EP1417700A2

EP1417700A2 - Tubular discharge lamp with ignition aid

Info

Publication number: EP1417700A2
Application number: EP02753000A
Authority: EP
Inventors: Gerhard DÖLL
Original assignee: Patent Treuhand Gesellschaft fuer Elektrische Gluehlampen mbH
Current assignee: Osram GmbH
Priority date: 2001-08-17
Filing date: 2002-07-09
Publication date: 2004-05-12
Also published as: TW569281B; KR100895369B1; WO2003019616A3; DE10140356A1; WO2003019616A2; US6960874B2; US20040021411A1; KR20040021571A; JP4272517B2; CA2429386A1; JP2005500664A

Abstract

A dielectric barrier discharge lamp (1) comprises a tubular discharge chamber (2), a fluorescent layer on at least one part of the inner wall of the discharge chamber (2) and longitudinal electrodes (3). A coating (10) is provided on a partial region of the inner wall at least at one end of the tubular discharge chamber (2), which, in addition, covers one end of at least one longitudinal electrode (3). The material of said coating (10) has a high secondary electron emission coefficient. The ignition behavior of the lamp is thus improved, especially on ignition in darkness.

Description

Tubular discharge lamp with ignition aid

Technical field

The invention relates to a dielectric barrier discharge lamp with a tubular discharge vessel and a phosphor layer.

Dielectric barrier discharge lamps are sources of electromagnetic radiation based on dielectric barrier gas discharges.

The discharge vessel is usually filled with an inert gas, for example xenon, or a gas mixture. So-called excimers are formed during the gas discharge, which is preferably operated by means of a pulsed operating method described in US Pat. No. 5,604,410. Excimers are excited molecules, such as Xe2 *, which emit electromagnetic radiation when they return to the generally unbound basic state. In the case of Xe ₂ *, the maximum of the molecular band radiation is approximately 172 nm (NUN radiation). The phosphor layer is used to convert the invisible NUN radiation into visible (NΙS) radiation (light).

Such lamps are used in particular in devices for office automation (OA = Office Automation), e.g. color copiers and scanners, for signal lighting, e.g. as brake and direction indicator lights in automobiles, for auxiliary lighting, e.g. interior lighting for automobiles, and for the backlighting of Displays, for example liquid crystal displays, are used as so-called “edge type backlights”. In these technical fields of application, particularly short start-up phases, but also temperature-independent luminous fluxes are required. That is why these lamps do not contain mercury.

Both high luminance and uniform luminance over the length of the lamp are necessary for the applications mentioned. For OA use, the inner wall of the discharge vessel is usually provided with a NUN / NIS reflection layer, for example A1 ₂ Ü3 and / or Ti0 ₂ . An aperture extending along the longitudinal axis of the lamp remains free of reflection layers, since the NUN / NIS reflection layer is also impermeable to the light emitted by the phosphor layer. The actual phosphor layer is located on the NUN / VTS reflection layer, and the aperture can optionally also be coated with phosphor or free of phosphor. In any case, due to the NUV / NIS reflection layer, the desired high luminance can be generated within the aperture without the reflection layer.

A dielectric barrier discharge lamp necessarily requires at least one so-called dielectric barrier electrode. A dielectric barrier electrode is separated from the inside of the discharge vessel by means of a dielectric barrier. This dielectric barrier can be designed, for example, as a dielectric layer covering the electrode, or it is formed by the discharge vessel of the lamp itself, namely when the electrode is arranged on the outer wall of the discharge vessel.

Because of the dielectric barrier, a time-variable voltage between the electrodes is required for the operation of such lamps, for example a sinusoidal AC voltage or pulse-shaped voltage as disclosed in the aforementioned US Pat. No. 5,604,410. State of the art

A dielectric barrier discharge lamp of the type mentioned at the outset is disclosed in US Pat. No. 6,097,155. The lamp has a tubular discharge vessel, on the inner and / or outer wall of which at least two elongate, conductor-like electrodes are arranged parallel to the longitudinal axis of the discharge vessel. However, the long ignition delay after the voltage is applied to the electrodes of the lamp when the lamp is in the dark, for example within an OA device, is disadvantageous. After a long period of time in the dark, it may even happen that the lamp can only be ignited with a voltage that is significantly higher than in normal operation.

DE-A 4203 594 discloses a lamp with a discharge tube which has a transparent tube filled with a discharge gas and two electrodes which produce a spatial discharge in the tube, the two electrodes running essentially parallel to the length of the tube and the one electrode is centrally located axially inside the tube and the other outside the tube. In addition, the surface of the inner electrode and / or the inner side of the tube is coated with a coating material made of a metal with a high secondary emission ratio and / or a dielectric. Rare earth oxides, aluminum oxide (A1 ₂ 0 ₃ ), silicon oxide (Si0 ₂ ) or magnesium oxide (MgO) is used as the coating material. The more preferred coating material is magnesium oxide, which can also act as a protective layer. Disadvantages of this lamp are, on the one hand, shadowing by the rod-shaped inner electrode, and on the other hand the small proportion of the phosphor layer based on the total area of the inner wall of the discharge vessel, which inevitably leads to a loss in the luminous flux of the lamp in relation to the maximum possible luminous flux. In DE-A 42 03 594 it is namely provided that along the discharge vessel, the upper half of the inner wall of the vessel is coated with a phosphor and the lower half with a layer with a high secondary electron emission coefficient (combination of the two FIGS. 4A and 4B).

Presentation of the invention

The object of the present invention is to provide a dielectric barrier discharge lamp with a tubular discharge vessel and a phosphor layer according to the preamble of claim 1, which has an improved ignition behavior.

This object is achieved in a lamp with the features of the preamble of claim 1 by the features of the characterizing part of claim 1. Particularly advantageous configurations can be found in the dependent claims.

The dielectric barrier discharge lamp according to the invention has a tubular discharge vessel and a phosphor layer on at least part of the inner wall of the discharge vessel. In addition, elongated, dielectrically impeded electrodes oriented parallel to the longitudinal axis of the discharge vessel are arranged on the vessel wall. At least one end of the tubular discharge vessel is provided on a partial region of the inner wall with a coating which also covers one end of at least one elongate electrode, the material of this coating having a high secondary electron emission coefficient (hereinafter referred to as SEE coating for brevity). The SEE coating is in direct contact with the filling gas enclosed by the discharge vessel. Therefore, the SEE coating is always the last of possibly several functional layers on the inner wall of the discharge vessel, ie each additional layer, for example fluorescent and / or NUN / NIS reflection layer is arranged between the SEE coating and the inner wall of the discharge vessel. In this way it is ensured that the SEE coating is hit by free electrons accelerated in the electrical field of the electrodes and secondary electrons are thereby triggered.

The advantage of this solution is that a large part of the phosphor layer also applied to the inner wall of the discharge vessel is uncoated, i.e. is actually also effective, since the SEE coating is limited to one or both ends of the tubular discharge vessel. In addition, a slight shade at the lamp ends is less of a problem than in the middle of the lamp. The SEE coating is therefore also limited to the area at the end of at least one elongated electrode. However, it does not matter if the coating extends beyond the end of the electrode to the corresponding end of the vessel, since there is no longer any discharge in this area and consequently this area is dark. This dark area is therefore preferably kept as small as possible with regard to the overall length of the lamp. The portion of the inner wall provided with the coating is preferably less than 25%, better less than 10% of the total area of the inner wall along the longitudinal axis of the tubular discharge vessel, i.e. the lateral surface.

In one embodiment, the SEE coating preferably overlaps one end of the elongated electrode, the overlap being in the range of greater than 0 and less than or equal to 10 mm, preferably in the range of greater than 2 and less than or equal to 6 mm. Since it is possible to operate lamps of different lengths due to the transverse discharge configuration, reference should also be made here to the relative overlap, which is typically in the range from greater than 0 and less than or equal to 20%, preferably in the range from greater than 0 and less than or equal to 10 % of the total length of the lamp. In the case of electrodes (inner wall electrodes) arranged on the inner wall of the discharge vessel, as disclosed in the already mentioned US Pat. No. 6,097,155, the overlap initially relates to the end of the electrode opposite the power supply. However, the SEE coating can of course also cover the end of the electrode on the power supply side. At this point, it should only be briefly pointed out that the inner wall electrode, the electrical feedthrough and the power supply are preferably implemented as functionally different areas of a single conductor track-like means. The means similar to a conductor track itself has no structural separation in the electrode, power supply, etc. The individual areas are rather defined by their function. The electrode is consequently the area of the conductor-like means, which is located within the discharge vessel. For further details, reference is made to US Pat. No. 6,097,155 and the exemplary embodiments. In this respect, the term “overlap” at the power supply end of an inner wall electrode is to be interpreted as an overlap.

Another advantage is that the lamp according to the invention is relatively easy to manufacture. Materials which have a secondary electron emission coefficient greater than one, in particular greater than two, preferably greater than 3, particularly preferably in the range between 3 and 15 are suitable for the SEE coating. Powdery Al ₂ θ3 or MgO in a pasty preparation is particularly suitable. The relevant end of the lamp is then simply dipped into the paste until the desired overlap with the corresponding electrode end is achieved. In this case, the SEE coating has the outer shape of a ring. The outer wall of the discharge vessel is advantageously covered during immersion. In principle, however, it is sufficient to improve the ignition behavior if the SEE coating is limited to a relatively small part of a ring, as long as the end of at least one electrode is covered with it. This can be accomplished, for example, by pasting with a suitable tool, for example a brush, possibly with the aid of an appropriate mask. A thin-walled hollow cylinder or longitudinal part of a hollow cylinder is suitable as a mask, the outer diameter of which corresponds approximately to the inner diameter of the discharge vessel. The wall of the hollow cylinder has an opening, the shape of which corresponds to that of the coating to be applied. The hollow cylinder is inserted at the end of the tubular discharge vessel until the opening lies above the electrode end and then the paste is applied inside the opening to the inner wall of the discharge vessel or the electrode end. After the paste has dried and possibly heated, the mask can be removed.

In addition, it is generally sufficient if at least one end of only a single electrode has an SEE coating. If the lamp is intended for operation with unipolar voltage pulses, the SEE coating must be arranged on the anode. Only then can primary electrons be accelerated in the direction of the SEE coating and secondary electrons can be triggered there for the further development of the ignition process. This distinction is irrelevant for lamps for operation with bipolar voltage pulses, since the electrodes change their roles in pairs (instantaneous anode or cathode) depending on the polarity of the instantaneous voltage pulse.

In addition, in bipolar operation, it is advantageous to provide the ends of both electrodes of a pair of electrodes with an SEE coating. This ensures that with every voltage pulse, regardless of its polarity, the current anode is in any case equipped with a SEE Coating is provided and thus a secondary electron emission can take place. This variant also increases the probability of a quick and reliable ignition.

Usually, but not necessarily, the discharge lamp according to the invention has a base at one or both ends. The SEE coating is then advantageously arranged on that part of the inner wall of the discharge vessel which is located within the base, since in this way there is no longer any additional shadowing from the SEE coating.

In addition, it can be advantageous to provide an SEE coating on both ends of the lamp, since the ignition then ideally starts from both ends. In any case, this variant increases the probability of a quick and reliable ignition. It may be sufficient if both coating zones are narrower than when coating at only one end. In addition, in the case of the variant coated on both sides, it can also be advantageous to design the coating zone in the base region to be wider than in the opposite end without a base. This variant combines the advantages of a stronger ignition in the wide coating zone in the base area with a slight shading of the narrower coating zone at the base-free end of the lamp.

Brief description of the drawings

The invention is to be explained in more detail below with the aid of two exemplary embodiments. Show it:

Figure la is a plan view of a first embodiment,

FIG. 1 b shows a cross section of the exemplary embodiment from FIG. 1 a along the line DD, Figure 2 shows a second embodiment.

Preferred embodiment of the invention

Figures la and lb schematically show a rod-shaped fluorescent lamp 1 in plan view or in cross section along the line DD. The lamp 1 consists essentially of a tubular discharge vessel 2 made of soda-lime glass with a circular cross section and two strip-shaped electrodes 3 (the second electrode is covered and therefore not visible) made of silver solder, which is arranged parallel to the longitudinal axis of the tube and diametrically arranged to one another on the inside of the wall of the Discharge vessel 2 are applied. Each of the inner wall electrodes 3 is covered with a dielectric barrier 4 made of glass solder. Furthermore, the inside of the wall of the discharge vessel is covered with a phosphor layer 5 and, with the exception of an aperture extending along the longitudinal axis of the lamp, with the VUV / VIS reflection layer 6 made of Al ₂ θ3 below the phosphor layer 5 (for illustrative reasons only in FIG. 1b shown).

A first end of the discharge vessel 2 is closed by means of a blunt fusion 7. The two electrodes 3 end at a distance A = 5 mm before this fusion 5. The electrodes 3 are passed gas-tight to the outside through the other end of the discharge vessel 2 and pass there into an external power supply 8. The second end of the discharge vessel 2 is closed by means of a plate-shaped closure element (not visible in this illustration). For this purpose, the edge of the plate-shaped closure element is fused with a constriction 9 of the discharge vessel 2. For further details, reference is made to DE-A 10048410, the disclosure content of which is hereby incorporated by reference. Due to the aforementioned technology, the inner wall electrode 3, the electrical leadthrough in the area the constriction 9 and the power supply 8 are realized as functionally different areas of a single conductor strip-like silver solder strip.

At the first end of the discharge vessel 2, an annular coating 10 of width B = 10 mm — viewed in the direction of the longitudinal axis of the discharge vessel 2 — made of MgO (porous magnesium oxide) is applied to the inner wall, more precisely directly on the phosphor layer 5. The ring-shaped MgO coating 10 closes on the one hand directly with the end 5 of the discharge vessel 2 and was produced by immersing this end of the vessel in an MgO paste. On the other hand, the width B of the ring-shaped MgO coating 10 was chosen such that the ring covers the end of the electrodes 3 by the overlap C = 5 mm (= B minus A). This ensures that the MgO ring 10, as a secondary electron emitter, improves the ignition properties of the lamp 1. At the same time, shadowing by the MgO ring 10 is limited to an annular partial area with a width B of only 5 mm. This is only approx. 1.5% based on the total light length of the lamp 1 of 350 mm (measured from the constriction 9 to the end of the electrodes 3).

FIG. 2 shows a schematic top view of a variant of the embodiment of FIGS. 1 a, 1 b (the same features are provided with the same reference numerals), in which an MgO coating in the form of two short 5 mm wide partial rings 11 on the plate seal or Constriction 9 directly adjacent ends of both electrodes 3 are applied. More precisely, each of the two partial rings 11 (one of the two partial rings 11 is covered due to the illustration) is applied to the phosphor covering the electrodes 3 or the dielectric 4. In addition, this end of the lamp 1 is provided with a base, not shown, which covers the two partial MgO rings 11.

Claims

claims

1. Dielectric barrier discharge lamp (1) with a tubular discharge vessel (2) and a phosphor layer (5) on at least part of the inner wall of the discharge vessel (2) and with dielectrically impeded, elongated electrodes (3), which are parallel to the longitudinal axis of the discharge vessel (2) are arranged oriented on the vessel wall, characterized in that at least one end of the tubular discharge vessel (2) is provided on a partial area of the inner wall with a coating (10; 11) which also has an end of at least one elongate electrode ( 3) covered, the material of this coating (10; 11) having a high secondary electron emission coefficient.

2. Discharge lamp according to claim 1, wherein the portion of the inner wall provided with the coating (10; 11) is less than 25%, better less than 10% of the total area of the inner wall along the longitudinal axis of the discharge vessel (2).

3. Discharge lamp according to claim 1 or 2, wherein the coating has the outer shape of a ring (10) or at least a part (11) of a ring.

4. Discharge lamp according to one of claims 1, 2 or 3, wherein the coating (10; 11) overlaps one end of at least one elongated electrode (3).

5. Discharge lamp according to claim 4, wherein the overlap (D) is in the range of greater than 0 and less than or equal to 10 mm, preferably in the range of greater than 2 and less than or equal to 6 mm.

6. Discharge lamp according to claim 4, wherein the overlap (D) is in the range of greater than 0 and less than or equal to 20%, preferably in the range of greater than 0 and less than or equal to 10%.

7. Discharge lamp according to one of the preceding claims with a base, the coating being arranged on the part of the inner wall of the discharge vessel which is located within the base.

8. Discharge lamp according to one of the preceding claims, wherein the lamp has at both ends a coating of material with a high secondary electron emission coefficient.

9. Discharge lamp according to claim 8 with a base at one end of the discharge vessel, the coating zone at the base end being wider in the direction of the longitudinal axis of the tubular discharge vessel than at the end of the lamp remote from the base.

10. Discharge lamp according to one of the preceding claims, wherein the material of the coating (10; 11) has a secondary electron emission coefficient greater than one, in particular greater than two, preferably greater than 3, particularly preferably in the range between 3 and 15.

11. Discharge lamp according to one of the preceding claims, wherein the coating material (10; 11) comprises powder-like A1 ₂ 0 ₃ or MgO.

12. Discharge lamp according to one of the preceding claims, wherein at least one of the electrodes (3) is arranged on the inner wall of the discharge vessel (2).

3. Discharge lamp according to one of the preceding claims, wherein a VUV / VIS reflection layer (6) is arranged between the inner wall of the discharge vessel (2) and the phosphor layer (5), an aperture extending along the longitudinal axis of the lamp being free of reflection layers ,