Electric lamp and discharge devices: systems – Pulsating or a.c. supply
Reexamination Certificate
1998-10-13
2001-04-17
Vu, David (Department: 2821)
Electric lamp and discharge devices: systems
Pulsating or a.c. supply
C315S2090SC, C313S637000, C313S643000
Reexamination Certificate
active
06218789
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a metal halide lamp which can be used as a light source in various apparatuses such as liquid-crystal projectors and lighting equipments.
2. Description of the Related Art
Liquid-crystal projectors enlarge images of characters and figures, and project and display the enlarged images. In general, light sources in the liquid-crystal projectors are required to output light at given power levels. Since metal halide lamps have high luminous efficiencies and excellent color rendering performances, they are frequently used as light sources in the liquid-crystal projectors.
Japanese published unexamined patent application
3-219546
discloses a metal halide lamp having an arc tube filled with metal halide. In the lamp of Japanese application
3-219546
, the metal halide uses iodide or bromide containing neodymium, dysprosium, or cesium.
In general, metal halide lamps are operated by rectangular electric waves having low frequencies equal to about 200 Hz. It is known to operate metal halide lamps by electric power having high frequencies. In this case, operation circuits for the metal halide lamps can be miniaturized.
When a metal halide lamp is operated by high-frequency electric power, an arc therein and a light emitting region around the arc tend to waver. Thus, in this case, resultant light outputted from the metal halide lamp tends to flicker.
Even when a metal halide lamp is operated by low-frequency rectangular electric wave, an arc therein sometimes flickers.
SUMMARY OF THE INVENTION
It is an object of this invention to provide a metal halide lamp which can develop a stable arc.
A first aspect of this invention provides a metal halide lamp comprising an arc tube containing at least mercury and metal halide; a pair of opposed main electrodes extending in the arc tube; means for applying a lamp voltage between the main electrodes; wherein the main electrodes have respective distal ends which are spaced from each other by a predetermined distance “d”, and the predetermined distance “d” and the lamp voltage “Vla” which occurs during stable rated operation of the lamp satisfy a relation as follows:
Vla/d
≦24(V/mm)
A second aspect of this invention is based on the first aspect thereof, and provides a metal halide lamp wherein the lamp-voltage applying means comprises means for applying an electric operation signal between the main electrodes, the electric operation signal having a predetermined frequency at which an acoustic standing wave occurs in a direction perpendicular to a direction of an axis connecting the main electrodes.
A third aspect of this invention is based on the first aspect thereof, and provides a metal halide lamp wherein the arc tube develops an arc therein, and the metal halide comprises molecule emitting light in a region around the arc.
A fourth aspect of this invention is based on the first aspect thereof, and provides a metal halide lamp wherein the metal halide contains at least one of La, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.
A fifth aspect of this invention is based on the first aspect thereof, and provides a metal halide lamp wherein the predetermined distance “d” is equal to or less than 5 mm.
REFERENCES:
patent: 3927343 (1975-12-01), Beijer et al.
patent: 4047069 (1977-09-01), Akutsu et al.
patent: 5773937 (1998-06-01), Miyazaki et al.
patent: 5814944 (1998-09-01), Saito et al.
patent: 5880561 (1999-03-01), Miyazaki et al.
patent: 3-219546 (1991-09-01), None
patent: 4-298994 (1992-10-01), None
patent: 6-314555 (1994-11-01), None
patent: 9-97591 (1997-04-01), None
Horiuchi Makoto
Kai Makoto
Kominami Satoshi
Miyazaki Kouji
Takahashi Kiyoshi
Matsushita Electric - Industrial Co., Ltd.
Parkhurst & Wendel LLP
Vu David
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