Electric lamp and discharge devices – With gas or vapor – Envelope with particular structure
Reexamination Certificate
2002-07-10
2004-08-10
Wong, Don (Department: 2821)
Electric lamp and discharge devices
With gas or vapor
Envelope with particular structure
C313S623000, C315S058000
Reexamination Certificate
active
06774566
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications JP2001-284841 and JP2001-284842 both filed on Sep. 19, 2001, the entire contents of which are incorporated herein by reference.
BACKGROUND
The inventions described herein relate to a high pressure discharge lamp which is provided with a light-transmissive discharge vessel made of ceramics (hereinafter, referred to as light-transmissive ceramic discharge vessel) and a luminaire using such a high pressure discharge lamp.
In recent years, a metal halide lamp equipped with a light-transmissive ceramic discharge vessel has been in widespread use. Such a metal halide lamp has features that the color temperature change and the dispersion of colors in lifetime are scarce in compared with a metal halide lamp equipped with a conventional silica glass discharge vessel, in addition to the features of having a longer life-expectancy and a high lighting efficiency
Conventional light-transmissive ceramic discharge vessels used for high pressure discharge lamps (prior-art I), such as metal halide lamps equipped with a light-transmissive ceramic discharge vessel, often have a structure wherein a cylindrical portion, a large-diameter cylindrical portion, and a tubular portion are assembled by shrink-fitting. In this configuration, a tubular portion forms slender cylindrical portion for the swollen portion in which, as for a light-transmissive ceramic discharge vessel, a cylindrical portion and a large-diameter cylindrical portion surround discharge space, respectively. The high pressure discharge lamp equipped with the configuration of light-transmissive ceramic discharge vessel has little change of the color-temperature when changing the lighting position. This is because the change of the coldest portion temperature is small. In the conventional high pressure discharge lamp as mentioned above, the coldest portion is defined in the vicinity of the end of a tubular portion. The temperature of this portion is determined by the balance of the conductive heat and the radiant heat from the electrodes, and the conductive heat from the light-transmissive ceramic discharge vessel. Although the conductive heat and the radiant heat from the electrodes hardly change when the lighting position is changed, the amount of heat conduction from the light-transmissive ceramic discharge vessel changes extensively. That is, at a horizontal position lighting, an arc bends upwards and approaches the wall of upper portion of the light-transmissive ceramic discharge vessel. Thus the upper portion is strongly heated. Meanwhile, the heat conductivity of ceramics, such as a light transmissive alumina used for the light-transmissive ceramic discharge vessel, is significantly high as compared with that of silica glasses
Therefore, it is normal to expect that an amount of heat conducted to the end of the slender cylindrical portion where occurs the coldest portion increases, the temperature of the coldest portion rises and thus the color temperature changes. However, the shrinkage fitting portion of the light-transmissive ceramic discharge vessel works as a heat resistance thus limiting in some degree the amount of heat transferred to the slender cylindrical portion where occurs the coldest portion, suppressing the change of the color temperature at a practically allowable level. This is the reason why the change of the color temperature is small when changing the lighting position, that is, the lighting position property is favorable.
On the other hand, in reference document II as disclosed in the Japanese Patents JP9-147803 and JP 11 204086, a light-transmissive ceramic discharge vessel is constructed in one piece by a cast-molding. This type of discharge vessel has a tendency that the heat capacitance goes relatively low. The reference document II is advantageous for keeping favorable the temperature of the coldest portion due to its nature having the relatively low heat capacitance. However, the reference document II still has a problem due to that the heat conductivity of the light-transmissive ceramic discharge vessel is significantly high.
Moreover, the reference document II falls into two categories, i.e., one that the inner surface and the outer surface of the discharge vessel are defined in gently continuous curves at the boundary portion between the swollen portion and the slender cylindrical portion, and another that the inner surface and the outer surface of the discharge vessel are defined in discontinuous inflected surfaces at the boundary portion between the swollen portion and the slender cylindrical portion.
Meanwhile, when lighting the high pressure discharge lamp with a high frequency current, it is necessary to avoid an acoustic resonance and. To that end, it is desirable to unify acoustic resonance modes of the light-transmissive ceramic discharge vessel. In order to realize the unification of the acoustic resonance modes, it is necessary to shape the inner wall of the swollen portion of a light-transmissive ceramic discharge vessel in spherical. However, in the reference document II, particularly the one having a uniform thickness at the swollen portion of the light-transmissive ceramic discharge vessel and a nearly spherical shape, as shown in the Japanese laid-open patent JP9-147803, a discontinuous inflection is defined in both of the inner and the outer surfaces around the boundary portion between the swollen portion and the slender cylindrical portion. Furthermore, since the electrode reaching a high temperature during lamp operation is located near the inflecting portion, a serious thermal stress occurs in the inflecting portion. Thus, there were problems that the slender cylindrical portion is broken during manufacturing, or a crack easily occurs during lamp operation. As a result of studying measures for solving the problems, the present inventors have found that when the inner surface and the outer surface of the discharge vessel are defined in gently continuous curves at the boundary portion between the swollen portion and the slender cylindrical portion, the mechanical strength of the boundary portion is improved and thus the problems can be eliminated.
In the shrink-fit structure shown in reference document I there is a tendency that a heat capacitance relatively increases. Therefore, when lamp wattage being reduced, there is a problem that it is impossible to maintain the coldest portion in a temperature required for securing high efficiency.
Further, the structure in that the inner surface and the outer surface of the discharge vessel are defined in gently continuous curves at the boundary portion between the swollen portion and the slender cylindrical portion in the prior-art II also fail to solve the problem regarding the lighting position property. That is, since when the inner and the outer surfaces around the boundary portion between the swollen portion and the slender cylindrical portion are both continuous surfaces the conductive heat and the convective heat during lamp operation become easy to be transferred to the coldest portion through the boundary, the problem of the lighting position property becomes serious. When increasing the amount of a metallic halide in the discharge vessel to reduce the problem of the lighting position property, it is effective since the metallic halide becomes hard to move when changing the lighting position. However, this causes an opposite difficulty that impurities, such as H
2
O, becomes easy to mix into the metallic halide, thus remarkably deteriorating the lamp property during life.
Our inventors have found that when a starting-aid conductor, i.e., a metal coil having the same potential as the opposite side the electrode is wound on a slender cylindrical portion, a weak discharge occurs across the coil and the electrode penetrating the slender cylindrical portion at the start of operation and thus the starting operation is aided.
In this configuration, a capacitive coupling is formed between the
Ashida Seiji
Honda Hisashi
Pillsbury & Winthrop LLP
Toshiba Lighting & Technology Corporation
Wong Don
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