Electric lamp and discharge devices: systems – Pulsating or a.c. supply
Reexamination Certificate
2001-03-26
2003-10-21
Philogene, Haissa (Department: 2821)
Electric lamp and discharge devices: systems
Pulsating or a.c. supply
C315S260000, C315S271000, C313S620000, C313S622000, C313S632000
Reexamination Certificate
active
06636004
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a discharge lamp which is designed for dielectrically impeded discharges. For this purpose, the discharge lamp has a discharge vessel filled with a discharge medium, and an electrode arrangement with at least one anode and at least one cathode. Since the discharge lamp is designed for dielectrically impeded discharges, a dielectric layer is situated at least between the anode and the discharge medium. The anode and the cathode thereby define between them a discharge spacing in which dielectrically impeded discharges can be produced.
The terms anode and cathode are not to be understood in this case such that the discharge lamp would only be suitable for unipolar operation. It can also be designed for a bipolar power supply, in which case there is then no difference between the anode(s) and cathode(s), at least electrically. Consequently, in this application, what is said for one of the two electrode groups applies in the case of a bipolar power supply for both electrode groups.
The discharge lamps considered here have a large number promising fields of application. An important example is the backlighting of flat image systems, in particular LCDs (Liquid Crystal Displays).
A further point is the backlighting or lighting of signaling devices and signal lamps themselves. Reference is made regarding these two last points to the disclosure content, hereby referred to, of EP 0 926 705 A1. Reference is made, furthermore, to WO98/43277, also with regard to backlighting of flat display screens, and the disclosure content thereof is also referred to.
PRIOR ART
Since discharge lamps for dielectrically impeded discharges can be designed in the most varied sizes and geometries, and in the process achieve a relatively high efficiency on avoiding the typical disadvantages of classic discharge lamps with a mercury-containing filling, they are promising candidates for a large number of different technical fields of use.
Many technical attempts have been undertaken for the purpose in this case of maximizing parameters such as the light yield, the luminous flux, the luminance, the homogeneity of the luminance etc.
Particular reference is made regarding the prior art to patent abstracts of Japan 1996, No. 6, dated Jun. 28, 1996 and to the associated JP 08031387 A. This prior art describes a discharge lamp which is designed for dielectrically impeded discharges and in which a region with a small discharge spacing is provided in order to reduce the starting voltage. In one exemplary embodiment, this small discharge spacing is 2 mm. However, during operation discharges also burn in the whole discharge lamp in the region of larger discharge spacings.
SUMMARY OF THE INVENTION
The invention is based on the technical problem of improving a discharge lamp for dielectrically impeded discharges such that its possibilities of use are further expanded, and to specify a corresponding operating method for the discharge lamp.
Firstly, the invention proceeds from the finding that there is a range of applications for which it is important, in addition to, or instead of, the qualities required at the beginning, for it to be possible to operate the discharge lamp with a very low luminous flux. It was necessary for this purpose in the case of the invention to improve the properties of the lamp such that it permits the injecting of very low supply powers. This is possible according to the invention by virtue of the fact that the discharge spacing between the electrodes is selected to be particularly small. According to the invention, this discharge spacing between cathodes and anodes is 3 mm or less, preferably 2 mm, 1.5 mm, 1 mm, 0.8 mm or below and, with particular preference, 0.6 mm and below.
It is important in this case that electrode pairs with such a small discharge spacing need not occur exclusively in the discharge lamp. It is also perfectly possible to make use of larger discharge spacings in the same discharge lamp, because then it is possible, if appropriate, to operate the lamp, if required, only with the small discharge spacing according to the invention.
The substantial advantage of the short discharge spacings consists in that they permit particularly long dead times between the individual active-power pulses in the case of a pulsed power supply, without the production in this case of locally undesired high current densities.
Firstly, reference is made with regard to the operating method with the pulsed active-power injecting to WO 94/23442 and DE-P 43 11 197.1, whose disclosure content is hereby referred to.
In the case of this operating method, dead times during which no discharge burns in the discharge lamp occur between individual pulses in which the discharge lamp is supplied with active power. During the injecting pulses of active power, the discharge certainly need not burn continuously in this case; it is equally as little necessary for the discharge to be terminated directly after the end of the injecting of active power. In any case, specific dead times without discharges occur between the discharge ignitions during operation of the lamp.
If, now, the dead times between the discharges are greatly lengthened, this reduces the mean power thereby injected into the lamp, and therefore also the mean emitted optical power, at least as long as the amount of energy injected per pulse is not increased to compensate. Rather, it is preferred in the invention that the energy injected per active-power pulse remains substantially constant—including in the case of a power adjustment still to be treated below—that is to say is not consciously changed. Of course, in this case it can change somewhat owing to the changing electroparameters and discharge parameters because of the lengthening of the dead time, but this does not invalidate the invention.
At the present state of knowledge, it is to be regarded as a purely empirical result that particularly long dead times are possible in the case of the small discharge spacings according to the invention. It was, rather, expected that arcs destroying the dielectric form, because there is virtually no longer any physical coupling owing to the excessively long dead times between the individual active-power pulses. In the case of the dead times “of normal length”, an individual discharge structure forms an ionization of the discharge medium which is removed after extinction of the discharge pulse. The next discharge pulse then ignites in a still somewhat preionized region of the discharge medium, thus also giving rise to the temporal and spatial homogeneity of the overall discharge picture which is the aim of the pulsed mode of operation.
If dead times now become too long, in the case of conventional discharge spacings this coupling no longer takes place between the individual discharge pulses, and so each discharge pulse is, as it were, comparable to a new ignition which initially exhibits an arc-shaped discharge. The arcs repeated with each pulse render completely impossible permanent operation of the lamp and efficient homogeneous production of light; the discharge lamp is, however, in general damaged and therefore destroyed earlier.
It was surprising, moreover, that also no substantial acoustic problems arose with the invention. In the case of “conventional” discharge spacings, bothersome piping noises were found at excessively low frequencies, that is to say frequencies in the audible range, these noises being produced by coupling of the pulse frequency of the discharges to the discharge vessel via various mechanisms of no interest here. However, it is to be seen in the case of the invention that such problems virtually do not occur any more, probably owing to the small discharge spacings with a thereby reduced coupling, on the one hand, and probably owing to the in any case greatly reduced powers, on the other hand.
The invention therefore relates to an operating method in which the dead time between the active-power pulses can be set in order to set the lamp power, and this corresponds to a dimming method in th
Hitzschke Lothar
Vollkommer Frank
Bessone Carlo S.
Patent-Treuhand-Gesellschaft fuer Elektrische Gluehlampen mBH
Philogene Haissa
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