Abstract:
Disclosed is a reflector for a lighting assembly comprised of a series of discrete facets connected to form an optical reflector. Each facet includes subdivisions that extend uninterrupted along substantially the length of the facet and serve to multiply the image of the light source for increased illumination. Further, the curvature of the facets are selected to maximize the length of the reflected image of the light source to further enhance optical output.

Description:
FIELD OF THE INVENTION 
   The present invention relates to lighting assemblies, and more particularly to a lighting assembly with a reflector that optimizes illumination using enhancement of the virtual image of the illumination source. 
   BACKGROUND OF THE INVENTION 
   Outdoor lighting assemblies are well known in the art and can be found in areas requiring overhead lighting such as parking lots, parks, public walkways, and outdoor shopping areas. Outdoor luminaries typically provide light from above, positioned on buildings, poles, masts or other means of support. Design of such overhead lighting should provide easy access for repair and replacement and be aesthetically pleasing while providing the necessary illumination. 
   Outdoor luminaries typically include a housing or base, an electrical system, and an optical assembly. The housing is usually exposed to the environment and encloses the electrical circuitry, and thus must be capable of protecting the electrical system from moisture and debris. The optical assembly contains a lamp for producing the light and a reflector that directs the light in a predetermined direction. Using different reflector configurations, luminaries are capable of different light distribution patterns such as symmetrical and asymmetrical. These light distribution patterns can be especially suited for roadway, parking and area applications. Lights that provide greater illumination for a given power input are obviously favored, and higher illumination outputs can reduce the number of required lights by increasing the spacing between lights. Depending on the height of the lighting fixture, the beam or area of illumination can be varied to adjust the primary lighting area. In every application, however, greater illumination can offset costs by reducing the number of lights and the wattage of the lights for a given illumination. 
   The primary emphasis of such lighting is the reflector, which takes many forms and arrangements. Reflectors can be manufactured from metals such as aluminum or polished steel, and can be painted, plated or applied with a chemical surface treatment to brighten the reflective surface. Other techniques for preparing a reflective surface include vacuum deposition or metalizing, and chemical or vapor deposition. These techniques apply a thin layer of metal or other reflective material on the surface of the reflector. There are also prismatic internal reflection glass and plastic reflectors that use the index of refraction to control the reflectance of light and redirect it into a distribution of light. Some glass reflectors are known to use a metal cover spun around the exterior to eliminate uplight, radiated by the large rounded portion of their prism peaks and roots, and the cover is used as a means of glare control and to maintain a clean exterior internal reflection surface. 
   U.S. Pat. No. 6,726,345 to Arumugusaamy et at. discloses an open type luminaire lens including non-circular reflective lens having a metalized exterior surface and a prism section, the non-circular reflective lens having a shape generally defined by the combination of two parabolas, the prism section including an array of external reflecting prisms of varying predetermined shapes and varying predetermined sizes for use in providing a desired light distribution. This disclosure proposes an aluminum coating directly deposited on an outer section of an elliptical lens. 
   U.S. Pat. No. 6,123,436 to Hough et al. discloses a reflector with an input aperture positioned near a point of minimum focus and has an output aperture that is larger than the input aperture. The surface is shaped to decrease the angles of incident light rays from the reflector so that an emerging light beam is bounded by a cone the angle of which is less than or equal to the acceptance cone of a projection lens. 
   U.S. Pat. No. 6,698,908 to Sitzema Jr. et al. discloses an improved optical assembly that includes a reflector device and a reflector collar for enhanced directional illumination control. The reflector/refractor has a predefined shape and has a plurality of prisms on an exterior body surface for reflecting and refracting light. The predetermined contour and the plurality of reflector impressions provide directional illumination control. 
   U.S. Pat. No. 6,494,596 to Burroughs discloses a reflector for a lighting fixture comprising a substantially bell shaped reflector wall with top and bottom openings and a substantially parabolic cross-section. The reflector wall includes an inner surface having a first top portion that is textured for diffusing light rays from the light source of the fixture, and a second bottom portion that has a smooth surface allowing the light rays to pass through the reflector. The reflector wall also has an outer surface with a plurality of curvilinear prisms for reflecting the light rays. 
   SUMMARY OF THE INVENTION 
   A reflector assembly for a light comprises of a series of discrete curved facets connected together to form an optical reflector. Each facet includes elongated vertical strips or subdivisions that extend uninterrupted along substantially the height of the facet and serve to multiply the image of the light source for increased illumination. Further, the curvature of the facets is selected to maximize the length of the reflected image of the light source to further enhance optical output. 
   Other features and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings which illustrate, by way of example, the features of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an exploded view of one preferred embodiment of the reflector assembly of the present invention; 
       FIG. 2  is an exploded view of a light assembly using the reflector assembly of  FIG. 1 ; 
       FIG. 3  is a cross sectional view of the reflector of  FIG. 1 ; and 
       FIG. 4  is a plot of a reflector curvature in accordance with the teachings of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The lighting fixture  5  including the reflector of the present invention is generally illustrated in  FIG. 2 . A housing  10  encases the reflector assembly and is formed of a sturdy, light weight material that can shield the electrical components from weather, moisture, dirt and other contaminants. The housing  10  is shown as rectangular although the particular shape of the housing is not critical to the present invention. The housing  10  further comprises an electrical plug or other coupling  15  for connecting the lighting fixture electrically to a power supply (not shown), mounted to the housing by threaded fasteners  17  passing through the housing rear wall  19  and secured by lock nuts  17   a . Inside the cavity of the housing  10  is a transformer  16  or other electrical converted to reduce the standard AC power to a more productive power, and includes electrical connectors  18  that complete an electrical current conduit with a remote source via cables  20  to power the light. Electrical wires  22  connect a lamp assembly  24  to the transformer  16  forming the electrical circuit that provides current to the bulb  24   a . The lamp assembly  24  is standard and may include an incandescent bulb of known wattage and illumination powered by the aforementioned electrical circuit. However, as shown in  FIG. 3  the length of the bulb  24   a  when configured in the reflector assembly  32  is somewhat shorter than the depth of the reflector assembly cavity. As will be explained in more detail below, the shape and curvature of the reflector assembly “stretches” or extends the image of the bulb such that the virtual or reflected image is commensurate with the length of each reflector panel to maximize the reflected light and enhance the illumination performance of the reflector. This is seen in  FIG. 3 , where the reflected images  27  of bulb  24   a  in the vertical segments of the reflector&#39;s inner surface  29  extend longitudinally to the edge  7  of the reflector  36 . This elongation of the virtual image  27  of the bulb  24   a  is accomplished through selective shaping of the individual facets that make up the reflector assembly, and leads to improved illumination output of the reflector  36 . 
   At the base of the housing  10  is a downwardly directed lower rim  14  including holes  26  for receiving fasteners (not shown) that connect the cover plate  28  to the housing  10 . A resilient seal  12  is preferably compressed between the lower rim  14  of the housing  10  and the cover plate  28  via pressure from the fasteners to form a weather-proof seal that prevents moisture from collecting in the housing. The seal  12  can be made of any suitable polymeric material that is easily compressed between the housing and the cover plate to shield moisture from entering the housing  10 . 
   The cover plate  28  may fit over and secure a protective glass or plastic lens  30 , or the cover plate  28  can be formed integrally with the lens in a single unit. The lens  30  fits over and engages a peripheral skirt  34  of a reflector assembly  36  described in more detail below. The reflector assembly  36  is received in the cavity  38  of the housing  10 , and secured by the cover plate&#39;s  28  engagement with the lower rim  14  of the housing  10 . The lighting fixture  5  is customarily mounted to a light pole or overhead structure with electrical connections that connect with the cables  20  to support and power the lighting fixture at some elevated position. 
     FIG. 1  shows an exploded view of the reflector assembly  36  comprising a skirt  34 , eight discrete facets  40 , a top plate  42 , a cover plate  44 , and a bracket  46 . The skirt  34  is formed of a thin plate of aluminum, steel, or other sturdy material having an outer perimeter  48  matched to the shape of the inner cavity  38  of the housing  10  (e.g., square) and having a polygonal window  50  formed in the skirt interior. The skirt  34  may include holes  49  that coincide with the holes  26  on the rim  14  of the housing  10  to also receive fasteners coupling the cover plate  28  to the housing  10 . Additionally, the inner edges  52  defining the perimeter of skirt window  50  each include an adjacent pair of apertures  54  that receive a fastener such as a rivet for coupling the facets  40  to the skirt  34 . The skirt  34  is a stand alone component that connects to the individual facets  40  at the apertures  54  to form a lower structural base of the reflector assembly  36 . 
   Each individual facet  40  is formed from a curved plate and is shown in plan form in  FIG. 1 . Two apertures  58  coincide with apertures  54  on the skirt to receive a pair of rivets that couple the facet  40  to the skirt  35 . A traverse lip or flap  60  is bent 90° into a parallel relationship with the skirt  34  so as to form a mating surface therebetween. With the mating surface of the traverse flap  60  in engagement with the upper surface of the skirt  34  at a respective edge  52 , the apertures  58  on the flap  60  coincide with the apertures  54  on the skirt  34  to align the respective surfaces and permit coupling with the rivets that bind the two surfaces. A top plate  42  similarly collects the upper surfaces of the respective facets  40 . Each facet  40  has a second traverse flap  62  that is bent approximately 38° to mate with an outer edge  63  of the top plate  42 , where a pair of apertures  64  on the traverse flap  62  of each facet coincide with a pair of apertures  67  on the periphery of the top plate  42  and a pair of fasteners such as rivets (not shown) couple the facets  40  to the top plate  42 . As with the traverse flap  60 , the traverse flap  62  is bent into a parallel relationship with the top plate  42  so as to form a mating surface therebetween. Also, because the facets  40  engage the outer edges  63  of the top plate  42 , the top plate perimeter will have a shape corresponding to the shape of the window  50  in the skirt  35 . That is, if there are eight facets suggesting an octagon as shown in  FIG. 1 , then the window  50  and the perimeter of the top plate  42  will be octagons. If there are six facets or seven facets, the shapes would be hexagons or heptagons, respectively. 
   The top plate  42  includes two holes  69 , and the cover plate  44  includes two holes  78 , that receive threaded fasteners  72  for securing the top plate  42 , cover plate  44 , and mounting bracket  46 . The mounting bracket  46  includes a circular opening  81  that receives the bulb  24   a  for supporting the bulb in the reflector assembly. 
   Each facet  40  is preliminarily punched, cut, or otherwise formed from a flat plate  40   a , whereupon traverse flaps  60 ,  62  are formed by bending the plate at the appropriate angles (90° and 38°, respectively). The facet is also subdivided into horizontal subsections  83  that extend from the top vertical flap  62  to the bottom vertical flap  60  in an uninterrupted manner to form a smooth surface. The subdivisions can be created by forming 5° angles at each intersection  85  of the subdivisions  83 , which adds a curvature to the facet in the horizontal direction. The facets  40  are further curved into a parabolic shape in the vertical direction to expand and lengthen the reflected image of the bulb  24   a , thereby increasing the illumination factor of the overall reflector assembly. Each facet is further formed with bendable tabs  91  that engage the back side of an adjacent facet to couple the facets together. Using the bendable tabs  91 , the reflector assembly can be shipped in a smaller compartment and quickly assembled without fasteners, adhesives, or other complicated joining methods. Each tab  91  is bent behind the adjacent facet, and the combination of tabs  91  lock the reflector in place. Once assembled, the skirt  34  and top plate  42  can be secured to the respective flaps  60 ,  62  to fix the reflector assembly. Fasteners  72  then pass through cover plate  44  and top plate  42  to tighten and rigidly join the reflector assembly into a single unit. 
   In  FIG. 3 , it can be seen that the discrete facets form multiple subdivisions, each subdivision reflecting a separate, elongate image of the illumination source. This multiplied virtual image of the illumination source, concentrated into each subdivision, has the effect of enhancing the illumination output of the reflector over a simple parabolic reflector. Each subdivision is a smooth, continuous surface from the top of the facet to the bottom, producing a clean image of the illumination source. Further, the reflected image is elongated to extend substantially the height of the subdivision due to the curvature of the facet in the vertical direction. Thus, the reflector by virtue of the multiplication of the virtual image and the elongation of the virtual image in each facet enhances the illumination output over standard lighting assemblies. 
   A plot of a curvature for the of the radius of the reflector of the present invention can vary with application and illumination source. For a given 1000 watt illumination source,  FIG. 4  illustrates a graphic representation of the radius versus axial length of the reflector. As shown, y (the radius of the reflector) is approximated by the third order polynomial
 
 y= 0.005 x   3 −0.1401 x   2 +1.3735 x +3.2731
 
where x is the axial distance along the reflector moving away from the illumination source. The two tables below present x versus y points for reflectors using 1000 watts and 400 watt illumination sources.
 
   
     
       
             
             
             
             
             
           
             
             
             
             
             
           
             
             
             
             
             
           
         
             
                 
               TABLE 1 
             
           
           
             
                 
                 
             
             
                 
               1000 W 
                 
               4000 W 
                 
             
           
        
         
             
                 
               x 
               y 
               x 
               y 
             
             
                 
                 
             
           
        
         
             
               0   
               0 
               3.35 
               0 
               2.45 
             
             
               ⅛ 
               1.3625 
               4.7 
               1.2 
               4.14 
             
             
               ¼ 
               2.725 
               6.2 
               2.41 
               5.26 
             
             
               ½ 
               5.45 
               7.438 
               4.81 
               6.61 
             
             
               ¾ 
               8.175 
               7.825 
               7.22 
               7.21 
             
             
               1.0 
               10.9 
               8.1 
               9.63 
               7.21 
             
             
                 
             
           
        
       
     
   
   EXAMPLE 1 
   In a parking lot test where light poles and light fixtures are located in the interior of the parking lot with double parking island spacing (120′×120′) with fixtures mounted at thirty-three feet above grade and four fixture heads per pole of equal wattage (400 watts), the present invention with an eight facet reflector displayed a 58% higher foot candle average, 76% more foot candles in the center of the grid between the four poles, and 35% more foot candles between poles than a comparable segmented reflector. 
   EXAMPLE 2 
   In a parking lot test where light poles and light fixtures are located in the interior of the parking lot with triple parking island spacing (180′×180′) with fixtures mounted at forty-two feet above grade and four fixture heads per pole of equal wattage (1000 watts), the present invention with an eight facet reflector displayed a 36% higher foot candle average, 50% more foot candles in the center of the grid between the four poles, and 24% more foot candles between the poles than a comparable segmented reflector. 
   EXAMPLE 3 
   In a parking lot test where light poles and fixtures are located on the perimeter of the parking lot with fixtures mounted at thirty-three feet above grade and one fixture head per light pole of 400 watts, the present invention with seven facets (heptagonal) displayed a 38% higher foot candle average, 57% more foot candles in the center of the grid between the four poles, and 28% more foot candles between the poles than a comparable segmented reflector. 
   EXAMPLE 4 
   In a parking lot test where light poles and fixtures are located on the perimeter of the parking lot with fixtures mounted at thirty-three feet above grade and one fixture head per light pole of 1000 watts, the present invention with seven facets (heptagonal) displayed a 62% higher foot candle average, and a maximum to minimum uniformity level that was three times as uniform than a comparable segmented reflector. 
   As the examples show, the present invention provides superior lighting characteristics that will save planners and developers costs by having more efficient lighting than previously possible. As the number of light poles is reduced due to enhanced lighting, greater energy saving and less clutter due to more light poses is realized. Reduced energy demands also lead to less pollution, less stress on local energy grids, and savings on installation costs of parking lots and the like. 
   The foregoing discussion is meant to be illustrative of the present invention but not limiting in its scope. All terms herein are used according to their ordinary usage, and the examples discussed herein should not be deemed limiting to the invention. Those of ordinary skill in the art will recognize that many variations to those described embodiments will operate in a like manner, and the scope of the invention is intended to cover all variations so recognized. Therefore, the scope of the invention is properly determined by the claims presented below, using the ordinary meanings of terms set forth therein.