Electric lamp and discharge devices – With optical device or special ray transmissive envelope – Reflector
Reexamination Certificate
1999-09-10
2001-01-30
Patel, Ashok (Department: 2879)
Electric lamp and discharge devices
With optical device or special ray transmissive envelope
Reflector
C313S634000, C313S573000
Reexamination Certificate
active
06181054
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention pertains to improvements for envelopes containing a fill for use in electrodeless lamps and has particular, although not limited, utility in lamps of the type disclosed in U.S. Pat. No. 5,404,076 and PCT International Publication No. WO 92/08240, the disclosures of which are expressly incorporated by reference herein in their entirety.
2. Discussion of Related Art
Electrodeless lamps of the type with which the present invention is concerned are comprised of a light transmissive bulb having an envelope containing a plasma-forming medium. A bulb is an envelope usually mounted on an elongate, radially projecting supporting stem. A microwave or radio frequency (RF) energy source has its output energy coupled through the envelope via a coupling arrangement to excite a plasma, resulting in a light discharge. The energy coupling arrangement customarily includes a microwave cavity to which microwave energy is coupled, and the bulb is mounted inside the cavity. Alternatively, the energy may be coupled to the fill through an inductive arrangement (e.g. an excitation coil surrounding the bulb) or a capacitive arrangement (e.g. a bulb between two electrodes). Electrodeless lamps may include an internal reflector or may be reflectorless, the latter requiring a separate light reflector to direct light emissions. A separate reflector is not readily inserted within the cavity since the cavity customarily includes a first solid conductive structure at one end, usually a cylindrical wall, joined to a second cylindrical structure formed of a mesh (e.g., tungsten mesh), such that microwave energy is contained within the cavity but light is transmitted outwardly. A separate reflector customarily has an axis of symmetry approximately coincident with the axis of the cavity and surrounds the cavity. The surface of the reflector may follow a simple geometric contour such as an ellipsoid or paraboloid and may be comprised of a plurality of annular facets, each sized and oriented to direct reflected light in a desired direction. A bulb is located along the axis of the cavity within the mesh structure and includes an envelope portion and a stem. The stem may also be located along the axis of the cavity or may be positioned at an angle with respect to the axis. The stem may be fixed (e.g. fastened to the first solid structure) or may be secured to a motor shaft for rotation of the bulb. If the envelope is essentially spherical and the light source is energized by microwaves, the resulting light produced is emitted with significant power in all directions. However, only a portion of the solid angle about the envelope corresponds to the mesh and substantial light is blocked by solid structure and not received by the reflector. The blocked portion of the solid angle about the envelope corresponds to the solid structure of the cavity and the end wall of the cavity (e.g. the wall with the coupling slot) and therefore light directed toward the blocked portion is occluded and lost.
In order to more efficiently direct the light outwardly and away from the coupling wave guide structure, various techniques have been suggested. For example, U.S. Pat. No. 5,334,913 (Ury et al) discloses a supplemental non-conductive optical reflector located within the cavity. Although reflectors disposed apart from the envelope but within the cavity can be effective, they consume space and add to the cost of the overall lamp.
Another problem encountered using spherical glass envelope structures is that significant thermal stresses are created in the envelope wall. In particular, internal heat from the plasma necessitates use of cooling fans to control the temperature of the envelope wall. In prior art lamps, rotation of the bulb about its support stem axis is commonly done for a number of reasons, one of which is to evenly distribute flow of cooling air over the envelope wall. Use of a separate non-conductive internal optical reflector has, therefore, presented additional problems in that special conduits for jets of cooling air must be routed around the internal reflector.
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of the present invention to overcome the aforesaid problems of the prior art.
It is another object of the present invention to provide an envelope with an integral reflector.
Another object of the present invention is to provide a method for joining a ceramic reflector to a glass segment, thereby making an envelope with an integral reflector.
The aforesaid objects are achieved individually and in combination, and it is not intended that the present invention be construed as requiring two or more of the objects to be combined unless expressly required by the claims attached hereto.
As part of the present invention, it has been discovered that an improved electrodeless discharge lamp bulb can be obtained by providing an integral ceramic reflector as a portion of the envelope. The reflector increases candle power along the axis of the bulb away from the lamp and reduces the light energy directed behind the bulb. In accordance with the present invention, a bulb envelope is fabricated from two pressure sealed portions or segments. The reflector portion may be, for example, cast quartz ceramic and the light transmissive portion may be, for example, clear fused silica. By using the manufacturing method of the present invention, a plurality of bulb shapes and designs are made possible. In one embodiment, the cast quartz ceramic portion or segment includes heat sink fins, providing an increased outside surface area to dissipate internal envelope heat.
In the method of the present invention, the quartz ceramic segment has an outside surface that is fused using a fire polishing technique to eliminate fill gas permeation. In order to prevent cracking of the ceramic during fire polishing along one surface, the opposing surface is preferably cooled with a gas jet.
The light transmissive portion and the reflective ceramic portion of the bulb envelope are fused together using a gas torch or a laser. Preferably, fused silica material is added to the fusion zone. The fusion zone is defined as having a radial thickness of 1 to 1.5 times the wall thickness of the clear quartz glass used in the light transmissive segment. The size of a high temperature hot zone is controlled to be within a range of at least about 2 times the wall thickness of the clear quartz glass.
With the bulb of the present invention, a significant improvement in light directivity is obtained. As compared to a spherical envelope of clear quartz glass, a spherical envelope of the same radius built in accordance with the present invention includes a hemispherical ceramic reflector mated to a hemispherical light transmissive segment and emits light with an increase of about 50% in peak light intensity along the 90° angle corresponding to the bulb axis.
The above and still further objects, features and advantages of the present invention will become apparent upon consideration of the following detailed description of a specific embodiment thereof, particularly when taken in conjunction with the accompanying drawings, wherein like reference numerals on the various figures are utilized to designate like components.
REFERENCES:
patent: 4924141 (1990-05-01), Taubner et al.
patent: 4950059 (1990-08-01), Roberts
patent: 5493170 (1996-02-01), Sheppard
patent: 5500574 (1996-03-01), Popov, et al.
patent: 5734221 (1998-03-01), Van Os
patent: 5949180 (1999-09-01), Walker
patent: 6005332 (1999-12-01), Mercer
patent: 0671758A2 (1995-09-01), None
patent: 0871205 A1 (1998-10-01), None
patent: WO 98/53475 (1998-11-01), None
Levin Izrail
Shanks Bruce
Sumner Thomas L.
Fusion Lighting Inc.
Patel Ashok
Steiner Paul E.
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