Electric lamp and discharge devices – With gas or vapor – Envelope with particular structure
Reexamination Certificate
2000-03-21
2001-10-23
Patel, Ashok (Department: 2879)
Electric lamp and discharge devices
With gas or vapor
Envelope with particular structure
C313S638000, C313S570000, C313S573000
Reexamination Certificate
active
06307321
ABSTRACT:
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 10-210120, filed Jul. 24, 1998.
BACKGROUND OF THE INVENTION
The present invention relates to a high-pressure discharge lamp that has a discharge vessel made of light-transmitting ceramic, and a lighting apparatus that uses the lamp.
There is a demand for a high-pressure discharge lamp having a smaller lamp power of 20 W or less, which is made of light-transmitting ceramic and which has a long lifetime and a high efficiency.
It was found that a leak occurs at the seal shortly after the lamp is turned on even if a small high-pressure discharge lamp is manufactured by proportionally reducing directly the specifications of the discharge vessel and electrodes of a conventional, relatively large, high-pressure lamp to meet the demand. This is because the modes of conveying heat to the seal from a heat source such as discharge plasma, i.e., heat conduction, convection and radiation, are unbalanced.
To realize small high-pressure discharge lamps, the prior art technology of high-pressure discharge lamps should therefore be reviewed fundamentally to create new specifications that are suitable for small, high-pressure discharge lamps.
In contrast, the present inventors have already invented a high-pressure discharge lamp comprising light-transmitting ceramic that has a desirable long lifetime and a preferable light-emission efficiency even with a small size. That invention has already been filed as Japanese Patent Application No. 10-196322. The invention according to this application discloses a light-transmitting ceramic discharge vessel comprising a bulging section having both ends narrowed by continuous curved surfaces, and small-diameter cylindrical sections communicating with the ends of the bulging section and having an inner diameter smaller than the bulging section. It is very advantageous for a small high-pressure discharge lamp to use this discharge vessel because the discharge vessel can be formed integral with ease and has no optically and thermally discontinuous portion.
It was found, however, a problem occurs depending on the size of the space in the bulging section around the electrodes in the light-transmitting ceramic discharge vessel having the shaped as described above. That is, when a high-pressure discharge lamp which has been lightened is turned off, vapor of fillings such as a halide and mercury which has been dispersed in the discharging space moves toward narrow gaps in the small-diameter cylindrical sections of the light-transmitting ceramic discharge vessel having a low temperature. At this time, a turbulent flow is generated around the electrodes. If a turbulent flow is generated, the fillings such as halide and mercury easily adhere to surfaces of distal ends of the electrodes. Once the fillings have adhered to the distal ends of the electrodes, the electric discharging power attenuates so operation errors are caused at starting or transition from a glow discharge to an arc discharge becomes difficult. As a result, sputtering is excited and blackening occurs in the light-transmitting ceramic discharge vessel due to the sputtering.
BRIEF SUMMARY OF THE INVENTION
The first object of the present invention is to provide a small, high-pressure discharge lamp which starts steadily.
The second object of the present invention is to provide a small, high-pressure discharge lamp which easily transits from glow discharge to arc discharge.
The third object of the present invention is to provide a small, high-pressure discharge lamp in which the light-transmitting ceramic discharge vessel is prevented from blackening due to sputtering.
The forth object of the present invention is to provide a lighting apparatus using the above described small, high-pressure discharge lamp.
The first high-pressure discharge lamp according to this invention is characterized by comprising: a light-transmitting ceramic discharge vessel having an internal volume of 0.1 cc or less and including a bulging section and small-diameter cylindrical sections communicating with both ends of the bulging section, the bulging section having both ends narrowed by a continuous curved surface, and the small-diameter cylindrical sections having an inner diameter smaller than the bulging section; power-supplying conductors each including a seal part and a halide-resistant section having a proximal end connected to a distal end of the seal part and inserted respectively in the small-diameter cylindrical sections of the light-transmitting ceramic discharge vessel, each of the halide-resistant sections forming a slight gap to the inner surface of the small-diameter cylindrical section; a pair of electrodes respectively arranged at the distal ends of one halide-resistant parts and located in the bulging section of the light-transmitting ceramic discharge vessel, with a distance d1 of 1.0 mm or above maintained between each of distal ends of the electrodes and the inner surface of the light-transmitting ceramic discharge vessel on a plane perpendicular to an axis of the light-transmitting ceramic discharge vessel including the distal ends of the electrodes; seals made of ceramic-sealing compound respectively making sealing between the small-diameter cylindrical sections of the light-transmitting ceramic discharge vessel and the seal parts of the power-supplying conductors; and a discharge medium containing metallic halide and filled in the light-transmitting ceramic discharge vessel.
In the present invention and each invention described below, the terms are defined to have the following technical meanings, unless otherwise specified:
(Light-transmitting Ceramic Discharge Vessel) “Light-transmitting ceramic discharge vessel” means a discharge vessel made of light-transmitting and heat-resistant materials. Among these materials are: a single-crystal metallic oxide such as sapphire; a polycrystalline metallic oxide such as translucent, airtight aluminum oxide, yttrium-aluminum garnet (YAG) or yttrium oxide; and a polycrystalline non-oxide such as aluminum nitride (AIN). The term “light-transmitting” is used in the sense that the light generated by discharge may be guided to the outside, passing through the discharge vessel. It may mean either transparency or light-diffusing property.
To manufacture the light-transmitting ceramic discharge vessel, the bulging section, or center section, and the small-diameter cylindrical sections connected to the ends of the bulging section is preferably formed integral first. Otherwise, the light-transmitting ceramic discharge vessel can be also formed in a manner that the bulging section is molded preliminarily with the both ends narrowed by a continuous curved surface integrally, and then a pair of small-diameter cylindrical sections preliminarily molded are fitted in the distal ends of the bulging section respectively and sintered.
The internal volume of the light-transmitting ceramic discharge vessel is defined to 0.1 cc or less because the present invention relates to the small, high-pressure discharge vessel.
The internal volume of the light-transmitting ceramic discharge vessel is measured in the following manner: the discharge vessel is put in water to fill the inside with water; opening ends of the small-diameter cylindrical section provided at the both ends of the discharge vessel are closed; the discharge vessel is taken out of water; and then water contained in the discharge vessel is measured.
(Power-Supplying Conductors)
The Power-Supplying conductor is provided to at least one of the small-diameter cylindrical section of the light-transmitting ceramic discharge vessel.
“Power-Supplying conductors” serve to supply power from a power supply through a ballast means, thus applying a voltage between the electrodes to start the high-pressure discharge lamp, and supplying a current to light the high-pressure discharge lamp. They are sealed airtightly to the small-diameter cylindrical sections by the means that will be described later.
The power-supplying conductor
Ashida Seiji
Honda Hisashi
Christensen O'Connor Johnson & Kindness PLLC
Patel Ashok
Toshiba Lighting & Technology Corporation
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