Electric lamp and discharge devices – With support and/or spacing structure for electrode and/or... – Electrode supported by envelope
Reexamination Certificate
2003-01-30
2004-08-24
Patel, Vip (Department: 2879)
Electric lamp and discharge devices
With support and/or spacing structure for electrode and/or...
Electrode supported by envelope
C313S625000, C313S570000
Reexamination Certificate
active
06781292
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications JP2002-348003 filed Nov. 29, 2002 and JP2002-21349 filed on Jan. 30, 2002, the entire contents of which are incorporated herein by reference.
FIELD OF THE INVENTION
The present invention relates to a high-pressure discharge lamp having a translucent ceramic discharge vessel, and a luminaire using such a discharge lamp.
BACKGROUND OF THE INVENTION
Developments for high-pressure discharge lamps have been widely continued since high-pressure discharge lamps are characterized by properties of high efficiency and long life of time.
Especially, a compact single-based metal halide lamp with a rated lamp wattage of about 10-30 W have been developed in recent-years as lighting sources for halogen lamps such as compact single-based high-pressure discharge lamps and headlights.
Such a compact single-based metal halide lamp is known in the conventional arts, JP-10-284004-A, JP-10-83796-A, JP-2001-76677-A, etc.
Such a conventional compact single-based metal halide lamp typically comprises, a translucent ceramic discharge vessel having a pair of cylindrical portions formed in communicating with a swollen portion at its opposite sides, the cylindrical portions respectively having an inner diameter shorter than that of the swollen portion, a pair of metal tubes each fit in the cylindrical portion, a pair of fusible metal plugs each closing the open end of the metal tube thereby an electrode supported to the metal plug facing the interior of the swollen portion, and ionizing filling such as halide, mercury, or rare gas filled in the discharge vessel.
Such a conventional compact single-based metal halide lamp has a lamp efficiency higher than halogen lamps by three to four times. Moreover, the size is remarkably smaller than compact single-based fluorescent lamps. Therefore, the compact single-based metal halide lamp can be used as a point source, and thus it is supposed as an arc tube for novel lighting system other than compact single-based high-pressure discharge lamps and headlights.
However, such a conventional compact single-based metal halide lamp still has a problem of spoiling the reliability on the lamp life time by leaks taking place at the sealing portion due to an incomplete fitting of the fusible metal plug to the open end of the metal tube and a difference between coefficient-of-thermal-expansions of the fusible metal plug and the metal tube.
Although such a problem of leaks occurring at the sealing portion could be avoided by, for example, lengthening the metal tube so as that the temperature of the sealing portion of the metal tube. However, there still remains a problem of that the size of the discharge lamp cannot be reduced.
SUMMARY OF THE INVENTION
In order to solve the above problems, an object of the present invention is to provide a high-pressure discharge lamp with less leaks of ionizing filling and thus capable of maintaining a high reliability for a long time and a luminaire equipped with such a high-pressure discharge lamp. Another object of the present invention is to provide a fixture, which having heat conductive member cools the fluorescent lamp effectively.
A translucent ceramic discharge vessel according to the one aspect of the invention comprises, a translucent ceramic discharge vessel having a swollen portion defining a discharge space and a pair of cylindrical portions formed in communicating with the swollen portion and extending from the swollen portion in the opposite directions with each other, metal tubes each having a outer diameter D and fit with its one end on the cylindrical portion, a pair of fusible metal plugs each plugged in the outer end of the metal tube, the fusible metal plug sealing the discharge vessel by being fused to the inner surface of the metal tube for a specified height T from the outer end of the metal plug, a pair of electrode systems each supported its one and to the fusible metal plug and facing the interior of swollen portion with its other end and ionizing filling filled in the discharge vessel, wherein the ratio T/D of the height T concerning the fusible metal plug and the diameter D satisfies the following equation.
0.40≦T/D≦0.95
In this application, some definitions and their technical meanings are presented for following specific terms, unless otherwise specified.
A discharge vessel defining discharge space has a swollen portion in a shape of spherical, oval, ellipse or cylindrical, and a pair of cylindrical portions extending from the swollen portion in the opposite directions with each other. The swollen portion and the pair of cylindrical portions may be formed in integral or may be separately formed and after that coupled together.
The ceramic material making the discharge lamp may be sapphire, aluminium oxide (Al2O3), yttrium aluminium garnet (YAG), yttrium oxide (YOx), or aluminium nitride (AlN) which has a translucency and a heat-resistivity.
The term “translucency” means an optical permeability in an order or penetrating outside a light generated by a discharge. Thus, it may not be restricted to be transparent, but may be diffusible. Although the swollen portion must be translucent, the cylindrical portions may simply have a light blocking effect.
In order to make the high-pressure discharge lamp compact, it is favorable that the internal volume of the discharge vessel is 0.06 cc or less, and more favorably it is 0.04 cc or less. It is favorable that the overall length of the discharge vessel is 35 mm or less, and more favorably it is in the range of 10-30 mm.
The metal tube is made of high melting point metal such as Molybdenum or Tungsten, which has a high corrosion resistance against the ionizing filling, and a high adhesiveness with the ceramics.
The metal tube is fixed to the inner surface or the outer surface of the cylindrical portion through a cermet, or a combination of cermet and sealing compound for ceramics. The fusible metal plug is plugged in the open end of the cylindrical portion after the ionizing filling has been filled in the discharge vessel. An electrode system is supported on the inner end of the fusible metal plug so as that an electrode formed on the end of the electrode system faces the interior of the swollen portion.
Fusible metals, such as platinum (melting point; 1772° C.), vanadium (melting point; 1980° C.) or Molybdenum (melting point; 2610° C.) which has a thermal expansion coefficient close to that of the metal tube or any alloy with either one of those can be used for the fusing metal plug. When the metal tube is made of Molybdenum and the open end is closed by fusing the end portion, the metal tube can also serve as the fusing metal plug.
The fusion of the fusible metal plug is carried out by applying a high-power energy of such a YAG laser, a CO2 laser or an electron beam.
In case of that the metal tube is fit on the inner surface of the cylindrical portion, if the ratio BD/PL, of the maximum inner diameter BD of the discharge vessel to tho distance PL between the center of the discharge vessel and the inner end of the metal tube is in the range of 0.5-1.5, the efficiency of the discharge lamp will increase. And also, leaks caused by the exfoliation or the metal tube from the cylindrical portion can be prevented.
That is, the ratio BD/PL less than 0.5 are unfavorable, since it causes the temperature of the coldest portion to lower and thus decreasing the lighting efficiency. On the other hand, the ratio BD/PL in excess of 1.5 also unfavorable, since it causes an excessive temperature rise in the scaling portion, and thus causing leaks in the sealing portion.
In each electrode system, the electrode provided on the tip end of the electrode rod faces the interior of the discharge vessel. While the electrode rod is fixed to the fusible metal plug by being the other end of the electrode rod embedded or welded to the fusible metal plug.
The electrode rod is made of high melting point metal such as Tungsten, doped-Tungsten, Tungs
Ishida Masazumi
Kashiwagi Takahito
Oku Shigemi
Sakaguchi Sadao
Patel Vip
Pillsbury & Winthrop LLP
Toshiba Lighting & Technology Corporation
Zimmerman Glenn
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