Metal halide lamp

Details Metal halide lamp Metal halide lamp

2002-06-27

2004-03-16

Clinger, James (Department: 2879)

Electric lamp and discharge devices

With gas or vapor

Having electrode lead-in or electrode support sealed to...

C313S621000

Reexamination Certificate

active

06707252

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a metal halide lamp.
2. Related Background Art
Recently, metal halide lamps having an arc tube made of semitransparent polycrystalline alumina ceramic have been developed actively as substitutes for lamps having a quartz tube. Since this alumina ceramic tube has the heat-resistant temperature of 1,200° C., which is higher than the heat-resistant temperature (1,000° C.) of the quartz tube that has been used conventionally, a load imposed on the wall of the arc tube (hereafter called wall load) can be set higher, so that a metal halide lamp with a higher lamp efficiency can be obtained. With regard to this kind of lamp, low watt type lamps with a lamp input of 70 to 150W used for general interior lighting have been developed and commercialized mainly. However, high watt type lamps with a lamp input of 200 to 1,000W used for general exterior lighting also are being demanded now by the market.
An available low watt type metal halide lamp for interior lighting (e.g. for shops) having an alumina ceramic tube, for example in a case of a 150W type, has excellent properties of the lamp efficiency of 90 lm/W, the average color rendering index Ra of 90 and the rated life of 6,000 h. It should be noted that “the rated life” refers to an aging elapsed time when the luminous flux of the lamp is lowered to 70% of the value at the aging time of 100 h.
FIG. 8
is a cross-sectional view showing the construction of the arc tube in such a lamp. The arc tube
115
includes a light-emitting portion
116
made of polycrystalline alumina ceramic, which functions as a discharge arc region, and narrow tubes
117
and
118
provided at the both ends of the light-emitting portion
116
. The light-emitting portion
116
and the narrow tubes
117
and
118
are integrated with each other by shrinkage fit. Inside of the light-emitting portion
116
, a pair of tungsten electrodes
119
and
120
is provided. Into the narrow tubes
117
and
118
, electrical supply members
121
and
122
made of niobium or an electrically conductive cermet are sealed hermetically with frit. At the discharge side ends of the electrical supply members
121
and
122
, electrode rods extending from the tungsten electrodes
119
and
120
are connected. Within the arc tube
115
, a light-emitting substance including metal halides such as DyI
3
, TmI
3
, HoI
3
, TlI, and NaI, Hg functioning as a buffer gas and a rare gas for supporting ignition such as Ar are each filled.
Basically, the shape of the arc tube in the above-stated low watt type metal halide lamp employing the alumina ceramic tube is the same as that of the conventional metal halide lamp having a quartz arc tube used for interior lighting. That is, the typical dimensions of the alumina ceramic arc tube with the configuration shown in
FIG. 8
, in a case of 150W type, for example, are the distance between electrodes Le of 10 mm and the inner diameter of tube &phgr;i of 10.6 mm. In this case, a so-called arc tube shape parameter Le/&phgr;i, which is a major parameter indicating the shape of the arc tube, becomes 0.94. The wall load “we”
0
on the arc tube during operation of the lamp is 27 W/cm
2
. Note here that, assuming that the lamp watt and the internal surface area of the arc tube are W
1a
and S
a
, respectively, then the wall load “we” can be represented by we=W
1a
/S
a
.
On the other hand, as for the conventional lamp with a quartz arc tube, dimensions of the typical 150W type lamp are the distance between electrodes Le of 13.5 mm and the internal diameter of the tube &phgr;i of 13 mm, so that the value of Le/&phgr;i becomes 1.04. That is, the values of arc tube shape parameter Le/&phgr;i are set at almost the same level for both lamps. Therefore, it can be said that both of the arc tube in the conventional low watt type alumina ceramic lamp for interior lighting and the quartz arc tube metal halide lamp have a relatively thick and short shape.
As another example, JP10(1998)-144261 A discloses a so-called short arc type metal halide lamp of a 20 to 250 W type, employing an alumina ceramic tube. The feature of this lamp resides in that, as illustrated in
FIG. 9
, a discharge light-emitting portion in an arc tube
123
includes a cylindrical-shaped center portion
124
and hemispherical end portions
125
and
126
. The value of arc tube shape parameter Le/&phgr;i of this lamp is specified within a range between 0.66 and 1.25, which corresponds to the low-watt type lamp for interior lighting shown in
FIG. 8
, whereas the wall load “we” is specified within a relatively high range of 25 to 35 W/cm
2
. In this way, this lamp can be grouped into a short arc type high-pressure discharge lamp for specialized lighting purpose, and the arc tube has a thick and short shape, which is the same as the above-stated low-watt type metal halide lamp for interior lighting. As for a light-emitting substance of this lamp, metal halides such as DyI
3
, TmI
3
, HoI
3
, TlI, and NaI as described above are filled therein.
Meanwhile, U.S. Pat. No. 5,973,453 discloses the shape of an arc tube in a high efficiency metal halide lamp for general exterior lighting, employing an alumina ceramic tube. In this lamp, a cerium halide based substance, whose emission spectrum lies in a wavelength region with a high spectral luminous efficiency, is filled as a light-emitting substance especially for realizing a lamp with a high luminous efficiency. As a specific light-emitting substance, cerium iodide (CeI
3
) and sodium iodide (NaI) are filled in a molar ratio of NaI/CeI
3
ranging 3 from 25. Thereby, excellent properties of a high lamp efficiency of 130 lm/w and an average color rendering index Ra of 58 are realized in a 150 W type lamp. In this case, the value of arc tube shape parameter Le/&phgr;i is specified within a range greater than 5 in order to attain a high luminous efficiency and a long life required for general exterior lighting sources. As described later, such an arc tube has a thin and long shape, which is common to the conventional high-pressure sodium lamp and metal halide lamp for general exterior lighting. The wall load of the lamp is specified to be 30 W/cm
2
or less.
Note here that the alumina ceramic tube was originally invented, developed, and adapted for a material of arc tubes for high-pressure sodium lamps for general exterior lighting. In this case also, the above-mentioned feature of the alumina-ceramic tube is exploited, so that, for instance in a 400 W type, a high luminous efficiency and long life high-pressure sodium lamp with a lamp efficiency of approximately 140 lm/W and a rated life of 2,000 h, and also with a relatively low average color rendering index Ra of 25, was developed and became widely available. Here, the arc tube of the high-pressure sodium lamp has a thin and long shape and the value of arc tube shape parameter Le/&phgr;i is increased with the increase in the lamp input. For example, the specific dimensions of the lamp of a 400 W type are the distance between electrodes Le of 84 mm and the inner diameter of arc tube &phgr;i of 7.65 mm, so that the value of Le/&phgr;i is set at 11.0. Whereas, those of the lamp of a 700 W type are 134 mm in Le and 9.7 mm in &phgr;I, so that the value of Le/&phgr;i is set at 13.0. The wall loads of the arc tube are set at approximately 15 W/cm
2
in the 400 W type and 13 W/cm
2
in the 700 W type.
In addition, also in the conventional quartz arc tube type metal halide lamp of a high watt type for exterior lighting, a relatively thin and long shaped arc tube is employed basically, as compared with the above-described thick and short shaped arc tube of a low watt type for interior lighting. In this case also, the value of arc tube shape parameter Le/&phgr;i is increased with the increase in the lamp input. For example, the typical values of Le/&phgr;i are set at 2.1, 2.2, 2.5, and 2.7 in a type of 300 W, 400 W, 700 W, and 1,000 W, respectively. In general, the rated life of the lamp is specified at 9,000 h or more.
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