EP2673796B1 - High-pressure discharge lamp having an ignition aid - Google Patents

Description

Technical area

The invention relates to a high-pressure discharge lamp according to the preamble of claim 1. Such lamps are in particular high-pressure discharge lamps for general lighting.

State of the art

From the US 5,811,933 a high-pressure discharge lamp with a ceramic discharge vessel is known in which a starting aid is used. The ignition aid is a so-called UV enhancer. Something similar is over DE 20 2010 011 029 known. There, a foil electrode is described.

It is also known that the distance of the inner electrode of the UV enhancer to the inner wall has a significant influence on the ignition voltage of the UV enhancer. WO 2010/131574 shows embodiments of a geometry variation of the inner electrode. There, in addition to the molybdenum foil, a further metallic component is introduced into the UV enhancer, which promotes the charge transport of the dielectrically impeded discharge. This is costly.

The document JP 2011-009090 A discloses a high pressure discharge lamp with a UV enhancer as an ignition aid. The UV enhancer has a UV-transparent can-like quartz glass container which is accommodated in an outer bulb of the high-pressure discharge lamp. The quartz glass container serves as a discharge vessel. For this purpose, the container encloses with its inner wall a cavity which is filled with a noble gas which can radiate W radiation. In addition, an inner electrode is arranged in the cavity, which has a bend or a kink. The inner electrode is housed in the cavity so that the bend or kink comes close to the inner wall of the container. On the outer wall of the container, an external electrode is mounted.

The document JP 2008-135194 A also discloses a high-pressure discharge lamp of the aforementioned type.

Presentation of the invention

The object of the present invention is to provide a high-pressure discharge lamp whose ignition is reliable.

This is especially true for metal halide lamps, where the material of the discharge vessel is quartz or ceramic.

This object is achieved by the characterizing features of claim 1.

Particularly advantageous embodiments can be found in the dependent claims.

UV radiation is used for the reliable ignition of krypton85-free high-pressure discharge lamps. This is often provided by UV enhancers. Reliable ignition of all high-pressure discharge lamps requires UV radiation in the wavelength range <280 nm. A lower threshold of about 160 nm results from the transmission range of the discharge vessel (quartz or ceramic). To solve this problem are mainly mercury-containing UV enhancer with radiation in o.g. Range, in particular at a wavelength of 254 nm have been used. To reduce the mercury content in high-pressure discharge lamps, UV enhancers without mercury with corresponding UV emission are necessary.

The vessel of the UV enhancer may consist of quartz or another UV-transparent glass, especially toughened glass. Also solutions with a UV enhancer, in which the discharge vessel made of ceramic, are possible, provided that the discharge vessel is translucent in the UV.

In the case of a quartz glass discharge vessel, a molybdenum foil is provided which ensures the gas-tight passage through the quartz glass and acts as a power supply. At the same time, it is the inner electrode of the UV enhancer. In the case of the UV-transmissive glass, the power supply through the glass can also be done with a wire or pencil. In a ceramic discharge vessel, appropriate techniques are used as well known from the construction of ceramic discharge vessels.

The ignition voltage of the UV enhancer is directly dependent on the distance between the inner electrode and the inner wall of the discharge vessel. This results in different solutions for different basic technologies.

For UV enhancer with discharge vessel made of quartz glass, the following embodiments are advantageous.

The part of the molybdenum foil, which is arranged inside the discharge vessel, is partially or completely bent. Thus, the distance to the inner wall is kept low.

It is particularly preferred if the molybdenum foil can be clamped by a spring action between opposite inner walls of the normally cylindrical discharge vessel. This reduces the distance to the inner wall to the conceivable minimum.

A high probability of a discharge in the UV enhancer is obtained in the area where the highest electric field strengths occur at the internal electrode. This is effectively achieved where there is the least distance between the external electrode and the inner electrode of the UV enhancer. For a high UV intensity of the UV enhancer, it is desirable to provide as many places as possible, at which there is a very small distance.

Another possibility is to reduce the distance of the inner molybdenum foil to a pump tip of the discharge vessel made of quartz glass.

High field strengths are generally favored by film edges that are as sharp as possible.

Preferably, the molybdenum foil used is doped, in particular with yttrium oxide, in particular with 0.2 to 2 wt .-%. Further advantageous oxides are cerium oxide and lanthanum oxide. These mentioned oxides can also be used in a mixture.

As filling conventional fillings can be used, in particular noble gases such as argon, Penninggemische such as argon other noble gas or mixtures of noble gases and halogens or halogen compounds such as dibromomethane in particular.

It is known that fluorine attacks glass. Therefore, fluorine compounds can preferably be used only in a ceramic UV enhancer or in a coated glass flask.

To generate the UV radiation of the halogen dimers Cl ₂ *, Br ₂ * and F ₂ * is a filling of the UV enhancer with 100% chlorine gas and the other above-mentioned gaseous halogen compounds and compounds with sufficient vapor pressure possible. But even with the addition of unmixed or mixed noble gases (helium, neon, argon, krypton and xenon), the halogen dimer radiation can be generated.

To generate the noble gas-halogen excimers ArCl *, KrCl *, ArF *, KrF *, ArBr * and KrBr *, the gaseous halogen compounds are mixed with the corresponding noble gases. In some cases, combinations of noble gases can also be mixed in here.

The pressure of the filling gas in the UV enhancer is in the range 1 mbar to 1 bar. The intensity of the generated UV radiation typically increases with the filling pressure, so that an upper limit for the pressure results from the ignition voltage of the UV enhancers, which must be designed for the ignition and operating devices of the lamp.

In principle, the realization of UV enhancers with two electrodes is possible, including the installation of other components, such as a capacitor ( US 4,987,344 ) or even more complex controls ( US 4,721,888 ) is possible to limit the current through the UV enhancer. In general, however, UV enhancers have prevailed which have an inner and an external electrode and use a dielectrically impeded discharge. These UV enhancers are relatively inexpensive.

Brief description of the drawings

Fig. 1

eine Hochdruckentladungslampe mit Zündhilfe, schematisch (Figur la) und im Ausschnitt (Figur 1b);

Fig. 2

verschiedene Ausführungsbeispiele eines UV-Enhancers in Quarzglasausführung (Figur 2a-d,f,h); sowie keinen Bestandteil der Erfindung bildende Alternativen (Fig. 2e,g) ;

Figur 3

die Draufsicht auf ausgewählte Ausführungsbeispiele aus Figur 2.

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

Fig. 1

a high-pressure discharge lamp with ignition aid, schematically (FIG. 1 a) and in the cut-out (FIG. FIG. 1b );

Fig. 2

Various embodiments of a UV enhancer in quartz glass execution ( Figure 2a-d . f . H ); and no alternatives forming part of the invention ( Fig. 2e . G );

FIG. 3

the top view of selected embodiments FIG. 2 ,

Preferred embodiment of the invention

In FIG. 1 a metal halide lamp 1 is shown schematically (Figure la), in which a discharge vessel 2 of PCA is contained in an outer bulb 3 made of quartz glass, which is closed with a base 4. The discharge vessel 2 has two ends, sit on the capillaries 5.

The discharge vessel 2 is provided with a metal halide filling, as known per se. It is supported in the outer bulb 3 by means of a frame 6, which has a short frame wire 7 and a long hanger wire 8. On a first capillary 5 sits a UV enhancer 10, which is connected to the short frame wire 7 via a feed line 11. The counter electrode to it, also called external electrode, is a foil strip 9, which extends from the hanger wire 8 to the UV enhancer 10 and this surrounds a semicircle. In principle, a wire or a sufficient proximity of the stirrup wire to the UV enhancer 10 for the function of the counter electrode is sufficient. Preference is given to the smallest possible distance as well as the largest possible contact area, which includes not only a tip, but at least a quarter circle to a semicircle, as in FIG. 1b shown.

FIG. 2a shows in detail a container or discharge vessel 12 of the UV enhancer 10. The container 12 is in principle a can or cup-like tube made of quartz glass with side wall 13, bottom part 14 and dome 15. The container can also be made of hard glass. Essential to the invention is that the container 12 is a filling of halogen gas, or halogen gas combined with noble gas, in particular a Penninggemisch or argon having.

The container 12 has a tubular cavity 17, in which from one side, the bottom part 14, an electrode 18 protrudes. The electrode is sealed in a pinch 16 associated with the bottom part 14.

The length of the electrode 18 in the container 12 is considerably longer than the length L of the cavity 17. It is preferably at least 20% longer than L. In this case, the electrode 18 according to FIG. 2a bent in the cavity so that it rests resiliently on two opposite side walls. The electrode thus has a bend near the bend.

In any case, the cavity 17 must be large enough to accommodate the single electrode 18, the UV enhancer operating on the dielectrically impeded discharge principle.

The electrode 18 is a pin or preferably a foil, usually made of W or Mo. It has attached a contact wire 11 at the outer end 19, see FIG. 1 , The electrode 18 is inserted into the cavity 17. Then, a filling gas is filled into the cavity 17 and the cavity, in particular with a pinch 16, closed.

In FIG. 2b an embodiment is shown in which the electrode has a kink, which sits in the vicinity of the dome 15.

In Figure 2c an embodiment is shown, in which the electrode 18 is cut in the axis and thereby forms an axial trunk 19 and two branches 20. The two branches 20 are bent to two sides. Of course, this shape can also be generated in other ways, for example, by attaching to a trunk 19 two separate branches or more branches.

In Figure 2d an embodiment is shown in which the electrode 18 is cut in the axis and thereby forms an axial stem 19 and two branches 20. The two branches 20 are bent to two sides. Of course, this shape can also be generated in other ways, for example, by attaching to a trunk 19 two separate branches or more branches.

In an alternative that does not form part of the invention, it is according to FIG. 2e the container 12 is provided with a thickened dome 25. The sheet-like electrode 18 abuts with its tip 26 on the inner wall of the thickened dome. This embodiment is made by compressing the silica glass toward the pinch 16 during the process of fusing the pump tip forming a dome. Due to a reduced pressure compared with the atmospheric pressure, the doughy glass of the pump tip is drawn into the interior of the UV enhancer during melting. The boundary conditions for the bulbous concerns of the Mo film to the cylindrical wall is the smallest possible thickness of the Mo film. Typically, Mo films are used with thicknesses <20 .mu.m, in particular 5 to 20 .mu.m, which then have a low rigidity and can easily bulge out through the overlying pump tip.

Alternatively, according to FIG. 2f a similar embodiment shown in which the film top edge 27 is embedded in the dome 25, which is formed by melting. For this variant, the length of the film is preferably settled in the range of 115 to 130% of L.

An embodiment which does not form part of the invention is disclosed in Figure 2g shown. In this case, the sheet-like electrode 18 is bent several times. It can also be compressed here in the process of melting the thickened dome 25, so that there are several break points 30 at which the electrode 18 approaches the inner wall of the container.

A concrete embodiment of the filling is a UV enhancer, in which krypton with a 0.5% by volume admixture of chlorine gas Cl _{2 is} used as filling gas. The UV enhancer shows strong UV radiation of the excimer line KrCl * at a wavelength of 222 nm. The cold filling pressure is in the range 500-700 mbar.

The embodiments of the FIG. 2 In principle, each work well for interacting with external electrodes. In this case, external electrodes are advantageously used, which surround the UV enhancer in the middle of the cylindrical part of the container 12 and annular in particular, have a planar extension. For example, a foil tape 32 or a flat-pressed wire is used. See the illustration in FIG. 2h ,

A high probability for the formation of a discharge is obtained in an area where the highest possible electric field strengths at the inner electrode 18 result. This can be achieved by the smallest possible distance between the external electrode 32 and the internal electrode 18. For the highest possible intensity of the UV radiation generated by the UV enhancer, it is advantageous to provide as many places as possible at which such a condition is met. Therefore, as many points of contact of the inner electrode 18 to the side wall 13, if possible in the amount of the external electrode 32, desirable.

FIG. 3a shows the embodiments of the FIGS. 2a and 2b in plan view. The width B of the film is preferably 40 to 80% of the inner diameter of the container 12.

FIG. 3b shows the embodiments of the FIGS. 2c and 2d in plan view. The width B of the film is preferably 40 to 80% of the inner diameter of the container 12. The branches 20 are in particular unsymmetrically cut from the film, so that their widths B1 and B2 differs by at least 20%. Where B = B1 + B2.

According to the embodiments according to FIGS. 2a and 2b One obtains four points at which the film-like electrode 18 of the side wall 13 is particularly close or even touched. According to the embodiments according to FIGS. 2c and 2d these are two points.

Typically, the electrode used is a film of molybdenum, which is doped in particular with substances which lower the work function of the electron work. Especially suitable for this purpose is an oxide of yttrium, cerium or lanthanum. Specific embodiments are a doping with 0.5 to 0.7 wt .-% Y2O3, mixed oxides Ce2O3 / Y2O3 or even mixtures Ce2O3 / Y2O3 / La2O3 can be used.

In addition, the Mo foil can be used to lower the ignition voltage using metallic alloys which contain, in particular, at least one element from the group Ru, Ti, Ta, Nb, or with ceramic layers which are selected, in particular, from the group consisting of nitrides, oxides, silicides. or with other readily ionizable materials, in particular tungsten material with very high potassium content, etc., are coated.

In addition, it has proven to be advantageous to roughen at least a portion of the film in the interior, in particular by sandblasting. This improves the ignitability due to the microtips produced thereby.

While conventional UV enhancers typically require an ignition voltage of typically 3.5 kV, an embodiment of the invention can lower the ignition voltage to values typically down to 1 kV.

Fillings with halide-containing filling gases, in particular noble gases with halogen, prevent blackening over the lifetime. They also increase the proportion of excimer radiation. Specific examples are argon with C12 or Br2 or J2. but it is also pure argon as a filling gas. In particular, a halide-containing additive such as dibromomethane (DBM) can be used. A concrete example is argon with an addition of 2000 to 10000 ppm DBM.

Claims (4)

1. High-pressure discharge lamp (1) having an ignition aid, having a discharge vessel (2) which is fitted in an outer bulb (3), wherein a UV enhancer (10) is fitted as an ignition aid in the outer bulb (3), the UV enhancer (10) comprising a UV-transparent can-like container (12) having an inner wall and end side and longitudinal axis, the container (12) enclosing with its inner wall a cavity (17) which is filled with a gas that can emit UV radiation, an inner bent electrode, which is a foil-like electrode (18) having a spring effect and has at least one bend or kink, being fitted in the cavity (17) in such a way that a bend or kink lie as close as possible to the inner wall of the container (12), and wherein an external electrode (9) is applied externally in the vicinity of the container (12), characterized in that the length of the foil exceeds the length of the cavity (17), a free end of the electrode (18) being either bent back against the longitudinal axis or fixed in a front surface of the container (12).
2. High-pressure discharge lamp according to Claim 1 having the mentioned bent-back free end of the electrode (18), further characterized in that the foil-like electrode (18) is divided at its free end into a plurality of branches (20), which are in turn bent back.
3. High-pressure discharge lamp according to Claim 1, characterized in that the external electrode (9) bears on the container (12) at the level of at least one bend or kink.
4. High-pressure discharge lamp according to Claim 1, characterized in that the container (12) is cylindrical.

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