Mercury gas discharge device

Details Mercury gas discharge device Mercury gas discharge device

2002-09-12

2004-11-30

Patel, Vip (Department: 2879)

Electric lamp and discharge devices

With getter

Electrode includes getter, supports getter, or is connected...

C313S490000

Reexamination Certificate

active

06825613

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to mercury gas discharge devices, in particular mercury vapour fluorescent lamps including hot cathode and cold cathode fluorescent lamps (CCFLs).
BACKGROUND OF THE INVENTION
Nowadays, cold cathode fluorescent lamps (CCFLs) are often used as miniature high luminous intensity light sources. They feature simple construction, are miniature in size, have high luminous intensity, exhibit small increases in lamp temperature during operation, and have a relatively long operating life. Because of these characteristics, CCFLs have been widely used as a light source in various backlit light units and scanners.
In recent years, rapid developments in information technology. communication equipment and office and consumer products have necessitated development of CCFLs with better performance, increased functionality and smaller size. Meanwhile, LCD backlit sources have been developed with the aim of increasing the area of coverage, reducing power consumption and extending operational lifetime. Currently, CCFLs are mass produced and have great difficulty meeting these ever increasing demands,
An example of a current CCFL is shown in FIG.
1
.
FIG. 1
shows a glass envelope
2
with a fluorescent powder film
4
coated onto its interior wall. Gas
5
such as a neon and argon mixture with a source of mercury vapour are confined in glass envelope
2
. Electrodes
1
are disposed at opposing ends of glass envelope
2
.
Electrodes
1
are a key component of the CCFL. They are responsible for conducting electricity, emitting electrons, forming a magnetic field, and for other lamp and heating functions. To a large extent, lamp performance depends upon the choice of the electrode material.
Electrodes commonly used in CCFLs include an electrode wire
6
formed of tungsten, dumet or kovar and a cathode in the form of a nickel tube or nickel bucket
3
welded onto the part of electrode wire
6
which is inside glass envelope
2
. Conventional nickel tubes or nickel buckets are made using high-ratio compression.
In conventional CCFL construction, the operating surface area of the nickel tube or nickel bucket
3
is limited by the inner diameter of glass envelope
2
and the length of the electrode. Accordingly, any increase in the lamp's luminous intensity during operation is limited by the surface area of the nickel tube or nickel bucket and the melting point of nickel which is approximately 1453° C. As a result of these limitations, current CCFL's are not able to withstand a large lamp electric current and the impact of a strung electron stream. The limited surface area of the nickel tube or nickel bucket also limits the amount of active alkaline metals such as barium, calcium, strontium and cesium that can be added. These metals can be added to the cathode to enhance electron emission efficiency.
During long term operation, the glass and fluorescent powder used in fluorescent lamps or current CCFLs continually discharge and deposit waste materials inside the glass tube. Waste gases, such as water, oxygen, nitrogen, carbon monoxide and carbon dioxide, develop and proliferate from the materials used. These waste gases enter into the interior of the lamp. They result in an increase in resistance to electrical conductivity within the lamp, and cause damage to the cathode by reacting with the active alkaline metals that can be added to the cathode. This reduces the functioning of the lamp and is known to present difficulties when attempting to produce high quality, small sized, high luminous intensity and high performance fluorescent lamps and CCFLs.
The aforementioned problems do not only exist in CCFLs, but are also found in any other mercury gas discharge device, including but not limited to mercury vapour sunlamp and germ-killing ultraviolet light tube utilizing mercury vapour.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a mercury gas discharge device such as a cold cathode fluorescent lamp (CCFL) with a construction that overcomes or at least ameliorates the problems of prior art. mercury gas discharge devices. Another object of the invention is to provide a mercury gas discharge device such as a CCFL that operates under a larger operating electric current without affecting the device's operational lifetime. It is a further object of the present invention to provide a mercury gas discharge device such as a CCFL that provides greater intensity and longer operational lifetime when compared with current mercury gas discharge devices. These and further objects and advantages of the present invention will be discussed in more detail throughout the description of the invention.
A mercury gas discharge device constructed according to an embodiment of the present invention comprises an envelope with inert gas and mercury vapour confined within the envelope. The envelope also includes a pair of electrodes. One or more sintered metal portions are also located in the envelope. The sintered metal portions have high gettering characteristics with respect to waste gases, but low gettering characteristics with respect to the mercury vapour.


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