Abstract:
A luminaire that includes a plurality of light emitting diodes (LEDs), a light diffuser having a planar surface facing the LEDs, and a reflector that surrounds a cavity formed between the light diffuser and the LEDs. Also disclosed is a light distribution system having a first plurality of lenses configured to convert incident light into a light distribution pattern and a second plurality of lenses configured to convert incident light into a different light distribution pattern. Further disclosed is a method of distributing light that involves emitting light towards a light diffuser, scattering a first portion of the light with the light diffuser, reflecting a second portion of the light with the light diffuser, reflecting the second portion of the light with a first reflective surface back towards the light diffuser, and scattering the second portion of the light with the light diffuser.

Description:
[0001]    The priority benefit of U.S. Application No. 61/798,411, filed Mar. 15, 2013, is claimed and incorporated by reference in its entirety. 
     
    
     FIELD OF DISCLOSURE 
       [0002]    The present disclosure relates generally to lighting systems and, more particularly, to outdoor lighting systems incorporating a light diffuser to reduce glare. 
       BACKGROUND 
       [0003]    The use of light emitting diode (LED) based lighting systems has become more commonplace due to their energy savings and significant lifespan. LEDs generate an intense point of light which is generally anisotropic and has a narrow incident beam. The directionality of the light emitted by the LEDs causes excessive glare which can make LEDs very bright and harsh to look at. In some cases, the glare created by LEDs temporarily impairs a person&#39;s vision, which makes the use of LEDs for parking lot lamps and street lamps problematic unless proper glare-reducing measures are taken. 
         [0004]    An ideal design of an LED lighting system provides sufficient illumination levels on the ground while creating the effect of minimal light at the LED. To help achieve this objective, many LED manufacturers place a primary optic or lens over the semi-conductor element of the LED to create a lambertian light distribution pattern. While this light distribution pattern reduces glare to some degree, some applications, such as roadway lighting, require an even greater amount of glare reduction. In these cases, a secondary optic or lens is placed over each of the LEDs to further distribute the light. Adding the secondary optic, as opposed to modifying the primary optic itself, is preferred because the primary optic is typically installed by the manufacturer and closely integrated with the semi-conductor element of the LED. 
         [0005]    The secondary optic typically employs a bubble refraction design that creates a batwing-shaped light distribution pattern in which light rays of greatest intensity extend from a central axis of the secondary optic at a relatively high angle. These high angle light rays, while effective at more evenly illuminating the ground surfaces beneath the luminaire, nevertheless create a significant glare for an individual approaching the luminaire. 
         [0006]    To address the high angle brightness of the secondary optic, a tertiary optic or lens is added to diffuse the directional light emitted from the secondary optic. The diffusing characteristic of the tertiary optic disperses light over a larger surface area and thus reduces glare. Known tertiary optics are substantially curved and cover the entire array of the LEDs. As light rays pass through the curved upper ends of the tertiary optic, the light rays are diffracted in the horizontal and upward directions. This results in an undesirable light distribution if the luminaire is to be used outdoors, for example, to illuminate a parking lot or road. It is generally preferred that outdoor luminaries do not emit light in the upward direction because such light tends to exacerbate the problem of light pollution (i.e., the haze of wasted light that envelops many large cities and towns). If the luminaire is configured as a parking lot lamp or street lamp, emitting light in the horizontal direction is also undesirable because doing so may illuminate adjoining properties instead of the intended parking lot surface or road. 
         [0007]    Another issue with known curved tertiary optics is that a local minimum or maximum of light intensity is created as the light rays pass through the curvature of the lens. This phenomenon is commonly referred to as pixilation. Pixilation casts shows that can change the look of an illuminated object and potentially create optical illusions. 
         [0008]    A need therefore exists for a lighting system incorporating a tertiary optic that reduces glare, and additionally, minimizes light pollution and pixilation. 
       SUMMARY 
       [0009]    One aspect of the present disclosure includes a luminaire that includes a plurality of LEDs, a light diffuser and a reflector. The LEDs are disposed on a mount surface and configured to emit light away from the mount surface. The light diffuser is spaced apart from the LEDs and includes a planar surface facing the LEDs. The reflector surrounds a cavity formed between the light diffuser and the LEDs. 
         [0010]    Another aspect of the present disclosure includes a light distribution system including first and second pluralities of lenses, a light diffuser and a reflector. The first plurality of lenses is disposed on a mount surface, with each of the lenses being configured to convert incident light into a first light distribution pattern. The second plurality of lenses is disposed on the mount surface and arranged around a periphery of the first plurality of lenses. Each of the second plurality of lenses is configured to convert incident light into a second light distribution pattern different from the first light distribution pattern. The light diffuser is spaced apart from the first plurality of lenses, and the reflector surrounds a cavity formed between the light diffuser and the first plurality of lenses. 
         [0011]    A further aspect of the present disclosure involves a method of distributing light. The method includes emitting light from a light source towards a light diffuser, scattering a first portion of the light with the light diffuser, and reflecting a second portion of the light with the light diffuser. Additionally, the method includes reflecting the second portion of the light with a first reflective surface back towards the light diffuser, and scattering the second portion of the light with the light diffuser. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is perspective view of one embodiment of a luminaire of the present disclosure; 
           [0013]      FIG. 2  depicts a cross-sectional view of the luminaire of  FIG. 1 ; 
           [0014]      FIG. 3  is a bottom view of the luminaire of  FIG. 1  with the light diffuser removed; 
           [0015]      FIG. 4  illustrates a cross-sectional view of one of the plurality of secondary lenses associated with the inner cluster of LEDs; 
           [0016]      FIG. 5  is a polar distribution graph of the light distribution pattern created by the secondary lens of  FIG. 4 ; 
           [0017]      FIG. 6  is a cross-sectional view of one of the plurality of secondary lenses associated with the outer cluster of LEDs; 
           [0018]      FIG. 7  is a polar distribution of the light distribution pattern created by the secondary lens of  FIG. 6 ; 
           [0019]      FIG. 8  is a cross-sectional view of one side of the luminaire of  FIG. 1  with one of the LEDs of the inner cluster turned ON; and 
           [0020]      FIG. 9  is a cross-sectional view of one side of the luminaire of  FIG. 1  with one of the LEDs of the outer cluster turned ON. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]      FIGS. 1-3  illustrate a luminaire  10  including a housing  12  enclosing a plurality of light sources, which in the present embodiment are configured as light emitting diodes (LEDs)  14 . Other embodiments may use different types of light sources including, but not limited to, incandescent, fluorescent, and/or high-intensity discharge bulbs. The LEDs are arranged in an array  16  that is mounted to the interior of the housing  12 . Each of the LEDs  14  is packaged with an integral primary optic or lens (not shown) that provides a lambertian light distribution. The array  16  includes a plurality of secondary optics or lenses  18   a,    18   b,  each of which covers a respective one of the LEDs  14  and distributes light in a batwing-shaped distribution pattern. The LEDs  14  are divided into an inner cluster  20  and an outer cluster  22 , with the outer cluster  22  being arranged around the periphery of the inner cluster  20 . The secondary lenses  18   a , which are aligned with the inner cluster  20  of the LEDs  14 , create a light distribution pattern that differs from the secondary lenses  18   b,  which are aligned with the outer cluster  22  of the LEDs  14 . After passing through the secondary lenses  18 , the light rays emitted by the LEDs  14  strike a tertiary optic or lens, which in the present embodiment is configured as a light diffuser  24 , which covers an open end of the housing  12 . The light diffuser  24  includes a substantially planar upper surface  25  that reflects a portion of the incident light back into the housing  12  and transmits a portion of the incident light downward toward the ground. The transmitted portion of the light is scattered or spread out by the light diffuser  24  and thereby results in the emission of relatively soft light. The reflected portion of the light bounces off a reflector  28  arranged inside the housing  12  and thereafter strikes the light diffuser  24  at a more optimal angle, causing the light to exit the luminaire  10  in a more focused and intended direction. 
         [0022]    So configured, the luminaire  10  of the present disclosure advantageously provides sufficient illumination at the ground level while creating the effect of minimal light at the luminaire  10 . The luminaire  10  thus minimizes the glare perceived by an individual looking at the luminaire  10 . Additionally, the generally planar upper surface  25  of the light diffuser  24  helps evenly distribute the light and thus reduces the effects of pixilation. In addition, the reflector  28  redirects high angle light rays at a more optimal angle so that the light rays exit the luminaire  10  in a generally downward direction. Accordingly, the luminaire  10  prevents the emission of upwardly directed light rays, which tend to cause light pollution, and also prevents light rays from exiting the sides of the luminaire  10  and illuminating objects outside an intended zone of illumination. 
         [0023]    Each of the foregoing components of the luminaire  10  and the methods of operating the luminaire  10  will now be described in more detail. 
         [0024]    The luminaire  10  is suitable for outdoor use, for example, as a parking lot lamp and/or a street lamp. The housing  12  may be constructed from a durable plastic and/or metal capable of withstanding weather elements such as rain, snow, ice, etc. An arm-like structure  30 , which extends from the side of the housing  12 , may be used to cantilever the housing from the top of a light pole (not shown). In one embodiment, the housing  12  is arranged approximately (e.g., ±10%) 15-30 feet above the ground. The housing  12  may be pivotally attached to the arm-like structure  30  so that the housing  12  can be easily opened to replace the LEDs  14  or to perform other maintenance-related tasks. As illustrated in  FIG. 2 , the housing  12  possesses a hollow interior  31  containing the LEDs  14 , the reflector  28 , mounting structures (not shown), a power source interface (not shown), and control electronics (also not shown). The light diffuser  24  extends across the open end of the housing  12  so that all light exiting the luminaire  10  passes through the light diffuser  24 . 
         [0025]      FIG. 3  depicts a bottom view of the luminaire  10  with the light diffuser  24  removed so that the array  16  of the LEDs  14  is visible. The array  16  shown in  FIG. 3  includes  52  individual LEDs  14  arranged in a generally hexagonal pattern. Other embodiments can be arranged differently, for example, with a different number of LEDs arranged in circular pattern. In one preferred form, the luminaire  10  can have  96  LEDs. The outer cluster  22  of the LEDs  14  shown in  FIG. 3  is formed by the radially outermost row of the LEDs. In other embodiments, the outer cluster  22  may be formed, for example, by several (e.g., 2, 3, 4, 5, 6, etc.) outer rows of the LEDs  14 . The array  16  carrying the LEDs  14  is removably attached to a planar downwardly facing reflective surface  32  of the reflector  28  by screws  35  ( FIGS. 8 and 9 ) or other suitable fasteners. The array  16  has a smaller diameter than the downwardly facing reflecting surface  32  of the reflector  28  so that a portion of the downwardly facing reflecting surface  32  of the reflector  28  is not covered by the array  16 . 
         [0026]    Referring back to  FIG. 2 , the reflector  28  includes a circumferential reflective surface  34  that surrounds a gap or cavity  33  formed between the LEDs  16  and the light diffuser  24 . The circumferential reflective surface  34  is flat (in a cross-sectional view) and intersects the downwardly facing reflective surface  32  at a relatively abrupt angle. In other embodiments, the circumferential reflective surface  34  gradually bends into the downwardly facing reflective surface  32  such that the surfaces form a continuous parabolic or hemispherical shape, or some other curved shape. The circumferential reflective surface  34  and the downwardly facing reflective surface  32  are preferably made from metal, plastic or other material having reflective properties. 
         [0027]    Still referring to  FIG. 2 , the light diffuser  24  includes an upwardly facing surface  36  spaced apart from and facing the LEDs  14 . In one embodiment, the upwardly facing surface  36  is offset from the LEDs  14  by a distance of approximately (e.g., ±10%) 2-3 inches, or lesser or greater. The present embodiment of the upwardly facing surface  36  is generally planar and orthogonal to a central axis A 1  of the luminaire  10 . The planar aspect of the upwardly facing surface  36 , coupled with the gap separating the upwardly facing surface  36  and the LEDs  14 , helps prevent pixilation of the light passing through the light diffuser  24 . 
         [0028]    Many of the light rays emitted from the LEDs  14  strike the upwardly facing surface  36  of the light diffuser  24  at a substantial angle. As a result, the upwardly facing surface  36  reflects a portion of the light rays back up into the luminaire  10 . In some cases, the upwardly facing surface  36  reflects approximately (e.g., ±10%) 20% of the incident light and transmits about (e.g., ±10%) 80% of the incident light. While there may be some energy losses associated with the reflection, it is generally desirable to reflect the light back up into the luminaire so that the reflector  28  can re-direct the light rays at a more optimal angle, and in a different location, so as to minimize pixilation. The reflection of high angle light rays also helps control the size of the illuminated ground area by limiting the number of light rays that exit the luminaire  10  in the horizontal, or substantially horizontal, direction. 
         [0029]    The upwardly facing surface  36  of the light diffuser  24  can be made from a variety of semi-transparent and/or semi-reflective surfaces such as plastic (e.g., acrylic or polycarbonate) or glass. Additionally, the upwardly facing surface  36  may be coated with a material that increases its reflectivity. In some embodiments, the light diffuser  24  is made of material that does not polarize the light. 
         [0030]    A downwardly facing surface  38  of the light diffuser  24  is textured so that it scatters the light rays exiting the light diffuser  24 . The texture can be formed by a mold having a mild acid etch that is used in an injection molding process to create the light diffuser  24 . The scattering effect of the downwardly facing surface  38  substantially reduces glare, and also, creates the effect of a uniformly luminous surface, which is generally considered more aesthetically pleasing than the distinct points of light created by the LEDs  14 . 
         [0031]    The angle at which the light rays initially strike the upwardly facing surface  36  of the light diffuser  24  is controlled by the shape of the secondary lenses  18   a,    18   b.  As mentioned above, each of the secondary lenses  18   a,    18   b  transforms the light emitted from one of the LEDs  14  into a batwing-shaped light distribution pattern. Generally speaking, a batwing-shaped light distribution pattern possesses at least one peak of light intensity arranged along a conical plane centered about a central axis of the lens. For reasons described below, the secondary lenses  18   a  associated with the inner cluster  20  of LEDs create a batwing-shaped light distribution pattern that differs from the one created by the secondary lenses  18   b  associated with the outer cluster  20  of LEDs. 
         [0032]      FIG. 4  illustrates a cross-sectional view of one example of how the secondary lenses  18   a  associated with one of the LEDs  14  of the inner cluster  20  could be structured. The center of the secondary lens  18   a  includes a cone-shaped cutout having a central surface  40 . A bundle of light rays  42  emitted from the LED  14  are internally reflected by the central surface  40  and thereafter strike and refract through an outer surface  44  of the secondary lens  18   a.  Each of the light rays  42  exits the secondary lens  18   a  at an angle relative to a central axis A 2  of the secondary lens  18   a  measuring approximately (e.g., ±10%) 45-75 degrees, and within the range of 55-65 degrees. For the sake of simplicity,  FIG. 4  depicts an angle θ 1  which represents an average angle of the light rays  42  emitted from the secondary lens  18   a.  The lens depicted in  FIG. 4  is merely an example, and other lenses can be used to create a similar light distribution. 
         [0033]      FIG. 5  depicts a polar distribution graph of the batwing-shaped light distribution pattern  50  created by the light emitted from the secondary lens  18   a  illustrated in  FIG. 4 . The batwing-shaped light distribution pattern  50 , if viewed in three dimensions, would extend symmetrically around the central axis A 2  of the secondary lens  18   a.  The light distribution pattern  50  has a peak of light intensity  52  arranged along an imaginary conical plane P 1  centered about the central axis A 2  of the secondary lens  18   a.  The angle at which the peak of light intensity  52  extends away from the central axis A 2  of the secondary lens  18   a  is generally equal to the angle θ 1 . 
         [0034]      FIG. 6  illustrates a cross-sectional view of one example of how the secondary lenses  18   b  associated with one of the LEDs  14  of the outer cluster  22  could be structured. The center of the secondary lens  18   b  includes a cone-shaped cutout having a central surface  60 . A first bundle of light rays  62  emitted from the LED  14  are internally reflected by the central surface  60  and subsequently strike and refract through a lower outer surface  64  of the secondary lens  18   b.  A second bundle of light rays  66  emitted from the LED  14  are internally reflected by the central surface  60  and thereafter strike and refract through an upper outer surface  68  of the secondary lens  18   b.  Each of the light rays  62  exiting the lower outer surface  64  forms an angle with a central axis A 3  of the secondary lens  18   b  of about (e.g., ±10%) 15-45 degrees, and within the range of 30-40 degrees. Each of the light rays  66  exiting the upper outer surface  68  forms an angle with the central axis A 3  of approximately (e.g., ±10%) 65-85 degrees, preferably within the range of 70-80 degrees. As such, an angle between the lower and upper outer surfaces  64 ,  69  can be in a range of about (e.g., ±10%) 100-155 degrees, or less or greater. For the sake of simplicity,  FIG. 6  depicts an angle  82  which represents an average angle of the light rays  62  emitted from the lower outer surface  64 , and illustrates an angle  83  which represents an average angle of the light rays  66  emitted from the upper outer surface  68 . In one embodiment, the central axis A 3  of the secondary lens  18   b  is parallel to the central axis A 2  of the secondary lens  18   a  and/or parallel to the central axis A 1  of the luminaire  10 . The lens of  FIG. 6  is merely an example and other lenses can be used to create a similar distribution. 
         [0035]    As seen in  FIG. 6 , a gap is formed between the first and second bundles of lights rays  62  and  66  as they exit the secondary lens  18   b.  This results in a double batwing-shaped light distribution pattern  70  shown in the polar distribution graph of  FIG. 7  (which if viewed in three dimensions would extend symmetrically around the central axis A 3 ). The light distribution pattern  70  possesses three peaks of light intensity  72 ,  74 ,  76 , each of which is arranged along a respective imaginary conical plane P 2 , P 3 , P 4  centered about the central axis A 3  of the secondary lens  18   b.  The angle at which the first peak of light intensity  72  extends away from the central axis A 3  is generally equal to the angle  82 , and the angle at which the second peak of light intensity  74  extends away from the central axis A 3  is generally equal to the angle  83 . The third peak of light intensity  76  is less than both the first and second peaks of light intensity  72  and  74 , and in some cases, may be equal to, or very close to, zero intensity. 
         [0036]    As described below in more detail, the double batwing-shaped light distribution pattern  70  of the secondary lens  18   b  advantageously directs the high angle light rays (i.e., the light rays  66 ) directly at the circumferential reflective surface  34  of the reflector  28  instead of at the light diffuser  24 . Accordingly, the high angle light rays do not first bounce off the light diffuser  24 , and then strike the reflector  28 , which tends to cause energy losses. Furthermore, the high angle light rays are prevented from exiting the light diffuser  24  in the horizontal direction which might otherwise occur if these light rays were to strike the outer edge of the light diffuser  24  at a shallow angle and then exit the outer edge of the light diffuser  24  in a scattered manner. 
         [0037]    Referring to  FIGS. 8 and 9 , the operation of the luminaire  10  will now be described. For the sake of simplicity,  FIG. 8  depicts the light emission of a single one of the LEDs  14  included in the inner cluster  20 , and  FIG. 9  illustrates the light emission of a single one of the LEDs  14  included in the outer cluster  22 . In actuality, all of the LEDs  14  would emit light simultaneously during operation of the luminaire  10 . 
         [0038]    As illustrated in  FIG. 8 , the LED  14  of the inner cluster  20  emits light that first passes through a primary optic (not shown) and then passes through the secondary lens  18   a  to create an incident beam  80 . The incident beam  80  includes the bundle of light rays  42  depicted in  FIG. 4  and corresponds to the peak of light intensity  52  illustrated in  FIG. 5 . A portion of the incident beam  80  is reflected by the upwardly facing surface  36  of the light diffuser  28  and becomes reflected beam  82 . The remainder of the incident beam  80  is transmitted through the light diffuser  28  and scattered by the texture of the downwardly facing surface  38  as the incident beam  80  exits the light diffuser  28 . Meanwhile, the reflected beam  82  bounces off the circumferential reflective surface  34  of the reflector  28  and then reflects off of the downwardly facing reflective surface  32  of the reflector  28 . The reflected beam  82  is thus redirected back at the light diffuser  28 , and exits the light diffuser  28  in a generally downward direction. 
         [0039]      FIG. 9  shows that the LED  14  of the outer cluster  22  emits light that initially passes through a primary optic (not shown) and then passes through the secondary lens  18   b  to create a first incident beam  90  and a second incident beam  92 . The first incident beam  90  includes the first bundle of light rays  62  illustrated in  FIG. 6  and corresponds to the first peak of light intensity  72  depicted in  FIG. 7 . The second incident beam  92  includes the second bundle of rays  66  illustrated in  FIG. 6  and corresponds to the second peak of light intensity  74  depicted in  FIG. 7 . The first incident beam  90  initially strikes the upwardly facing surface  36  of the light diffuser  28 , whereas the second incident beam  92  initially strikes the circumferential reflective surface  34  of the reflector  28 . Little or no light is emitted from the secondary lens  18   b  in the region between the first and second incident beams  90  and  92 . Accordingly, the LED  14  of the outer cluster  22  is prevented from emitting light rays that would otherwise strike the outer edge of the light diffuser  24  at a shallow angle and potentially exit the light diffuser  24 , after being scattered, in a substantially horizontal direction, thereby illuminating an adjoining property. 
         [0040]    A portion of the first incident beam  90  is reflected by the upwardly facing surface  36  of the light diffuser  28  and becomes the first reflected beam  96 . Relatively speaking, only a small portion of the first incident beam  90  may be reflected by the upwardly facing surface  36  since the first incident beam  90  strikes the upwardly facing surface  36  of the light diffuser  28  at a relatively steep angle (e.g.,  82  may be within the range of 30-40 degree). The remainder of the first incident beam  90  is transmitted through the light diffuser  28  and scattered by the texture of the downwardly facing surface  38  as the first incident beam  90  exits the light diffuser  28 . The first reflected beam  96  meanwhile bounces off the circumferential reflective surface  34  of the reflector  28  and then reflects off of the downwardly facing reflective surface  32  of the reflector  28 . The first reflected beam  96  is thus redirected back at the light diffuser  28 , and exits the light diffuser  28  in a generally downward direction. 
         [0041]    With regard to the second incident beam  92 , this beam initially reflects off the circumferential reflective surface  34  of the reflector  28  in the downward direction, and then passes through downwardly facing surface  38  of the light diffuser  24  which causes scattering of the beam. One benefit of aiming the second incident beam  92  directly at the circumferential reflective surface  34  of the reflector  28  is that the first incident beam  90  experiences a single reflection prior to exiting the luminaire, and thus is more likely to retain its original intensity. This improves the efficiency of the luminaire  10 . Also, aiming the second incident beam  92  at the circumferential reflective surface  34  of the reflector  28  prevents the second incident beam  92  from passing through the outer portion of the diffuser  24  at a shallow angle, which helps prevent unintended illumination of an adjoining property next to the intended area of illumination. 
         [0042]    While the present embodiment of the luminaire utilizes LEDs as the light sources, as mentioned above, other embodiments of the luminaire can utilize other light sources such as, e.g., incandescent bulbs, fluorescent bulbs, high-intensity discharge bulbs, etc. 
         [0043]    The luminaire of the present disclosure advantageously reduces glare while providing a significant degree of control over the direction of the emitted light, and also, minimizing pixilation and energy losses due to internal reflections. These aspects of the luminaire make it particularly suitable for lighting outdoor areas such as a parking lot or a street, and anywhere else where light pollution is a concern. Additionally, by reducing the effects of pixilation and glare, the luminaire can sufficiently illuminate an area without impairing an individual&#39;s vision. 
         [0044]    While the present disclosure has been described with respect to certain embodiments, it will be understood that variations may be made thereto that are still within the scope of the appended claims.