Patent Publication Number: US-8985809-B2

Title: Diffusion globe LED lighting device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 13/355,561 filed on Jan. 22, 2012, the contents of which are hereby incorporated by reference. 
    
    
     BACKGROUND 
     The present disclosure relates to a light fixture that uses light emitting diodes (LEDs) as light sources. Specifically, the disclosure relates to LED illuminated lighting fixtures that can be mounted on a ceiling, wall, or dropped into a drop ceiling frame. 
     Lighting fixtures with LED light sources are being used to replace conventional commercial fluorescent ceiling and wall mounted light fixtures because they can potentially have several desirable characteristics such as higher efficiency, more pleasing light quality, and longer light-source life. 
     LED ceiling and wall mounted lighting fixtures designers face several potential challenges as compared with fluorescent ceiling lighting fixtures. For example, most LEDs are point sources of light making it challenging to create even illumination. Further, direct viewing of bright, or so-called “high-brightness” LEDs can potentially cause eye damage. In addition, many commercially available high efficiency white LEDs utilize a near ultra-violet LED with a phosphor coating that can include, for example, europium plus copper and aluminum-doped zinc sulfide so that the light appears white. Direct viewing of ultra-violet (UV) light leaked from phosphor-coated LEDs can also be a potential source of eye damage. 
     Another potential challenge LED wall and ceiling mounted fixtures face compared to fluorescent wall and ceiling light fixtures is that unlike fluorescent bulbs that dissipate heat across their glass envelope, LED dissipate heat mostly through their non-illuminating bottom surface. 
     In addition, LED ceiling light fixtures that are designed to replace fluorescent ceiling troffers or as drop-in fluorescent ceiling tile replacements are often difficult to service. In many cases, the entire fixture needs to be removed from the ceiling for servicing. 
     Attempts to address the problem of potential eye damage or eyestrain include, for example, indirect LED lighting fixtures. However, depending on the specifics of the design, indirect LED lighting fixtures can cast a shadow or otherwise have a visual dark spot where the light source is blocked. In some applications, this may be undesirable. Attempts to make LED ceiling light fixtures that are designed to replace fluorescent ceiling troffers or as drop-in fluorescent ceiling tile replacements more serviceable include LED replacement lights in the form factor of a fluorescent replacement tubes. While these are often satisfactory in some residential or commercial settings, they may not be appropriate for circumstances requiring certain aesthetics or specific form factors. 
     It would therefore be desirable for there to be an LED lighting fixture that attempts to address at least some of the above-mentioned challenges. 
     SUMMARY 
     This Summary introduces a selection of concepts in simplified form that are described in the Description. The Summary is not intended to identify essential features or limit the scope of the claimed subject matter. 
     One aspect of the present disclosure describes an LED lighting fixture that provides approximately even illumination across the outer illumination surface of the light fixture. Another aspect of the invention describes an LED light for producing the same. 
     In the first aspect, a light emitting diode (LED) lighting fixture includes a plurality of hollow gradient diffusion globes, a plurality of LED clusters, and a planar reflective sheet. Each gradient diffusion globe includes a hollow cover including an aperture, a wall bound by an exterior surface having the shape of a globe, the wall of varying thickness with a thickest wall portion opposite the aperture, a diffusing-particulate homogenously distributed within the wall, and the wall and the diffusing-particulate in combination form a continuously graduated diffusive surface. The gradient diffusion globe can also include a hollow base portion surrounding the aperture and projecting outward from the hollow cover. Each LED cluster positioned within a corresponding gradient diffusion globe of the plurality of gradient diffusion globes, the LED cluster including a top surface facing and normal to the thickest wall portion. The planar reflective sheet forms an outer illumination surface of the light fixture, the planar reflective surface including a plurality of apertures, each aperture receiving therethrough a corresponding base portion. The apertures arranged so that the plurality of gradient diffusion globes, the plurality of LED clusters, and the planar reflective surface in combination produce substantially uniform illumination along the outer illumination surface of the light fixture. 
     In the later aspect, an LED lamp, includes a hollow cover that includes an aperture, a wall bound by an exterior surface having the shape of a globe, the wall of varying thickness with a thickest wall portion opposite the aperture, a diffusing-particulate homogenously distributed within the wall, and the wall and the diffusing-particulate in combination form a continuously graduated diffusive surface. In addition, an LED is positioned within the globe cover, the LED including a top LED surface facing and normal to the thickest wall portion. 
     In yet another aspect, a light emitting diode (LED) lighting fixture includes a plurality of hollow diffusion globes, a plurality of LED clusters, a planar reflective sheet, a backplane, and a plurality of retaining rings. The plurality of retaining rings, the plurality diffusion globes, and the planar reflective sheet form a first assembly. The plurality of LED clusters and backplane form a second assembly. The first assembly is separable from the second assembly. 
     In this aspect, each diffusion globe includes a hollow cover including an aperture and a hollow base portion surrounding the aperture and projecting outward from the hollow cover. Each of LED cluster of the plurality of LED clusters is positioned within a corresponding diffusion globe. The planar reflective sheet forms an outer illumination surface of the light fixture. The planar reflective surface includes a plurality of apertures, each aperture receiving therethrough a corresponding base portion. The apertures arranged in a grid pattern. The backplane, which is separate from and parallel to the planar reflective sheet, forms a continuous planar heat sink and defines a bottom outer surface of the light fixture. Each LED cluster can be thermally and mechanically coupled to the backplane. Each retaining ring receives and secures a corresponding base portion to the planar reflective sheet. 
    
    
     
       DRAWINGS 
         FIG. 1  depicts a relative LED light intensity versus viewing angle for an exemplary LEDs and LED arrays in the prior art. 
         FIG. 2  depicts a bottom perspective view a light fixture according to an embodiment in accordance with the present invention. 
         FIG. 3  depicts a top view of embodiment of the lighting fixture of  FIG. 2  illustrating exemplary relative spacing of the diffusion globes. 
         FIG. 4  depicts a light dispersion pattern of the lighting fixture of  FIG. 2  where the diffusion globes have a fixed diffusion pattern. 
         FIG. 5  depicts a light dispersion pattern of the lighting fixture of  FIG. 2  where the diffusion globes have a graduated diffusion pattern. 
         FIG. 6  depicts a sectional view of a portion of the LED lighting fixture of  FIG. 2 , showing an embodiment of a globe diffuser and the resulting ray trace diagram. 
         FIG. 7  depicts a sectional view of a portion of the LED lighting fixture of  FIG. 2 , showing an alternate embodiment of a globe diffuser and the resulting ray trace diagram. 
         FIG. 8  depicts a perspective view of an embodiment of a globe diffuser and ring assembly in accordance with principles of the invention. 
         FIG. 9  depicts an alternative embodiment of a globe diffuser and ring assembly in accordance with principles of the invention. 
         FIG. 10  depicts a bottom perspective exploded view of the light fixture of  FIG. 2 . 
         FIG. 11  depicts a front exploded view of the lighting fixture of  FIG. 10 . 
         FIG. 12  depicts an exploded partial assembled perspective view of  FIG. 2  showing an integrated reflective sheet and diffuser assembly. 
         FIG. 13  depicts an exploded partial assembled front view of  FIG. 12  showing an integrated reflective sheet and diffuser assembly. 
         FIG. 14  depicts a front assembled view of the light fixture of  FIG. 2 . 
         FIG. 15  depicts an electrical block diagram in one embodiment of the disclosed lighting fixture. 
         FIG. 16  depicts an alternative electrical block diagram in one embodiment of the disclosed lighting fixture. 
         FIG. 17  depicts an electrical block diagram of an LED drive circuit in one embodiment of the disclosed lighting fixture. 
         FIG. 18  depicts an electrical block diagram with a low voltage power distribution. 
         FIG. 19  depicts an electrical block diagram with AC supplied power distribution. 
         FIG. 20  depicts an alternative embodiment of an LED lighting system in accordance with principles of the invention in front perspective view. 
         FIG. 21  depicts a removable LED lamp of  FIG. 20  in partial cutaway view. 
         FIG. 22  depicts and alternative embodiment of a removable LED lamp of  FIG. 20  in partial cutaway view. 
         FIG. 23  depicts a portion of the LED lighting system of  FIG. 20 , in partial cutaway view. 
         FIG. 24  depicts an alternative view of the portion of the LED lighting system of  FIG. 20 . 
     
    
    
     DESCRIPTION 
     The following description is made with reference to figures, where like numerals refer to like elements throughout the several views.  FIG. 1  depicts a graph  10  of relative LED light intensity in percent (vertical axis) versus viewing angle in degrees (horizontal axis) for an exemplary LEDs and LED clusters in the prior art. LEDs typically have a top surface and a heat dissipating bottom surface. The graph  10  depicts the percent of maximum intensity where 0-degrees is normal to top surface and +90 degrees and −90 degrees are parallel to the mounting plane of the LED. The graph  10  depicts an exemplary LED or LED cluster with maximum intensity on axis or normal to the top surface of the LED with intensity falling off from the normal in a bell shaped or semi-parabolic shaped curve. 
     As used throughout this disclosure, an LED cluster means one or more LEDs configured to act as a point source of light. For example, an LED cluster can mean a single LED such as a Cree XLamp XP-G, a multi-chip LED such as a Cree XLamp MC-E or BridgeLux BRXA series LEDs, or a plurality of LEDs clustered together to act as a point source. The above-mentioned LEDs are exemplary and are not meant to limit the meaning of LED Cluster to those particular models and manufacturers. 
     The characteristic of the LEDs and LED clusters exemplified in  FIG. 1  makes it difficult to obtain uniform illumination, or uniform luminous flux density, across the surface of a planar light fixture from the direct illumination of LED clusters, especially when the LED clusters are spaced a distance larger than many times the diameter of the LED clusters, for example, at a distance of over five times the diameter of each LED cluster. 
       FIG. 2  depicts a bottom perspective view an LED lighting fixture  20  of an embodiment in accordance with the present invention illustrating a lighting fixture capable of conveying nearly uniform illumination across the surface of a planar light fixture with LED clusters spaced at a distance many times the diameter of each LED cluster. Each LED cluster is surrounded by hollow gradient diffusion globe  22 , the exterior surface having the shape of a globe. Each hollow gradient diffusion globe  22  is affixed to a planar reflective sheet  24 . The planar reflective sheet  24  forms an outer illumination surface of the LED lighting fixture  20 . 
     As defined in this disclosure, a planar reflective sheet  24  includes a top reflective, diffusive, or combination reflective and diffusive surface, and can optionally include a bottom surface that forms an electrically non-conductive electrically insulative barrier. For example, the top surface can be coated with a diffuse-reflective white paint or powder coat finish that has both diffusive and reflective properties. In addition, a reflective planar sheet can be have a top surface with aluminum anodized finished or an anodized brushed aluminum finish and may be painted white or left unpainted and can include a non-conductive backing such as ABS, polyethylene, polypropylene, or polyester. The planar reflective surface can have a sheeting material applied to a rigid or semi-rigid backing The sheeting material can comprise glass beads enclosed in a translucent pigmented substrate, for example, Scotchlite Engineer Grade 3200 series by 3M, or M-0500 or W-0500 series by Avery Denison. The semi-rigid backing can be constructed from an electrically non-conductive material to prevent electrical shorting or interference with the operation of the LEDs. The planar reflective sheet can be constructed from other diffuse reflective material; for example, Gore Diffuse Reflector Product, or Dupont Diffuse Light Reflector (DLR). These examples are meant to be illustrious and not meant to limit the meaning of a planar reflective sheet, those skilled in the art may readily recognize other equivalents from these examples. In order to form a continuous illumination surface, the reflective sheet can be continuous and seamless. 
     In the illustrated embodiment of  FIG. 2 , a power and electronics assembly  26  supplies power to LEDs. In one embodiment, the power and electronics assembly  26  can include a DC-to-DC power supply capable of receiving distributed DC voltage into the light fixture. In an alternative embodiment, the power and electronics assembly  26  can include an AC-to-DC power supply capable of receiving standard line voltage, for example 120 VAC in the United States, from a commercial or residential branch circuit and converting it to the DC supply voltage capable of powering the LED clusters. The power and electronics assembly  26  can be affixed a backplane  28 , the backplane  28  forms a bottom outer surface of the light fixture and can be used as a continuous planar heat sink to dissipate the heat from the LED clusters. 
       FIG. 3  depicts a top view of embodiment of the LED lighting fixture  20  of  FIG. 2  illustrating exemplary relative spacing of the hollow gradient diffusion globes  22 , the hollow diffusion globes having a diameter depicted by distance s. In the illustrated embodiment, the hollow gradient diffusion globes  22  are arranged in a grid pattern with each hollow gradient diffusion globe  22  separated from each other by a distance d. The hollow gradient diffusion globes  22  are spaced by a distance d/2 from the perimeter of the planar reflective sheet  24 . For example, in accordance with principles of the invention, is should be possible to create nearly uniform lighting for ceiling tile replacement fixture with a 0.61 m (2 ft.)×0.61 m (2 ft.) planar reflective sheet  24 , and nine of the hollow gradient diffusion globes  22  each of diameter s=0.038 m (1.5 in.), each hollow gradient diffusion globe  22  spaced by a distance d=0.2 m (8 in.). For example, for a typical multiple LED of diameter 0.02 m (0.8 in.), such as a BridgeLux BRXA-C2000, the LEDs are separated by a distance d=0.2 m (8 in.) that is approximately 10 times the diameter of each LED. Using the same exemplary spacing, a 0.61 m (2 ft.)×1.22 m (4 ft.) ceiling tile replacement lighting fixture can be constructed using eighteen LED clusters, each LED cluster enclosed by corresponding hollow gradient diffusion globe  22 . If, for example, each LED cluster comprised three to four closely spaced LEDs such as XP-G series LEDs, with each LED having a mounting edge of 0.00345 m (0.135 in.), then the effective diameter across the LEDs could be as small as approximately 0.01 m (0.394 in.). In this example, a distance d=0.2 m (8 in.) would be approximately twenty times the effective diameter of the LED cluster. 
       FIG. 4  depicts an exemplary light pattern of the LED lighting fixture  20  with diffuser globes  30  that are non-gradient diffusers. For purposes of illustration, the light pattern radiated from each diffuser globe  30  can be divided into four zones: a central zone  32 , the zone within the diffuser globe circumference  34 , a first reflection zone  36 , and a second reflection zone  38 . The central zone  32  represents a hot spot on the diffuser globe  30  and representing the area of highest illuminance. The majority of light appears to be radiating from a combination of the area from within the zone within the diffuser globe circumference  34  and the central zone  32  with most of the rest of the light being reflected or diffused in the first reflection zone  36 . 
       FIG. 5  depicts an exemplary light pattern of the LED lighting fixture  20  with hollow gradient diffusion globes  22 . The light pattern can be divided into two zones, the zone within the diffuser globe circumference  34  and an expanded reflection zone  40 . The expanded reflection zone  40  approximately encompasses both the first reflection zone  36  and the second reflection zone  38  of  FIG. 4 . From the plane view perspective of  FIG. 5 , the luminous flux density of the zone within the diffuser globe circumference  34  and the expanded reflection zone  40  are approximately equal. This creates an overall appearance uniform lighting across the outer illumination surface of the light fixture with virtually no hot spots. 
     The approximately uniform luminous flux density over the entire surface of the planar reflective sheet  24  is determined by the combination of the illumination pattern of the LED clusters, the light diffusion and illumination pattern of the hollow gradient diffusion globes  22 , the distance of separation between each hollow gradient diffusion globe  22 , and the reflective and diffusive characteristic of the planar reflective sheet  24 . The characteristics of LEDs and LED clusters used for commercial and residential lighting applications is well known, for example, as in the lighting curve of  FIG. 1 , and is generally published by LED lighting manufacturers. 
     Another consideration is heat dissipation. It may be desirable to provide adequate heat dissipation distance across the backplane  28  of  FIG. 2  without the need of any additional heat sinks. The life expectancy of an LED is typically related to the LED operating temperature or more specifically to the LED junction temperature. Many LED or LED clusters dissipate the majority of the heat through their bottom surface. Depending on the LED design and manufacturer, the lighting system designer can be faced with different heat dissipation strategies. For example, BridgeLux, provides LED arrays, such as the BRLX-C series, that are designed to screw directly into a heat dissipating surface. They have a large non-conductive heat dissipation contact point on the bottom surface and have solder points for the LED&#39;s electrical connections (anode and cathode) on the upper surface. Cree LED arrays, such as the MC-E series, have both electrical connection and non-conductive heat dissipation contact on the bottom of the LED array. The Cree recommends having solid copper traces (vias) going through the PCB in order to dissipate the heat. Regardless of the method, the LED arrays can be thermally and mechanically coupled to the backplane  28 , such that, the backplane acts as a heat-dissipating surface. 
     One of the considerations in disclosed lighting system is spacing the LED clusters to obtain approximately uniform lighting across the entire surface of the planar reflective sheet  24  while at the same time providing adequate spacing between the LED clusters to keep the junction temperatures of the LED clusters well within the recommended manufacturer&#39;s specifications. Those skilled in the art will readily recognize how to calculate using thermal modeling or by using simulation tools such as National Semiconductor Workbench LED Architect, Luxeon Star LED heatsink calculator without undue experimentation. Once the heat dissipation requirement for each LED cluster is known, and the area of the backplane required to dissipate the requirement amount of heat is calculated, the hollow gradient diffusion globe  22  construction can be chosen so that the LED clusters are spaced to obtain approximately uniform lighting across the entire surface of the planar reflective sheet  24  and provide adequate area from the each of the LED clusters to dissipate the requirement amount of heat. 
       FIG. 6  depicts a sectional view of a portion of the LED lighting fixture  20  of  FIG. 2 , showing an embodiment of the hollow gradient diffusion globe  22  and the resulting ray trace diagram. LED cluster  42  is illustrated for the sake of simplicity as a single LED. However, in addition to a single LED, it should be understood that this can include two or more LEDs physically clustered closely together to act as a single point source. The LED cluster  42  is mounted to a printed circuit board (PCB)  44 . The LED cluster  42  is both thermally and physically coupled to the backplane  28  either through the PCB  44  or directly, for example if the LED is manufactured with a non-conductive thermal pad. The hollow gradient diffusion globe  22  includes a the hollow cover portion  46  receiving the LED cluster  42  through an aperture  48  and a hollow base portion  50  projecting outward from hollow cover portion  46  and surrounding the aperture  48 . The planar reflective sheet  24  includes an aperture for receiving the hollow base portion  50 . The hollow base portion  50  can be secured to the planar reflective sheet  24 , for example, by a retaining ring  52 . 
     The hollow cover portion  46  includes a wall bound by the exterior surface of the hollow cover portion  46 . The exterior surface of the wall has the shape of a globe. As defined in this disclosure a globe means a shape approximating a spheroid. A spheroid can include a sphere, an oblate spheroid or a prolate spheroid. Hollow gradient diffusion globes  22  can be injection molded or otherwise formed from a semi-transparent or translucent plastic material such as acrylonitrile butadiene styrene (ABS), polyacrylate (acrylic plastic), polycarbonate, or polyvinyl chloride (PVC). A diffusing-particulate  54  is homogenously distributed within the wall. The particulate is made of a material that has a light scattering effect when encapsulated within clear or translucent plastic, for example Titanium Dioxide, Zinc Oxide, or metallic particulates. A continuously graduated diffusive wall is created by the combination of diffusing-particulate  54  homogenously distributed within the wall, and by smoothly and continuously varying the thickness of the wall. 
     It may be desirable, for reasons already disclosed, to filter UV light from reaching the eye of an observer. Embedding UV light filtering material in the plastic or by alternatively coating the hollow gradient diffusion globe  22  with UV filtering material may facilitate the filtering of UV light. 
     The wall bounding the interior surface has approximately the same shape as the wall bounding the exterior surface but with a smaller radius. The interior surface is approximately axial to and non-concentric with the exterior surface. This arrangement creates a wall thickness that is thickest opposite the aperture  48  and the LED cluster  42 , progressively and smoothly thinning where the thinnest portions are adjacent to the LED cluster  42 . The great amount of diffusion and most random internal reflection take place where the wall is thickest since there is the most diffusing particulate. The least amount of diffusion and least internal reflection take place where the wall is the thinnest. With this arrangement, harsh direct light from the LED cluster  42  is attenuated and the overall illumination across can be made to be equal across the entire lighting fixture illumination surface. 
     Continuing to refer to  FIG. 6 , an illustrative ray trace diagram shows a typical light pattern emanating from the LED cluster  42 . A portion of the rays are diffused externally with respect to the hollow cover portion  46  and are represented by rays normal to the hollow cover portion  46 . Some of the rays are refracted and are illustrated by broken lines. Some of the rays are internally reflected by not shown for simplicity. Greater amounts of internal reflection come from the regions of greatest diffusion as compared with areas of less diffusion. For example, greater amount of internal reflection would occur where the wall of the hollow cover portion  46  is the thickest near the top of the globe, opposite the LED cluster  42  as compared to portions of hollow cover portion  46  adjacent to the LED. The area of greatest refraction, least diffusion, and least internal reflection occur where the wall of the hollow cover portion  46  is the thinnest which is adjacent to the LED cluster  42 . 
     The arrangement, shape and size of the inner wall with respect to the outer wall of the hollow cover portion  46  depicted in  FIG. 6  can potentially create an approximately complementary light emission pattern as the relative intensity pattern of  FIG. 1 , this in combination with the internal reflection, and diffusion, creates the appearance of even lighting across the hollow gradient diffusion globe  22 . The combination of the ray emission pattern from the hollow gradient diffusion globe  22 , the reflection from the planar reflective sheet  24 , and the spacing between the hollow gradient diffusion globes  22 , creates the appearance of uniform lighting across the entire an outer illumination surface of the light fixture. 
       FIG. 7  depicts a sectional view of a portion of the LED lighting fixture  20  of  FIG. 2 , showing an alternate embodiment of a hollow gradient diffusion globe  56  and the resulting ray trace diagram. The hollow cover portion  58  includes wall bound by the exterior surface of the hollow cover portion  58 . In  FIG. 7 , the exterior surface of the wall has the shape of a sphere. A diffusing-particulate  54  is homogenously distributed within the wall. The particulate is made of a material that has a light scattering effect when encapsulated within clear or translucent plastic, as previously described. The wall bounding the interior surface is an oblate spheroid. The interior surface is approximately axial to and non-concentric with the exterior surface. This arrangement creates a wall thickness that is thickest opposite the aperture  48  and the LED cluster  42 , progressively and smoothly thinning where the thinnest portion along the circumference between the upper and lower hemisphere of the hollow cover portion  58 . The great amount of diffusion and most random internal reflection take place where the wall is thickest since there is the most diffusing particulate. The least amount of diffusion and least internal reflection take place where the wall is the thinnest. With this arrangement, harsh direct light from the LED cluster  42  is attenuated. The overall illumination across can be made to be equal across the entire lighting fixture illumination surface with the relative distance between each hollow gradient diffusion globe  56  being further than with the hollow gradient diffusion globe  22  of  FIG. 6 . 
       FIG. 8  depicts a bottom perspective view of an embodiment of the hollow gradient diffusion globe  22  and ring assembly in accordance with principles of the invention. In order to help facilitate manufacturing of the hollow gradient diffusion globe  22 , for example by injection molding, the hollow gradient diffusion globe  22  can be molded, or otherwise formed in two hemispheres: an upper hemisphere  60  and a lower hemisphere  62 . The upper hemisphere  60  includes an aperture  64  and a base portion  66  surrounding the aperture and projecting outward from the top of the upper hemisphere  60 . The base portion  66  illustrated is approximately shaped like a hollow cylinder, however other shapes are possible. 
     The lower hemisphere  62 , as illustrated includes an inner circumferential inset  68  the couples and joins with the interior circumference of the upper hemisphere  60  to form the hollow gradient diffusion globe  22 . The joining can be accomplished by adhesive, ultrasonic welding, or by snap fitting. A retaining ring  52  includes an interior aperture  72 . Referring to  FIGS. 6 and 8 , the interior aperture  72  is configured to secure the base portion  66  of the hollow gradient diffusion globe  22  to the planar reflective sheet  24  of  FIG. 2 . In one embodiment, the outer circumference of the base portion  66  passes through the aperture  48  of the planar reflective sheet  24 . The diffusion globe  22  is secured to the planar reflective sheet  24  by the retaining ring  52 . The outer circumference of the base portion  66  fits snuggly into the interior aperture  72  of the retaining ring  52 . The base portion  66  and retaining ring  52  can be secured by adhesive. The planar reflective sheet  24  is sandwiched between the diffusion globe  22  and the retaining ring  52 . 
     In an alternative embodiment for securing the diffusion globe  22  to the planar reflective sheet  24 , the interior aperture  72  of the retaining ring  52  and the outer circumference of the base portion  66  include complementary threading. The outer circumference of the base portion  66  passes through the aperture  48  of the planar reflective sheet  24 . The outer circumference of the base portion  66  and the interior aperture  72  of the retaining ring  52  screws securely together. The planar reflective sheet  24  is sandwiched between the diffusion globe  22  and retaining ring  52 . 
       FIG. 9  depicts an alternative embodiment of the hollow gradient diffusion globe  22  and ring assembly in accordance with principles of the invention shown in a top perspective view. As in  FIG. 8 , in order to help facilitate manufacturing of the diffusion globe, for example by injection molding, the hollow gradient diffusion globe  22  can be molded, or otherwise formed in two hemispheres: an upper hemisphere  74  and a lower hemisphere  76 . The upper hemisphere  74  includes an inner circumferential inset  77  that can couple and join with the interior circumference of the lower hemisphere  76  to form the hollow gradient diffusion globe  22 . The joining can be accomplished by adhesive, ultrasonic welding, or by snap fitting as previously described. 
     The upper hemisphere  74  includes an aperture  78  and a base portion  80  surrounding the aperture  78  and projecting outward from the top of the upper hemisphere  74 . The base portion  80  includes an upper planar surface  82  that includes a plurality of holes  84 . The holes  84  are sized and positioned to receive corresponding projections  86  projecting outward from a retaining ring  88 . The retaining ring  88  includes an interior aperture  90 . The outer circumference of the base portion  80  passes through the aperture  48  of the planar reflective sheet  24  of  FIG. 2 . The planar reflective sheet  24  of  FIG. 2 , for the this embodiment, can include a plurality of holes positioned and sized to line up with the plurality of holes  84  of the planar reflective sheet  24  of the base portion  80 . The outer circumference of the base portion  80  and the interior aperture  90  of the retaining ring  88  fit snuggly together and can be secured by adhesive; the planar reflective sheet  24  sandwiched between them. Alternatively, the projections  86  can snap fit into the holes  84  enabling the hollow gradient diffusion globe  22  to secure to the planar reflective sheet  24  of  FIG. 2 , without adhesive. 
       FIG. 10  depicts a bottom perspective exploded view of the light fixture of  FIG. 2 .  FIG. 11  depicts a front exploded view of the lighting fixture of  FIG. 2 .  FIGS. 10 and 11  depict a plurality of the hollow gradient diffusion globes  22 , the planar reflective sheet  24  with the corresponding plurality of apertures  48 , and retaining ring  52  for securing a corresponding hollow gradient diffusion globe  22  to the planar reflective sheet  24 . In addition, illustrated is one of the LED clusters  42  mounted on one of the PCBs  44 . The PCB  44  is mounted and secured to the backplane  28 . The PCB  44  can secure to the backplane  28 , for example, by screwing or by a snap fit arrangement. The power and electronics assembly  26  is shown mounted to the backplane  28 . The backplane  28  can act as a heatsink surface for both the LED clusters  42  and the power and electronics assembly  26 . 
     In one embodiment, the planar reflective sheet  24  and backplane  28  can be joined together by a mounting frame  92 , a portion of which is shown in  FIG. 10 . Alternative, the planar reflective sheet  24  and the backplane  28  can be joined directly by threaded fasteners through the surface of the planar reflective sheet  24  into the corresponding threads or threaded inserts, such as PEMs, on the backplane  28 . 
       FIG. 12  depicts an exploded partial assembled perspective view of  FIG. 2  showing an integrated reflective sheet and diffusion globe assembly.  FIG. 13  depicts an exploded partial assembled front view of  FIG. 12 . Referring to  FIGS. 12 and 13 , the plurality of retaining rings  52 , the plurality of hollow gradient diffusion globes  22 , and the planar reflective sheet  24  forms a first assembly  94 . The backplane  28 , the power and electronics assembly  26 , plurality of PCBs  44 , and corresponding plurality of LED clusters  42 , forms a second assembly  96 . The first assembly  94  forms an outer illumination surface for the second assembly  96 . The second assembly  96  forms the active light-generating portion. This arrangement allows for easy servicing. The first assembly  94 , or cover portion, can be removed easily and as an integrated assembly from the second assembly  96 , or active light-generating portion. In one embodiment, the first assembly  94  can be removed from the second assembly  96  by simply removing the mounting frame  92 , a portion of which is shown. Alternatively, the first assembly  94  can be removed from the second assembly  96  by removing fasteners from the surface of the planar reflective sheet  24 . 
       FIG. 14  depicts a front assembled view of the LED lighting fixture  20  of  FIG. 2 . Depicted in  FIG. 14  are the hollow gradient diffusion globes  22 , the power and electronics assembly  26 , a side view of the mounting frame  92  encompassing the backplane  28  and planar reflective sheet  24 . The edge of backplane  28  and the edge of the planar reflective sheet  24  are both shown. 
       FIG. 15  depicts an electrical block diagram in one embodiment of the disclosed lighting fixture. The electronics can be encompassed within the power and electronics assembly  26  of  FIG. 2 . The electronics include a power supply  102 , an LED driver  104 , a microcontroller  106 , and can include an ambient light sensor  108 . The LED driver  104  and the microcontroller  106  can be separate devices, or an integrated device. A field programmable logic array (FPGA) or other programmable logic device (PLD) can be used instead of the LED driver  104  and the microcontroller  106 . In any of the above combinations, the LED driver  104  be include power driver devices, such as n-channel or p-channel mosfets or can be used in combination with external n-channel or p-channel mosfets. For example, the LED driver  104  can include a combination of an LM3904HV p-channel mosfet buck controller with p-channel mosfets suitable to drive the LED clusters  42 , such as SI2337DS. This design would be capable of receiving distributed power from DC voltage. Alternatively, the LED driver  104  can include an LM3464 capable of receiving 120 VAC and suitable for driving the LED clusters  42  in combination with mosfet transistors such as FDD2572. 
     The microcontroller  106  can be capable of processing and acting on signals external signals such as brightness adjust signal  110  or a signal from the ambient light sensor  108  capable of measuring the ambient light in room. The microcontroller  106  can be disposed to act on these signals and signal the lamp controller to adjust the brightness of the LED clusters  42 . 
       FIG. 16  depicts an alternative electrical block diagram in one embodiment of the disclosed lighting fixture.  FIG. 16  depicts the power supply  102 , LED driver  104 , microcontroller  106 , ambient light sensor  108 , and brightness adjust  110  as previously described for  FIG. 15 . In  FIG. 16 , the system is able to adjust the color temperature of the LED lighting fixture  20  of  FIG. 2 . Each LED cluster  42  in  FIG. 16  includes a first LED  114  and a second LED  116 . The first LED  114  and second LED  116  have different color temperature outputs. Based on factors such as time of day, ambient light conditions determined by the ambient light sensor  108 , or manual color adjustment  112 , the microcontroller  106  can signal the LED driver  104  to adjust the current output to the first LED  114  and second LED  116  of each LED cluster  42  in order to obtain a desired color balance. 
       FIG. 17  depicts a simplified electrical block diagram of an LED drive circuit in one embodiment of the disclosed lighting fixture. In  FIG. 17  a switching power supply  120  that can be enclosed within the power and electronics assembly  26 , supplies power to the LED clusters  42  that can be connected in strips  122 . Average current is sensed by an average current sensing circuit  124  and feedback to the switching power supply  120 . 
       FIG. 18  depicts a system level diagram of LED lighting fixture  20  with a low voltage power distribution.  FIG. 19  depicts a similar system level diagram of LED lighting fixture  20  with AC supplied power distribution. Referring to  FIGS. 18 and 19 , the power and electronics assembly  26  receives externally supplied power. In  FIG. 18 , the power is received from distributed low voltage AC power, for example, 24-28 VAC depicted by the remote power block  126 . In many jurisdictions, lighting systems using low voltage distributed power as described can be wired without the need of a licensed electrician. In  FIG. 19 , the power is received from commercial or residential line voltage; in the U.S. this is typically 120 VAC. The power and electronics assembly  26  supplies the required current to LED drivers  104 . In  FIGS. 18 and 19 , the LED drivers  104  are depicted diagrammatically external from the power and electronics assembly  26 . As previously described, however, the LED drivers  104  can be included within the power and electronics assembly  26 . The LED driver  104  supplies each LED cluster  42 . Depicted in both  FIGS. 18 and 19  are nine of the LED clusters  42  as shown in  FIG. 9 . It should be understood that this quantity could be modified as required by the application. While each LED cluster  42  is represented by a single LED, this is only for the sake of diagrammatic simplicity. 
     Also depicted in  FIGS. 18 and 19  is an ambient light sensor  108  as previously described. The ambient light sensor  108  can be integrated into the surface of power and electronics assembly  26  facing the backplane  28  of  FIG. 2 . Both the backplane  28  and the planar reflective sheet  24  of  FIG. 2  can each include an aperture aligned and sized to receive the ambient light sensor  108  through outer illumination surface of the light fixture. 
       FIG. 20  depicts an alternative embodiment of an LED lighting fixture  220  in accordance with principles of the invention in front perspective view.  FIG. 20  depicts an LED lamp  222 , a planar reflective sheet  224 , a power and electronics assembly  226 , and a backplane  228 . The planar reflective sheet  224  forms an outer illumination surface of the LED lighting fixture  220 . The planar reflective sheet  224  includes a plurality of apertures  229 . Each aperture  229  is sized and shaped to receive a portion of a corresponding LED lamp  222 . The power and electronics assembly  226  supplies power to the LEDs. The power and electronics assembly  226  can include a DC-to-DC power supply capable of receiving distributed DC voltage into the light fixture. In an alternative embodiment, the power and electronics assembly  226  can include an AC-to-DC power supply capable of receiving standard line voltage, for example 120 VAC in the United States, from a commercial or residential branch circuit and converting it to the DC supply voltage capable of powering the LED clusters  242 . The power and electronics assembly  226  can be affixed to the backplane  228 . The backplane  228  forms a bottom outer surface of the light fixture. The backplane  228  can be used as continuous planar heatsink to dissipate the heat from the LED lamps  222  and can dissipate heat generated by the power and electronics assembly  226 . 
       FIG. 21  depicts an LED lamp  222  of  FIG. 20  in partial cutaway view. The lamp can be an Edison screw-in or plug-in type such as double contact bayonet type. Depicted is a lamp that is screw-in type with a threaded cap  230  and electrical contact  232 . In one embodiment, the threaded cap  230  and electrical contact  232  can be standard screw base, for example, Edison screw base E10, E14, or E26. Coupled to the threaded cap  230  is a base portion  234  that can include a finned heat sink  236  and a pedestal  238 . The base portion  234  is thermally coupled to the LED cluster  242 . The LED lamp  222  includes a hollow cover portion  246 . The cover portion is constructed in a similar manner as is described for the hollow cover portion  46  of  FIG. 6 . 
     The hollow cover portion  246  includes wall bound by the exterior surface of the hollow cover portion  246 . The exterior surface of the wall has the shape of a globe. The hollow cover portion  246  can be injection molded or otherwise formed from a semi-transparent or translucent plastic material such as ABS, acrylic plastic, polycarbonate, or PVC. A diffusing-particulate  254  is homogenously distributed within the wall. The particulate is made of a material that has a light scattering effect when encapsulated within clear or translucent plastic, for example Titanium Dioxide, Zinc Oxide, or metallic particulates. A continuously graduated diffusive wall is created by the combination of diffusing-particulate  254  homogenously distributed within the wall, and by smoothly and continuously varying the thickness of the wall. 
     The wall bounding the interior surface has approximately the same shape as the wall bounding the exterior surface but with a smaller radius. The interior surface is approximately axial to and non-concentric with the exterior surface. This arrangement creates a wall thickness that is thickest opposite the LED cluster  242 , progressively and smoothly thinning where the thinnest portions are adjacent to the LED cluster  242 . The great amount of diffusion and most random internal reflection take place where the wall is thickest since there is the most diffusing particulate. The least amount of diffusion and least internal reflection take place where the wall is the thinnest. With this arrangement, harsh direct light from the LED cluster  242  is attenuated and the overall illumination across can be made to be equal across the entire lighting fixture illumination surface. 
     Continuing to refer to  FIG. 21 , an illustrative ray trace diagram shows a typical light pattern emanating from the LED cluster  242 . A portion of the rays are diffused externally with respect to the hollow cover portion  246  and are represented by rays normal to the hollow cover portion  246 . Some of the rays are refracted and are illustrated by broken lines. Some of the rays are internally reflected by not shown for simplicity. Greater amounts of internal reflection come from the regions of greatest diffusion as compared with areas of less diffusion. For example, greater amount of internal reflection would occur where the wall of the hollow cover portion  246  is the thickest near the top of the globe, opposite the LED cluster  242  as compared to portions of hollow cover portion  246  adjacent to the LED. The area of greatest refraction, least diffusion, and least internal reflection occur where the wall of the hollow cover portion  246  is the thinnest which is adjacent to the LED cluster  242 . 
     The arrangement, shape and size of the inner wall with respect to the outer wall of the hollow cover portion  246  depicted in  FIG. 21  can potentially create an approximately complementary light emission pattern as the relative intensity pattern of  FIG. 1 . The arrangement, shape and size of the inner wall with respect to the outer wall of the hollow cover portion  246  in combination with internal reflection and diffusion within the hollow cover portion  246  creates the appearance of even lighting across the hollow cover portion  246  of the LED lamp  222 . This in combination with the ray emission pattern from the hollow cover portion  246 , the reflection from the planar reflective sheet  24 , and the spacing between the LED lamps  222 , create the appearance of uniform lighting across the entire an outer illumination surface of the light fixture. 
       FIG. 22  depicts an alternative embodiment of an LED lamp  222  of  FIG. 20  in partial cutaway view. The LED lamp  222  of  FIG. 22  includes threaded cap  230 , electrical contact  232 , base portion  234 , finned heat sink  236 , pedestal  238 , LED cluster  242 , and the diffusing-particulate  254  as described in  FIG. 21 . The hollow cover portion  258  is configured similar to the hollow cover portion  58  of  FIG. 7 . 
     In  FIG. 22 , the hollow cover portion  258  includes wall bound by the exterior surface of the hollow cover portion  258 . The exterior surface of the wall has the shape of a sphere. The diffusing-particulate  254  is homogenously distributed within the wall as previously described. The particulate is made of a material that has a light scattering effect when encapsulated within clear or translucent plastic, as previously described. The wall bounding the interior surface has is an oblate spheroid. The interior surface is approximately axial to and non-concentric with the exterior surface. This arrangement creates a wall thickness that is thickest opposite the LED cluster  242 , progressively and smoothly thinning where the thinnest portion along the circumference between the upper and lower hemisphere of the hollow cover portion  258 . The great amount of diffusion and most random internal reflection take place where the wall is thickest since there is the most diffusing particulate. The least amount of diffusion and least internal reflection take place where the wall is the thinnest. With this arrangement, harsh direct light from the LED cluster  242  is attenuated. The overall illumination across can be made to be equal across the entire lighting fixture illumination surface with the relative distance between each LED lamp  222  being further than with the LED lamps  222  of  FIG. 21 . 
       FIG. 23  depicts a portion of the LED lighting fixture  220  of  FIG. 20  in partial cutaway view with the LED lamp  222  separated from the structure of the LED lighting fixture  220 .  FIG. 24  depicts an alternative view of the portion of the LED lighting fixture  220  of  FIG. 23  with the LED lamp  222  electrically and mechanically secured to the socket. Referring to  FIGS. 22 and 23 , a hollow flange  260  spaces the backplane  228  from the planar reflective sheet  224 . The flange may have apertures along its sidewall to allow air to circulate around the finned heat sink  236 . Within the aperture of the hollow flange  260  is a lamp socket  262 . The lamp socket  262  is disposed to receive the threaded cap  230  and the electrical contact  232 . For example, the lamp socket  262  can be an Edison type E 26  base for receiving an E 26  cap. The lamp socket  262  can be configured with a heat-conducting portion that thermally couples to the pedestal  238  of the LED lamp  222 . For example, both the pedestal  238  and lamp socket  262  can include complementary parallel surfaces disposed to act as an efficient heat-conducting interface. The pedestal  238  can be thermally coupled to the backplane  228  so that the pedestal  238  is thermally coupled to the backplane  228 . 
     An apparatus (method, device, machine, etc.) has been described. It is not the intent of this disclosure to limit the claimed invention to the examples, variations, and exemplary embodiments described in the specification. Those skilled in the art will recognize that variations will occur when embodying the claimed invention in specific implementations and environments. For example, it is possible to implement certain features described in separate embodiments in combination within a single embodiment. Similarly, it is possible to implement certain features described in single embodiments either separately or in combination in multiple embodiments. It is the intent of the inventor that these variations fall within the scope of the claimed invention. While the examples, exemplary embodiments, and variations are helpful to those skilled in the art in understanding the claimed invention, it should be understood that the scope of the claimed invention is defined solely by the following claims and their equivalents.