Metal halide lamp

Details Metal halide lamp Metal halide lamp

1998-08-14

2001-09-04

Day, Michael H. (Department: 2879)

Electric lamp and discharge devices

With gas or vapor

Having specified electrode spacing

C313S639000, C445S026000

Reexamination Certificate

active

06285130

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to improvements in metal halide lamps and, more particularly, to improvements in metal halide lamps for use in optical instruments.
2. Description of the Prior Art
Metal halide lamps are used in optical instruments such as liquid crystal projectors and OHPs as incorporated in their reflectors. In recent years, to increase the screen brightness, metal halide lamps of the type having a pair of electrodes with a reduced spacing therebetween have been developed and widely used so that light from the lamp can be effectively utilized by a reflector. However, such a metal halide lamp causes an undesirable decrease in its own emission efficiency (lm/W) due to the reduced spacing between the electrodes. (“lm” means lumen.)
Attempts have been made to increase the emission efficiency of such metal halide lamp by encapsulating an excessive amount of a metal halide in the lamp. However, although the metal halide excessively encapsulated in the lamp enhances the emission efficiency of the lamp as intended, the screen brightness tends to decrease contrary to the expectation.
One conceivable reason for this problems is that the excessive metal halide encapsulated in the lamp does not sufficiently vaporize during the operation of the lamp and adheres to an inner wall surface of the lamp. This causes shadow and hence a decrease in the screen brightness.
Further, the metal halide excessively encapsulated in the lamp causes devitrification of the light-emitting tube formed of quartz glass and corrosion of the electrodes, which leads to the lamp with a shorter life time. Furthermore, convection occurring within the tube during the operation of the lamp is disturbed due to the excessive encapsulation of the metal halide, resulting in flicker.
It is, therefore, an object of the present invention to provide a metal halide lamp which is capable of increasing a screen brightness with less flicker and enjoys a longer life time by restricting the amount of a metal halide to be encapsulated in the lamp to a specific range.
SUMMARY OF THE INVENTION
In accordance with a first aspect of the present invention, there is provided a metal halide lamp for use with a reflector, comprising a pair of electrodes with a spacing therebetween, an envelop enclosing the pair of electrodes, and at least one metal halide other than a mercury halide which is encapsulated in the envelop in an amount of from 0.04 to 0.3 mg/cc.
In accordance with a second aspect of the present invention, there is provided a metal halide lamp for use with a reflector, comprising a pair of electrodes with a spacing therebetween, an envelop enclosing the pair of electrodes, a mercury halide encapsulated in the envelop, and at least one metal halide other than the mercury halide which is encapsulated in the envelop in an amount of from 0.04 to 0.3 mg/cc, the molar ratio of the mercury halide to the at least one metal halide other than the mercury halide being in the range of from 1.3 to 4.4.
In these constructions, the amount of the metal halide other than a mercury halide, or the molar ratio of the mercury halide to the at least one metal halide other than the mercury halide is restricted to a limited range. When such lamp is used in the reflector of an optical instrument as a light source, extra light emission which does not contribute to an improvement in the screen brightness is decreased, while on the other hand light emission which leads to an increase in the screen brightness is increased. Further, the lamp enjoys a longer life time with less flicker.
The foregoing and other objects, features and attendant advantages will become readily apparent from the reading of the following detailed description of the invention in conjunction with the attached drawings.


REFERENCES:
patent: 4020377 (1977-04-01), Popp et al.
patent: 4686419 (1987-08-01), Block et al.
patent: 5451838 (1995-09-01), Kawai
patent: 5691601 (1997-11-01), Frey et al.
patent: 5831388 (1998-11-01), Genz et al.
patent: 7-32004 (1995-04-01), None

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