Electric lamp and discharge devices – With gas or vapor – Having electrode exterior to envelope
Reexamination Certificate
2001-10-05
2004-04-27
Patel, Ashok (Department: 2879)
Electric lamp and discharge devices
With gas or vapor
Having electrode exterior to envelope
C313S234000, C313S594000
Reexamination Certificate
active
06727649
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This invention relates to a fluorescent lamp and a discharge lamp and more particularly to a fluorescent lamp that is suited for a light source for the backlighting liquid crystal displays that are used in various electronic devices such as personal computers, car-navigation displays, etc.
BACKGROUND OF THE INVENTION
A fluorescent lamp is used as a light source for the backlighting of liquid crystal displays to irradiate uniform light to liquid crystal panels from the back in liquid crystal displays that are used in, for instance, personal computers or car-navigation displays. Accompanied with demands for large-sized, thin and high performance display area of liquid crystal displays, stable and sufficient light intensity, uniform distribution of luminance in the axial direction of lamp tube in the wide temperature range from −40° C. to 85° or under the control of light intensity from several % to 100%, are demanded for a fluorescent lamp itself as a light source for the backlighting jointly for small-sized luminance tube diameter and extended tube length.
However, because the light intensity of the conventional fluorescent lamp which contains mercury as discharge gas is insufficient at a low ambient temperature and mercury may cause the environmental pollution, the development of a fluorescent lamp without using mercury gas is demanded.
A small discharge lamp or a fluorescent lamp using inert gas such as neon gas, krypton gas or xenon gas is disclosed in Japanese Laid-Open Patent Publication (Kokai) No.57-63756. In this discharge lamp, one of two electrodes is provided in a glass tube and the other electrode is provided outside the glass tube. One of the electrodes is provided which extends along an almost entire length of a glass tube and the other electrode is provided on the outer surface of the glass tube against the electrode provided in the glass tube. It was disclosed that this lamp is a small discharge lamp with diameter of 2~10 mm and 50~200 mm long, which is used as a luminous display for displaying characters, numerals or symbols, in which a single lamp or plurarity of lamps having a straight or curved tube is or are used. It is also disclosed that such lamps are used as an energy-saving pilot lamp or a beacon light.
However, for the conventional discharge lamp or the fluorescent lamp in this structure, it is difficult to keep a uniform discharge distance from the inner electrode to the outer electrode along the overall length of the inner electrode and as a result, such problems are caused that a partial discharge is produced and a stable positive column cannot be formed on the entire length of a glass tube. In other words, since a slender fluorescent lamp using a glass tube of 1.6~10 mm in outer diameter and 100~500 mm in length, for example, is used for a backlighting source of a liquid crystal display, it is extremely difficult, in view of the manufacturing technology, to provide electrodes having a uniform discharge distance along the entire length of the glass tube.
Further, in a liquid crystal display, a fluorescent lamp is often subject to influence of vibration depending on the using condition and the inner electrode is deformed locally. Therefore, it is difficult to maintain a discharge distance at always constant value.
Furthermore, glass tubes having complicated shapes such as W or U-shaped tube may be often used for the backlighting sources in the liquid crystal displays. However, it is extremely difficult for the glass tube having such structure to form the electrodes having a uniform discharge distance between the inner electrode and the outer electrode along the entire length of them.
Further, even if a glow discharge region is formed along the entire length of the discharge lamp or the fluorescent lamp having the structure described above, there was a problem that electrons are actively emitted around an inner electrode and thus a diffused positive column is hardly formed thereby resulting a phenomenon that generation of ultraviolet rays is suppressed, in particular when a discharge medium containing xenon is used as discharge gas. Accordingly, when this type of the electrode structure is used for a fluorescent lamp having a glass tube inner wall of which is coated with phosphor for generatining luminance excited by ultraviolet rays, sufficient brightness cannot be obtained.
For the purpose of solving such problems involved in the conventional fluorescent lamps as described above, the applicant of the present invention filed an application as PCT/JP00/06491 (International Filing Date: Sep. 22, 2000) for a fluorescent lamp comprising a glass tube both ends of which are sealed airtight and filled with a discharge medium; a phosphor layer formed on an inner surface of the glass tube; an inner electrode arranged at one end of the glass tube and being given a electric potential; and an outer electrode composed of a conductor spirally wound round the glass tube between the both ends along an axis the tube at a prescribed pitch and being given with another electric potential.
It is an object of the present invention to provide a discharge lamp or a fluorescent lamp which are capable of stably emitting sufficient bright light for the entire length of a glass tube composing the discharge lamp by further improving the invention described above.
It is a further object to provide a discharge lamp or a fluorescent lamp capable of stably emitting light in an uniform luminance distribution for the overall length of a glass tube composing the discharge lamp or the fluorescent lamp.
SUMMARY OF THE INVENTION
A fluorescent lamp according to the present invention comprises a glass tube having both ends sealed airtight and containing a discharge medium filled therein, a fluorescent layer formed on the inner wall of the glass tube, an inner electrode arranged at one end of the glass tube which is given with one electric potential, and an outer electrode composed of a linear conductor spirally wound around the glass tube between its both ends at a prescribed pitch along an axis of the tube and is given with another electric potential, the outer electrode is so designed as to satisfy the formula:
w×n≦
0.3
where w(cm) is a width of the conductor comprising the outer electrode and n(turns/cm) is the average number of turns of the conductor in the unit length in the axial direction of the glass tube.
Further, a fluorescent lamp according to the present invention comprises a glass tube with a phosphor film formed on the inner surface thereof and with sealing portions so formed at each end thereof that a discharge medium is filled therein, a first feeding lead wire penetrating one of the sealing portions of the glass tube airtight, an inner electrode connected to an end of the feeding lead wire extending into the glass tube, a second feeding lead wire composed of a linear conductor which is spirally wound around an outer surface of the glass tube along an axial direction of the glass tube and an end of which is electrically connected to the second feeding lead wire, wherein the outer electrode is so designed that a winding pitch of the linear conductor becomes continuously or step wisely small corresponding to a distance from the inner electrode in the axial direction of the glass tube.
Further, a fluorescent lamp according to the present invention comprises a translucent tube with sealing portions formed at its both ends, a phosphor film formed on an inner surface of the translucent tube, a discharge medium containing rare gas filled in the translucent tube, a first feeding lead wire penetrating one of the sealing portions of the translucent tube and sealed therein airtight, an inner electrode provided at an end of the first feeding lead wire, and an outer electrode composed of a linear conductor which is spirally wound around the translucent tube for almost entire length of the tube in its axial direction and an end of which is connected to the second feeding lead wire, wherein the outer electrode is provided with a tube power
Ueno Takanobu
Yano Hidetoshi
Banner & Witcoff , Ltd.
Harison Toshiba Lighting Corporation
Leurig Sharlene
Patel Ashok
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