Abstract:
Area lighting with a luminaire constructed from an array of light-emitting diodes (LEDs) distributed along the convex surface segment of an elliptic torus provides a uniform light output to the surrounding area.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to luminaires for area lighting that utilize light-emitting diodes (LEDs) distributed along the convex curved surface of a plurality of supporting members. 
       BACKGROUND OF THE INVENTION 
       [0002]    Light-emitting diodes are quickly becoming a popular light source for indoor task and area lighting, providing high energy efficiency and long life expectancy. One drawback of the light-emitting diode is that for a typical installation of an LED-based luminaire mounted on a ceiling and directed straight down, the LEDs only provide light through a range of 120°, failing to illuminate the first 30° from the ceiling. 
         [0003]    For example, the attached  FIG. 1  illustrates a prior art installation  100  of a single LED  110  mounted on a ceiling  120  and pointed straight down, in which the LED  110  only provides light through a range of 120°, failing to illuminate the first 30° from the ceiling  120 . 
         [0004]      FIG. 2A  illustrates another prior art installation  200  of a first, second, and third band of LEDs  210 ,  220 , and  230 , respectively. Such a prior art design may be seen, for example, in FIG. 14 of U.S. Pat. No. 8,750,671, granted to Kelly et al. on Jun. 10, 2014. In this configuration, each of the three bands of LEDs  210 ,  220 , and  230  follows an arc, with the LEDs oriented normal to the arc. Thus, the center LED is aimed straight down, or nearly straight down, and the other LEDs are directed or aimed at an angle to the floor. Note that when this description mentions the orientation of an LED, it is with regard to the aimpoint of the output light. 
         [0005]    As may be seen in  FIG. 2B , if one assumes that an LED has a typical light distribution of 120°, then obtaining 180° coverage along one axis can be obtained by distributing a plurality of LEDs into a 60° arc  250 , i.e., with the LED  260  at one end of each arc aimed at 30° above the floor in one direction, e.g., north, and with the LED  270  at the other end of each arc aimed at 30° above the floor in the opposite direction, e.g., south. 
         [0006]    While this prior art design is an improvement over the problem presented by the construction where all LEDs are simply aimed straight down and directly at the floor below, e.g., as illustrated in  FIG. 1 , it still only provides a 180° lighting distribution along one axis. That is, as discussed above, each of the three bands of LEDs  210 ,  220 , and  230  follows an arc. The apexes of each arcuate LED band  210 ,  220 , and  230  are placed along horizontal line  240 , being an axis perpendicular to the length of arcuate LED bands  210 ,  220 , and  230 . The center LEDs of LED bands  210 ,  220 , and  230  are aimed straight down. Thus, the 180° distribution will only be present in the axis parallel to the length of arcuate LED bands  210 ,  220 ,  230 , i.e., perpendicular to axis  240 . Thus, in the example given, the 180° distribution would be present along the north-south axis, but the east-west axis would still only provide a 120° distribution. 
         [0007]    What is required is an improved luminaire based on LEDs that provides illumination through a greater angular range, including up to 180°. 
       SUMMARY OF THE INVENTION 
       [0008]    The present invention provides a substantial improvement in the distribution of illumination of an LED-based luminaire. The luminaire comprises a plurality of elliptical arcuate bands on each of which band are mounted in predetermined spaced-relation a plurality of LEDs, each having its axis of light emission aimed normal to the convex side of the band. For convenience, the bands on which the LEDs are mounted may be referred to hereinafter as the “LED bands”. 
         [0009]    The LED bands are arranged in an array such that the longitudinal axes of the bands are parallel when projected on the planar surface defined by the luminaire&#39;s adjacent base member. The apexes of the bands define an elliptical arc perpendicular to the longitudinal axes of the bands. The LED bands are oriented normal to the elliptical arc. 
         [0010]    In a preferred embodiment, the LED array defines a portion of the outer surface of a torus. In an embodiment described in more detail below, the array includes 60° of the outer torus surface. 
         [0011]    The luminaire configured and arranged as described to support the elliptical arcuate bands in the defined torroidal array will provide improved light output and can be constructed using any known combination of materials. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    Preferred embodiments of the invention are described herein below with reference to the drawings wherein: 
           [0013]      FIG. 1  illustrates a prior art ceiling-mount of a single LED; 
           [0014]      FIG. 2A  illustrates a prior art arcuate distribution of multiple LEDs; 
           [0015]      FIG. 2B  illustrates a prior art 180° light distribution along one axis; 
           [0016]      FIG. 3  illustrates an embodiment of the present invention; and 
           [0017]      FIG. 4  illustrates another embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0018]    Referring now to  FIG. 3 , there is illustrated a preferred embodiment of the present invention in which the luminaire  300  includes a planar base member  360  and a plurality of identical elliptical arcuate LED bands  310 , each with opposing end portions and an intermediate apex. The LED bands  310  define a segment of an ellipse having a first major axis and first minor axis. In a preferred embodiment, the first major axis and first minor axis are equal, so that the LED bands  310  define arcs of a circle. Each LED band  310  is oriented so that a projection of the longitudinal axes of the bands onto the base member are parallel to each other. Distributed along the convex surface of LED band  310  are a plurality of LEDs, each of which are oriented and aimed normal to the adjacent surface of the band on which they are mounted. 
         [0019]    Identical first and second elliptical arcuate members  325  and  327  are mounted perpendicular to base member  360 , and preferably positioned on either side of the base member  360 . The first and second elliptical arcuate members  325 ,  327  define arcs  320 ,  321  that are segments of an ellipse with a second major axis and a second minor axis. The plurality of LED bands  310  are secured in spaced-apart relation along a mounting surface of the first and second elliptical arcuate members  325 ,  327 , such that the opposing end portions of each LED band  310  are positioned, respectively, on a mounting surface of the first and second arcuate members  325 ,  327 , and each band of LEDs  310  is oriented normal to the surface defined by the first and second arcs  320 ,  321 . 
         [0020]    In a preferred embodiment, the second major axis and second minor axis of arcs  320 ,  321  are equal, defining arcs or segments of a circle. The first minor axis of the ellipse defined by LED bands  310  equals the second minor axis upon which the arcs  320 ,  321  of first and second elliptical arcuate members  325 ,  327  are based. The LEDs on each LED band  310  that are closest to the end portions of their respective LED bands are oriented at a predetermined angle below the plane defined by the surface of the base member  360 . 
         [0021]    From the above, it will be understood that the LED bands  310  each define a first arc that is a segment of an ellipse with a first major axis equal to 2c and a first minor axis equal to 2a. Arcs  320 ,  321  of first and second elliptical arcuate members  325 ,  327  each define a second ellipse that is a segment of an ellipse with a second major axis equal to 2b and a second minor axis equal to 2a. 
         [0022]    The overall effect is that the LEDs are uniformly distributed along the convex surface segment of an elliptic torus, and thereby provide a more uniform light output. In an embodiment where the minor and major axes of the ellipse are equal, the torus is defined by the rotation of a circle about a line. 
         [0023]    The first major axis, 2c, is preferably from one foot to eight feet in length. The second major axis, 2b, is preferably from one foot to two feet in length. The first and second minor axes, 2a, are preferably 21 inches to 45 inches in length. The luminaire  300  is preferably constructed with 10 to 25 LED bands  310 . 
         [0024]    In the embodiment of  FIG. 4 , a center LED band  330  is secured in position at the apex of the arcuate members  325 ,  327 . In other embodiments, the distribution of LED bands along arcuate members  325 ,  327  does not include an LED band placed at the apex. The specific configuration and spacing of the LEDs and the bands in the luminaire of this invention to obtain optimum lighting to meet predetermined requirements is within the skill in the art. Factors include distance from the luminaire to surfaces and/or areas to be lighted, light intensity desired, and the like. 
         [0025]    While the typical LED has a light distribution of 120°, other distributions are possible. Thus, the aforementioned predetermined angle is preferably in a range from 15°-45°, and more preferably is approximately 30°. 
         [0026]    In an embodiment of the invention illustrated in  FIG. 3 , base  360  of luminaire  300  is made preferably of a rigid material, such as steel, aluminum, or a reinforced thermoplastic. Each of the two elliptical arcuate members  325 ,  327  to which the ends of the bands of LEDs  310  is secured are fabricated from an elongated element of metal, i.e., a strip of aluminum or steel, or a polymer reinforced with glass fibers or carbon filaments. The elliptical arcuate members  325 ,  327  can also be in the form of an “L”-shaped flange, a “T” or a “C” to provide greater rigidity, should that characteristic be required due to the size of the luminaire. The opposing ends of each of the elliptical arcuate members  325 ,  327  of this embodiment can be dimensioned and configured to facilitate its secure mounting on the base member  360  by mechanical fasteners, e.g., rivets, or by spot welding, or by other means known in the art. 
         [0027]    The contact surfaces of elliptical arcuate members  325 ,  327  can be constructed of the same or similar rigid material as base  360 . Alternatively, instead of arcuate members  325 ,  327  being formed from narrow strips as described above, they can be the elliptical arcuate edges of side support panels  322 . If side support panels  322  are utilized, they can be solid, or can be perforated to reduce weight and/or provide a decorative pattern.  FIG. 4  shows an embodiment in which side support panels  322  are formed from the same metal sheet as base member  360 , e.g., by bending it to a position normal to the base. The panels  322  are perforated to form a decorative sunburst pattern which also reduces the weight of the luminaire. It is to be noted that in  FIG. 4  the edges of side support panels  322  appear scalloped in nature, but the apexes of the scallops are dimensioned and arranged to define the respective elliptical arcuate surface for mounting as with elliptical arcuate members  325 ,  327 . 
         [0028]    The LED bands  310  can be made of any rigid or flexible substrate materials that are approved for LED-mounting. The LED bands  310  are securely attached to the arcuate members  325 ,  327  by any known means such as screws, bolts, and/or rivets, or by spot welding. 
         [0029]    A wide range of LEDs are suitable for use in this invention. In a preferred embodiment, LEDs with a color temperature of 3000 to 7000 Kelvin can be used, and from 30 to 60 LEDs are mounted to each LED band  310 , with uniform longitudinal spacing along the band. 
         [0030]    The luminaire  300  can also include a power supply, which in a preferred embodiment can be a dimmable driver with an input (line) voltage of 120-480 VAC +/−10%, and wiring between the LEDs and the driver. Conventional means can be provided for wiring the luminaire  300 , such as a pigtail or a wiring terminal. 
         [0031]    In another embodiment (not shown), an LED-based luminaire is constructed of similar elements, except that the LED bands  310  are replaced by a solid toroidal surface having a configuration as defined above with LEDs uniformly distributed across the convex side of the surface. Such an embodiment is equivalent to increasing the number of LED bands  310 , or increasing their width, until there is no gap between bands. 
         [0032]    The invention includes flush and surface ceiling mounting, as well as pendant-mounted luminaires. 
         [0033]    While preferred embodiments of the present invention have been illustrated and described herein, it will be apparent that such embodiments are provided by way of example only. Numerous variations, changes and substitutions will be apparent to those skilled in the art without departing from the invention, the scope of which is to be determined by the following claims.