EP0990262B1 - Discharge lamp with dielectrically impeded electrodes - Google Patents

Abstract

A discharge lamp (1) including a tubular discharge vessel (2), filled with inert gas and, optionally, a fluorescent layer, having at least three elongated electrodes (3, 4, 5) arranged parallel to the longitudinal axis of the tubular discharge vessel (2). The electrodes are arranged in such a manner that the relationshipis satisfied, wherein s is the maximum spacing between an imaginary connecting line of an electrode pair and the most closely neighboring point on the wall of the tubular discharge vessel, and a is the mutual spacing between the electrodes of such electrode pair. A higher luminous density is achieved in this way. The lamp is particularly advantageous for a pulsed, dielectrically impeded discharge.

Description

Technical field

The invention is based on a discharge lamp according to the preamble of claim 1. The invention also relates to a lighting system according to the preamble of claim 14 with this discharge lamp.

It is a discharge lamp, in particular also a discharge lamp Fluorescent lamp with all electrodes on the outer wall of the Discharge vessel are arranged. The outer wall serves under other than dielectric layer, which during the operation of the lamp separates the electrodes from the discharge. This type of discharge is called hence double-sided dielectric discharge.

The spectrum of the electromagnetic emitted by this lamp Radiation can affect both the visible area and the UV (ultraviolet) / VUV (vacuum ultraviolet) range and the IR (infrared) range include. A phosphor layer can also be used for conversion be made invisible in visible radiation.

Furthermore, it is a discharge lamp with a tubular, Discharge vessel sealed on both sides. The cross section of the discharge vessel is preferably circular. However, they are only approximate circular cross-sections, for example regular polygons, e.g. Secksecke etc. The term "tubular" is not just tubular here Discharge vessels limited but also includes curved, for example angled, tubular discharge tubes. Because the discharge direction runs essentially perpendicular to the lamp longitudinal axis there is also no general limit on the length of the lamp.

Such lamps are particularly in equipment for office automation (OA = O ffice A utomation), such as color copiers and scanners, for the signal light, for example as brake and turn signal light in automobiles, for the auxiliary lighting, including interior lighting of motor vehicles, and for the Backlighting of displays, for example liquid crystal displays, used as so-called "edge type backlights".

In these technical fields of application, both are particularly short Start-up phases, but also temperature-independent luminous fluxes required. That is why these lamps do not contain mercury. Much more are these lamps usually with noble gas, preferably xenon, or Noble gas mixtures filled.

For the applications mentioned there is both a high luminance as well a uniform luminance over the length of the lamp is necessary. to The lamps for OA use are usually increased in luminance provided with an aperture along the longitudinal axis. To the It is not enough to increase the luminance in previous systems coupled power to increase because the load of a lamp for one permanent and reliable operation cannot be increased arbitrarily can. To make matters worse, the previously in the copiers and Systems used by scanners increase the efficiency of the discharge Power coupling decreases.

State of the art

A noble gas discharge lamp is already known from the document US Pat. No. 5,117,160 OA devices known. On the outer surface of the wall of a tubular discharge vessel are two strip-shaped electrodes along the longitudinal axis of the lamp arranged. The lamp is preferred with AC voltage Frequency operated between 20 kHz and 100 kHz. Operational the 147 nm xenon line is excited. The one with the operating mode used achievable radiation efficiency and consequently the resulting Luminance is relatively low.

From US-PS 5,604,410 it is also known that the efficiency of dielectrically disabled discharges with the help of a on the special conditions (Stroke distance, electrode configuration, electrode geometry, filling gas and filling pressure) adapted pulse operation (pulsed, dielectric disabled Discharge) compared to the dielectric excited with AC voltage disabled discharges (see US Patent 5,117,160) significantly increase leaves.

In EP-A-0 766 286 there is a rare gas discharge lamp with a tubular one Discharge vessel disclosed. The discharge vessel is on the outer wall with three or more strip-like electrodes parallel to the longitudinal axis Mistake. With the exception of one intended for light emission strip-like areas parallel to the longitudinal axis cover the strip-like areas Electrodes cover almost the entire remaining surface area of the discharge tube. The strip-like electrodes are relatively narrow from each other Separate areas that are filled with insulating material. Thereby are supposed to cause sliding discharges on the outer wall between the individual strip-like Electrodes are prevented.

Presentation of the invention

It is an object of the present invention to eliminate the disadvantages mentioned and a discharge lamp according to the preamble of the claim 1, especially a fluorescent lamp, with improved To provide luminance.

This object is achieved by the characterizing features of claim 1 solved. Particularly advantageous configurations can be found in the dependent ones Claims.

For a better understanding of the following, the term "pair of electrodes" is first introduced. Below that are two lines to each other understand parallel electrodes with different polarities during operation, between which a "discharge level" burns during operation. In the event of according to the preferred pulse-like active power coupling US Patent 5,604,410, the discharge plane is a planar discharge structure that consists of a large number of individual discharges.

According to the invention, the discharge lamp has three or more line-like electrodes which are arranged on the outer wall of the tubular discharge vessel of the lamp and parallel to the longitudinal axis of the tubular discharge vessel in such a way that the following relationship is fulfilled: s a ≥ 0.1, where s defines the maximum distance that the imaginary connecting line of an electrode pair has to the next adjacent wall of the discharge vessel and where a defines the mutual distance of the electrodes of this electrode pair (measured in the center from the electrodes). In this context, reference is also made to FIG. 6, which shows the maximum distance s that the imaginary connecting line 20 of a pair of electrodes 3, 4 or 3, 5 has to the next-adjacent wall of the discharge vessel 2, using the example of a discharge lamp 1 with three electrodes 3 - 3. 5 shows schematically.

During operation, at least two discharge levels are generated, which are: between corresponding pairs of electrodes and along the longitudinal axis extend the discharge vessel. In this level are a variety of Single discharges lined up alongside each other along the electrodes, which are in the Borderline transition into a kind of curtain-like discharge form.

The discharge planes can also have a common electrode, for example in the case of three electrodes in which the two electrodes same polarity, only a common counter electrode with an opposite one Have polarity. In other words, two are shared in this case Electrode pairs a common electrode. This is preferred for unipolar ones Voltage pulses are the cathode and the other two electrodes switched as anodes. To increase the luminance of the lamp can increase further discharge levels within the discharge vessel be generated.

In the case of three electrodes, these are preferably arranged, viewed in cross section, at least approximately at the corner points of an imaginary isosceles or equilateral triangle. The latter case has the advantage that the lamp can be manufactured relatively easily, since the lamp only has to be rotated through 120 ° in order to apply the second and third electrodes. In addition, it can be shown on the basis of simple geometric considerations that in this case the quotient s / a always has the value 1 / (2 3 ) ≈0.29, regardless of the lamp diameter, and consequently fulfills the relationship mentioned above. The arrangement in the form of an isosceles triangle, on the other hand, has the advantage that larger striking distances (and therefore higher electrical power coupling, see below) can be achieved for the two discharge levels, provided that the angle formed by the two discharge levels is chosen to be less than 120 °.

With four electrodes, two independent discharge levels can be created or realize three discharge levels with a common electrode, depending on whether the four electrodes as unipolar excitation two cathodes and two anodes or as one cathode and three anodes (or an anode and three cathodes) are connected.

In principle, more than three discharge levels can be created in this way produce. However, it essentially depends on the diameter of the discharge tube depending on whether there are three or more discharge levels at all can still find an electrode arrangement which has the above relationship Fulfills.

With the help of the teaching according to the invention, a higher useful radiation efficiency achieved. Among other things, this is due to the higher electrical power coupling by means of several discharge levels with simultaneously optimized Striking distance of the discharges and low wall losses.

It has been shown that by more than two electrodes can initially couple a higher electrical power into the lamp. Indeed increases the efficiency of the generation of useful radiation with increasing The number of electrodes may decrease again. For this, after the current state of knowledge including increasing wall losses held responsible, namely that of a pair of electrodes generated discharges too close to the inner wall of the discharge vessel run or even a surface sliding discharge is formed. It is also advantageous to aim for the longest possible range, because this increases the ignition or burning voltage and consequently a higher one electrical power can be coupled. For this reason it is Number of electrodes as well as their polarity and positioning dependent to choose the diameter of the discharge vessel so that the above Relationship is satisfied. With an even number of electrodes in principle operation with both unipolar and bipolar voltage pulses suitable for coupling active power according to US Pat. No. 5,604,410. If the number of electrodes is odd, the operation is unipolar Voltage pulses preferred.

Furthermore, it has been shown that the electrode arrangement according to the invention enables relatively high filling pressures of the active discharge gas, typically approximately 20 kPa (150 torr) and more, without any discharge instabilities, for example discharge arcs, which are detrimental to efficient useful radiation generation. The higher filling pressure of the active discharge gas - this includes the gas component that generates the radiation - also contributes to higher useful radiation efficiency. A noble gas, in particular xenon, or a noble gas mixture, for example xenon and krypton, is suitable as the active gas filling within the discharge vessel. In addition, a buffer gas can be added to the active discharge gas, which is not directly involved in the generation of radiation, for example neon. Excimers, for example Xe ₂ * excimers, are produced in the discharge as particles which emit electromagnetic radiation.

Each outer wall electrode is as an electrically conductive, line-like Stripes formed - but which also have a substructure can - and parallel to the longitudinal axis of the tubular discharge vessel oriented. The width of a strip is typically approx. 1 mm and less. In this way, shadowing by three or more electrodes kept small even with small diameter lamps. To the others have shown that this results in higher efficiency in the production of useful radiation is achieved.

In addition, at least part of the inner wall can have a phosphor layer. In addition, one or more reflection layers for visible light, for example made of Al ₂ O ₃ and / or TiO ₂ , can be applied below the phosphor layer. This may prevent some of the light emitted by the phosphor layer from being transmitted through the vessel wall. Rather, the light is essentially directed onto the aperture by reflection or multiple reflection and consequently the luminance is increased there. Alternatively, the phosphor layer itself can also be additionally used as a reflection layer by applying the phosphor layer with a sufficient thickness. In both cases, only a strip-shaped aperture remains uncoated or is only coated with a relatively thin phosphor layer. As a result, the aperture has an increased luminance during operation.

For reasons of protection against contact, it may be advantageous to use the lamp with transparent electrical insulation, e.g. with a see-through Plastic shrink tubing, protective varnish or similar to encase.

Description of the drawings

Fig. 1

einen Querschnitt durch eine erfindungsgemäße Leuchtstofflampe mit Apertur und mit drei Außenwandungselektroden,

Fig. 2

einen Querschnitt durch eine erfindungsgemäße Leuchtstofflampe mit Apertur und mit vier Außenwandungselektroden,

Fig. 3

ähnlich Figur 2, aber mit geänderter Anordnung der Elektroden und Polaritätsverteilung,

Fig. 4

ein Beleuchtungssystem mit der Apertur-Leuchtstofflampe aus Figur 1 und Impulsspannungsquelle,

Fig. 5

qualitativen Vergleich zweier Meßkurven der Lampe aus Figur 1 mit einer Lampe mit nur zwei Außenwandungselektroden.

Fig. 6

eine schematische Prinzipskizze zur Erläuterung des maximalen Abstands s, den die gedachte Verbindungslinie eines Elektrodenpaares zur nächstbenachbarten Wand des Entladungsgefäßes aufweist.

The invention will be explained in more detail below with the aid of several exemplary embodiments. Show it:

Fig. 1

3 shows a cross section through a fluorescent lamp according to the invention with an aperture and with three outer wall electrodes,

Fig. 2

3 shows a cross section through a fluorescent lamp according to the invention with an aperture and with four outer wall electrodes,

Fig. 3

similar to FIG. 2, but with a different arrangement of the electrodes and polarity distribution,

Fig. 4

1 shows an illumination system with the aperture fluorescent lamp from FIG. 1 and a pulse voltage source,

Fig. 5

qualitative comparison of two measurement curves of the lamp from FIG. 1 with a lamp with only two outer wall electrodes.

Fig. 6

is a schematic diagram to explain the maximum distance s, which the imaginary connecting line of a pair of electrodes to the next adjacent wall of the discharge vessel.

FIG. 1 shows a cross section of an aperture fluorescent lamp 1 for OA applications in a highly schematic representation. Here are particular the thicknesses of the wall, the reflective layer and the phosphor as well the width of the electrode strips clearly for illustrative reasons shown enlarged. The lamp 1 consists essentially of a tubular Discharge vessel 2 with a circular cross section and a first, a second and a third strip-shaped electrode 3-5. The inner wall of the discharge vessel 2 points with the exception of a rectangular one Aperture 6 has a reflection layer 7. On this reflective layer 7 as well the inner wall in the area of the aperture 6 is a phosphor layer 8 applied. The discharge vessel 2 is dome-shaped at both ends sealed gastight (not shown). Inside the discharge vessel 2 Xenon is at a fill pressure of approximately 21.33 kPa (160 torr).

The three electrodes 3-5 are designed as metal foil strips. The first The electrode is provided as a cathode 3 and the other two as anodes 4, 5 (unipolar operation). The electrodes 3-5 are viewed in cross section at the corner points of an imaginary isosceles triangle on the outer wall of the discharge vessel 2 arranged. Consequently, in the pulsed operation according to US Pat. No. 5,604,410 two levels with dielectric disabled single discharges from (not shown). A first level of discharge extends within the discharge vessel 2 between the Cathode strip 3 and the first anode strip 4. The other level of discharge extends accordingly between the cathode strip 3 and the second anode strip 5.

The respective width of the anode strips 4, 5 is 0.9 mm. The width of the cathode strip 3 is 0.8 mm. The outer diameter of the tubular discharge vessel 2 made of glass is approximately 9 mm with a wall thickness of approximately 0.5 mm. The width and length of the aperture 6 are approximately 6.5 mm and 255 mm, respectively. The phosphor layer 7 is a three-band phosphor. It consists of a mixture of the blue component BaMgAl ₁₀ O ₁₇ : Eu, the green component LaPO ₄ : Ce, Tb and the red component (Y, Gd) BO ₃ : Eu. The resulting color coordinates are x = 0.395 and y = 0.383, ie white light is generated.

The lamp in Figure 2 - similar features are given the same reference numerals as designated in Figure 1 - has four outer wall electrodes 9-12 on. Of these, two are electrodes as cathodes 9, 10 and the rest two electrodes are provided as anodes 11, 12. The two pairs of electrodes 9, 12 and 10, 11 are arranged on the outer wall such that the both discharge levels burning during operation between a pair of electrodes (not shown) are oriented parallel to each other. adversely is the slightly shorter stroke distance compared to FIG. Indeed this electrically symmetrical arrangement is well suited for a bipolar Business. The aperture 6 is arranged centrally between a pair of electrodes such that the surface normal over large areas of the aperture 6 quasi is oriented perpendicular to the two discharge planes.

The lamp from FIG. 2 is intended for automotive lighting and depending on the phosphor used, for example as a brake light or Flashing light.

The lamp in Figure 3 differs from that in Figure 1 by another Electrode 13, which is arranged between the two anodes and also is provided as an anode. In preferably unipolar pulsed operation A total of three discharge levels are thus formed, in each case between the first cathode 3 and one of the three anodes 4, 13 and 5. The inner wall of the discharge vessel 2 has a phosphor layer 6 on. There is no reflection layer or aperture here.

FIG. 4 shows a lighting system for OA devices. The aperture fluorescent lamp 1 from FIG. 1 additionally points at its second end a base 14. The base 14 consists essentially of a Socket pot 15 and two connecting pins 16a, 16b. The base pot 15 serves primarily the inclusion of the lamp 1. Also inside the base pot 15 the outer wall cathode 3 and the anodes 4 and 5 (from Discharge vessel 2 covered and therefore not visible) with the two connecting pins 16a and 16b connected (not shown). The connector pins 16a, 16b are in turn connected to the two via electrical lines 17a, 17b Poles 18a and 18b of a pulse voltage source 19 connected.

The pulse voltage source 19 supplies a sequence of unipolar voltage pulses with pulse heights of approximately 3 kV and with a repetition frequency of 80 kHz. The pulse duration is approx. 1.1 µs each. With a lamp length of 300 mm, up to approx. 20 W electrical power can be efficiently coupled. When using a pure green phosphor (LaPO ₄ : Ce, Tb), a luminance of approx. 45000 cd / m ^{2 is} achieved with a power consumption of 10 W.

Since this is a dielectric barrier discharge on both sides, is not only the operation with unipolar voltage pulses but also possible with bipolar voltage pulses.

FIG. 5 shows the luminance L [cd / m ² ] measured by the aperture in arbitrary units as a function of the time-averaged electrical power P in W. Curve 20 relates to an illumination system according to FIG. 4 with the operating parameters specified there and three outer wall electrodes. Curve 21 relates to a comparable lamp with only two electrodes. From the figure it can be seen qualitatively that the lamp according to the invention with three electrodes achieves a significantly higher luminance than the conventional lamp with electrical powers of more than 10 W. In addition, curve 20 rises even with an electrical power of 20 W, whereas curve 21 already flattens slightly, ie shows a saturation behavior.

Claims (15)

1. Discharge lamp (1) having an at least partially transparent, closed tubular discharge vessel (2) filled with a gas filling, and having a number of electrodes (3-5, 9-12, 13) which are arranged parallel to the longitudinal axis of the tubular discharge vessel (2) and on the external wall of this discharge vessel (2), characterized in that

   the electrodes (3-5, 9-12) are linear

   the number of electrodes (3-5, 9-12) is three or more, and the following relationship is satisfied:

   s / a ≥ 0.1

   s defining the maximum spacing between the imaginary connecting line (20) of an electrode pair (3, 4; 3,5) and the most closely neighbouring wall of the discharge vessel (2), and a defining the mutual spacing between the electrodes of this electrode pair.
2. Discharge lamp according to Claim 1, it being the case that s / a ≥ 0.2, in particular preferably > 0.25.
3. Discharge lamp according to Claim 1 or 2, the number of the electrodes of one polarity (3) differing from the number of the electrodes of the other polarity (4, 5, 13).
4. Discharge lamp according to Claim 3, the number of electrodes being exactly three.
5. Discharge lamp according to Claim 4, the electrodes (3-5) being arranged, when seen in cross section, at least approximately at the corner points of an imaginary equilateral triangle.
6. Discharge lamp according to Claim 4, the electrodes being arranged, when seen in cross section, at least approximately at the corner points of an imaginary isosceles triangle.
7. Fluorescent lamp according to one or more of the preceding claims, characterized in that the gas filling consists of an inert gas or inert gas mixture.
8. Fluorescent lamp according to Claim 7, characterized in that the filling pressure is more than 13 kPa.
9. Fluorescent lamp according to Claim 7 or 8, characterized in that the gas filling contains xenon.
10. Discharge lamp according to one or more of the preceding claims, the width of the electrodes being 1 mm or less.
11. Discharge lamp according to one or more of the preceding claims, the discharge vessel (2) having on at least part of its wall a layer of fluorescent material or a mixture of fluorescent materials (8) and, optionally, a reflective layer (7) in addition.
12. Fluorescent lamp according to Claim 11, the wall of the discharge vessel (2) having an aperture (6) which is excepted at least by the reflective layer (7).
13. Fluorescent lamp according to one or more of the preceding claims, the tubular discharge vessel (2) having a circular cross section with an inside diameter of less than 20 mm, in particular less than 15 mm.
14. Illuminating system having a fluorescent lamp (1) according to one of claims 1-[illegible] and an electric pulsed voltage source (19) which is suitable for delivering active-power pulses separated from one another by pauses during operation, characterized in that the fluorescent lamp (1) has features of one or more of Claims 1 to 13, the pulsed voltage source (19) being connected in an electrically conducting fashion to the two external supply leads (17a, 17b) of the fluorescent lamp (1).
15. Illuminating system according to Claim 14, characterized by the following operating parameters:

    repetition frequency of the active-power pulses greater than or equal to 20 kHz,

    pulse duration of the active-power pulses of less than 2 µs.

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