Abstract:
The present subject matter is directed to a system and method for producing a batwing light distribution. A lens is illuminated with a light source, preferably an LED, and the lens is configured to internally reflect a portion of the illuminating light back in a direction generally opposite to the initial illumination direction. Another portion of the light from the light source may pass through other lens surfaces but may also be reflected back past the light source with a reflector positioned on the other side of the lens from the light source. The light source may be mounted on a frame so as to obscure light therefrom from view.

Description:
BACKGROUND 
     The present subject matter relates to lighting. More particularly, the present subject matter relates to LED (light emitting diode) based lamps and associated lens and reflector assemblies and methods. 
     Currently batwing light distribution may be preferred for illuminating rooms, streets and commercial stores to create uniform intensity over the illuminated area. Several prior art patents use LED sources with lens and/or reflector combinations. Representative examples include US Published Patent Applications US 2009/0225543, US 2010/0165637, US 2011/0141729, and US 2011/0141734. 
     An issue has arisen, however, in that in many of these cases, lit LEDs are visible to the observer since the LEDs are facing the light direction and sending light rays directly through the lens. 
     In view of these known issues, it would be advantageous, therefore, to provide a lens and reflector configuration that will allow for uniform illumination operations using LED lamps while avoiding direct observation of the LED lamps. 
     BRIEF DESCRIPTION OF THE INVENTION 
     Aspects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention. 
     The present subject matter relates to a LED lamp, lens, and reflector configuration wherein LEDs are arranged to face in the opposite direction to the light direction and, in some embodiments, are completely hidden by, for example, a supporting frame or heat sink. A portion of the light from an LED source is sent by total internal reflection from a curved surface and by refraction through a second surface of the lens to create a batwing portion of the light distribution. The remainder of the light from the LED source is sent through the lens to a highly reflective reflector which diffuses the light towards the center portion of the batwing distribution. 
     In a first exemplary embodiment of the present subject matter a light distribution system is provided comprising a lens having a first and second surface. An LED light source is configured such that light from the LED is directed toward the first surface. Light directed toward the first surface passes through the lens and is at least partially reflected back from the second surface to produce a batwing light distribution in a light direction generally opposite to the initial direction of light from the LED. Depending on the construction of the lens, it is possible to obtain total internal reflection from the second surface thereby avoid light leaks (stray light) through the second surface. 
     In other embodiments of the present subject matter, a reflector is positioned opposite the second surface of the lens (e.g., on the other side of the second surface, away from the LED light source), so that at least a portion of the light passing through the lens and emerging from the second surface and a third surface corresponding to side surfaces of the lens is reflected back by the reflector to provide fill light in a central area of the batwing light distribution produced by the lens. 
     In selected other embodiments of the present subject matter the second surface is bifurcated along a central line into two symmetric portions thereby producing a symmetric batwing light distribution. In certain of such embodiments, the second surface is bifurcated along a central line into two asymmetric portions thereby producing an asymmetric batwing light distribution. In some embodiments each of the two asymmetric portions has an angle defined from a central axis to the point of peak intensity wherein the differences between the angles is in the range of about 5° and 30° and in particular embodiments have peak differences of about 10°. In other embodiments the surface is bifurcated along a central line into two asymmetric portions so that light flux from the LED is directed to a first portion such that the relative ratio of amount of light between the first portion and the second portion is approximately in a range from about 20:80 to 40:60. In particular such embodiments the ratio is about 30:70. 
     In still further embodiments of the present subject matter, the lens may be axially symmetric or linearly elongated. In selected embodiments of the present subject matter the first surface of the lens is generally flat and the second surface is bifurcated. In certain such embodiments, the bifurcated surfaces are symmetrical while in other such embodiments, the bifurcated surfaces are asymmetrical. In particular embodiments the first surface may include a recessed area for at least partially receiving the LED light source. 
     The present subject matter also relates to a method for producing a batwing distribution of light. According to such method, a source of light illuminates a lens having a first and second surfaces in an initial light direction such that a portion of the illuminating light strikes the first surface and is internally reflected within the lens from the second surface in a direction generally opposite to the initial light direction of the source of light. In some embodiments, the method also provides for obscuring the source of light from direct view in a direction toward the first surface. 
     In other embodiments, the method further provides for reflecting a portion of the illuminating light passing through the second surface and a third surface corresponding to side surfaces between the first and second surfaces in a direction generally opposite to the initial light direction. For example, the side surfaces of the lens may connect the first and second surfaces; thus, in such manner, the side surfaces may be between the first and second surface. In certain such embodiments the second surface is bifurcated along a central line into two symmetric portions thereby producing a symmetric batwing light distribution. In other such embodiments the second surface is bifurcated along a central line into two asymmetric portions thereby producing an asymmetric batwing light distribution. In particular embodiments the method provides that the two asymmetric portions have peak differences between about 5° and 30° from a point along a central axis while in other embodiments the method provides that the two asymmetric portions distribute light between the first portion and the second portion in a ratio range from about 20:80 to 40:60. 
     These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures, in which: 
         FIG. 1  is an illustration of light from an LED through a first exemplary lens in accordance with the present subject matter; 
         FIG. 2  is an illustration of light from an LED through a first exemplary lens and reflector in accordance with the present subject matter; 
         FIG. 3  is a graphical representation of a typical light distribution from the lens-reflector and a support frame combination in accordance with a first embodiment of the present subject matter; 
         FIG. 4  is an illustration of a first variation of an asymmetric lens in accordance with the present subject matter; 
         FIG. 5  is an illustration of light from an LED through the first variation asymmetric lens as reflected from an associated reflector and accounting for the effect of a support frame; 
         FIG. 6  is a graphical representation of the light distribution from the lens-reflector and a support frame combination in accordance with a first variation asymmetric lens embodiment of the present subject matter; 
         FIG. 7  is an illustration of a second variation of an asymmetric lens in accordance with the present subject matter; 
         FIG. 8  is an illustration of light from an LED through the second variation asymmetric lens as reflected from an associated reflector and accounting for the effect of a support frame; 
         FIG. 9  is a graphical representation of the light distribution from the lens-reflector and a support frame combination in accordance with the second variation asymmetric lens embodiment of the present subject matter; 
         FIG. 10  is an illustration of an extruded lens embodiment of the present subject matter; 
         FIGS. 11A and 11B , respectively, illustrate phantom cross section and isometric views of an axial symmetric lens in accordance with a further embodiment of the present subject matter; and 
         FIGS. 12A ,  12 B,  12 C, and  12 D illustrated rotated lens embodiments of the present subject matter. 
     
    
    
     Repeat use of reference characters throughout the present specification and appended drawings is intended to represent same or analogous features or elements of the invention. 
     DETAILED DESCRIPTION 
     Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents. 
       FIG. 1  illustrates representative light paths  102 ,  104 ,  106 ,  108  from LED  110  through a first exemplary lens  100  in accordance with the present subject matter. In accordance with this first embodiment of the present subject matter, LED  110  is mounted on a support frame  130  such that light produced by LED  110  is directed toward lens  100  and is substantially blocked (obscured) by support frame  130 . In this manner, light from LED  110  is desirably not directly seen by an observer, but rather light produced by LED  110  is diffused (refracted and reflected) through lens  100 . 
     In accordance with the present subject matter, lens  100 , as well as other lenses described herein, may be formed of a rigid optical polymer, for example, polycarbonate, polymethylmethacrylates, and other known material, via an extrusion process. In general, other embodiments of the lens could be formed from other transparent polymers, silicones, glasses, or ceramics via other processes including machining and polishing, injection molding, and casting. More generally lenses employed in the implementation of the present subject matter may be constructed in accordance with known and accepted construction techniques from known materials or by techniques yet to be developed using existing or newly discovered materials. 
     As can be seen in  FIG. 1 , light from LED  110  traveling in an initial direction may enter a first surface  150  of lens  100  to emerge as light paths  102 ,  104  from generally flat side surfaces  146 ,  148  of lens  100 . Light paths  102 ,  104  emerge generally in the initial direction of light from LED  110 . Others of the light paths, for example, paths  106 ,  108  are internally reflected from a second surface  152  corresponding to curved surfaces  142 ,  144  of the lens  100  and emerge through a third surface  154  corresponding to side surfaces  146 ,  148 , respectively of lens  100 . Still other of the light paths, for example, stray light paths  132 ,  134 , are partially refracted within lens  100  and emerge from the curved surfaces  142 ,  144  generally in the initial direction of the light from LED  110 . In this manner, lens  100  is configured to provide a batwing light distribution in a light direction generally opposite to the initial direction of light from LED  110  while support frame  130  not only supports LED  110  but also desirably blocks (obscures) direct view of LED  110  by observers. It should be appreciated that LED  110  may, in fact correspond to an array or group of LEDs, e.g., a linear series of LEDs; while lens  110  may correspond to a linear device, for example, as illustrated in  FIG. 10 , to be described more fully later. It should be understood that any reference to LED or “an LED” may suitably also refer to a plurality of LEDs, or may only refer to a single LED. 
       FIG. 2  is an illustration of light paths from LED  210  through first exemplary lens  200  and from reflector  220  in accordance with the present subject matter. As previously illustrated in  FIG. 1 , support frame  130  generally blocks (obscures) light in the direction of an observer which, for purposes of concealing LED  210 , is beneficial but results in a less uniform distribution of light. With reflector  220  placed on the opposite side of lens  200  from LED  210 , certain of the light paths, for example, paths  202 ,  204  that previously, per  FIG. 1 , followed a path away from an observer now follow a path from LED  210  through lens  200  and toward reflector  220  where they are reflected so as to be redirected into a direction generally opposite from their initial path from LED  210 . It will also be appreciated that light paths  232 ,  234  illustrated in  FIG. 1  as stray paths  132 ,  134 , will also be redirected into a direction generally opposite from their initial path from LED  210 . In this manner the reflected light paths  202 ,  204 ,  232 ,  234  are able, with similar such light paths, to “fill in” the otherwise less illuminated area  222  resulting, in part, from light blocked by the support frame (not separately number here) from LED  210 . Others of the light paths, for example, paths  206 ,  208  are internally reflected from a surface of the lens  200 . 
       FIG. 3  is a graphical representation  300  of an exemplary light distribution pattern from an exemplary lens-reflector and a support frame combination as illustrated in  FIG. 2  in accordance with a first embodiment of the present subject matter. As seen in  FIG. 3 , light distribution is represented in cross-sectional view as a batwing distribution with an origin point  310  indicative of light from the area of LED  110  and support  130  and with major lobes  306 ,  308  indicating illumination intensity along the radial direction of the graph but also includes an area of illumination  322  that, without reflector  220  ( FIG. 2 ) present, would have been provided with significantly less illumination due to the initial light direction from the LED source and blockage from the LED support structure. By redirecting this light that would otherwise continue to follow its initial path, the reflector also increases the optical efficiency of the overall system. 
     With reference now to  FIGS. 4-6 , a second exemplary embodiment of the present subject matter will be described. In this regard,  FIG. 4  is an illustration of a first type of an asymmetric lens  400  in accordance with the present subject matter. Although not illustrated with superimposed light rays, support frame and LED as in  FIG. 1 , it should be appreciated that light paths through and from lens  400  are quite similar to those illustrated in  FIG. 1  except that the batwing light distribution is slightly asymmetric based on the asymmetrical shape of lens  400 . For example, in the exemplary configuration of lens  400  illustrated in  FIG. 4 , the difference in peak locations  402 ,  404  is such that the angular difference between the lobes  606 ,  608  and reference line  620 , i.e., the difference in the angles ⊖ 1  and ⊖ 2  is approximately 10°. In other embodiments this difference may range from about 5° to about 30° for added control of light distribution. In this embodiment of the present subject matter it should be appreciated that the asymmetry produced by lens  400 , indicated as Type 1 in  FIG. 6 , involves one lobe  606  of the intensity distribution being centered at a different angle (⊖ 1 ) from the central axis  620  when compared to the other lobe  608  (⊖ 2 ). 
     With the addition of reflector  520  as illustrated in  FIG. 5 , light paths from LED  510  through asymmetric lens  500  are formed where some of the light paths are reflected from an associated reflector  520  while others are blocked by support frame  530  and still others are reflected within lens  500  to produce, along with those paths reflected from reflector  520 , a batwing distribution of light from the LED  510  in a light direction generally opposite to the initial direction of light from LED  510 . 
       FIG. 6  is a graphical representation  600  of an exemplary batwing light distribution  606 ,  608  from the lens-reflector and support frame combination illustrated in  FIG. 5 . As will be apparent from inspection of  FIGS. 4-6 , lens  400 ,  500  is asymmetrically formed so as to at least partially skew the batwing distribution  606 ,  608  to one side ( 608  in  FIG. 6 ) as a mechanism for controlling light distribution. 
     With reference now to  FIGS. 7-8 , a third exemplary embodiment of the present subject matter will be described. In this regard,  FIG. 7  is an illustration of a second type of an asymmetric lens  700  in accordance with the present subject matter while  FIG. 8  illustrates light paths from LED  810  through asymmetric lens  800 , some of which being reflected from an associated reflector  820  while others of which are blocked by support frame  830 .  FIG. 9  is a graphical representation  900  of generally batwing light distribution  906 ,  908  from the lens-reflector and support frame combination illustrated in  FIG. 8 . 
     As will be apparent from inspection of  FIGS. 7-9 , lens  700 ,  800  is asymmetrically formed so as to at least partially skew the batwing distribution  906 ,  908  to one side ( 908  in  FIG. 9 ) as a mechanism for controlling light distribution. In the exemplary configuration of  FIGS. 7-9 , the difference in peak locations  702 ,  704  of lens  700 , indicated as Type 2 in  FIG. 9 , together with the additional asymmetric formation of lens  700  in area  706  provide a configuration where significantly more light flux is directed to the right side  908  despite the fact that the angles ⊖1 and ⊖2 indicating the peaks of the two lobes of the intensity distribution are centered approximately equally on either side of central axis  920  such that the relative ratio of distribution of light between the left side  906  and right side  908  is approximately 30:70. In other embodiments this ratio may range from about 20:80 to 40:60 for added control of light distribution. 
     Referring to  FIG. 10 , there is illustrated a linearly elongated extruded lens  1000  embodiment of the present subject matter. As may be seen from a comparison of  FIG. 10  with  FIG. 4 , the cross section as seen at end view  1002  in  FIG. 10  of each of these lenses is substantially the same. It should be appreciated that a lens such as lens  100  of  FIGS. 1 and 700  of  FIG. 7  may also be formed as an extrusion. In this manner a linear array of LEDs may be accommodated with a similar linear reflector having a cross section as illustrated, for example, at  220 ,  520  and  820 , respectively in  FIGS. 2 ,  5  and  8 . Of course those of ordinary skill in the art will appreciate that other reflector types, including, for example, parabolic, free-form, and prismatic reflectors, may also be employed together with various lens configurations corresponding to variations of those lenses  400 ,  700  illustrated in  FIGS. 4 and 7 . The LED and lens combinations herein disclosed may also be used together with troffers, including many known troffers, as well as street light reflectors. 
       FIGS. 11A and 11B  illustrate a further embodiment of the present subject matter employing an axial symmetric lens wherein the lens cross-section is rotated axially a full 360°. As may best be seen in  FIG. 11A , lens  1100 , in cross section, is similar to lens  100  of  FIG. 1 . In this embodiment, lens  1100  may be more particularly suited for use with a single LED or group of LEDs configured in a generally circular or grouped formation. 
       FIGS. 12A-12D  illustrate three-dimensional lens embodiments of the present subject matter where the lens cross-section is rotated through only 180°. As may be seen most readily in  FIGS. 12A and 12D , lens  1200  has a generally flat underside  1202  with a recessed area  1204  for at least partially receiving one or more LED light source(s) (not separately illustrated). Further, as best seen in  FIGS. 12B and 12C , the upper surfaces  1210 ,  1212  are formed as generally elliptically shaped bifurcated portions configured to provide variations in light distribution similar to those previously described with reference to  FIGS. 1-9 . In this regard the two rotated portions of the lenses may be symmetrical or asymmetrically configured in a manner similar to the lenses illustrated in  FIGS. 1 ,  4 , and  7  so as to provide symmetric or asymmetric light distribution patterns. 
     This written description uses examples to disclose the present subject matter, including the best mode, and also to enable any person skilled in the art to practice the subject matter, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.