Electric lamp and discharge devices: systems – With load device temperature modifier – Electric heater for the load device
Reexamination Certificate
2001-03-16
2003-07-22
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
With load device temperature modifier
Electric heater for the load device
C315S291000, C313S639000
Reexamination Certificate
active
06597118
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a high-pressure mercury lamp, and particularly to a high-pressure mercury lamp with at least 0.15 mg/mm
3
of mercury sealed into the discharge vessel so as to have a pressure of well over 100 atmospheres when lit for use as a back light in liquid crystal projectors or projection-type liquid crystal display equipment.
2. Description of Related Art
Projection-type liquid crystal display equipment is required to project an image on a rectangular screen, evenly and with good brightness, efficiency and color characteristics. For that reason, metal halide lamps, in which are sealed mercury and a metal halide, are commonly used as light sources. In recent times, these metal halide lamps have come to have very small inter-electrode gaps, making them smaller and more nearly point light sources.
Against this backdrop, high-pressure mercury lamps, having well over 100 atm. of mercury vapor pressure when lit, have been proposed to replace metal halide lamps. Making the mercury vapor pressure higher is intended to suppress the spread of the arc and make the light output even higher. Examples include U.S. Pat. No. 5,109,181 (JPO kokai patents H2-148561) and U.S. Pat. No. 5,497,049 (H6-52830).
For high-pressure mercury vapor lamps of this sort to achieve high brilliance, high efficiency and good color characteristics, it is necessary to have a mercury vapor pressure well over 100 atmospheres, and so at least 0.15 mg/mm
3
of mercury must be sealed into the discharge vessel. In this way, after the lamp has been started up, mercury that is reserved in the light emission tube in liquid form is heated and vaporizes; several minutes of time is required for the vapor pressure to rise and bring the light output to the desired level. This phenomenon is one which did not arise to a noticeable extent in low-pressure mercury lamps or in conventional high-pressure mercury lamps in which the mercury vapor was not high enough (internal pressure up to 80 atmospheres when lit, for example.) Moreover, a glow discharge generally occurs when a discharge lamp is started up, but the high cathode drop voltage causes sputtering of the tungsten that makes up the cathode; the tungsten adheres to the inside wall of the discharge vessel, and the light output of the lamp is reduced. That is a problem in terms of the longevity of short-arc, high-pressure mercury lamps
SUMMARY OF THE INVENTION
Accordingly, the problem to be resolved by this invention is the provision of a high-pressure mercury lamp luminescent device, with a method of ignition, that shortens the rise time of the light output and enables prevention of a glow discharge when the lamp is started up.
This problem is solved in accordance with a first aspect of the present invention by using a high-pressure mercury lamp luminescent device with a pair of electrodes placed opposite one another within a discharge vessel made of quartz glass with seals formed on both ends and at least 0.15 mg/mm
3
of mercury sealed into the discharge vessel, in which there is a means of increasing the temperature of the outer wall of the luminescent portion of the discharge vessel to at least 100° C. before the high-pressure mercury lamp is lit.
In accordance with one specific form of the invention, the high-pressure mercury lamp luminescent device with a pair of electrodes placed opposite one another within a discharge vessel made of quartz glass with seals formed on both ends and at least 0.15 mg/mm
3
of mercury sealed into the discharge vessel, has a conductive heater wrapped around the seals of the discharge vessel and there is a means of passing electricity through the conductive heater and thus controlling the temperature of the outer wall of the luminescent portion of the discharge vessel at or above the desired temperature before the high-pressure mercury lamp is lit. More specifically, the conductive heater is wrapped around one seal of the discharge vessel, then straddles the luminescent portion of the discharge vessel by means of a metallic wire and wraps around the other seal, and the conductive heater being connected electrically to one of the external leads of the high-pressure mercury lamp, especially, the external lead on the cathode side of the high-pressure mercury lamp.
Furthermore, in accordance with another feature of the invention, a lamp power supply circuit provided to ignite the high-pressure mercury lamp, is used to supply power to the heater to increase the temperature of the outer wall of the luminescent portion of the discharge vessel before the high-pressure mercury lamp is lit.
In accordance with another aspect of the invention, a heater is wrapped around at least the seal on the cathode side and one end of the heater faces the cathode through the seal, the other end of the heater being connected electrically to the cathode, such that when power is supplied to the heater, the high potential side of the heater voltage is impressed on the other end of the heater.
The invention also provides the possibility of applying heating before the high-pressure mercury lamp is lit and while it burns.
In accordance with yet another feature of the invention, by the lamp power supply circuit and the heater power supply circuit being powered by the same power source, the output from the heater power supply circuit can be controlled such that the total power output of the two circuits does not exceed a specified value.
Furthermore, a detection means can be provided that detects the temperature of the luminescent portion, and stops the supply of power to the heater when the temperature passes a specified value.
With a method of lighting a high-pressure mercury lamp luminescent device with a pair of electrodes placed opposite one another within a discharge vessel made of quartz glass with seals formed on both ends and at least 0.15 mg/mm
3
of mercury sealed into the discharge vessel according to the invention, it is possible to increase the temperature of the outer wall of the luminescent portion of the discharge vessel to at least 100° C. before the high-pressure mercury lamp is lit.
With this invention, it is possible to shorten the rise time of the light output of the high-pressure mercury lamp, and also to prevent the glow discharge that occurs when a high-pressure mercury lamp is lit. Specifically, a high-pressure mercury lamp within which at least 0.15 mg/mm
3
of mercury is sealed, and the outer surface of the luminescent portion of the discharge vessel is heated to at least 100° C. before lighting, so that it is possible to fully vaporize the mercury in the discharge vessel before ignition. Following dielectric breakdown when the lamp is lit, the mercury vapor pressure within the discharge vessel will have risen adequately. It is therefore possible to shorten the rise time of the light output of the high-pressure mercury lamp, and to prevent the glow discharge that occurs when a high-pressure mercury lamp is lit.
As a heating means, a conductive heater is wrapped around the seals of the discharge vessel and electricity is passed through it to constitute a conductive heater. In this way, it is possible, with a simple structure, to control the temperature of the outer wall of the luminescent portion of the discharge vessel at or above the desired temperature, which is at least 100° C., before the high-pressure mercury lamp is lighted.
The heating means can be constituted by having a conductive heater wrap around one seal of the discharge vessel, then straddle the luminescent portion of the discharge vessel by means of a metallic wire and wrap around the other seal, with the conductive heater connected electrically to one of the external leads of the high-pressure mercury lamp. In this way it is possible to make the metallic wire that straddles the luminescent portion work as a trigger wire before lighting. In other words, the passage of electricity to the conductive heater is stopped prior to lighting, but the heater is connected electrically to one of the external leads, the diele
Arimoto Tomoyoshi
Okamoto Masashi
Takaya Izumi
Dinh Trinh Vo
Nixon & Peabody LLP
Safran David S.
Ushiodenki Kabushiki Kaisha
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