Fluorescent lamp with spacers and locally reduced...

Details Fluorescent lamp with spacers and locally reduced... Fluorescent lamp with spacers and locally reduced...

1999-12-16

2001-06-19

Patel, Vip (Department: 2879)

Electric lamp and discharge devices

With support and/or spacing structure for electrode and/or...

Supporting and/or spacing elements

C313S493000, C313S495000, C313S292000

Reexamination Certificate

active

06249079

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a fluorescent lamp for dielectrically impeded discharges. Such a fluorescent lamp has a discharge vessel filled with a gas filling, in the case of which at least one wall contains a transparent surface for the exiting of light. Moreover, the fluorescent lamp naturally has a fluorescent layer, consideration being given in the case of this invention to the case that at least a portion of the fluorescent layer is situated on said transparent surface. The electrodes and the dielectric layer thereon are not addressed further here.
It is possible in the case of such fluorescent lamps to use spacers which connect parts of the discharge vessel and keep them at a spacing from one another. In this case, the spacers can themselves be part of the discharge vessel, for example connecting, as frame, two plates of a flat radiator discharge vessel. On the other hand, particularly in the case of discharge vessels of planar extent and when the pressure of the gas filling is considerably below atmospheric pressure, it is necessary also to provide, inside the discharge vessel, spacers which are intended to prevent an implosion of the discharge vessel, but which do not belong directly to it in the sense of a boundary. It can also be advantageous for other reasons than the risk of implosion to undertake additional stabilization using spacers in a discharge vessel.
DESCRIPTION OF PRIOR ART
As regards the prior art, reference is made to the following applications, which represent fluorescent lamps of the type described for dielectrically impeded discharges, and whose disclosure content is also incorporated here:
DE 196 36 965.7=WO 97/01989
DE 195 26 211.5=WO 97/04625 and
DE-Patent 43 11 197.1=WO 94/23442.
SUMMARY OF THE INVENTION
This invention is based on the technical problem of developing a fluorescent lamp of the type mentioned at the beginning such that it exhibits good light-emitting properties in conjunction with good mechanical stability.
According to the invention, this problem is solved with the aid of a fluorescent lamp for dielectrically impeded discharges, having a discharge vessel filled with a gas filling, and at least one spacer for supporting at least one wall of the discharge vessel which has a surface, at least partially transparent to visible radiation, with a fluorescent layer, the spacer supporting this wall on this surface, wherein the fluorescent layer has a reduced thickness in a surrounding region of the spacer.
It has emerged in developing the invention that spacers in the region of a surface, provided for the light emission, of the discharge vessel lead to irregularities, in particular to shadows. However, for many applications it is very disadvantageous if the luminance of the light exit surface of the fluorescent lamp varies too greatly. Rather, the aim is for the light to be generated uniformly as far as possible. This relates chiefly to flat radiators for the backlighting of display devices, in particular for the backlighting of liquid crystal display screens. In order not to disturb the appearance and the legibility of the display device or of the display screen, it is preferable for luminance fluctuations of 15% not to be exceeded. However, the invention is not limited to the field of flat radiators or backlightings for display devices.
It has emerged in the case of the invention that a local reduction in the layer thickness of the fluorescent layer does not, as might be expected at first, lead to darkening because of the smaller available quantity of fluorescent material generating visible light. On the contrary, the locations with a thinned fluorescent layer appear comparatively brighter than the surrounding region, even if the layer thickness is reduced to zero, that is to say a local cutout is formed. This can be understood in retrospect by the diffuse character of the generation of light inside the fluorescent lamp, the visible radiation captured from neighboring regions encountering a lesser absorption/reflection in the region of the thinned fluorescent layer thickness. The invention accordingly provides a local reduction in layer thickness in the surrounding region of the spacer on the partially transparent surface with the fluorescent layer. In this case, the invention includes the case when the reduced thickness (in accordance with claim
1
) is zero, that is to say the local change in layer thickness corresponds to a cutout.
Consequently, it is possible on the one hand to compensate a shadow from the spacer situated therebelow given suitable geometric coordination. On the ocher hand, it is also possible in the case of the solution according to the invention for there to remain in the region of the immediate contact between the spacers and transparent wall a somewhat darker spot which is, however, optically resolved, as it were, according to the invention in a brightened surrounding region. On the one hand, this is a question of the observers distance and the geometric extent of the brighter surface and the darker spot. On the other hand, an already known compensatory measure such as optical diffusers, prismatic disks and the like can be used to effect, as it were, a local averaging in the case of which the dark spot and the brightened surrounding region compensate one another.
One refinement of this invention consists in that said surrounding region of the spacer has a relatively finely configured geometric structure composed of many surfaces each having a different luminous layer thickness. In this case, a gradation of an effective luminous layer thickness, resulting to a certain extent from a local averaging, into discrete stages or as a continuous course can be performed by varying the different luminous layer thicknesses or varying the different surface proportions. Regarding this refinement, reference is made to the parallel application entitled “Leuchtstofflampe mit auf die geometrische Entladungsverteilung abgestimmter Leuchtstoffschichtdicke” [“Fluorescent lamp having a fluorescent layer thickness coordinated with the geometric discharge distribution”], which was filed on the same date by the same applicant.
A further idea of the invention is aimed at configuring the bearing surface between the spacer and the wall considered here to have as small an extent as possible. Certainly, mechanical considerations oppose this, specifically the avoidance of a punctiform loading of the wall (generally made from glass) by the spacer. However, this disadvantage is accepted for the benefit of minimizing the surface which can be brightened up by the reduction in layer thickness according to the invention. It is preferred in this case to limit this bearing surface in a two-dimensional fashion, that is to say to extend it less in each direction conceivable in this plane. On the other hand, there are cases, chiefly in the case of spacers running linearly, for example as frames of a discharge vessel, in which limiting the bearing surface in only one direction (perpendicular to the line of the spacer) is advantageous.
A quantitative characterization of this limitation of the bearing surface relates usefully to the spacing, bridged by the spacer, of the discharge vessel, that is to say, for example, to the plate spacing of a flat radiator fluorescent lamp. In this case, the small extent described for the bearing surface should be less than 30%, preferably less than 20% or 10% of this spacing.
A further important refinement of the invention relates to the stability of the discharge vessel with the spacers in the case of thermal cycles, such as unavoidably occur in practice during operation of the lamp. When developing the invention, it emerged in this case as essential for the coefficients of thermal expansion of the various main components of the discharge vessel and the spacers to be coordinated with one another. In particular, the coefficient of thermal expansion of the spacers should be in the region of ±30% of the coefficients of expansion of the main components of th

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