Abstract:
An LED lamp assembly with a central light guide supplying light to a primary reflector where the reflective surface has a circular cross section in the horizontal medial plane and has a parabolic cross section in the vertical plane medial plane and regular combinations of the two planar sections in rotating round the axis from the vertical to the horizontal.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The Applicant hereby claims the benefit of his provisional application, Ser. No. 60/962,844 filed Aug. 1, 2007 for ASYMMETRIC LED BULB OPTIC. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to electric lamps and particularly to electric lamps assemblies with reflectors. More particularly the invention is concerned with electric lamps with reflectors and LED light sources. 
     2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98 
     Projection beam lamps frequently have circular cross sections. It is convenient to machine the smooth parabolic reflectors. However, in automobiles the beam spread is substantially in a line along the horizon, much wider than higher, so there is a need for asymmetrical patterns. Also because the front of a vehicle is typically wider than high, there is a consistent design preference for a more horizontal lay out of the optical system. Similarly for tail lamp mounted to the sides of a trunk lid, the convenient lamp shape is again rectangular albeit in a vertical orientation. LED systems have been organized for efficiency in circular patterns around a forward pointing axis. This circular arrangement in a horizontally elongated lamp system does not of itself lead to a properly spread beam pattern. There is then a need for an LED lamp system that provides even illumination in an elongated rectangular reflector. 
     BRIEF SUMMARY OF THE INVENTION 
     An automotive lamp assembly to evenly illuminate an elongated rectangular shell type secondary reflector may be constructed from a light source; a light guide with an input window facing the light source for the receipt of light. A body section axially extends in a forward (Z) direction away from the input window, having an internally reflective surface and an output window perpendicular to the axis. A primary reflector has a reflective surface positioned opposite the output window and has an axially projected size and shape sufficient to span the output window. The primary reflector in a first plane (e.g. horizontal) containing the axis, and a first perpendicular (e.g. horizontal) to the axis (the medial XZ plane), has a cross section providing a first reflection pattern of light from the light guide at angles varying from 0 to 90 degrees from the axis in a first (horizontal) plane. The primary reflector has in a second plane (e.g. vertical) containing the axis and a second perpendicular to the axis (e.g. vertical), (the medial YZ plane), has a cross section providing a second reflection pattern of light from the light guide at angles from 0 to 90 degrees to the axis in the second plane (e.g. vertical), different from the first reflection pattern. The primary reflector in planes containing the axis intermediate the first plane (e.g. horizontal) and second plane (e.g. vertical) having cross sections that are combinations of the first cross section (e.g. horizontal) and the second cross section (e.g. vertical) providing reflection patterns of light from the light guide at angles from 0 to 90 degrees intermediate the first reflection pattern and the second reflection pattern. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  shows a cross sectional view of a preferred embodiment of an LED lamp with an asymmetric LED bulb optic. 
         FIG. 2  shows a side perspective view of a preferred embodiment of the reflective surface of an asymmetric LED bulb optic sectioned in two places to show cross sectional views of two surfaces at 90 degrees. 
         FIG. 3  shows a chart of computer modeling of light emitted by LEDs into light guide illuminating an asymmetric LED bulb optic. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a cross sectional view of a preferred embodiment of an LED lamp with an asymmetric LED bulb optic. An automotive lamp assembly  10  may be made with a light source  12 , a light guide  14 , and a primary reflector  34  that supplies light to a secondary reflector (not shown). The secondary reflector may be typical of headlamp reflectors specifically designed to fit the particular vehicle&#39;s hull design, and to optically provide the preferred format of the legal forward beam pattern. Alternatively the secondary reflector may provide a tail lamp distribution pattern. The reflectors may be approximately rectangular in form having a greater dimension in one direction than in a second perpendicular direction. For discussions sake, the chosen orientation will regard a horizontally elongated secondary reflector with a less elongated vertical dimension. It should be understood that in actual application the elongated reflector may have any orientation. Preferable the light source  12  comprises a ring of LEDs  16  located in a plane facing in the forward axial  18  direction so as to supply light to an input window  20  of the light guide  14 . 
     The light guide  14  has at a first end an input window  20 , being a surface perpendicular to the axis  18  and facing the light source  12  for the receipt of light. The light guide  14  has a body section  22  that extends axially  18  in the forward (Z) direction away from the input window  20 , and has an internally reflective surface  24 . At a second end, the light guide  14  has an output window  26 , also perpendicular to the axis  18 . In the preferred embodiment the light guide  14  is a circular cylinder and in a more preferred embodiment the light guide  14  has the form of a hollow cylindrical tube  28  with a reflective cylindrical outer wall  30  and a reflective cylindrical inner wall  32 . The preferred light guide  14  is positioned so the output window  26  is closely positioned to be directly opposite the primary reflector  34 , and therefore directly illuminate the primary reflector  34 . 
     The primary reflector  34  has a reflective surface  35  positioned opposite the output window  26  and preferably has an axially  18  projected size and shape sufficient to span the output window  26  to thereby intercept most if not all the light emitted from the output window  26 . The preferred reflective surface  35  has the form of a ring, sized shaped and positioned to be opposite and span the preferred ring shaped output window  26  of the preferred hollow cylindrical tube  28 . 
       FIG. 2  shows a side perspective view of a preferred embodiment of the reflective surface of an asymmetric LED bulb optic sectioned in two places to show cross sectional views of two surfaces at 90 degrees. The preferred bulb optic, the primary reflector, may be made as a stamped metal ring with a polished surface or a resin ring with a reflective metallized surface. The reflective surface  35 , when the lamp is appropriately oriented with the axis  18  horizontal, is generally configured, to spread light right and left in a defined wedge or V shaped pattern, while constraining the light vertically to a horizontal band. The reflector surface  35  in a horizontal plane containing the axis  18 , (the medial XZ plane), has across section providing a first reflection pattern of light from the light guide  14  at angles varying from 0 to 90 degrees from the axis in the horizontal plane, zero degrees being opposite the forward axial  18  direction, and 90 degrees being perpendicular to the axis  18  (horizontal to the side). The preferred reflective surface  35  in the horizontal cross section is a circular section  38  with the center point  40  of the circular section  38  located so as to be axially  18  projected onto the output window  26 . The reflective surface  35 , when the lamp is appropriately oriented with the axis  18  horizontal, has in a vertical plane containing the axis  18 , (the medial YZ plane), has a cross section providing a second reflection pattern of light from the light guide  14  at angles from 0 to 90 degrees to the axis  18 , zero degrees being opposite the forward axial  18  direction, and 90 degrees being perpendicular to the axis  18  (vertical). The reflection pattern from the vertical cross sectional plane is different from the reflection pattern from the horizontal cross sectional plane. The preferred vertical cross section of the reflective surface  35  is a parabola  42  with the focal point  44  located so as to be axially  18  projected onto a middle point  46  between the outer wall  30  and the inner wall  32  of the light guide  14  along the output window  26 . The reflective surface  35  in planes containing the axis  18  and intermediate the horizontal plane (the medial XZ plane) and vertical plane (the medial YZ plane) have respective cross sections being combinations of the first cross section, for example the circular cross section  36 , and the second cross section, for example the parabolic cross section  48 , and provide respective reflection patterns of light from the light guide  14  at angles from 0 to 90 degrees intermediate the first reflection pattern and the second reflection pattern. 
     The primary reflector  34  may be defined as surface in a cylindrical coordinate system (r, w, z) where r is the radius, or distance from the z axis, w is the angle around the z axis, and z is the distance along the z axis. The parametric representation r(z, w) is a function giving the radius r of a surface point given the coordinate z and angle w. At each value of z the function gives an ellipse with the half axis a(z) and b(z). 
     
       
         
           
             
               r 
               ⁡ 
               
                 ( 
                 
                   z 
                   , 
                   w 
                 
                 ) 
               
             
             = 
             
               
                 
                   a 
                   ⁡ 
                   
                     ( 
                     z 
                     ) 
                   
                 
                 · 
                 
                   b 
                   ⁡ 
                   
                     ( 
                     z 
                     ) 
                   
                 
               
               
                 
                   
                     
                       
                         a 
                         ⁡ 
                         
                           ( 
                           z 
                           ) 
                         
                       
                       2 
                     
                     · 
                     
                       
                         cos 
                         2 
                       
                       ⁡ 
                       
                         ( 
                         w 
                         ) 
                       
                     
                   
                   + 
                   
                     
                       
                         b 
                         ⁡ 
                         
                           ( 
                           z 
                           ) 
                         
                       
                       2 
                     
                     · 
                     
                       
                         sin 
                         2 
                       
                       ⁡ 
                       
                         ( 
                         w 
                         ) 
                       
                     
                   
                 
               
             
           
         
       
       
         
           
             
               a 
               ⁡ 
               
                 ( 
                 z 
                 ) 
               
             
             = 
             
               R 
               + 
               c 
               - 
               
                 
                   
                     c 
                     2 
                   
                   - 
                   
                     
                       ( 
                       
                         z 
                         + 
                         c 
                       
                       ) 
                     
                     2 
                   
                 
               
             
           
         
       
       
         
           
             
               b 
               ⁡ 
               
                 ( 
                 z 
                 ) 
               
             
             = 
             
               R 
               + 
               
                 
                   1 
                   
                     4 
                     ⁢ 
                     F 
                   
                 
                 ⁢ 
                 
                   
                     ( 
                     
                       z 
                       + 
                       h 
                     
                     ) 
                   
                   2 
                 
               
             
           
         
       
     
     where 
     z= is from −h to 0 
     where w is the angle around the axis from 0 (horizontal) to 360 degrees, 
     z is the axial distance from −h to 0 
     h is a constant indicating the axial height of the primary reflector. 
     R is a constant indicating the radial distance from the axis to the parabola 
     c is a constant indicating the radius of the circle. 
     F is a constant indicating the eccentricity of the parabola. 
     In one preferred embodiment the following constants were used: 
     h=−3.0 mm; R=5.12 mm; c=2.75 mm; F=0.5 mm 
       FIG. 3  shows a chart of computer modeling of light emitted by LEDs it to light guide illuminating an asymmetric LED bulb optic. The lamp construction was optically modeled under a ray tracing program for lamp structures and model showed, the structure should provide a good light distribution pattern with light emitted from a ring of LEDs. The light distribution in the horizontal direction, line  50  indicates broad spreading in the horizontal directions. The light distribution in the vertical direction, line  52  indicated acceptably distribution in the vertical direction. Final beam shaping by typical secondary reflectors can easily shape the light from the primary reflector into a final beam pattern. The output pattern, and indicated in the chart in  FIG. 3  light from the lamp should be well fitted into a desirable, beam pattern. Light reflected by the primary reflector  34  is directed to a secondary reflector which may have further optical features, but may also have a simple or standard parabolic section in vertical planes and a parabolic or a circular surface section in horizontal planes. The secondary reflector has a greater horizontal medial spanning distance than vertical medial spanning distance about the axis  18 . The preferred secondary reflector has an approximately rectangular axial  18  projection with a greater horizontal medial spanning distance than vertical medial spanning distance. 
     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.