Metal halide lamp

Details Metal halide lamp Metal halide lamp

2002-06-27

2004-06-29

Cariaso, Alan (Department: 2875)

Electric lamp and discharge devices

With temperature modifier

Double wall, jacket or casing for envelope

C313S567000, C313S637000

Reexamination Certificate

active

06756721

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to an arc tube used for a metal halide lamp.
BACKGROUND OF THE INVENTION
Metal halide lamps using ceramic arc tubes have been used widely for indoor lighting in stores and shops because such metal halide lamps have higher luminous efficiency, higher color rendering and longer service lives when compared to metal halide lamps using quartz arc tubes.
FIGS. 5 and 6
show respectively a metal halide lamp using a conventional ceramic arc tube. An arc tube
28
comprises an arc tube container
29
composed of a discharge arc tube portion
30
of a polycrystalline alumina ceramic material and a pair of thin tube portions (
31
,
32
) sintered at the both ends of the discharge arc tube portion
30
. A pair of tungsten coil electrodes (
33
,
34
) are arranged at the both ends of the arc tube
28
. Feeding portions (
35
,
36
) of niobium or conductive cermet are adhered hermetically to the thin tube portions (
31
,
32
) by means of frit
37
, and the tungsten electrodes (
33
,
34
) are connected to the respective feeding portions (
35
,
36
). A luminescent material
38
comprising a metal halide, mercury as a buffer gas, and a start-aiding rare gas such as argon are filled in the arc tube
28
. As illustrated in
FIG. 6
, the arc tube
28
composing a lamp
39
is disposed inside an outer bulb
40
of either quartz or hard glass, and a base
41
is attached to the outer bulb
40
. About 50 kPa of a nitrogen-based gas is filled in the outer bulb
40
. In general, the lamp
39
is turned on by means of a copper-iron inductance ballast or an electron ballast with a built-in starter.
For example, references such as JP-57(1982)-92747 A and U.S. Pat. No. 5,973,453 describe the use of cerium iodide in combination with sodium iodide for a luminescent material applicable for a typical metal halide lamp for indoor/outdoor use. The luminescent material of cerium iodide can provide improved luminous efficiency since many of the emission spectra of cerium are distributed in a region with a higher relative luminosity factor regarding human eyes. U.S. Pat. No. 5,973,453 and Tokuhyo-2000-501563 (published Japanese translation of PCT international publication for patent application) describe a suitable NaI/CeI
3
molar composition ratio in a range from 3 to 25 (corresponding to a CeI
3
composition ratio from 12.2 wt % to 53.7 wt %), which is suitable for obtaining white light source color.
However, a conventional metal halide lamp filled with a luminescent material of cerium iodide and sodium iodide has a problem of a drastic change in the lamp color temperature as well as a remarkable lowering in the flux maintenance factor over the lighting time.
SUMMARY OF THE INVENTION
For solving the above-described problems, a metal halide lamp according to the present invention comprises an arc tube having an envelope as an arc tube container made of an oxide-based translucent ceramic material, and the arc tube is filled with a luminescent materials comprising at least a cerium halide, a sodium halide, a thallium halide and an indium halide.


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European Search Report.

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