Electric lamp and discharge devices – With gas or vapor – Envelope with particular structure
Reexamination Certificate
2003-02-24
2004-06-01
Patel, Vip (Department: 2879)
Electric lamp and discharge devices
With gas or vapor
Envelope with particular structure
C313S491000, C313S493000, C313S620000
Reexamination Certificate
active
06744206
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to metal halide lamps, and in particular relates to a metal halide lamp that uses an arc tube made of alumina ceramic.
(2) Related Art
In recent years, arc tubes made of alumina ceramic have become mainstream ones for use in metal halide lamps, replacing conventional silica glass arc tubes. Alumina ceramic has higher heat-proof properties than silica glass, and therefore is a suitable material for arc tubes used in such high-pressure discharge lamps as metal halide lamps, which reach high temperatures during lighting.
The temperature of such a metal halide lamp using an alumina ceramic arc tube can be raised to high during lighting of the lamp. Therefore, the lamp is enabled to exhibit higher color rendition and higher luminous efficiency.
Further, alumina ceramic has a lower reactivity to metal halide enclosed in an arc tube than silica glass. With the use of such alumina ceramic arc tubes, therefore, metal halide lamps are expected to have a longer life.
Here, a method for sealing electrodes in this type of lamp is different from a sealing method employed for a lamp using a silica glass arc tube. The sealing method employed for the silica glass arc tube is to seal electrodes by heating and crushing ends of side-tube parts of the arc tube. Unlike this method, the sealing method employed for the alumina ceramic arc tube is to first insert a power feeding member into a space formed within each of two thin-tube parts, and then inject a melted sealing material, e.g., a glass frit, into the space, thereby sealing the power feeding member in each thin-tube part. According to this method, however, the power feeding member and the thin-tube part are sealed only at the end of each thin-tube part not facing the discharge space via the sealing material, and the unsealed area results in a gap between the power feeding member and the thin-tube part (see e.g., Japanese Laid-open Patent Application No. S57-78763). Such a gap is inevitably large for a large-size lamp with a high wattage.
As described above, a conventional metal halide lamp that uses an alumina ceramic arc tube has gaps between its power feeding members and thin-tube parts of the arc tube. When this conventional lamp is lit with the electrodes being oriented in the vertical direction, a light-emitting metal enclosed within the arc tube is likely to flow into the gap in the lower one of the thin-tube parts in the vertical direction.
If a portion of the light-emitting metal flows into the gap during a test-life of the lamp (hereafter simply a “life”) the amount of metal contributing to light emission in the discharge space decreases accordingly. If this happens, a sufficiently high vapor pressure cannot be obtained. The lamp then suffers from the problem that its color temperature changes greatly as the lamp is lit for long hours.
To solve such problems, Japanese Laid-open Patent Application No. 2000-340171 discloses the lamp construction where, in each thin-tube part, at least a predetermined distance is provided between (a) one end of the thin-tube part facing the discharge space and (b) the electrode coil.
FIG. 1
shows a metal halide lamp with the conventional construction according to the disclosure. This metal halide lamp is made up of a light-emitting unit
102
, thin-tube units
103
a
and
103
b
, a pair of electrodes
105
a
and
105
b
, electrode holding members
106
a
and
106
b
, and sealing members
107
a
and
107
b
. The light-emitting unit
102
is made of translucent ceramic and in which a discharge space
101
is formed. In the discharge space
101
, a light-emitting metal is enclosed. The thin-tube units
103
a
and
103
b
are respectively provided at both ends of the light-emitting unit
102
. The pair of electrodes
105
a
and
105
b
respectively have coils
104
a
and
104
b
at their tops. The electrode holding members
106
a
and
106
b
respectively hold the electrodes
105
a
and
105
b
at their one ends. The other ends of the electrode holding members
106
a
and
106
b
extend from the ends of the thin-tube units
103
a
and
103
b
not facing the discharge space
101
. The sealing members
107
a
and
107
b
are respectively provided to seal the electrode holding members
106
a
and
106
b
to the thin-tube units
103
a
and
103
b
. According to the disclosure, the metal halide lamp is to be constructed to satisfy the condition “X>0.0056P+0.394”, where “P [W]” represents a lamp wattage, and “X [mm]” represents a distance from one end of the coil
104
a
(
104
b
) facing the thin-tube unit
103
a
(
103
b
) to one end of the thin-tube unit
103
a
(
103
b
) facing the discharge space
1
.
By satisfying this condition, the temperature of the ends of the thin-tube units
103
a
and
103
b
facing the discharge space can be lowered to such a degree that an excess of light-emitting metal enclosed in the discharge space can exist in a liquid form therein. Therefore, the amount of light-emitting metal flowing into the gaps in each thin-tube unit can be reduced, thereby reducing the color temperature change.
According to the above disclosure, however, means for occupying the gap “&lgr;” formed within each of the thin-tube units
103
a
and
103
b
is not provided. Even if a certain conventional technique provides a member as this means for occupying the gap “&lgr;”, the member is entirely embedded in a thin-tube unit so as to be recessed from the end of the thin-tube unit, and fails to prevent a light-emitting metal from easily flowing info the gap “&lgr;”, thereby failing to prevent the color temperature from being greatly changed after continuous lighting of long hours.
SUMMARY OF THE INVENTION
The present invention therefore aims at providing a metal halide lamp that exhibits stable characteristics with a reduced change in the color temperature even after continuous lighting of long hours, by reducing the amount of light-emitting metal flowing into gaps formed in thin-tube units of an arc tube.
The above aim can be achieved by a metal halide lamp, including: a bulb that is made up of a light-emitting unit in which a discharge space is formed, and a pair of thin-tube units each being fitted into an opening in a different one of both ends of the light-emitting unit; a pair of electrodes that extend into the discharge space so that tops thereof are opposed to each other, each electrode having an electrode coil at a top part thereof; a pair of electrode holding members each being provided through a different one of the thin-tube units so that one end thereof holds the electrode and the other end thereof extends from one end of the thin-tube unit not facing the discharge space, each electrode holding member being sealed to the thin-tube unit via a sealing member; a tubular member that is provided in at least one of the thin-tube units, so that the electrode and/or the electrode holding member therein is inserted through the tubular member, the tubular member being made of a heat-proof and heat-conductive material, wherein the expressions “X≧0.0056P+0.194” and “0 ≦L≦0.44X” are satisfied, where “P” is a lamp wattage [W], “X” is a distance [mm] from one end of the thin-tube unit facing the discharge space to one end of the electrode coil facing the thin-tube unit, and “L” is a length [mm] of a part of the tubular member protruding from the end of the thin-tube unit facing the discharge space into the discharge space.
The above aim can also be achieved by a metal halide lamp, including: a bulb that is integrally made up of a light-emitting unit in which a discharge space is formed, and a pair of thin-tube units; a pair of electrodes that extend into the discharge space so that tops thereof are opposed to each other, each electrode having an electrode coil at a top part thereof; a pair of electrode holding members each being provided through a different one of the thin-tube units so that one end thereof holds the electrode and the other end thereof exte
Kakisaka Shunsuke
Miura Mikio
Nishiura Yoshiharu
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