standard (JEL 215) for white light. The gas filling of this lamp contains an indium halide mixture, namely comprising 4 μg/mm³ to 12 μg/mm³ of InI, Tl halide mixture, namely comprising 4 μg/mm³ to 16 μg/mm³, and Na halide mixture, namely comprising 4 μg/mm³ to 12 μg/mm³, wherein the aforementioned problem is not solved. One disadvantage of the high intensity discharge lamps known from the prior art is thus that, during the run-up, the color point of the emitted light according to the CIE 1931 diagram does not lie in the so-called "white region" according to ECE R98 (Section 6.1) and ECE R99 (Section 3.9), shown in Fig. 1. In Fig. 1, the spectral region which corresponds to the standard ECE R99 for light in the "white region" is shown as an area, within the dashed line, in the CIE 1931 diagram, which is also the relevant spectral region of the invention.

Independently thereof, it is assumed by those in the field, for example in EP 1 288 998 Al, that mercury-free high intensity discharge lamps with a percentage of InJ of 0 to 3% in the gas filling cannot be used for applications as a light source for headlamps for vehicles, in particular front headlamps, in the "white region".

In Fig. 2, a curve of a mercury-free high intensity discharge lamp, determined during laboratory experiments, is plotted in a CIE 1931 diagram, said curve being produced in the run-up phase, in this case approximately between 2 to 12 seconds after the cold start. After approx. 2 seconds from the cold start, the color location can be described (Fig. 2) by x = 313 and y = 308; after approx. 6 seconds it can be described by x = 287 and y = 248. The indium content in the metal halide mixture of the ionizing gas filling of this lamp is approx. 0.25 μg/mm³. This content is way below the contents known from the prior art, such as for example the range of 4 - 12 μg/mm³ specified in EP 1 288 998 Al and the range of 7.3 - 24.2 μg/mm³ specified in EP 103 7258 Al.

It is an object of the present invention to provide a high intensity discharge lamp in which the color point of the emitted light lies within the white region according to ECE R98 and ECE R99 even during the run-up.

In the case of the white light according to the invention ("white region" according to ECE R98 (Section 6.1) and ECE R99 (Section 3.9)), the color features must lie within the range which is defined by the following limit values: against blue x> 0.310 against yellow x < 0.500 against green x < 0.150 + 0.640 x against green y < 0.440 against violet y > 0.050 + 0.75O x against red y > 0.382

The x, y value of the color location of the xenon HID lamp in the stable operating state is intended to lie within the partial range of the ECE white region: x > 0.345; y < 0.150 + 0.640 x x < 0.405; y > 0.050 + 0.750 x according to ECE regulation R99, measured after 15 seconds.

The value of the color location which is preferred in this respect should be x = 0.375 and y = 0.375.

An ionizing gas filling within the context of the invention comprises at least one customary noble gas, such as for example xenon (Xe), and also 0 mg to 10 mg of mercury.

A color temperature in the "white region" allows the vehicle driver to see better, in particular in poor weather conditions, for example in fog. The visible white light emitted by the high intensity discharge lamp according to the invention is better adapted to the natural sensitivity of the human eye, so that overstressing and thus associated tiring of the eyes is prevented. In particular, this results in greater traffic safety.

The high intensity discharge lamp according to the invention can be used for lighting purposes of a general nature. In particular, the high intensity discharge lamp can be used as a light source for example in transport means such as aircraft, motor vehicles, motorcycles or the like.

The use of the high intensity discharge lamp for headlamps, in particular for front headlamps in motor vehicles, such as cars, is particularly preferred.

The object of the invention is achieved by a high intensity discharge lamp having the features as claimed in claim 1. It is essential to the invention that the metal halide mixture contains at least

0.01 to 0.07 μg/mm³ of InI. It has surprisingly been found that the aim of the invention can be achieved during run-up and in continuous operation only if InJ in the aforementioned narrow range is added to the metal halide mixture.

It is furthermore preferred that the gas filling contains no mercury. It is also preferred that the gas filling contains at least Na, Sc and/or Zn halides.

The invention is also achieved by a lighting unit which contains at least one headlamp comprising at least one high intensity discharge lamp as claimed in claims 1 to 3.

The invention will be further described with reference to examples of embodiments shown in the drawings to which, however, the invention is not restricted.

Fig. 3 shows a high intensity discharge lamp according to the invention with a bulb and an outer tube. Fig. 4 shows a CIE 1931 diagram for the "white region" of the high intensity discharge lamp shown in Fig. 3.

Fig. 3 schematically shows, in section, a lamp tube 1 with a discharge space 2 of a xenon HID high intensity discharge lamp for a front headlamp of a car. The one-piece lamp tube 1, which hermetically seals the discharge space 2 filled with a customary ionizing gas filling and the material of which is usually quartz glass, comprises two cylindrical regions of the sealed areas 31, 32 which lie opposite one another, between which there is an essentially elliptical region 33. The discharge chamber 2 has a volume of approx. 20 mm³.

The electrode arrangement comprises essentially a first electrode 41 and a second electrode 42, between the opposed tips of which in the discharge chamber 2 an arc discharge is produced, wherein the arc serves as a light source of the high intensity discharge lamp. The electrode spacing is approx. 3.6 mm. The electrodes 41, 42 consist mainly of a tungsten material and are shaped in a cylindrical manner.

The ends of the electrodes 41, 42 are connected to the molybdenum wires 61, 62 via the molybdenum tapes 51, 52. The molybdenum wires 61, 62 are furthermore connected to the electrical terminals of the lamp (not shown in Fig. 3), via which the supply voltage required to operate the lamp is fed by a power supply, possibly with a ballast, designed for a general mains voltage.

The ionizing gas filling comprises at least one customary noble gas, in this case xenon (Xe) at 8 bar (at room temperature), but no mercury (Hg). The following are also contained in the gas filling as metal halide mixture (salt):

NaI: 147 μg (7.35 μg/mm³) ScI₃: 86.4 μg (4.32 μg/mm³)

ZnI₂: 60 μg (3 μg/mm³)

InI: 0.6 μg (0.03 μg/mm³)

ThI₄: 6 μg (0.3 μg/mm³)

The overall metal halide mixture comprises approx. 300 μg. In Fig. 4, the spectral region according to the invention, which corresponds to the standard ECE R99 for light in the "white region", is shown as an area, within the dashed line, in the CIE 1931 diagram.

Also plotted in a CIE 1931 diagram in Fig. 4 is a curve, determined during laboratory experiments, of a mercury-free high intensity discharge lamp according to the invention, as shown in Fig. 3, said curve being produced in the run-up phase, in this case approximately between 2 to 12 seconds after the cold start.

After approx. 2 seconds from the cold start, the color location can be described (Fig. 4) by x = 357 and y = 363; after approx. 6 seconds it can be described by x = 334 and y = 315. The indium content in the metal halide mixture of the ionizing gas filling of this lamp is approx. 0.035 μg/mm³.

When the lamp cools, a small amount of salt usually condenses on the electrodes. In the first half-second after ignition, that is to say during run-up of the lamp, this salt is evaporated by the electrodes, and therefore the color location is initially relatively high. This salt initially deposits as a condensate on the cold quartz wall of the lamp tube. The lamp or the color location thereof is thus determined essentially as xenon at this point in time.

After approximately 6 seconds of run-up, the color location reaches a minimum. The run-up power heats up the lamp. The temperature of the coldest spot, where the condensate has deposited, increases and the salt evaporates again. As a result, the values (x, y values in the CIE 1931 diagram) of the color point increase again. A stable color location is usually achieved after approximately 60 seconds in these lamps.

Claims

CLAIMS:

1. A high intensity discharge lamp (1), at least

- comprising a bulb (2) which has a discharge chamber,

- comprising two electrodes which extend into the discharge chamber,

- comprising an ionizing gas filling in the discharge chamber, which contains at least one noble gas and a suitable metal halide mixture,

- and comprising an outer tube (3) which is fixed to the bulb (2), characterized in that the metal halide mixture contains at least 0.01 to 0.07 μg/mm³ of InI.

2. A high intensity discharge lamp as claimed in claim 1, characterized in that the ionizing gas filling contains no mercury.

3. A high intensity discharge lamp as claimed in claim 1, characterized in that the gas filling contains at least Na, Sc and/or Zn halides.

4. A lighting unit which contains at least one headlamp comprising at least one high intensity discharge lamp as claimed in claims 1 to 3.