EP0912992A2

EP0912992A2 - Flat light emitter

Info

Publication number: EP0912992A2
Application number: EP98925421A
Authority: EP
Inventors: Frank Vollkommer; Lothar Hitzschke; Simon Jerebic
Original assignee: Patent Treuhand Gesellschaft fuer Elektrische Gluehlampen mbH
Current assignee: Osram GmbH
Priority date: 1997-03-21
Filing date: 1998-03-20
Publication date: 1999-05-06
Anticipated expiration: 2018-03-20
Also published as: TW414917B; EP0912992B1; DK0912992T3; CN1220770A; DE59809916D1; JP2000500917A; WO1998043278A2; US6252352B1; ES2209149T3; HUP0000674A2; HUP0000674A3; HU223639B1; WO1998043278A3; DE19711893A1; CN1165961C; KR100385009B1; JP3249538B2; KR20000015789A

Abstract

The invention relates to a flat light emitter with dielectrically impeded strip-like cathodes (12; 15) and anodes (8; 9a) which are alternately arranged on the wall of the discharge vessel (14). The inventive device has an additional anode (9b) between each adjacent cathode (12; 12, 15), i.e. a pair of anodes (9) is respectively arranged between said cathodes (12; 12, 15). The cathodes (15) have nose-shaped extensions (28) facing each adjacent anode (8). Said extensions are more densely arranged as they advance towards the edges (26, 27) of the light emitter (13). Alternately or additionally, both anode strips (9a; 9b) of each anode pair (9) are wider on one side in the direction of each partner strip (9b or 9b) as they advance towards the edges (26, 27) of the light emitter (13). Such a design enables the surface luminance of the flat light emitter (13) to remain substantially constant even at the edges (26, 27, 29, 30).

Description

Flat radiator

Technical field

The invention is based on a flat radiator according to the preamble of claim 1. The invention also relates to a system comprising this flat radiator and a voltage source according to the preamble of claim 10.

The term "flat radiator" here means radiators with a flat geometry that emit light, i.e. visible electromagnetic radiation, or also ultra violet (UV) and vacuumuitraviolet (VUV) radiation.

Depending on the spectrum of the emitted radiation, such radiation sources are suitable for general and auxiliary lighting, e.g. Residential and office lighting or background lighting of displays, for example LCDs (Liquid Crystal Displays), for traffic and signal lighting, for UV radiation, e.g. Disinfection or photolytics.

These are flat radiators that are operated by means of dielectric barrier discharge.

In this type of radiator, either the electrodes of one polarity or all electrodes, that is to say both polarities, are separated from the discharge by means of a dielectric layer (one-sided or two-sided dielectric barrier discharge, see for example WO 94/23442 or EP 0 363 832). Such electrical These are also referred to in the following as "dielectric electrodes".

State of the art

A flat radiator is known from DE-OS 195 26 211, in which strip-shaped electrodes are arranged on the outer wall of the discharge vessel. The radiator is operated with the aid of a sequence of active power pulses separated by pause times. As a result, a multiplicity of similar discharges, similar to delta-like (Δ), burn in a plan view, that is to say perpendicular to the plane in which the electrodes are arranged, between adjacent electrodes. These individual discharges are lined up along the electrodes, each widening in the direction of the (current) anode. In the case of changing polarity of the voltage pulses of a bilaterally dielectric discharge, an overlay of two delta-shaped structures appears visually. The number of individual discharge structures can be influenced, inter alia, by the electrical power that is coupled in.

According to the equidistantly arranged strips, the individual discharges - assuming sufficient electrical input power - are distributed almost evenly within the planar discharge vessel of the radiator. A disadvantage of this solution, however, is that the surface luminance drops significantly towards the edge. One of the reasons for this is the lack of radiation from the neighboring areas outside the discharge vessel.

A further disadvantage is that the individual discharges preferably form between the anodes and only one of the two immediately adjacent cathodes. Apparently, individual discharges do not form simultaneously on both sides of the anode strips. Rather, it cannot be predicted from which of the two adjacent cathodes the discharges will form in each case. In relation to the flat radiator as a whole, this results in an irregular discharge structure and, consequently, in a temporally and spatially non-uniform surface luminance.

A uniform surface luminance is desirable for numerous applications of such spotlights. For example, backlighting LCDs requires visual uniformity, the modulation depth of which does not exceed 15%.

Presentation of the invention

The object of the present invention is to provide a flat radiator with strip-like electrodes according to the preamble of claim 1, the surface luminance of which is almost uniform up to the edge.

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

The term “strip-like electrode” or, to shorten it, “electrode strip” is to be understood here and below to mean an elongated structure which is very thin in comparison to its length and which is capable of acting as an electrode. The edges of this structure need not necessarily be parallel to one another. In particular, substructures should also be included along the long sides of the strips.

The basic idea of the invention is to compensate for the drop in luminance typical of flat radiators from the center to the edges by means of an adapted electrode structure. For this purpose, the electrical The structure designed in such a way that the electrical power density increases towards the edges of the flat radiator.

In a first embodiment, the strip-like electrodes are arranged next to one another on a common wall of the discharge vessel (type I). This results in an essentially flat discharge structure during operation. The advantage is that scraping through the electrodes on the opposite wall is avoided. Between the cathode strips are two parallel anode strips, i.e. a pair of anodes instead of a single anode strip. This solves the problem described at the outset that, in the cited prior art, individual discharges burn from only one of two adjacent cathode strips in the direction of the individual anode strip lying between them.

In the following basic explanation of a first implementation of an electrode structure according to the invention for a flat radiator of type I, reference is made to the schematic illustration in FIG. 1. In order to be able to recognize the details better, only a section of the electrode area is shown. The aim is to ensure that the individual discharges form spatially denser towards the edges 1-3 of the flat radiator during operation than in the remaining part of the discharge vessel. For this purpose, the cathode strips 4 are specifically shaped such that they have spatially preferred starting points for the individual discharges. These preferred starting points are realized by nose-like extensions 6 facing the respectively adjacent anode 5. They cause locally limited amplifications of the electric field and consequently that the delta-shaped individual discharges 7 ignite only at these points. The extensions 6 are arranged more densely in the direction of the narrow sides of the cathodes 4, 4 ', ie in the direction of the edges 1, 3 oriented perpendicularly with respect to the electrode strips 4, 5. The mutual distance between the extensions 6 on the is typical Margins 1.3 only half as large as in the middle. In the immediate vicinity of the corner points of the flat radiator, the distance between the extensions 6 is finally reduced to approximately one third. In the immediate vicinity of the edges 2 oriented parallel to the electrode strips 4, 5 (the corresponding opposite second edge of the flat radiator is not shown in the selected section of FIG. 1), a single anode strip 5 'is preferably arranged in each case. Consequently, during operation the base sides of the delta-shaped (Δ) individual discharges lined up along these individual anode strips 5 'are immediately adjacent to the corresponding edges 2. As a result, the drop in luminance is relatively low even in the vicinity of these edges 2. In addition, the extensions 8 of the immediately adjacent cathode strips 4 'facing the two individual anode strips 5' can additionally be arranged overall more densely than in the case of the other cathode strips 4 '. However, the average power density is lower than the maximum achievable power density. Consequently, the maximum luminance, averaged over the entire area radiator, cannot be achieved with this solution either.

The second basic realization of an electrode structure for a type I flat radiator aims to increase the luminance of the individual discharges the closer they are to the edge. This is achieved (see the partial schematic representation of the principle in FIG. 2) in that the two anode strips 9a, 9b of each anode pair 9 are widened in the direction of the edges 10, 11 of the flat radiator oriented perpendicularly thereto. Typical values for the widening are approx. Up to a factor of two for the edge areas of the flat radiator and approx. Up to a factor of three for the corner areas.

In a first variant, the anode strips are asymmetrical with respect to their longitudinal axis in the direction of the respective anodic partner strip 9b or 9a widened. As a result of this measure, the respective distance d from the adjacent cathode 12 remains constant, despite the widening of the anode strips 9a, 9b. Consequently, the ignition conditions for all individual discharges (not shown) along the electrode strips 9, 12 are also the same during operation. This ensures that the individual discharges are lined up along the entire length of the electrode (provided there is sufficient electrical input power).

In a second variant (not shown), the anode strips are widened in the direction of the respective neighboring cathode. In this case, however, the broadening is only relatively weak. This prevents the discharges from occurring only at the location of the greatest width of the anode strip, i.e. at the location of the shortest stroke distance in this case. The broadening is significantly smaller than the stroke distance, typically about a tenth of the stroke distance. Furthermore, both widening variants can also be combined, i.e. the widening is formed both towards the respective anode partner strip and towards the neighboring cathode.

Along the widening, an increasing electrical current density and consequently also an increasing luminance of the individual discharges is achieved, as a result of which the luminance distribution up to the edges 10, 11 can be well balanced. However, the maximum luminance can no longer be achieved due to the luminance increase in the edge regions of the flat radiator in its central region. The advantage over the first solution is, however, that - provided there is sufficient electrical input power - the maximum spatial density of the individual discharges can be achieved anywhere within the discharge vessel, ie in this case the individual discharges essentially adjoin one another. In addition, the two basic realizations of targeted electrode shaping can also be combined with one another (cf. FIG. 3a).

In the anode widening, the cathodes do not necessarily have to be provided with extensions, as shown only by way of example in FIG. 2. Rather, in the case of the widened anode strips, the cathodes can also be designed as simple parallel strips.

In order to minimize the edge drop in the surface luminance, an experimental optimization of the compression of the extensions and / or the anode widening is required in the specific individual case.

In a further embodiment, the anode and cathode strips are arranged on opposite walls of the discharge vessel (type II). In operation, the discharges consequently burn from the electrodes of one wall through the discharge space to the electrodes of the other wall. Two anode strips are assigned to each cathode strip in such a way that when viewed in cross-section with respect to the electrodes, the imaginary connection of the cathode strips and corresponding anode strips results in the shape of a “V”. In this way, the stroke length is greater than the distance between As has been shown, this arrangement can achieve higher UV yields than if anodes and cathodes are alternately arranged next to one another on the same wall. According to the current state of knowledge, this positive effect is attributed to reduced wall losses The double anode strips are preferably arranged on the ceiling plate, which primarily serves to decouple light, and the cathode strips are arranged on the base plate of the flat spotlight For the lowest possible edge waste In terms of luminance, the cathode strips, as in the case of the type I flat radiator, have projections which are increasingly densely arranged toward their narrow sides. Additionally or alternatively, the widening of the anode strips towards the edge of the flat lamp, which was also explained in the case of the type I flat radiator, is also advantageous.

Description of the drawings

In the following, the invention will be explained in more detail using an exemplary embodiment. Show it:

FIG. 1 shows a schematic illustration to explain the principle of a first shaping of the electrodes according to the invention,

FIG. 2 shows a schematic illustration to explain the principle of a second shaping of the electrodes according to the invention,

FIG. 3a shows a schematic representation of a partially broken top view of a flat radiator according to the invention,

3a shows a schematic illustration of a side view of the flat radiator from FIG. 3a.

Figures 3a, 3b show a schematic representation of a top view and side view of a flat fluorescent lamp, i.e. a flat spotlight that emits white light during operation. This flat spotlight is suitable for general lighting or for backlighting displays, e.g. LCD (Liquid Crystal Display). In the following, features similar to those in FIGS. 1 and 2 are designated by the same reference numbers.

The flat radiator 13 consists of a flat discharge vessel 14 with a rectangular base area, four strip-like metallic cathodes 12, 15 (-) and dielectric anodes (+), three of which are elongated Double anodes 9 and two are designed as individual strip-shaped anodes 8. The discharge vessel 14 in turn consists of a base plate 18, a cover plate 19 and a frame 20. The base plate 18 and cover plate 19 are each gas-tightly connected to the frame 20 by means of glass solder 21 such that the interior 22 of the discharge vessel 14 is cuboid. The base plate 18 is larger than the cover plate 19 in such a way that the discharge vessel 14 has a peripheral free-standing edge. The inner wall of the cover plate 19 is coated with a phosphor mixture (not visible in the illustration), which converts the UV / VUV radiation generated by the discharge into visible white light. In one variant (not shown), in addition to the inner wall of the cover plate, the inner wall of the base plate and the frame are additionally coated with a mixture of fluorescent materials. Furthermore, a light-reflecting layer of A1 ₂ 0 ₃ or Ti0 _{2 is} applied to the base plate.

The breakthrough in the cover plate 19 is used only for illustrative purposes and provides a view of part of the anodes 8, 9 and cathodes 12, 15. The anodes 8, 9 and cathodes 12, 15 are arranged alternately and in parallel on the inner wall of the base plate 18. The anodes 8, 9 and cathodes 12, 15 are each extended at one end and guided outwards on the bottom plate 18 from the inside 22 of the discharge vessel 14 on both sides such that the associated anodic or cathodic bushings on opposite sides of the Base plate 18 are arranged. On the edge of the base plate 18, the electrode strips 8, 9, 12, 15 each merge into a cathode-side 23 and anode-side 24 bus-like conductor track. The two conductor tracks 23, 24 serve as contacts for the connection to an electrical voltage source (not shown). In the interior 22 of the discharge vessel 14, the anodes 8, 9 are completely covered with a glass layer 25 (cf. also FIGS. 1 and 2), the thickness of which is approximately 250 μm. The double anodes 9 each consist of two parallel strips, as already shown in detail in FIG. 2. The two anode strips 9a, 9b of each anode pair 9 are widened on one side in the direction of the edges 26, 27 of the flat radiator 13 oriented perpendicularly thereto in the direction of the respective partner strips 9b and 9a. The anode strips 9a, 9b are approx. 0.5 mm wide at the narrowest point and approx. 1 mm wide at the widest point. The mutual greatest distance g _max (cf. FIG. 2) of the two strips of each anode pair 9 is approximately 4 mm, the smallest distance g ^ is approximately 3 mm. The two individual anode strips 8 are each arranged in the immediate vicinity of the two edges 29, 30 of the flat radiator 13 which are parallel to the electrode strips 8, 9, 12, 15.

The cathode strips 12; 15 have nose-like projections 28 facing the respectively adjacent anode 8; 9. They cause locally limited amplifications of the electric field and consequently that the delta-shaped individual discharges (not shown in FIGS. 3a, 3b, but see FIG. 1) ignite only at these points. The extensions 28 of the two cathodes 15, which are immediately adjacent to the edges 29, 30 of the flat radiator 13 parallel to the electrode strips 8, 9, 12, 15, are along the respective longitudinal sides facing the said edges 29, 30 in the direction of the narrow sides the cathodes 15 arranged increasingly densely. The distance d (cf. FIG. 2) between the extensions 28 and the respective directly adjacent anode strip is approximately 6 mm.

The electrodes 8, 9, 12, 15, including feedthroughs and power supply lines 23, 24, are each formed as a coherent, conductor-like structure on the cathode or anode side. The two structures are applied directly to the base plate 18 by means of screen printing technology.

Inside the flat radiator 13 there is a gas filling made of xenon with a filling pressure of 10 kPa. A variant (not shown) differs from the flat radiator shown in FIGS. 3a, 3b only in that not only the anodes but also the cathodes are separated from the inside of the discharge vessel by a dielectric layer (discharge which is dielectric-impeded on both sides).

In a complete system, the anodes 8, 9 and cathodes 12, 15 of the flat radiator 13 are connected via the contacts 24 and 23, respectively, to one pole of a pulse voltage source (not shown in FIGS. 3a, 3b). During operation, the pulse voltage source supplies unipolar voltage pulses, which are separated from one another by pauses. A large number of individual discharges (not shown in FIGS. 3a, 3b) are formed, which burn between the extensions 28 of the respective cathode 12; 15 and the corresponding immediately adjacent anode strip 8; 9.

The invention is not limited by the exemplary embodiments specified. Features of different exemplary embodiments can also be combined.

Claims

claims

1. Flat radiator (13) with an at least partially transparent, closed (14) or gas-filled open, flat discharge vessel made of electrically non-conductive material and with strip-like electrodes (8) arranged on the wall of the discharge vessel (14) ; 9; 12; 15), at least the anodes (8,9) being separated from the inside of the discharge vessel (14) by a dielectric material (25), characterized in that the electrodes (8; 9; 12; 15) for the purpose of specifically influencing the electrical power density distribution in the discharge are shaped in such a way that the surface luminance of the flat radiator (13) is largely constant up to its edges (26, 27, 29, 30) during operation.

2. Flat radiator according to claim 1, characterized in that the shaping of the electrodes consists in that the cathodes (15) have nose-like projections (28) facing the respectively adjacent anodes (8), which projections (28) in the direction of the respective on both narrow sides of the cathode (15) are spatially increasingly densely arranged.

3. Flat radiator according to claim 1, characterized in that the shape of the electrodes consists in a widening of the anode strips (9a; 9b) in the direction of their respective two narrow sides.

4. Flat radiator according to claim 1, characterized by the features of claims 2 and 3.

5. Flat fluorescent lamp according to claim 1, characterized in that the strip-like electrodes (8; 9; 12; 15) are arranged side by side on a common inner wall of the discharge vessel (14) are arranged between adjacent cathode strips (12, 12) or (12, 15) respectively two anode strips (9a, 9b), ie one pair of anodes (9).

6. Flat radiator according to claim 5, characterized in that the shape of the electrodes is that the two anode strips (9a; 9b) of each anode pair (9) in the direction of their respective two narrow sides and with respect to their longitudinal axis asymmetrically in the direction of the respective Partner strips (9b and 9a) are broadened out, so that the respective distance (d) to the neighboring cathode (12; 15) is constant throughout, so that the luminance of the

Single discharges to the edges (26, 27) increases.

7. Flat radiator according to claim 1, characterized in that the electrode strips (9; 12; 15; 16) on the inner wall of the discharge vessel (14) are arranged, wherein at least the anode strips (9; 16) by a dielectric layer (25) completely are covered.

8. Flat radiator according to one or more of the preceding claims, characterized in that the electrodes (8, 9, 12, 15), including bushings and current leads (23, 24), are each designed as different functional areas of a coherent cathode- or anode-side conductor track-like structure are.

9. Flat radiator according to claim 1, characterized in that at least a part of the inner wall of the discharge vessel has a layer of a phosphor or phosphor mixture.

10. System with a flat radiator and an electrical pulse voltage source, which is suitable to deliver separate voltage pulses during operation by pauses, characterized in that the Flat radiator features of one or more of claims 1 to 9.