Flat fluorescent lamp with specific electrode structuring

Details Flat fluorescent lamp with specific electrode structuring Flat fluorescent lamp with specific electrode structuring

1998-11-17

2000-03-07

Patel, Vip

Electric lamp and discharge devices

With luminescent solid or liquid material

With gaseous discharge medium

313491, 313483, H01J 6100, H01J 6500

Patent

active

060344709

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The invention relates to a flat fluorescent lamp for background lighting. Moreover, the invention relates to a lighting system and having this flat fluorescent lamp. Furthermore, the invention relates to a liquid crystal display device and having this lighting system.
The designation "flat fluorescent lamp" is understood here to mean fluorescent lamps having a flat geometry and which emit white light. They are first and foremost designed for background lighting of liquid crystal displays, also known as LCDs.
Also at issue here are flat lamps having strip-like electrodes, in which either the electrodes of one polarity or all the electrodes, that is to say of both polarities, are separated from the discharge by means of a dielectric layer (discharge dielectrically impeded at one end or two ends). Such electrodes are also designated as "dielectric electrodes" below for short.
The term "strip-like electrode" or "electrode strip" for short is to be understood here and below as an elongated structure which is very thin and narrow by comparison with its length and is capable of acting as an electrode. The edges of this structure need not necessarily be parallel to one another in this case. In particular, substructures along the longitudinal sides of the strips are also to be included.
The dielectric layer can be formed by the wall of the discharge vessel itself by arranging the electrodes outside the discharge vessel, for example on the outer wall. An advantage of this design with external electrodes is that there is no need to lead gas-tight electrical feedthroughs through the wall of the discharge vessel. However, the thickness of the dielectric layer--an important parameter which, inter alia, influences the starting voltage and the operating voltage of the discharge--is essentially fixed by the requirements placed on the discharge vessel, in particular the mechanical strength of the latter.
On the other hand, the dielectric layer can also be realized in the shape of an at least partial covering or coating, at least of the anodic part of the electrodes arranged inside the discharge vessel. This has the advantage that the thickness of the dielectric layer can be optimized with regard to the discharge characteristics. However, internal electrodes require gas-tight electrical feedthroughs. Additional production steps are thereby required, and this generally increases the cost of production.
Liquid crystal display devices are used, in particular, in portable computers (laptop, notebook, palmtop or the like), but recently also for stationary computer monitors. Further fields of application are information displays in control rooms of industrial plants or flight control equipment, displays of point-of-sale systems and automatic cash dispensing systems as well as television sets, to name but a few. Liquid crystal display devices are also being used increasingly in automotive engineering for so-called driver information systems. Liquid crystal display devices require background lighting which illuminates the entire liquid crystal display as brightly and uniformly as possible.


PRIOR ART

WO 94/23442 discloses a method for operating an incoherently emitting radiation source, in particular a discharge lamp, by means of dielectrically impeded discharge. The operating method provides for a sequence of effective power pulses, the individual effective power pulses being separated from one another by dead times. Consequently, a multiplicity of individual discharges, which are delta-like (.DELTA.) in top view, that is to say at right angles to the plane in which the electrodes are arranged, burn in each case between neighbouring electrodes of differing polarity. These individual discharges are lined up next to one another along the electrodes, widening in each case in the direction of the (instantaneous) anode. In the case of alternating polarity of the voltage pulses of a discharge dielectrically impeded at two ends, there is a visual superimposition of two delta-shaped structures. Since these discharge stru

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