Patent Publication Number: US-6705748-B2

Title: Lamp with ceramic light shield

Description:
TECHNICAL FIELD 
     The invention relates to electric lamps and particularly to electric lamps with integral reflectors. More particularly the invention is concerned with an electric lamp with an integral reflector and a light shield. 
     BACKGROUND ART 
     Reflector lamps are commonly coated to reflect light forward. It can be difficult to adequately coat the neck region of the reflector to block light from exiting incorrectly through the neck, or to adequately shield the neck region from heat. As a result, light can shine through the neck, which may be unaesthetic or even unacceptable in display lighting applications. Similarly the light, including infrared heat, may shine into the socket region causing an undesirable or unacceptable heating of the lamp base, and socket region. To prevent such transmission, the neck regions of lamps have been coated with reflective material. This is reasonably functional in larger volume lamps where the neck is sufficiently open to receive the metal vapor. In smaller lamps good metallization in the small neck region is difficult to achieve. In dichriocally coated lamps, the multiple coatings are even more difficult to apply accurately. An alternative blocking method is to insert a metal shield in the neck region. Metal shields work well in larger lamps. Metal shields do have the problem of darkening with repeated heating. For example, nickel, steel and stainless steel shields, commonly darken. This darkening reduces the amount of reflected light, and enhances heat absorption and therefore retransmission of heat into the neck and socket region. The lost light is one detriment. The darkening can also be unaesthetic in display lighting where the original high quality lamp color (dichrioc or silvered) is expected as part of the jeweled display pattern. Aged, and variably discolored lamps are then felt to detract from the display. Heating the socket and seal regions can have other problems. Metal shields also provide conduction paths that at times can short circuit the lamp leads. This is a particularly difficult aspect of shielding small volume lamps were the leads are close together, and there is little surrounding volume to contain the metal shield. There is then a need for a small volume reflector lamp that does not project light into or through the base region, does not discolor and does not short circuit the lamp leads. 
     DISCLOSURE OF THE INVENTION 
     A reflector lamp may be made with a glass shell having an interior surface extending from a reflector region that defines a reflector cavity to a neck region that defines a neck cavity. Positioned in the reflector and neck cavity regions is a light source offset from the interior shell surface and electrically connected by a first lead and a second lead extending respectively through the neck cavity region to an exterior of the shell. The lamp additionally includes an opaque ceramic shield positioned in the neck cavity intermediate the light source and the neck region having a first surface facing the light source and a second surface facing the neck region. The ceramic shield then blocks light into the neck region while thermally and electrically insulating the lamp and the associated lamp leads. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a cross sectional view of a preferred reflector lamp. 
     FIG. 2 shows a cross sectional view of a preferred alternative reflector lamp. 
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     FIG. 1 shows a cross sectional view of a preferred reflector lamp. The preferred reflector lamp  10  comprises a lamp capsule  12 , a reflector  14 , a base  16  and a ceramic shield  18 . The reflector lamp  10  may optionally include a lens  20 . 
     The lamp capsule  12  may be any small electric light source. The preferred lamp capsule  12  is a single ended, press-sealed tungsten halogen lamp. Tungsten halogen lamps are typically made from hard glass or quartz with a tubular shape. A first lead  22  and a second lead  24  extend from a press seal  26  and extend through the reflector  14  for electrical connection. 
     The preferred reflector  14  is a glass body of revolution defining a reflector region  28  with a reflective coating  30 . The reflector may define a parabolic, elliptical or similar optically useful reflective surface. The reflective surface may be smooth, faceted, dimpled or have other features as is known in the art. The reflective coating  30  may be a metal coating of the interior surface defining the reflector region, such as an aluminum coating. The reflective coating  30  may alternatively be a dichroic coating of the same region. The reflector  14  extends from the reflector region  28  defining the reflector cavity to a neck region  32  defining a neck cavity. The lamp capsule  12  is positioned in the defined reflector cavity and neck cavity with the first lead  22  and the second lead  24  extending through the neck region  32  to the exterior of the reflector  14  for electrical connection. The neck region  32  may be closed by a base wall  34  that may include one or more through holes for the first lead  22  and the second lead  24 . Formed on the exterior of the reflector  14  may be indentations, protuberances or similar features to which the base  16  may be attached. The preferred reflector  14  includes two indentations (not shown) formed on the exterior. The base wall  34  of the reflector  14  may include eyelets lining the holes to help position or align the lamp leads  22  and  24 . 
     The base  16  may be any appropriate structure for holding the reflector  14  and adequately coupling the lamp  10  in a lamp socket. The preferred base  16  is a typical threaded metal base having a center contact  36  coupled to the first lead  22  and a conductive metal threading  38  coupled to the second lead  24 . An edge of the preferred metal base is peened into the indentations formed in the exterior of the reflector  14  to hold the reflector  14  and the base  16  together firmly. Glues and other methods of attaching the reflector  14  to the base  16  are known in the art and may be used. 
     Positioned intermediate the lamp capsule  12  and the reflector neck region  32  is a ceramic shield  18 . The preferred ceramic shield  18  is cup shaped to surround an end portion of the lamp capsule  12 , for example the press seal region  26 . The first lead  22  and the second lead  24  extend through a hole or holes  40 ,  42  (as shown) formed in the ceramic shield  18 . The preferred cup is formed not to be light transmissive, and may further have a reflective interior surface  44 . The ceramic cup may additionally, or alternatively include eyelets lining the cup holes  40 ,  42  to help position or align the first lead  22  and second lead  24 . FIG. 2 shows a cross sectional view of a preferred alternative reflector lamp. A reflector passage  50  may be lined with an eyelet  52 . A lead, such as lead  22  may be threaded through the eyelet  52 , and then coupled to the eyelet  52  by crushing, crimping, soldering, swaging or by other means, the lead and eyelet, as known in the art, along their lengths  54 . Alternatively, a passage  60  through the shield and reflector may be lined with an eyelet  62 . A lead, such as lead  24  may be threaded through the eyelet  62 , and then coupled to the eyelet  62  along their lengths  64 . The eyelets  52  and  62  help align the lamp capsule  12  in the reflector  14 . 
     The neck cavity and the exterior surface of the ceramic shield  18  may be formed to define an acceptably close fit between the two pieces. Some or the entire exterior surface  46  of the ceramic shield may then conformally fit with the adjacent interior of the reflector neck to brace the ceramic shield  18  in the reflector neck. Similarly, the interior of the ceramic shield may be formed to brace or conformally fit with the lamp capsule  12 , the press seal  26  or the leads  22 ,  24 . The ceramic shield  18  may then be pinned in the hollow of the neck region and locked by the penetrating leads  22 ,  24  between the lamp capsule  12  and the reflector  14 . Alternatively, or additionally, a small quantity of a ceramic cement or high temperature epoxy may be positioned between the reflector  14  and the ceramic shield  18  to fill the gap between them and lock the ceramic shield  18  in place. A metal spring clip or other locking piece may also be used to couple the ceramic shield  18  in place. 
     The reflector lamp  10  may optionally include a lens  20 . The lens  20  may seal with a forward rim portion of the reflector  14  to enclose the lamp capsule  12  in the reflector cavity. 
     The preferred assembly sequence of the lamp  10  is to insert the ceramic shield  18  in reflector neck, and then insert the lamp capsule  12  in the ceramic shield  18  and align the lamp capsule  12  relative to the reflector  14 . In doing this, the capsule lead wires  22 ,  24  are fed through the holes in the ceramic shield  18  and then fed through the holes (and eyelets if any) in the bottom wall  34  of the reflector  14 . After the leads  22 ,  24  are fed through the holes (or eyelets), the leads are then swaged, soldered, welded or otherwise sealed, just as if the light shield  18  was not included in the lamp structure. The base  16  is then peened in place to the reflector  14 , and the leads  22 ,  24  connected to the base  16 . Finally a lens  20 , if any, is glued or otherwise attached in place. 
     The ceramic light shield may be metallized instead of glazed while maintaining the initially desired color. Pre-metallizing the ceramic shield is easier than metallizing the reflector neck interior. Glazing is easier still and less expensive than metallizing. One reason is that glazing can be included in the ordinary sintering process used in constructing the ceramic shield. Since the ceramic and glaze are insulators and do not interfere with the electrical conduction to the lamp capsule, there is greater flexibility in attaching the lamp reflector, base, lamp leads, or lamp capsule as the case may be. The preferred method of making the ceramic shield is to injection mold steatite. After initially sintering and cooling the ceramic shield green body, the ceramic shield  18  is dipped in or sprayed with a selected glaze. The ceramic shield is then finally sintered, which sets the ceramic density and size while also hardening the glaze. 
     PAR  20  reflectors may not have consistently good alignment of the lamp capsule with respect to the reflector due to how the leads pass through the base wall holes. The ceramic shield helps correct this. The ceramic shield can sit on top of the reflector eyelets that the capsule leads go through or the eyelets may be threaded into or through the ceramic shield. The lamp capsule leads may then be threaded through the reflector eyelets. In either case the leads are held closer to their preferred positions, meaning the lamp capsule is positioned in the reflector closer to its preferred (optically ideal) position. In still a further variation, the reflector may have a large single hole in the back for the leads. The ceramic shield may then be attached to the capsule leads by swaging to ceramic shield eyelets, if any. The ceramic shield and lamp assembly may be attached in the reflector with epoxy. In each case the eyelet may be swaged to the capsule leads. It is understood that the assembly steps may take place in alternative sequences, as may be convenient. 
     In one embodiment the reflector was made of glass with an interior dichroic coating to reflect visible light forward. The reflector had an exterior axial length of 52.76 millimeters, a reflector inside diameter of 53.31 millimeters and a neck inside diameter of 19.37 millimeters narrowing to a neck base diameter of 15.64 millimeters. The ceramic shield was cup shaped with a cup height of 21.42 millimeters and a cup outside diameter of 18.94 millimeters narrowing to 15.20 millimeters. The cup wall was about 1.12 millimeters thick. The interior of the cup was glazed with glass frit to give smooth reflective surface with an overall color of silver gray. The lamp capsule was a 50 watt, 120 volt tungsten halogen lamp with a tubular envelope 10 millimeters in diameter and an overall glass dimension of 38.71 millimeters. The single ended lamp capsule had two leads extending from the press seal that extended through the ceramic cup and the reflector to be electrically connected to a threaded brass base. 
     Photo tests show that there is a gain in the amount of useful light emitted through the front of the lamp. There is also a very large reduction in the stray light emitted out the back of the reflector. The preferred ceramic shield is glazed with a glaze color that looks from the outside like the color of the surrounding dichroic coating of the reflector. The ceramic shield additionally offers some light reflection back into the useful area. 
     The ceramic shield is much more effective than a metal shield. Three lamps were made according to this disclosure and were tested for total light output. The prototype lamps showed about 25-50 lumens more output than dichroic lamps that were otherwise similar but had no ceramic shield or metal shield. The tested lamps also showed practically no light emerging out of the back, which is highly undesirable in many applications. A significant advantage of ceramic shield is that the shield does not discolor the way metal can, thereby causing a loss in the amount of the light output by the lamp during its life. 
     The preferred ceramic shield is made of steatite ceramic, and can be less expensive than a metal shield. Both the metal and steatite shields have been tested. The ceramic shield has been found to be much more effective than a metal shield. Dichroic coated lamps and lamps with aluminized necks were also tested. They were found to be very nearly block light as well as the ceramic shield, but the cost of accurately coating the neck region is greater than the cost of the ceramic shield. 
     While there have been shown and described what are at present considered to be the preferred embodiments of the invention, it will 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.