Electric lamp and discharge devices – With gas or vapor – Envelope with particular structure
Reexamination Certificate
2002-09-19
2004-06-15
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
With gas or vapor
Envelope with particular structure
C313S637000, C313S573000, C313S493000
Reexamination Certificate
active
06750612
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an arc tube for a discharge lamp unit, having a closed glass bulb held between pinch seal portions located at opposite ends of the closed glass bulb, and a pair of electrodes provided in the closed glass bulb so as to be opposite to each other. Particularly it relates to a mercury-free arc tube for a discharge lamp unit, having a closed glass bulb not containing mercury but containing main light emitting metal halide and starting rare gas enclosed in the closed glass bulb.
2. Description of the Related Art
FIG. 4
shows a discharge bulb which is a conventional discharge lamp unit used as a light source of an automotive lamp. The discharge bulb has a structure in which an arc tube
2
having a closed glass bulb
2
a
as a light emitting portion is integrated with an electrically insulating plug body
1
made of a synthetic resin. A rear end portion of the arc tube
2
is gripped by a metal support member
8
fixed to the electrically insulating plug body
1
. A front end portion of the arc tube
2
is supported by a metal lead support
9
which serves also as a current conduction path extended out from the electrically insulating plug body
1
.
The arc tube
2
has a structure in which main light emitting metal halide, buffer mercury and starting rare gas are enclosed in the closed glass bulb
2
a
which is held between pinch seal portions
2
b
and
2
b
located at opposite ends of the close glass bulb
2
a
and which is provided with a pair of electrodes
3
and
3
so as to be opposite to each other. Light is emitted on the basis of arc generated by electric discharge between the pair of electrodes
3
and
3
. The discharge bulb is superior to that of an incandescent bulb because a large quantity of emitted light, a long lifetime, etc. can be achieved by the discharge bulb. For this reason, nowadays there is a tendency for the discharge bulb to be used as a light source for a head lamp or a fog lamp.
The reference numeral
4
designates a lead wire led out from each pinch seal portion
2
b
. The reference numeral
5
designates a sheet of molybdenum foil for connecting the lead wire
4
to a corresponding tungsten electrode
3
. Further, ultraviolet-shielding shroud glass
6
is integrally welded to the arc tube
2
to thereby form a structure in which the closed glass bulb
2
a
is surrounded by a closed space formed by the shroud glass
6
. Hence, the closed glass bulb
2
a
is kept at a high temperature while ultraviolet rays in a wavelength range harmful to the human body are cut off from light emitted from the arc tube
2
.
Mercury enclosed in the conventional closed glass bulb
2
a
is a substance toxic to the environment. In response to the social needs of reducing the cause of global environmental pollution as much as possible, it is desirable that a mercury-free arc tube not containing mercury, which is a substance toxic to the environmental, is developed.
SUMMARY OF THE INVENTION
The following findings have been obtained in the process of research and development on a mercury-free arc tube not containing mercury.
Mercury acts mainly as buffer substance for keeping the tube voltage constant to reduce the amount of electrons colliding with electrodes to thereby buffer the damage of is the electrodes. Mercury acts also as a light emitting substance for emitting white light. For this reason, if mercury was removed from the substances enclosed in the closed glass bulb, the following changes (problems) occurred in the characteristic as the arc tube.
Firstly, the tube voltage is reduced. That is, because the tube electric power required for electric discharge cannot be obtained, it is necessary to increase the tube current in order to increase the tube electric power. Hence, the load imposed on the electrodes increases, so that luminous efficacy is lowered. Moreover, the amount of heat generated in ballast increases because of the increase of the tube current, so that system efficiency is lowered.
Secondly, the rising edge of luminous flux is delayed. That is, a sufficient quantity of emitted light cannot be obtained at an initial stage of operation (electric discharge) because mercury high in vapor pressure is absent.
Thirdly, luminous flux in a visible region is reduced because light emitted due to mercury is absent.
Fourthly, the color of emitted light is different (reddish) from the color of light emitted from the conventional mercury-containing arc tube.
Fifthly, luminous intensity distribution control can be hardly performed because the curvature of arc generated by electric discharge between the electrodes is large.
The spectral characteristic of a mercury-free arc tube having main light emitting metal halide (NaI and ScI
3
) and a rare gas enclosed in a closed glass bulb was as represented by the solid line in FIG.
5
. It has been found that the mercury-free arc tube generally exhibits substantially the same spectral characteristic as that of the conventional mercury-containing arc tube except that the intensity of light particularly in wavelength ranges near to 435 nm and 546 nm in the mercury-free arc tube is lower (lower in peak) by the quantity represented by the broken line in
FIG. 5
than that in the conventional mercury-containing arc tube.
Therefore, experiments have been performed to examine whether characteristics approaching the characteristics of the conventional mercury-containing arc tube can be obtained or not. The experiments are directed to a selection of metal halide to be enclosed, which has a buffer function and is effective in increasing the intensity of light in wavelength ranges near to 435 nm and 546 nm in spectral characteristic. Such metal halide should be selected as a substitute of mercury having a buffer function and be enclosed while the charged pressure of a rare gas enclosed in the closed glass bulb and a quantity and ratio of enclosure of the main light emitting metal halide are adjusted without changing the shape and dimensions of the conventional mercury-containing arc tube as possible. As a result, it has been confirmed that the characteristic can be improved. Thus, Japanese patent application No. 2001-286252 is proposed (applied).
After then, as a result of continuous experiments by the inventors, it is confirmed that there can be provided a mercury-free arc tube which has characteristics approaching the characteristics of a conventional mercury-containing arc tube even if buffer metal halide is not enclosed in the closed glass bulb while a total amount and ratio of the main light emitting metal halide and the charged pressure of starting rare gas enclosed in the closed glass bulb are adjusted. Thus, Japanese patent application No. 2002-243489 is proposed (applied).
The present invention is based on the problems in the conventional art and the inventor's knowledge and an object thereof is to provide a mercury-free arc tube for a discharge lamp unit in which characteristics approaching the characteristics of the conventional arc tube can be obtained.
In order to achieve the object, according to a first aspect of the invention, there is provided a mercury-free arc tube, which is not containing mercury, for a discharge lamp unit, in which electrodes are opposite to each other and provided in a closed glass bulb held between pinch seal portions, and main light emitting metal halide is enclosed; wherein starting rare gas has a charged pressure set to be in a range of from 8 to 20 atmospheres.
Preferably, according to a second aspect of the invention, buffer metal halide is enclosed in the closed glass bulb together with the main light emitting metal halide and the starting rare gas.
(Operation) Substances used in the conventional case are used as the main light emitting metal halide and the starting rare gas. That is, sodium-scandium-based halide such as NaI and ScI
3
is used as the former and Xe is used as the latter.
The buffer metal halide in place of mercury is at least one selected from the group consisting of halides of Al, Bi, Cr,
Fukuyo Takeshi
Irisawa Shinichi
Shido Masaya
Takagaki Michio
Koito Manufacturing Co. Ltd.
Patel Nimeshkumar D.
Santiago Mariceli
Sughrue & Mion, PLLC
LandOfFree
Mercury-free arc tube for discharge lamp unit does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Mercury-free arc tube for discharge lamp unit, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Mercury-free arc tube for discharge lamp unit will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3347574