Electric lamp and discharge devices – With luminescent solid or liquid material – With gaseous discharge medium
Patent
1997-11-13
1999-11-09
O'Shea, Sandra
Electric lamp and discharge devices
With luminescent solid or liquid material
With gaseous discharge medium
313346R, 313346DC, 313631, 313632, H01J 162
Patent
active
059820888
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a small sized fluorescent discharge lamp used as a back light in a liquid crystal display device, and/or a light source for reading in a facsimile device or a scanner.
BACKGROUND OF THE INVENTION
Lately, interest in a liquid crystal display device (LCD) has rapidly progressed because of its low power consumption, small size and light weight. Thus, a small sized fluorescent discharge lamp has been developed as a light source for a liquid crystal display. Similarly, interest in a fluorescent lamp which is compatible with a socket of an incandescent lamp has progressed because of low power consumption and long life as compared with an incandescent lamp.
Fluorescent lamps are classified as hot cathode fluorescent discharge lamps using arc discharge by hot electron emission, and cold cathode fluorescent discharge lamps using glow discharge by secondary electron emission. A hot cathode fluorescent discharge lamp has a lower cathode fall voltage and higher light efficiency for the input power used than does a cold cathode fluorescent discharge lamp. Further, the former has higher luminance because of hot electron emission, and higher luminance is obtained as compared with a cold cathode discharge lamp. Therefore, a hot electron discharge lamp is suitable as a light source which provides a large amount of light flux, like a light source for a back light in a large screen liquid crystal display device, a fluorescent lamp in the shape of an incandescent lamp, a light source for reading in a facsimile device and a scanner. In a prior hot cathode lamp, a fluorescent lamp having a cathode made of a tungsten (W) coil plated with a part of transition metal and an alkaline earth metal including Barium (Japanese patent laid open 59-75553), and a cathode having a porous tungsten impregnated by an electron emission material including barium aluminate (Japanese patent laid open 63-24539) are known.
Because liquid crystal display devices are small and thin, the lamp itself must be thin. However, in a hot cathode lamp in which preheating is essential, a thin structure, like a cold cathode lamp is difficult to accomplish. A thin structure which has no preheating, as shown in Japanese patent laid open 4-73858, has the disadvantage of short lifetime. Further, the deterioration of a cathode because of ion sputtering in which Hg ions and/or Ar ions generated during discharge operations collide with a cathode and splashing of electron emission material occurs. Thus, electron emission material is exhausted during discharge operation, and stable arc discharge for a long time period is impossible. Further, splashed electron emission material is attached on an inner surface of a tube, which is then colored black, so that light flux is decreased rapidly.
The present inventors have proposed a fluorescent lamp having a ceramic cathode in Japanese patent publication 6-103627, a thin tube and high luminance hot cathode fluorescent lamp having an improved lifetime by preventing sputter and evaporation of ceramic cathode material in Japanese patent laid open 2-186550, and a ceramic cathode in which transition from glow discharge to arc discharge is starting time is easy in Japanese patent laid opens 4-43546 and 6-267404.
Those hot cathode discharge lamps have the advantage that transition from glow discharge to arc discharge is easy, and have long lifetime, however, it is still insufficient for the request of 5-6 thousand hours lifetime.
In those prior fluorescent lamps having a ceramic cathode, with an inner diameter of 2.0 mm, and Ar gas with pressure of 5 Torr, the lifetime on average is short, up to around 1000 hours, when lamp current is 15 mA.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a fluorescent discharge lamp having a ceramic cathode, excellent discharge starting characteristics for a long time from initial time to end of lifetime, thin tube structure, high luminance, and long lifetime.
In order to achieve the above object, the present inven
REFERENCES:
patent: 3505553 (1970-04-01), Piree
patent: 4882520 (1989-11-01), Tsunekawa et al.
patent: 5654606 (1997-08-01), Weijtens et al.
patent: 5814937 (1998-09-01), Mehrotra et al.
patent: 5841222 (1998-11-01), Heuvelmans et al.
Hamada Munemitsu
Masuda Takeshi
Taguchi Haruo
Takeishi Akira
Yamaguchi Yasutoshi
DelGizzi Ronald E.
O'shea Sandra
TDK Corporation
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