EP0990259B1 - Fluorescent lamp with spacers and locally reduced luminescent material layer thickness - Google Patents

Description

The present invention relates to a fluorescent lamp for dielectric disabled discharges. Such a fluorescent lamp has one a discharge vessel filled with gas, in which at least one Wall to emit light contains a transparent surface. Also has the fluorescent lamp naturally over a fluorescent layer, with this Invention is considered the case that at least part of the phosphor layer lies on the said transparent surface. The electrodes and the The dielectric layer thereon will not be dealt with further here.

Spacers can be used with such fluorescent lamps, connect the parts of the discharge vessel and at a distance from each other hold. These spacers can themselves be part of the discharge vessel be, e.g. B. two plates of a flat radiator discharge vessel connecting as a frame. On the other hand, it is particularly in the case of extensive areas Discharge vessels and well below atmospheric pressure Pressure of the gas filling necessary, also within the discharge vessel Spacers to be provided, which implosion of the discharge vessel should prevent this, but not directly in the sense of a limitation belong. It can also be for reasons other than the risk of implosion be advantageous with spacers in a discharge vessel an additional To carry out stabilization.

DE 196 36 965.7 = WO 97 / 01989

DE 195 26 211.5 = WO 97 / 04625 sowie

DE-P 43 11197.1 = WO 94 / 23442.

With regard to the prior art, reference is made to the following applications, which represent fluorescent lamps of the type described for dielectrically impeded discharges:

DE 196 36 965.7 = WO 97/01989

DE 195 26 211.5 = WO 97/04625 and

DE-P 43 11197.1 = WO 94/23442.

This invention is based on the technical problem of a fluorescent lamp of the type described above so that they are good mechanical stability shows good light emission properties.

According to the invention, this problem is solved with a fluorescent lamp for Dielectric barrier discharges with a gas filled Discharge vessel, at least one spacer for support at least one wall of the discharge vessel, one for visible Radiation at least partially transparent surface with a phosphor layer the spacer supports this wall on this surface, characterized in that the phosphor layer in an environment of the spacer has a reduced thickness.

In the elaboration of the invention it has been found that spacers in the area of a surface of the Discharge vessel for irregularities, in particular for shadowing to lead. However, for many applications it is very disadvantageous if the Luminance of the light exit surface of the fluorescent lamp varies too much. Rather, the greatest possible uniformity of the light generation desirable. This particularly affects flat spotlights for backlighting of display devices, in particular for the backlighting of Liquid crystal screens. The appearance and legibility the display device or the screen should not be disturbed preferably fluctuations in luminance of 15% are not exceeded become. However, the invention is not in the field of flat radiators or of the backlights for display devices.

In the invention it has now been found that a local reduction the layer thickness of the phosphor layer is not, as one would initially expect could cause darkening due to the smaller amount available leads to visible light-generating phosphor. On the contrary, they appear Places with a thin layer of fluorescent material comparatively brighter than the surroundings, even if the layer thickness is reduced to zero, i.e. a local one Recess is formed. This can be understood in retrospect the diffuse character of the light generation within the fluorescent lamp, the visible radiation captured from neighboring areas in the Range of the thinned phosphor layer thickness to a lower absorption / reflection encounters. Accordingly, the invention provides in the area of the spacer on the partially transparent surface with the To provide a local layer thickness reduction in the phosphor layer. there the invention includes the case that the reduced thickness (According to claim 1) is zero, so the local change in layer thickness corresponds to a recess.

On the one hand, this can result in shading with a suitable geometric coordination be compensated for by the spacer underneath. On the other hand, the solution according to the invention can also be used in the area the direct contact between spacers and more transparent Wall remain a somewhat darker stain, which, however, according to the invention in in a lightened environment is optically resolved. For one thing this is a question of the observer distance and the geometric extent the lighter area and the dark spot. On the other hand, a already known compensatory measure such as optical diffusers, prismatic lenses and the like a local averaging, so to speak, where the dark spot and the lightened environment are mutually exclusive compensate.

An embodiment of this invention is that the environment mentioned the spacer has a relatively finely designed geometric structure has many surfaces, each with a different luminescent layer thickness. In doing so, a gradation can, so to speak, be made from a local Communication resulting effective luminescent layer thickness in discrete steps or as a continuous process by varying the different luminescent layer thicknesses or variation of the different areas. To this configuration is referred to the parallel application "Fluorescent lamp with a matched to the geometric discharge distribution Phosphor layer thickness "of the same applicant, the same Day was submitted.

Another idea of the invention is that the contact surface between the spacer and the wall considered here expanded as little as possible to design. Although there are mechanical considerations namely the avoidance of a selective loading of the (in general made of glass) through the spacer. However, this will Disadvantage in favor of minimizing that caused by the invention Reduction of the layer thickness of the lightenable surface is accepted. Prefers is to limit this contact surface two-dimensionally, d. H. to expand less in every possible direction in this plane. on the other hand there are cases, especially in the case of linear spacers for example as a frame of a discharge vessel, in which a restriction the contact surface in only one direction (perpendicular to the spacer line) is advantageous.

A quantitative characterization of this limitation of the investment area sensibly refers to the one bridged by the spacer Distance of the discharge vessel, so z. B. on the plate spacing one Flat radiator fluorescent lamp. Here, the described small Extension of the contact surface less than 30%, preferably less than 20% or 10% of this distance.

Another important embodiment of the invention relates to stability the discharge vessel with the spacers in the case of thermal cycles, as practically unavoidable in lamp operation. When working out the invention, it has been found to be essential coefficient of thermal expansion of the various main components the discharge vessel and the spacers to match. In particular, the thermal expansion coefficient of the spacers should in the range of ± 30% of the coefficient of expansion of the The main components of the discharge vessel are. With main components The discharge vessel means those components whose thermal Expansion due to their geometric dimensions and their Function in the discharge vessel for the thermal expansion of the overall discharge vessel is essential. In the case of a flat radiator, these are e.g. B. the two plates and the frame connecting them. mismatches lead in this area, depending on the extent of the thermal loads in the Operation, internal tension and displacement of the vessel components and the spacer with each other and thus to instabilities and for loosening connections or breaking the lamp.

Soft glasses have proven to be cheap materials for the spacers. Such soft glasses can also be used in material-related form, e.g. B. as a flour or glass solder held together by a binding material. Finally, various ceramic materials come into question, in particular Al ₂ O ₃ ceramic. With regard to the question of the choice of material and the coefficient of expansion, reference is made to the exemplary embodiment.

With regard to the minimization of the contact surface of the spacer already mentioned on the transparent surface of the wall it turned out that a firm connection between the spacer and the wall is not is absolutely an advantage. Rather, it can be advantageous to use the spacer only to the other side, i.e. on the opposite wall fasten, with which it is fixed for the overall assembly. By suitable The wall with the transparent surface then lies geometrically only on the spacer, with no other connection materials such as glass solders, adhesives or the like are provided. Thereby the contact area can be reduced to a minimum.

This also offers an advantage in terms of any thermal Expansion differences between the two from the spacer connected walls. In the event of transverse displacements can just slip the wall against the spacer, before too high voltages occur.

Another way to reduce optical interference from an image of the spacer consists in a casing of the same through a fluorescent layer. This will cause the spacer to appear on the other side of the transparent wall is not more or less pronounced as shadowing, apart from the immediate area of the System between spacer and wall. Too little ultraviolet gets there Light to stimulate the phosphor to a significant extent.

Since the fluorescent sheathing of the spacer is the contact surface on the Wall enlarged, it should be made clear that by lighting this Fluorescent layer the area of a system of the fluorescent layer on the Wall so far not comparable to the uncoated spacer Extent as shadow appears as sufficient ultraviolet light to Suggestion is available. Accordingly, it is in the sense of the above Comments on the minimization of the investment area effective contact surface that of the spacer without the phosphor layer (or only with insufficiently excited areas of the Phosphor layer).

Another way to brighten the area around the spacer consists according to the invention in a reflective coating the transparent wall facing area of the spacer. Thereby the coupling of the inside of the discharge vessel becomes diffuse distributed light in the area of the phosphor layer thinned according to the invention reinforced on the wall.

As already mentioned at the beginning, can be represented by the different Measures brought about brightening of an environment of the spacer be distributed with diffusely scattering media, so that the at least in Area of direct contact between the spacer and the wall is unavoidable dark spot after passing through the diffusely scattering medium dissolved in the bright surroundings or averaged against them.

A layer of frosted glass has been found to be special in the work on this invention favorable compromise between a strongly diffuse scattering effect on the one hand and the highest possible transmission capacity in favor a high efficiency of the overall arrangement on the other hand exposed. For technical reasons, it can be useful to immediately the discharge volume-limiting layer from another technical considerations while building out certain glass the frosted glass layer is designed as an overlay.

In the sense of simplifying the overall construction, it is for a corresponding one Production of special milk glasses reasonable quantities also possible, the transparent wall basically (in one layer) to build from a frosted glass.

With the possibility already mentioned at the beginning of a frame for a flat radiator discharge vessel results as a spacer in the sense of the invention the advantage of increasing the effective luminous area. This is explained in the embodiment.

Figur 1 eine schematisierte Ausschnittsdarstellung, die einen Abstandshalter in einer erfindungsgemäßen Flachstrahler-Leuchtstofflampe im Querschnitt darstellt, wobei der Abstandshalter ringsum von einer Aussparung in einer Leuchtstoffschicht umgeben ist; und

Figur 2 eine schematisierte Ausschnittsansicht, die einen weiteren Abstandshalter in der erfindungsgemäßen Flachstrahler-Leuchtstofflampe im Querschnitt darstellt, wobei der Abstandshalter einem Flachstrahlerrahmen entspricht und zu einer Seite hin von einer Aussparung in der Leuchtstoffschicht umgeben ist.

A specific exemplary embodiment of the invention is described in more detail below, which is illustrated in the accompanying figures. In detail shows:

Figure 1 is a schematic sectional view showing a spacer in a flat radiator fluorescent lamp according to the invention in cross section, wherein the spacer is surrounded all around by a recess in a fluorescent layer; and

Figure 2 is a schematic sectional view showing a further spacer in the flat radiator fluorescent lamp according to the invention in cross section, wherein the spacer corresponds to a flat radiator frame and is surrounded on one side by a recess in the phosphor layer.

Figure 1 shows a cross-sectional view of a flat radiator fluorescent lamp according to the invention. The fluorescent lamp is for dielectric disabled Discharges designed and largely built up in a known manner, whereby reference is made to the already cited prior art. In particular The electrode arrangements and the for the dielectric barrier discharge characteristic dielectric Layers not treated any further.

Figure 1 shows a detail view in which only the area of a spacer 6 with part of a base plate 1 and a summary with 2 designated cover plate around the spacer 6 is shown.

The spacer 6 consists of a precision glass ball with a Diameter of 5 mm. For example, with a flat lamp fluorescent lamp with dimensions of approximately 315 mm x 239 mm x 10 mm with a thickness of the base plate 1 and the cover plate 2 of 2.5 mm each an arrangement of 48 such spacers 6 is used.

The base plate 1 is produced with a reflection layer 7 for reflecting the visible light to the transparent ceiling plate 2. On the the discharge volume side of the reflection layer 7 and the A phosphor layer 3 is provided in each case for the ceiling plate 2. The spacer 6 is attached to the base plate 1 with a glass solder 5, which as viscous mixture of a soft glass powder with a binder applied and dried and hardened by a thermal treatment becomes. On the ceiling plate 2, the spacer 6 is due to its spherical shape almost punctiform, with the remaining unavoidable contact surface from an elastic deformation and unevenness of those involved Surfaces results. Around this contact surface between the spacers 6 and the ceiling panel 2 is the phosphor layer 3 on the ceiling panel obliterated; d. H. the contact surface lies in the middle of a recess 8 the phosphor layer.

In addition, the glass ball forming the spacer 6 has another one Fluorescent layer 3 'coated. Due to its finite thickness this increases Fluorescent layer 3 'the contact surface between the spacer 6 and the ceiling panel 2 slightly, as already stated, the phosphor layer 3 'hardly contributes to shading.

The ultraviolet generated in a dielectric barrier gas discharge Light is converted into visible light in the phosphor layers 3 and 3 ', with a largely diffuse distribution of visible light results in the discharge volume. This is due to the reflection on the reflective layer 7 supports to the losses in the area of the base plate 1 too minimize. Accordingly, in the phosphor layer free area 8 couple visible light around the spacer 6, the Contribution in particular of the half of the ceiling plate 2 facing Phosphor layer 3 'on the spacer 6 is particularly important.

Because of the more distant areas with normal Thickness of the phosphor layer 3 on the ceiling panel 2 no absorption and reflection of the phosphor can be in the vicinity of the spacer 6 penetrate a particularly large amount of light through the ceiling panel 2.

Figure 1 also shows that the ceiling panel 2 is composed of two sub-layers, namely a lower glass layer 2a, which like the base plate 1 for reasons of material technology for a more detailed below B270 glass, and an overlying frosted glass overlay 2b for the diffuse scattering of the emerging visible light. This material-technical reasons relate on the one hand to the processing properties, namely a conveniently located softening temperature of 708 ° C, further good chemical resistance to the plasmas occurring as well against alkali migration within the glass, which was discussed in more detail below thermal expansion coefficients and finally favorable Transmission properties.

There is still a prism film over the frosted glass overlay layer 2b 4, which narrows the solid angle of the light emission with focus (so-called brightness enhancement film from the manufacturer 3M). Besides the prism foil also has the property of an additional averaging of the Luminance beyond the effect of the frosted glass overlay 2b.

So-called DBEF films from the manufacturer 3M (or films comparable function) are used, which are essentially partially reflective Are polarizers. Matched to the polarization properties A liquid crystal display can thus reduce the yield in use for liquid crystal screen backlighting can be further increased.

Overall, the combination of the frosted glass overlay 2b carries along the prism sheet 4 for a largely smoothing of the inhomogeneities the luminance distribution, that of the direct contact of the spacer 6 on the ceiling plate 2 caused small dark spots the lighter environment in the area of the fluorescent recess 8 is compensated becomes. In addition, the lighter environment in area 8 compensates for this Absence of the light contribution from the area of the base plate 1 under the spacer 6, in particular from the area of the glass solder 5.

Furthermore, the glass ball forming the spacer 6 could in its in the figure top half instead of the phosphor layer 3 'or below provided a reflection layer corresponding to the reflection layer 7 his.

FIG. 2 shows a cross-sectional illustration largely comparable to FIG. 1, however, one edge of the flat panel fluorescent lamp is shown. There there is a spacer 6 'in the form of a discharge vessel on the edge and between the plates 1 and 2 forming glass frame from the below described B270 glass. This glass frame is on its top and on its underside via glass solder layers 5 with the base plate 1 and Ceiling plate 2 connected. For reasons of stability, it is still here no minimization of a contact surface on the ceiling plate 2 is provided. Rather, the glass frame 6 'has the cross-sectional shape of an upright Rectangle with flat contact up and down.

The spacer is to the side of the discharge volume, to the right in the figure or the glass frame 6 'is provided with a phosphor layer 3', which has the analog function to the corresponding phosphor layer the glass ball in the previous figure. According to the elongated (Quasi one-dimensional) geometry of the spacer 6 'is also closed one side, namely towards the discharge volume, a dilution 8 in the phosphor layer 3 of the ceiling panel 2 is formed. At this dilution 8, the layer thickness of the phosphor layer 3 decreases with decreasing lateral distance from the spacer 6 'to approximately zero at the Place of contact with the phosphor layer 3 '. From the beginning of the Reduction in layer thickness, this transition is essentially linear, the exact mathematical course of this smooth reduction in layer thickness and the exact layer thickness (theoretically zero) in the immediate The surroundings of the phosphor layer 3 'are only limited in terms of production technology have it checked.

The structure of the layers corresponds completely to the structure from Figure 1 and is not described here. It's just about to a cross section through another point of the same thing Layer structure.

The advantage of the invention at this point is that darkening the lamp in the vicinity of the frame or the spacer 6 ' due to the lack of contribution from the side of the glass frame 6 'diffuse Radiation can be compensated. A typical width for area 8 the reduction in layer thickness is up to 1 cm and corresponds to the darkened Area without reduction in layer thickness.

In addition, it can also be achieved that the effective glowing Area can be increased by the smoothing effect of the frosted glass overlay 2b or an external optical diffuser and the Prism film 4 for "smearing" the increased brightness in area 8 beyond the already darkened area of the glass frame 6 ' provides.

The glass frame 6 'is in the form shown as a rectangle in one Ground plan of rectangular flat radiator geometry. So that results there is an expansion of the illuminated area on all sides of the flat spotlight and thus overall an enlarged "visible diagonal" of the luminous area.

The following can be stated regarding the various glass materials in question: In general, a distinction is made between soft glasses and hard glasses, the distinguishing criterion being the level of the softening temperature (with 10 ^7.6 dPas). In this invention, predominantly intermediate glasses but also soft glasses are used, specifically in a range of the thermal expansion coefficient of 9 x 10 ^-6 K ^-1 ± 30% (preferably 20%, 10%). Hard glasses usually fall in the range of 4 x 10 ^-6 K ^-1 and soft glasses in the range of 9 x 10 ^-6 K ^-1 .

Glass B270 from the manufacturer DESAG (Deutsche Spezialglas AG in Grünenplan) with a coefficient of expansion of 9.5 x 10 ^-6 K ^-1 and a softening temperature of 708 ° C is particularly preferred here. Most soft glasses also lie in this range of the thermal expansion coefficient, which is why soft glass or materials based on soft glass are preferred for the spacers. A so-called AR glass (No. 8350) from the manufacturer mentioned with a coefficient of thermal expansion of 9.1 x 10 ^-6 K ^-1 is also suitable. (The technical reasons already mentioned for B270 also largely apply to the AR glass). Furthermore, Al ₂ O ₃ ceramic can also be used with an expansion coefficient of 8.5 - 8.8 x 10 ^-6 K ^-1 .

Quartz glass, on the other hand, is disadvantageous because it is used more frequently in this technical area due to the good UV transparency. Firstly, its average linear expansion coefficient is about 4.5 - 5.9 x 10 ^-7 K ^-1 and is thus only about 5-6% of the coefficient of the material used for the discharge vessel. In addition, quartz glass has the disadvantageous property of poor adhesion of most of the phosphors in question. It is also expensive and is therefore only considered in exceptional cases for the manufacture of the discharge vessel itself and basically also of the spacers.

Claims (14)

1. Fluorescent lamp for dielectrically impeded discharges, having a discharge vessel (1, 2, 6') filled with a gas filling, and at least one spacer (6, 6') for supporting at least one wall (2) of the discharge vessel which has a surface, at least partially transparent to visible radiation, with a fluorescent layer (3), the spacer (6, 6') supporting this wall (2) on this surface, characterized in that the fluorescent layer (3) has a reduced thickness in a surrounding region (8) of the spacer (6, 6').
2. Fluorescent lamp according to Claim 1, in which the surrounding region has a geometric structure composed of surfaces of different fluorescent layer thickness.
3. Fluorescent lamp according to Claim 1 or 2, in which the surrounding region (8) has surfaces without a fluorescent layer.
4. Fluorescent lamp according to one of the preceding claims, in which the spacer (6, 6') supports the wall (2) by bearing against it with a surface of small extent.
5. Fluorescent lamp according to Claim 4, in which the bearing surface is of small extent in every direction in its plane.
6. Fluorescent lamp according to Claim 4 or 5, in which the small extent is less than 30% of the plate spacing.
7. Fluorescent lamp according to one of the preceding claims, in which the spacer (6, 6') has a coefficient of thermal expansion which corresponds with a tolerance of ± 30% to that of the main components (1, 2, 6') of the discharge vessel.
8. Fluorescent lamp according to one of the preceding claims, in which the spacer (6, 6') consists essentially of soft glass, a material essentially containing soft glass or a ceramic material.
9. Fluorescent lamp according to one of the preceding claims, in which the spacer (6) bears against the wall (2) in a fashion free from connecting material.
10. Fluorescent lamp according to one of the preceding claims, in which the spacer (6, 6') has an outer fluorescent coating (3').
11. Fluorescent lamp according to one of the preceding claims, in which the spacer has a reflecting coating in a region facing the wall.
12. Fluorescent lamp according to one of the preceding claims, in which the surface (2) has a milk-glass layer (2b).
13. Fluorescent lamp according to one of the preceding claims, except for Claim 5 and Claim 9, in which the spacer (6') forms a boundary wall of the discharge vessel (1, 2, 6').
14. Fluorescent lamp according to Claim 13, in which the spacer (6') is a frame of a flat radiator fluorescent lamp which connects a base plate (1) and a cover plate (2) forming the wall.

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