Abstract:
A PAR lamp may be formed with a highly domed lens. The domed lens enables increased beam spread to as much as 90 degrees from the lamp axis. This fills in the shadow gaps between adjacent lamps. The domed lens may also extend beyond the forward edge of a recessed fixture and thereby washing the adjacent walls with light instead of leaving shadowed regions intermediate adjacent fixtures.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     The Applicants hereby claim the benefit of their provisional application, Ser. No. 60/490,143 filed Jul. 25, 2003 for REFLECTOR LAMP WITH A HIGH DOMED LENS. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. FIELD OF THE INVENTION  
         [0003]     The invention relates to electric lamps and particularly to PAR lamps. More particularly the invention is concerned with an electric PAR lamp with a domed lens.  
         [0004]     2. DESCRIPTION OF THE RELATED ART INCLUDING INFORMATION DISCLOSED UNDER 37 CFR 1.97 AND 1.98  
         [0005]     The common flood lamp, referred to more technically as a PAR lamp comprises a light source in a glass parabolic reflector. The reflector is sealed with a lens that may be flat or have a shallow curvature. The reflector commonly has a threaded base for mounting in a standard screw type socket. The reflector is designed to project light generally forward to a field to be illuminated. The covering lens may further adjust this spread. The lamp reflector and lens then set the beam spread. The largest beam spread from such lamps is thought to be about 65 degrees. A recessed lighting fixture, such as a typical ceiling fixture (“can”) has either no effect on the beam spread or it cuts off some of the beam when the lamp is recessed too far. Such lamp and fixture combinations therefore enable only at most about a 65 degrees beam spread. There is then a need for a PAR lamp with a beam angle greater than what currently exists.  
         [0006]     Most if not all PAR lamps using press ware reflectors and lenses have beam distributions that are not optically smooth. Irregularities in the filament, reflector and lens or in their mutual coordination result in streaks, splotches or other projected light pattern defects that can be visible in the resulting beam. This is due first to the fact that the light source itself may vary from sample to sample, and is not an ideal point source. It is also due to the fact that there are irregular optical features, boundaries, labels, defects and other features formed in or on the lens or on the reflector surface. There is effort to reduce this optical “noise,” by increasing the number of reflective facets, and overlapping multiple projected images to average the beam features. Efforts to overlap images undermine the ability to spread the beam. Lens and reflector quality may also be increased, but only at increased manufacturing expense. There is then a need for a PAR lamp with a high spread angle and reduced optical noise.  
         [0007]     A standard PAR lamp may have a flat or slightly a curved lens. This lens curvature may be quantified as the dome height or as the ratio of the dome height H relative to the plane intersecting the mounting edge to the radius R of the dome, as measured in the plane intersecting the mounting edge. Standard PAR20, PAR30, and PAR38 lenses have ratios of their axial heights to radii (H/R) as follows: PAR20=0.251 (7.97 mm/31.75 mm); PAR30=0.257 (12.24 mm/47.63 mm); and PAR38=0.203 (12.45 mm/61.21 mm) or from about one fifth to one quarter. At most, a standard PAR20 lens has an axial height equal to about one quarter of the dome radius.  
       BRIEF SUMMARY OF THE INVENTION  
       [0008]     A reflector lamp may be made with a reflective shell having a base end, a wall defining a cavity surrounding an axis extending towards a field to be illuminated. The reflector wall has an edge encircling and thereby defining a light opening leading from the defined cavity to the field to be illuminated. An electric lamp capsule is located in the defined cavity, the capsule having electric leads extending through the base end for electrical connection. A lens is sealed to the shell to cover the light opening and enclose the lamp capsule in the defined cavity, the lens having a domed structure with a maximum (outer) axial height greater than one half the maximum (outer) transverse radius. An electrical and mechanical coupling is coupled to the base end for electrical coupling of the electrical leads and mechanical support of the reflector lamp. The domed lens enables a greater spread (field angle) in the projected light. The light may also be more evenly spread. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0009]      FIG. 1  shows a cross sectional view of a prior art PAR lamp lens.  
         [0010]      FIG. 2  shows a cross sectional view of a domed PAR lamp with a smooth frosted lens.  
         [0011]      FIG. 3  shows an exploded view of a domed PAR lamp with a facetted lens.  
         [0012]      FIG. 4  shows a beam spread chart of a prior art PAR lamp.  
         [0013]      FIG. 5  shows a beam spread chart of a domed PAR lamp.  
         [0014]      FIG. 6  shows a schematic view of a domed PAR lamp mounted in a recessed fixture.  
         [0015]      FIG. 7  shows a cross sectional view of a domed PAR lamp lens with a continuous lens feature.  
         [0016]      FIG. 8  shows a cross sectional view of a domed PAR lamp lens with Fresnel optical features.  
         [0017]      FIG. 9  shows a cross sectional view of a domed PAR lamp lens with ribbed optical features. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]      FIG. 2  shows a cross sectional view of a domed par lamp  10 . The preferred domed par lamp  10  comprises a threaded base  12 , a molded glass reflector  14 , eyelets  16 , a lamp capsule  18  and a domed lens  20   
         [0019]     The threaded base  12  may be one typical of standard lamps, and may be made of brass, aluminum or other materials. A threaded base  12  is not required and the invention here may be used in conjunction with a bayonet, pin base or any other convenient coupling for mounting a lamp in a socket. The threaded base  12  is preferred for downward suspension from a ceiling socket.  
         [0020]     The preferred reflector is a molded glass reflector  14  that has a base wall  22 , and a neck region  24  that couples in the base  12 . The base wall  22  may be formed with one or more through passages  26  that provide electrical access to the enclosed lamp capsule  18 . The Applicants mold indentations (dimples) in the neck region  24  into which a portion of the base  12  may be pressed or peened to form a firm attachment. Glues, and other convenient methods may be used to mount the base  12  to the reflector  14 . The reflector  14  has a wall  28  that defines an internal reflective surface  30 . The Applicants prefer a parabolic reflective surface  30 , as the manufacture of such reflector units already exists, and is well understood. Hyperbolic and elliptical or other reflective surface shapes of revolution may be used. The reflector surface  30  may segmented into include subsections (facets, panels, etc.) for beam blending purposes as is known the art. The preferred reflective surface  30  is aluminized for high reflection as is known in the art. Other reflective surface materials may also be used, for example dichroic coatings. The reflector  14  has a forward edge  32  designed to support the domed lens  20 . Various couplings between reflectors and lenses are known in the art. The preferred coupling is an outward facing tongue  33  that may be mated, for example by glue to an inward facing groove  35  of the domed lens  20 . Matched steps, face to face, threaded, splined, and similar coupling structures may also be used to mate the reflector  14  and the lens  20 . The reflector  14  and the domed lens  20  may also be flame sealed as is known in the art. The reflector  14  may similarly include facets and other light dispersing features in the reflective surface  30  as is know in the art.  
         [0021]     A frosted domed lens  20  provides excellent filament image blending and light dispersion results. The reflector  14  may then be less expensively made as a simple smooth surfaced parabola of rotation. In the alternative the reflector  14  may have a reflective surface  30  that is a section of an ellipse of rotation. The near focal point may be placed at or near the location of the light source. The second focal point may be placed at or near the reflector and lens axis  34 , and in or near the plane of the reflector edge  32  and lens rim  40  coupling. In these ways the light from the light source (filament  19 ) either directly or by reflection encounters the steep sides of the domed lens  20  and is refracted sharply to the side, away from the axis  34  thereby giving a large and even beam spread. By incorporating a frost, a coating or similar feature to the domed lens inner surface  46 , the light may be dispersed both widely and evenly. In the preferred embodiment, the domed lens  20 , or a substantial portion of the domed lens  20  extends beyond the standard recessed lighting fixture depth. The domed lens  20  may then project exteriorly from a fixture recess, and may direct light to the sides of the lamp  10  to fill in otherwise dark areas intermediate lamps recessed in sequential fixtures. Light is of course similarly dispersed to the sides when used with no recessed type fixture.  
         [0022]     In the preferred embodiment, mounted to reflector  14  are eyelets  16  extending through the passages  26  of base wall base wall  22 . The eyelets  16  may be brass tubes with rolled ends that fit snuggly in the through passages  26 .  
         [0023]     The preferred lamp capsule  18  is a tungsten halogen lamp with a filament  19 , a press sealed base and two protruding leads  36 ,  38 . The leads  36 ,  38  are extended into the eyelets  16  for secure electrical connection and mechanical support. The eyelets  16  and the leads  36 ,  38  may be soldiered, or similarly electrically and mechanically coupled together. The lamp capsule  18  may be any convenient light source, whether incandescent, discharge, solid-state or any other electrical light source. The preferred position of the lamp capsule  18  is with respect to the optical features designed in the reflector. For the preferred parabolic reflector  14 , the filament  19  of the preferred tungsten halogen lamp capsule is position to be axially aligned with the filament  19  overlapping the focal point for the preferred parabolic surface of the reflector  14 .  
         [0024]     The domed lens  20  has a rim  40  that mates to the reflector  14  along forward edge  32 . The preferred domed lens  20  is substantially a body of revolution with a radius  42  in the plane of the rim  40 , and an axial height  44  measured perpendicular to the plane of the rim  40  to the highest external point of the domed lens  20 . The dome height  44  is greater than one half the lens radius  42  and preferably equal to (hemispherical) or greater than (semi-ovoid) the lens radius  42 . It is understood that the domed lens  20  may be further elongated so that the axial height  44  is greater than one times the dome&#39;s radius. The domed lens  20  may be substantially elongated with no theoretical limit on the axial height  44  to radius  42  ratio. For practicality, the ratio of the axial height  44  to radius  42  ratio is likely limited to about 3.0. The degree of doming may then range from 0.50 to 3.0. The preferred axial height  44  is 1.0 giving a hemispherically domed lens.  
         [0025]     The domed lens  20  inner surface  46  and outer surface  48  are preferably smooth. Either or both may include facets, Fresnel ribbings, lenticules or other refractive optical features as may be convenient and as are know in the art. The inner surface  46  and the outer surface  48  of the domed lens  20  may have differing rates of curvature, thereby creating an additional lens feature to refract the light. For example, the region near the rim  40  may be thicker  50  than the region near the crown  52  (axial top), resulting in refraction away from the axis  34 . The domed lens  20  may optionally include a coating  54 , or surface treatment, for example a color filter layer, dichroic coating, frosting, etching, metallization or similar coating as known in the art. The preferred domed lens  20  for a smooth parabolic reflector  14  incorporates an inside frost to diffuse the light.  
         [0026]      FIG. 3  shows an exploded view of a domed PAR lamp with a facetted lens  58 .  
         [0027]      FIG. 4  shows a beam spread chart of a prior art PAR lamp. The chart shows the amount of light  60  projected by a standard PAR lamp at different angles from the lamp axis. The standard beam angle is about 41.5 degrees. The standard field angle is about 65.6 degrees. These are fairly representative of what is currently available in PAR type reflector lamps. The beam pattern can be seen to be somewhat irregular.  FIG. 5  shows a similar beam spread chart of a smooth, frosted domed lens PAR lamp. Again the chart shows the amount of light  62  projected by the domed lens reflector lamp at different angles from the lamp axis. The beam angle is also 41.5 degrees, while the field angle is 90.4 degrees, showing the substantial increase in spreading the light to the sides by the domed lens. The beam pattern is also very smooth with no intensity bumps.  
         [0028]      FIG. 6  shows a schematic view of a domed PAR lamp mounted in a recessed (ceiling) lighting fixture. The domed lens  20  may extend beyond the plane of a standard fixture opening. As shown, the domed lens  20  extends almost as a hemisphere beyond the plane of the ceiling  80  and the fixture  82 . Light  84  may then be brought around the corner defined by the fixture opening.  
         [0029]      FIG. 7  shows a cross sectional view of a domed PAR lamp lens with a continuous lens feature. The wall at the rim  86  is thicker than the wall at the crown. with a continuous variation inbetween to provide a smooth optical lens.  FIG. 8  shows a cross sectional view of a domed PAR lamp lens with Fresnel optical features  90 . The Fresnel elements  90  extend around the domed lens in bands transverse to the dome axis.  FIG. 9  shows a cross sectional view of a domed PAR lamp lens with ribbed optical features. The ribs  92  extend around the domed lens in bands transverse to the dome axis.  
         [0030]     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.