Patent Application
20050212396
The invention relates to electric lamps and particularly to electric lamps with reflectors. More particularly the invention is concerned with an electric PAR lamp with a lamp capsule light source.
PAR lamps commonly comprise a light source such as a tungsten halogen capsule or arc tube mounted in a pressed borosilicate glass reflector having a reflective coating formed on the inner parabolic surface. A pressed glass lens with optical elements to shape the beam usually covers the front. PAR lamps usually have the form of a parabolic bowl forming the reflector and a neck extending between the parabolic reflector section and a medium screw lamp base used for electrical connection. The base is typically designed to receive normal line power (100 V to 240 V). The neck provides room for the capsule's press seal, leads, capsule mounting components, electrical wiring, and also separates the filament from the threaded base to reduce the base temperature. Small holes in the base of the neck penetrate the reflector to enable electrical connection to the capsule. Most PAR lamps are assembled by inserting the capsule from the front aperture and attaching the capsule leads through the reflector heel by means of eyelets, ferrules, ceramic body, cement, or metal clip. A metal clip is also sometimes also used in the neck region to align and support the capsule.
Both the inner and outer surfaces of the prior art reflector need a suitable draft angle for removal from the mold. Pressed glass used for PAR lamps typically requires a minimum draft angle of about 3 degrees and in practice, a 5 degree draft angle is used. The bottom of the reflector neck must have an adequate diameter to fit the capsule's press seal and the capsule mounting elements. The opening at the parabolic reflecting surface is therefore significantly larger than the capsule diameter. This wide opening allows light to enter the neck region that is then lost due to multiple reflections and absorption by mount and capsule components. This lost light does not contribute to the output beam, and only heats the base.
A way to reduce neck opening diameter is described in U.S. Pat. No. 5,281,889. A substantial portion of the open reflector neck volume is replaced by a separate ceramic extender and the capsule is mounted with a metal disk between the ceramic extender and the reflector. A disadvantage of this approach is the relatively high part count and the complicated assembly requiring the use of cement to attach the various components. The ceramic extender adds significantly to the total lamp cost.
A reflector lamp assembly may be formed from a reflector having the form of a shell with an interior surface and an exterior surface, the interior surface defining a reflective surface. The reflector is formed with an internal wall defining a passage extending through the reflector from the interior surface to the exterior surface. A lamp capsule encloses a light source with a first electrical lead and a second electrical lead, the capsule having an exterior wall, the lamp capsule being shaped and sized to extend through the passage. The light source exterior wall is closely positioned by the internal wall of the reflector adjacent the reflective surface to accurately locate the light source relative to reflective surface and expose the reflective surface to light emitted by the light source. A threaded base having a first electrical contact coupled to the first lead and a second electrical contact coupled to the second lead, mechanically supports the capsule. The threaded base is mechanically then coupled to the exterior of the reflector.
The preferred lamp construction eliminates the need for eyelets and a separate wire connecting the first capsule lead to threaded base center eyelet 30. A fuse wire 30 is welded to the trimmed capsule lead 28. Lamp lead 26 is attached directly to the medium screw threaded base 20 by welding or soldering the long capsule lead 26 to the center eyelet 30. The lamp capsule 22 and threaded base 20 assembly may be coupled as a unit in advance and then attached to the reflector 14 by peening the top skirt of the brass threaded base 20 into fixed coupling with the reflector 14. An adhesive may also couple the reflector 14 and threaded base 20. The lens 12 may then be attached to the reflector 14 by glue.
The PAR lamp with negative draft neck provides the performance advantages associated with small reflector opening along with cost advantages of the simplified assembly process. The Applicants measured a ten percent (10%) increase in center beam candlepower for a PAR20 lamp with the lamp construction as shown in
In general, the standard pressed glass reflector used in a PAR lamp may be replaced with a reflector having similar external shape but with an opening in the parabolic reflecting surface only slightly larger than the light source capsule diameter. The draft angle of the reflector neck passage is reversed so that the neck diameter is greatest at the bottom near the threaded base, and least near the reflector region. In the preferred embodiment the internal diameter of the neck is narrowest adjacent the reflective surface, and is slightly larger than the outside diameter of the lamp capsule. The narrow fit between the two parts centers the capsule on the lamp axis, and therefore properly locates the enclosed filament. The lamp capsule is positioned along the axis by setting the first electric lead length, the one extending from the center eyelet contact. Alternatively the lamp capsule could be positioned along the lamp axis by abutting contacts formed on the lamp capsule and the reflector. The lamp may use a conventional medium screw threaded base that is attached without cement. The threaded base can be securely attached to the reflector by being deformed into slots or depressions or around protuberances on the nose of the reflector near the threaded base seat. The reflector may be made from glass, ceramic, or high temperature plastic. Molding the reflector may leave a thin web of material adjacent the parabolic surface and crossing the neck opening. A hole can be subsequently formed between upper reflector cavity and lower neck cavity by punching, drilling, or burning through this thin residual web.
The new reflector shape enables a new manufacturing process. The lamp capsule is inserted from the bottom of the reflector and need not be attached directly to the reflector with eyelets or a clip. Instead, a rigid first capsule lead can be bent and attached directly to the center eyelet of the threaded base by welding or soldering. A simple fuse wire can be used to make electrical contact between a second lead and the threaded base shell. The second capsule lead may alternately be bent outward and attached directly to the threaded base shell by welding or soldering to the inside surface and a fuse wire connected to the center eyelet. To avoid the need to bend capsule lead wires, a wire or clip may be used as an intermediate component between the capsule lead and threaded base shell or center eyelet. This new lamp assembly eliminates two metal eyelets and possibly the side wire needed to connect a capsule lead to the threaded base, reducing the total part count by at least twenty-five percent.
The capsule mount needs adequate strength to maintain proper capsule centering in the reflector. In the new structure, the small opening of the neck adjacent the reflector braces the lamp capsule and prevents the capsule from moving off axis. At the same time, the stiff capsule lead or leads prevent axial movement of the capsule. This accurate capsule positioning substantially reduces the variation in center beam candlepower and beam shape that occurs with typical PAR lamps.
The new design eliminates two assembly process steps (eyelet staking and capsule insertion) that historically have limited production line speed and reduced line efficiency. Instead, the capsule may be attached directly to the lamp's threaded base in one of the final process steps. The capsule is the most expensive lamp component and the new process substantially reduces the cost of scraping defect parts discovered just before the final assembly.
With a clear glass reflector, it may be desirable to coat the inner or outer surface of the neck with an opaque coating to prevent light escaping out the reflector back. Opaque ceramic or plastic can also prevent or minimize this effect.
While there have been shown and described what are at present considered to be the preferred embodiments of the invention, it may be apparent to those skilled in the art that various changes and modifications can be made herein without departing from the scope of the invention defined by the appended claims.
