EP2390902A1 - Noble gas short arc discharge lamp - Google Patents

Abstract

The lamp has a discharge vessel (1) arranged in an anode (2) and a cathode (3). The discharge vessel comprises a coating (8) in sections for reflection of infrared rays. The coating is provided for visible light. The coating comprises multiple layers made of silicon oxide and niobium oxide in an alternative manner, where the coating ranges from 37 to 80 layers. The coating is adjacently attached to the anode at the discharge vessel. The discharge vessel is coated to a large extent or completely. The discharge vessel is filled with pure xenon gas.

Description

Technical area

The invention is based on noble gas short arc discharge lamps according to the preamble of patent claim 1.

The term noble gas short-arc discharge lamp here refers to short-arc discharge lamps with a discharge vessel made of quartz glass, which is filled exclusively with a noble gas or noble gas mixture. Such lamps are usually operated with direct current or pulsed direct current. These lamps are suitable for a variety of applications, in particular for the cinema projection, effect and searchlights, as well as microscopy and endoscopy.

State of the art

As a measure to increase the luminance of a rare gas short arc discharge lamp (AC, DC, pulsed operation), it is known in the prior art, for example, to increase the pressure in the discharge vessel. However, the ignition behavior of the discharge lamp changes negatively, since the required ignition voltage (cold ignition and hot re-ignition) increases.

The patent EP 1 217 644 B1 shows in the FIG. 1 a generic noble gas short arc discharge lamp with xenon filling for the cinema projection.

Presentation of the invention

The object of the present invention is to provide a noble gas short-arc discharge lamp whose cold-ignition behavior is improved while the luminance remains the same or whose luminance is increased with constant cold-ignition behavior. This object is achieved by a noble gas short-arc discharge lamp having the features of patent claim 1.

Particularly advantageous embodiments can be found in the dependent claims.

The noble gas short-arc discharge lamp according to the invention has a discharge vessel and electrodes arranged therein, between which an arc forms during operation of the lamp. According to the invention, the discharge vessel has, at least in sections, a coating for at least partial reflection of the electromagnetic radiation emitted during operation by the lamp components in the discharge vessel and by the excited filling gas, in particular the infrared (IR) thermal radiation. As a result of the IR radiation back reflection caused thereby, the wall of the discharge vessel, the filling gas and the lamp components of the discharge vessel struck by the reversion are additionally heated during operation of the lamp. This leads to an increase in the operating pressure of the filling gas and to an extension of the electrode rods due to the greater thermal expansion and consequently to a shortening of the electrode spacing. By contrast, without the IR reflection coating, the IR radiation would largely be emitted through the discharge vessel into the environment.

These relationships can be used to advantage for the following two goals. The starting point for the following considerations is a conventional reference lamp without IR reflection coating. If now an otherwise identical lamp provided with the inventive IR reflection coating, the filling pressure is higher in operation with the same power consumption than in the reference lamp, whereby the discharge arc contracts more. As a result, and by the shortening of the electrode spacing during operation, a higher luminance is achieved in comparison to the reference lamp.

Alternatively, the resulting due to the above-described heating effect increase the operating pressure of the lamp can be used to lower the cold pressure of the lamp so that the regular operating pressure of the lamp adjusts that would have set even with normal filling without heat reflection coating but at the same power consumption. Due to the lower cold pressure, the advantage is achieved that the necessary ignition voltage (cold ignition and hot re-ignition) of the discharge lamp is lower than in the reference lamp. At the same time, however, due to the IR reflection coating, the filling pressure during operation and consequently the luminance is the same as in the reference lamp.

Particularly good reflection properties in the infrared spectral range and thus optimized thermal insulation of the noble gas short arc discharge lamp according to the invention can be achieved if the reflection coating comprises a layer system with a plurality of layers.

Preferably, one layer of the layer system is alternated between a low refractive index material and a high refractive index material layer.

The layer of the low refractive index material may comprise a material consisting of an oxide or a nitride or an oxynitride of one of the metals Si, Zr, Al, Sn, ZN and mixtures thereof (for example SiO ₂ , ZrO ₂ , Al ₂ O ₃ ). A preferred material for the layer of low refractive index material is SiO ₂ .

The material of the high-refractive-index layer includes, for example, a material of an oxide or a nitride or an oxynitride of one of the metals Nb, Ti, Ta, Hf, and mixtures thereof (for example, Nb ₂ O ₅ , TiO ₂ , HfO ₂ ). , It has proven to be advantageous to use Nb ₂ O ₅ as a layer.

The layer system has at least 30 and at most 80 layers.

Since in DC operation of the noble gas short-arc discharge lamp according to the invention, the anode heats up particularly strong due to their size and therefore emits a lot of heat, it is preferred according to a first embodiment, when an anode adjacent to the region of the discharge vessel is coated.

To as much as possible of the heat produced in the interior of the noble gas short-arc discharge lamp for pressure increase used, it is preferred according to another embodiment, when the discharge vessel is largely or even completely coated. Thus, the entire discharge vessel can be heated in operation by the infrared-reflective effect of the coating. However, the layer system in this case is preferably to be designed so that it is sufficiently transparent to light.

In one embodiment, the discharge vessel is filled with pure xenon gas or a xenon-krypton gas mixture.

Brief description of the drawings

• Fig. 1 ein Ausführungsbeispiel einer Xenon-Kurzbogen-Entladungslampe(XBO) mit erfindungsgemäßer Beschichtung;
• Fig. 2 ein Reflexions-Diagramm; und
• Fig. 3 ein weiteres Ausführungsbeispiel einer Xenon-Kurzbogen-Entladungslampe.

In the following, the invention will be explained in more detail with reference to exemplary embodiments. The figures show:

• Fig. 1 an embodiment of a xenon short arc discharge lamp (XBO) with inventive coating;
• Fig. 2 a reflection diagram; and
• Fig. 3 Another embodiment of a xenon short-arc discharge lamp.

Preferred embodiment of the invention

FIG. 1 shows a section of an embodiment of a designed for DC operation (DC) with a power consumption of 450 W rare gas short arc discharge lamp in a view. The lamp has a discharge vessel 1 made of glass in which an anode 2 and a cathode 3 are arranged at a distance from one another are. The two electrodes 2, 3 are held in the discharge vessel 1 via respective electrode rods 4, 6. The electrode rods are in turn mounted in the respective end regions of the lamp or guided gas-tight to the outside to be able to be connected to external power supply lines (not shown). The discharge vessel 1 is filled with pure xenon gas at a cold filling pressure of 10 bar. This corresponds to the cold filling pressure of a conventional 450 W xenon short arc lamp.

In the region of the anode 2, the outside of the discharge vessel 1 is provided with a coating 8. The coating 8 consists alternately of silicon oxide (SiO ₂ ) and of niobium oxide (Nb ₂ O ₅ ) layers. These layers have significantly different refractive indices.

To operate the noble gas short-arc discharge lamp according to the invention, an arc is initially ignited via a comparatively high ignition voltage between the two electrodes 2, 3, which arc extends through the xenon gas. The burning voltage that occurs between the electrodes after ignition is significantly lower than the ignition voltage. In operation, in the discharge vessel 1 and in particular by the hot anode 2, infrared heat radiation is generated, which increases the gas pressure in the entire discharge vessel 1. The heat radiation is incident in part on the coating 8 and is largely reflected by this back into the discharge vessel 1. The coating 8 is largely transparent to visible light. By the reflection of the heat radiation, the interior of the discharge vessel 1 is further heated, whereby the operating pressure is further increased. This leads to a narrowing (concentration) of the arc and specifically the point of highest luminance directly in front of the cathode tip (hot spot) which in consequence increases the luminance of the arc and the hot spot luminance in an advantageous manner.

FIG. 2 shows a reflection diagram of the rare gas short arc discharge lamp. In this case, the percentages of the radiation reflected back into the discharge vessel 1 are applied over different wavelengths of the radiation emitted by the interior of the noble gas short arc discharge lamp. The visible light range of approx. 400 to 700 nm is plotted in the diagram on the left.

A comparatively thick curve 10 represents the nominal spectrum of the coating 8 (cf. Fig. 1 ), while the three different thinner curves 12a, 12b, 12c show the proportion of the reflected radiation at three different exemplary measuring points of the noble gas short arc discharge lamp coated according to the invention.

In the range of the wavelength from about 1050 to about 1200 nm, no measured values are available due to a change in the measuring range of the spectrometer.

The diagram shows a low reflection in the visible light range through the coating 8, while in the infrared range (up to 2100 nm) the majority of the thermal radiation is reflected by the coating 8 back into the discharge vessel 1.

During operation, the infrared-reflecting (IR) coating 8 according to the invention produces an increased operating pressure in the discharge vessel 1, which increases by about 10% which results from comparable noble gas short arc discharge lamps (according to the prior art) increased luminance.

In an alternative variant of the above-described embodiment of a 450 W xenon short-arc discharge lamp, the cold filling pressure of the discharge vessel is reduced by approximately 10% to approximately 9 bar. As a result, the necessary ignition voltage (cold ignition and hot re-ignition) of the discharge lamp is lowered by about 15%. This reduces the device complexity (ignitors, wiring). In operation, due to the IR reflection coating, the gas pressure increases to the operating pressure originally provided for this type of lamp. As a result, despite the reduced cold filling pressure, the luminance achieved in the conventional counterpart without IR reflection coating is achieved.

FIG. 3 shows a section of another embodiment. It is also a 450 W xenon short-arc discharge lamp 1. In contrast to the in the Fig. 1 However, the IR reflection coating is not limited here to the area of the lamp vessel around the anode 2. On the anode side, the IR reflection coating 81 extends substantially in the region of the tip of the anode 2 along the anode rod 4. In addition, the lamp in Fig. 3 also on the cathode side on the outside of the lamp vessel to an IR reflective coating 82, which extends substantially along the cathode rod 6. Due to the expansion of the IR reflection coating of the lamp vessel on the region of the electrode rods 4, 6 is achieved that IR radiation on the electrode rods 4, 6 is reflected back and these are additionally heated. Due to the additional heating of the electrode rods 4, 6, these expand in length, whereby the distance between the anode 2 and cathode 3 is shortened. The shorter electrode distance contributes - as the above in the Fig. 1 explained gas pressure increase - also to a higher luminance at. In this way, an increase in luminance of about 10% is achieved with the help of the two effects of operating pressure increase and electrode rod expansion.

Claims (9)

Noble gas short arc discharge lamp with a discharge vessel (1) and arranged therein electrodes (2, 3), characterized in that the discharge vessel (1) at least in sections, a coating (8) for reflection of infrared rays. A noble gas short arc discharge lamp according to claim 1, wherein the coating (8) is transparent to visible light. A noble gas short arc discharge lamp according to any one of the preceding claims, which is a high pressure or high pressure rare gas short arc discharge lamp. Noble gas short-arc discharge lamp according to one of the preceding claims, wherein the coating (8) comprises a plurality of layers. Noble gas short arc discharge lamp according to one of the preceding claims, wherein the coating (8) has 37 to 80 layers. The noble gas short arc discharge lamp of claim 5, wherein the layers alternately comprise silicon oxide and niobium oxide. Noble gas short arc discharge lamp according to one of the preceding claims, wherein the coating (8) to an anode (2) adjacent to the discharge vessel (1) is mounted. Noble gas short arc discharge lamp according to one of claims 1 to 6, wherein the discharge vessel (1) is largely or completely coated. Noble gas short arc discharge lamp according to one of the preceding claims, wherein the discharge vessel (1) is filled with pure xenon gas.

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