Patent Publication Number: US-2013250569-A1

Title: Configurable light emitting diode lighting unit

Description:
RELATED APPLICATIONS 
     This application is a Continuation of U.S. application Ser. No. 13/345,138, filed Jan. 6, 2012, which claims the benefit of U.S. Provisional Application No. 61/485,904, filed May 13, 2011. The entire teachings of the above application are incorporated herein by reference. 
    
    
     BACKGROUND 
     1. Technical Field 
     This application relates generally to the field of lighting. More particularly, this application relates to the technology of high power light emitting diode (LED) lighting units, e.g., providing approximately 9,000 lumens of total illumination at 150 watts power dissipation, and, in particular, to a higher power LED lighting unit for indoor and outdoor lighting functions, such as architectural lighting, having a dynamically programmable single or multiple color array of high power LEDs and improved heat dissipation characteristics. 
     2. Background Information 
     Developments in LED technology have resulted in the development of “high powered” LEDs having light outputs on the order of, for example, 70 to 80 lumens per watt, so that lighting units including arrays of high powered LEDs have proven practical and suitable for high powered indoor and outdoor lighting functions, such as architectural lighting. Such high powered LED array lighting units have proven advantageous over traditional and conventional lighting device by providing comparable illumination level outputs at significantly lower power consumption. Lighting units including arrays of higher powered LEDs are further advantageous in providing simple and flexible control of the color or color temperature of the lighting units. That is, and for example, high powered LED lighting units may include arrays of selected combinations of red, green and blue LEDs and white LEDs having different color temperatures. The color or color temperature output, of such an LED array, may then be controlled by dimming control of the LEDs of the array so that the relative illumination level outputs, of the individual LEDs in the array, combine to provide the desired color or color temperature for the lighting unit output. 
     A recurring problem with such higher powered LED array lighting units, however, is the heat generated by such high powered LED arrays, which often adversely effects the power and control circuitry of the lighting units and the junction temperatures of the LEDs, resulting in shortened use life and an increased failure rate of one or more of the power and control circuitry and the LEDs. This problem is compounded by the heat generated by, for example, the LED array power circuitry and is particularly compounded by the desire for LED lighting units that are compact and of esthetically pleasing appearance as such considerations often result in units having poor heat transfer and dissipation characteristics with consequently high interior temperatures and “hot spots” or “hot pockets.” 
     The present invention provides a solution to these and related problems of the prior art. 
     SUMMARY 
     Wherefore, it is an object of the present invention to overcome the above mentioned shortcomings and drawbacks associated with the prior art. 
     An object of the present invention is to provide a higher power LED lighting unit approaching about 9,000 lumens of total illumination at 150 watts power dissipation. 
     Another object of the present invention is to provide an improved heat transfer element, which further improves the conduction of heat, generated by the LEDs and through and out of the LED lighting unit so that the LED lighting unit operates at a cooler temperature and thereby reduces the possibility or likelihood that the generated heat from the LEDS will adversely affect the power supply and/or the associated electronic circuitry. 
     A further object of the present invention is to provide a centrally located chimney, formed in at least one of a rear surface of the power supply housing, and a front surface of the LED array housing, which directly communicates with the air flowing into and through the heat transfer element and thereby facilitates improved convection airflow into and out of the LED lighting unit, which provides a more efficient cooling of the LED lighting unit and thereby increases the durability of the LED lighting unit incorporating the same. 
     Another object of the present invention is to provide the chimney with a reduced area throat section as well as a suitable cross sectional airflow area which avoids restricting pass natural convention flow of air into and through the chimney and thereby improves the overall cooling of the LED lighting unit and, in turn, the LEDs and the internal components accommodated within the LED lighting unit. 
     Another object of the present invention is to provide a standardized configuration in which various subassemblies or modules can configured in the LED lighting unit to achieve a desired illumination. 
     Yet another object of the present invention is to provide a lighting unit configuration in which various LED subassemblies or modules can be physically accessed, for example during repair, without disturbing other subassemblies, such as power supplies and/or control circuitry. 
     The present invention is directed to a lighting unit including a thermally conductive array housing and having an array of LEDs and LED control circuits mounted on a first surface of a printed circuit board, and a heat transfer element located on a second surface of the printed circuit board and forming a thermally conducting path between the array of LEDs and a rear side of the LED array housing, and a power supply housing spaced apart from the read side of the LED array housing and including a power supply. The LED array housing includes more than one vertically oriented (e.g., with respect to a plane of the LED array) heat dissipation elements located in an airflow space between the LED array housing and power supply housing and extending toward but not touching a front side of the power supply housing. The heat dissipating elements, the rear side of the LED array housing and the front side of the power supply housing form multiple convective circulation air passages for the convective dispersal of heat from the heat dissipating elements with thermal isolation gaps between the heat dissipation elements and the power supply housing to thermally isolate the power supply housing from the LED array housing and LED array. 
     The LED array may include a selected combination of high powered LEDs selected from among at least one of red LEDs, green LEDs, blue LEDs and white LEDs of various color temperatures and the control circuits may include dimming circuits to control a light spectrum and illumination level output of the array of LED by controlling the power levels delivered to the diodes of the LED array. 
     The LED array housing and the power supply housing are mounted to each other by one or both of a conduit providing a path for power cabling between the power supply housing and the LED array housing and thermally isolating support posts. 
     In at least some embodiments the heat dissipation elements extend in parallel across a width of a rear surface of the LED array housing as elongated, generally rectangular fins having a major width extending across a rear side of the LED array housing and tapering to a lesser width extending toward the power supply housing and of a height extending generally from the rear side of the LED array housing and toward a front side of the power supply housing with a thermally isolating gap between the heat dissipation elements and the front side of the power supply housing. 
     In at least some embodiments, the LED array housing and the power supply housing are each substantially cylindrical in shape with a substantially circular transverse cross section having a diameter greater than the axial length of the housing and a circumferential side wall sloping from a first diameter at the front side of the respective housing to a lesser second diameter at the rear side of the respective housing. 
     In one aspect, at least one embodiment described herein provides a solid-state lighting unit including a solid-state array housing defining an internal compartment and having at least one transparent lens for sealing the internal compartment. The lighting unit also includes a number of solid-state lighting circuit card assemblies disposed within the solid-state array housing. Each circuit card assembly includes a common circuit card and a respective number of solid state lighting elements. A respective number of solid state lighting elements of at least one circuit card assembly differ in performance with respect to a respective number of solid state lighting elements of at least another circuit card assembly of the number of solid-state lighting circuit card assemblies. 
     In another aspect, at least one embodiment described herein provides a process for assembling a solid-state lighting unit. The process includes providing a solid-state array housing defining an internal compartment and having at least one transparent lens for sealing the internal compartment. A number of common solid-state lighting circuit cards are also provided. At least one circuit card of the number of common solid-state lighting circuit cards is populated with a first number of solid-sate lighting elements. At least another circuit card of the number of common solid-state lighting circuit cards is populated with a second number of different solid-sate lighting elements. The populated circuit cards are disposed within the solid-state array housing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is further described in the detailed description which follows, in reference to the noted drawings by way of non-limiting examples of exemplary embodiments of the present invention, in which like reference numerals represent similar parts throughout the several views of the drawings, and wherein: 
         FIGS. 1A and 1B  are respectively front and rear perspective views of an embodiment of a LED lighting unit; 
         FIGS. 2A ,  2 B and  2 C are respectively front, top and right side elevational views of the LED lighting unit of  FIGS. 1A and 1B ; 
         FIG. 2D  is a diagrammatic cross sectional view of  FIG. 2C , while  FIG. 2E  is a diagrammatic exploded cross sectional view of  FIG. 2C ; 
         FIGS. 2F and 2G  are respectively rear and left side elevational views of the LED lighting unit of  FIGS. 1A and 1B , with an embodiment of a mounting bracket shown in dashed lines; 
         FIG. 3A  is an exploded front perspective view of the higher powered LED lighting unit of  FIGS. 1A and 1B ; 
         FIG. 3B  is an exploded rear perspective view of the higher powered LED lighting unit of  FIGS. 1A and 1B ; 
         FIG. 4  is a diagrammatic front view of an embodiment of a configurable LED lighting unit; 
         FIG. 5  is a schematic diagram of an embodiment of a configurable LED lighting unit; 
         FIG. 6A  is a diagrammatic side elevation view of an illumination pattern of an embodiment of a configurable LED lighting unit; 
         FIG. 6B  is a diagrammatic front elevation view of the illumination pattern illustrated in  FIG. 6A ; 
         FIG. 7  is a diagrammatic top plan view of an embodiment of a heat transfer element; 
         FIG. 7A  is a diagrammatic cross-sectional view along section line  4 A- 4 A of  FIG. 7 ; 
         FIG. 7B  is a diagrammatic right side elevational view of  FIG. 7 ; 
         FIG. 7C  is a diagrammatic bottom plan view of  FIG. 7 ; 
         FIG. 8  is a diagrammatic cross-sectional view of an embodiment of a chimney accommodated within and extending through the power supply housing  14 ; 
         FIG. 9  is a diagrammatic cross-sectional view of the LED lighting unit of the first embodiment showing the measured average temperature readings for selected regions of the LED lighting unit according to the first embodiment; 
         FIG. 10  is a diagrammatic top plan view of a second embodiment of the heat transfer element; 
         FIG. 10A  is a diagrammatic cross-sectional view along section line  7 A- 7 A of  FIG. 10 ; 
         FIG. 10B  is a diagrammatic right side elevational view of  FIG. 10 ; and 
         FIG. 11  is a diagrammatic perspective view of a third embodiment of the heat transfer element; 
         FIGS. 12A and 12B  are respectively cross sectional schematic views of an embodiment of the LED lighting unit positioned for down lighting and side lighting applications; 
         FIG. 13  is a cross sectional schematic view of an alternative embodiment of an LED lighting unit; and 
         FIG. 14  is a cross sectional schematic view of another alternative embodiment of an LED lighting unit. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the following detailed description of the preferred embodiments, reference is made to accompanying drawings, which form a part thereof, and within which are shown by way of illustration, specific embodiments, by which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the invention. 
     The particulars shown herein are by way of example and for purposes of illustrative discussion of the embodiments of the present invention only and are presented in the case of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the present invention. In this regard, no attempt is made to show structural details of the present invention in more detail than is necessary for the fundamental understanding of the present invention, the description taken with the drawings making apparent to those skilled in that how the several forms of the present invention may be embodied in practice. Further, like reference numbers and designations in the various drawings indicate like elements. 
     Referring first to  FIGS. 1A and 1B , an LED lighting unit  10 , according to the invention, is illustrated which includes a solid state LED array assembly, e.g., an LED array assembly  13 , positioned and oriented at a front of the lighting unit  10 , and a power supply assembly  15 , positioned at a rear of the lighting unit  10 , coupled to but located directly behind the LED array assembly  13 . The LED array assembly  13  and the power supply assembly  15  of the illustrative embodiment are both generally cylindrical in shape, that is, are of generally circular cross section with a diameter greater than their respective heights and/or thicknesses. 
     The LED assembly  13  includes a solid-state array housing including, for example LED lighting elements, referred to herein as an LED array housing  12 . In an illustrative embodiments, the LED array housing  12  has a front diameter of approximately 17.25 inches and tapers to a rear side diameter of approximately 15.6 inches over a total housing thickness of approximately 3.25 inches. The power supply assembly  15  includes a power supply housing  14 , which is spaced apart from a rear surface of the LED array housing  12 , for example, by approximately 1.75 inches having a front diameter of approximately 14.9 inches and tapering to a rear side diameter of approximately 14.25 inches over a thickness of approximately 2.8 inches. Both the LED array housing  12  and the power supply housing  14  include a thermally conductive and supportive material, such as cast aluminum, for example, having a wall thickness of about 0.25 to 0.5 inches, provided with a polyester powder coat finish and sealed according to International Safety Standard IP66. 
     It will be appreciated and understood, however, that in at least some embodiments, the cross sectional shapes of the array housing  12  and the power supply housing  14  are generally defined by the shape of the LED array, which is described in detail in a following description, as are the dimensions of the LED array housing  12  and the power supply housing  14 . It will also be understood that other cross sectional and longitudinal shapes, such as square, rectangular or polygonal for example, are possible and fall within the scope of the present invention. 
     As shown, the lighting unit  10  is typically supported by a conventional mounting bracket  16  which allows for adjustment of the lighting unit as may be beneficial in causing or otherwise directing illumination in a preferred direction. For example, the mounting bracket  16  can allow for vertical rotation of the lighting unit  10  about a horizontal axis HA, which passes through the lighting unit  10  at a location approximately centrally between the LED array housing  12  and the power supply housing  14  at approximately a center of balance of the lighting unit  10 . Alternatively or in addition, the mounting bracket  16  can allow for horizontal rotation about a vertical axis VA. It will be understood, however, that a lighting unit  10  may be supported or mounted by any of a wide range of other conventional mounting designs and/or configuration, including both fixed mounts and positional mounts of various types. 
     A power/control cable  18  supplies power and control signals to the LED array and enters the lighting unit  10  though a conventional weather tight fitting  20  that is mounted in a side wall of the power supply housing  14  (see  FIG. 2F ). It is to be appreciated that the power/control cable  18  may include separate power and control cables or a single combined power and control cable. In other embodiments, and in particular embodiments having separate power and control cables, the power cable  18  may enter power supply housing  14  through the power cable fitting  20  while the control cable may enter through a side or a rear wall of the LED array housing  12  via a separate control cable fitting (not shown). 
     Referring now to  FIGS. 2A ,  2 B,  2 C,  2 D,  2 E,  2 F,  2 G,  3 A and  3 B, the LED array housing  12  is shown as being generally frusto-conical in shape, and may also be cylindrical in shape, with a generally circular transverse cross section having a diameter greater than the axial length of the LED array housing  12  and a circumferential side wall  22  that gradually slopes from its full diameter, at the front face  24  of the LED array housing  12 , to a smaller diameter forming the rear surface  26  of the LED array housing  12 . 
     The LED array assembly  13  includes a solid state array module, e.g., an LED array  28  including a symmetrically packed array of solid state lighting elements, e.g., LEDs  30  mounted on one or more printed circuit modules  42   a,    42   b,    42   c  (generally  42 ) for generating and forming a desired light beam to be generated and transmitted by the lighting unit  10 , when powered, with the LED array  28  being covered and protected by one or more optical/sealing elements  32 , such as a transparent lens. The optical/sealing element(s)  32  sealing mate with ( FIG. 3A ) the front face  24  of the LED array housing  12 , in a conventional manner, providing an internal compartment, and sealing the internal components, e.g., the LEDs  30  and the circuit board(s)  38 , from the external environment, thereby protecting the LED array  28  as well as the other lighting unit components contained within the LED array housing  12 , and may include optical elements for shaping and forming the light beam generated and projected by the LED array  28 . For example, such optical/sealing elements  32  may include a beam shaping lens(es), an optical filter(s) of various types, an optical mask(s), a protective transparent cover plate(s), etc. 
     The power supply housing  14 , in turn, contains a power supply  34  that is connected with the power leads of the power/control cable  18  and supplies electrical power outputs to the LED array  28 , as discussed in further detail below. 
     According to the present invention, each of the individual LEDs  30  of the LED array  28  is mounted on a front surface  36  of a printed circuit board  38  (see generally  FIGS. 1A ,  2 A and  3 A) that sized and shaped to be accommodated and mounted within the interior compartment  40  defined by the LED array housing  12 , i.e., in close abutting and intimate contact with the bottom surface  26  of the LED array housing  12  to facilitate heat transfer thereto. The LEDs  30  include any desired and selected combination of high powered LEDs, such as red, green, blue or white LEDs of various color temperatures, such as 2,700K, 3,000K and/or 4,000K white light LEDs, depending upon the desired output spectrum or spectrums of the LED lighting unit  10 . 
     According to one embodiment of the LED lighting unit  10 , the LED array  28  includes three separate groups, channels or arrays each including a total of  36  LEDs. The  36  LEDs of each separate group, channel or array are arranged in a 6×6 LED array  42  generally in the shape of a diamond. Each one of the three diamond shaped 6×6 LED arrays  42  are clustered together closely adjacent one another to thereby form a generally hexagonally shaped LED array  28 , as shown in  FIG. 3A , of  108  LEDs (see  FIGS. 1A and 2A , for example). The three separate diamond shaped arrays  42  are located closely adjacent one another and are capable of providing approximately 9,000 lumens of total illumination at 150 watts power consumption with an output beam having a radiating angle of between 6° and 30°, that is, radiating angle somewhere between a narrow spotlight beam and a floodlight beam, depending upon the selection, type and the arrangement of LEDs  30 , as described below, as well as the utilized optical elements  32 . 
     It will be appreciated, however, that the LED lighting unit  10  may be constructed with either more or less than  108  LEDs, depending upon the particular illumination application, with any desired combination of LED output colors, e.g., such as red, blue, green, amber, cyan, royal blue, yellow, warm white and cool white, and with greater or lesser output power and power consumption by suitable adaptation of the embodiments described herein, as will be readily understood by and be apparent to those of ordinary skill in the relevant art. 
     Another embodiment of a compound solid-state lighting assembly  11  is illustrated in  FIG. 4 . The compound lighting assembly  11  includes a solid-state array housing  12 ′ defining an internal compartment. In some embodiments, the compound lighting assembly  11  has at least one transparent lens for sealing the internal compartment of the solid-state array housing  12 ′. The lighting unit  11  includes a number of solid-state lighting circuit card assemblies  42   a ′,  42   b ′,  42   c ′ (generally  42 ′) disposed within the solid-state array housing  12 ′. Each circuit card assembly  42 ′ includes a common circuit card  38 ′ and a respective number of solid state lighting elements  30   a ′,  30   b ′,  30   c ′ (generally  30 ′). In the illustrative embodiments, a respective number of solid state lighting elements  30   a ′ of the first card assembly  42   a ′ differ in performance with respect to a respective number of solid state lighting elements  30   b ′ of the second circuit card assembly  42   b ′, both of which differ in performance with respect to the solid state lighting elements  30   c ′ of the third circuit card assembly  42   c′.    
     By way of illustrative example, the first circuit card assembly  42   a ′ is configured with 36 LED lighting elements  30   a ′ having a relatively narrow illumination beamwidth (e.g.,) 6°. Likewise, the second circuit card assembly  42   b ′ is similarly configured with 36 LED lighting elements  30   b ′ having a different illumination beamwidth, such as relatively wide beamwidth (e.g.,) 30°. The third circuit card assembly  42   c ′ is also similarly configured with 36 LED lighting elements  30   c ′ having yet another different illumination beamwidth, such as relatively medium beamwidth (e.g.,) 20°. Such different illumination beamwidths can be provided by the LED lighting elements themselves, optics (e.g., lenses, shrouds) provided in combination with the lighting elements, or some combination of the lighting elements and optics. 
     An example of illumination provided by such a configuration of different beamwidth LED lighting elements within the same lighting unit  11  is illustrated in  FIGS. 6A and 6B . In particular, the different beamwidths of illumination originating from a common lighting unit provide a compact profile lighting source configured to provide a wide range of illumination. Such illumination can be advantageous in at least some applications in which a relatively uniform illumination is desired on a given structure, such as a building or other structure (e.g., bridge, sign). 
     In the illustrative example, an upward illumination is provided by the lighting unit  11  to illuminate the side of a structure  41 , such as a building. The relatively wide illumination beamwidth θ 1  (e.g., 30°) illuminates above a relatively low height H 1 . Likewise, a relatively medium illumination beamwidth θ 2  (e.g., 20°) illuminates above a relatively medium height H 2 , greater than H 1 ; whereas, a relatively narrow illumination beamwidth θ 3  (e.g., 6°) illuminates above a relatively tall height H 3 , which is greater than either H 1  and H 2 . A front elevation view of illumination provided by such a configuration is illustrated in  FIG. 6B . 
     Referring next to  FIG. 5 , a schematic diagram of an embodiment of the configurable LED lighting unit  11  is shown. The lighting unit  11  includes an LED array housing  12 ′ including three lighting circuit card assemblies  42   a ′,  42   b ′,  42   c ′. Each circuit card assembly  42 ′ includes a respective printed circuit board  38 ′, which in at least some embodiments, can be identical, despite differences in illumination provided by the lighting circuit card assemblies  42 ′. Such common elements enhance manufacturability and tend to reduce production costs. In at least some embodiments, different illumination is provided by populating each respective printed circuit board  38 ′ with different LED lighting elements  30 ′. Alternatively or in addition, other differing features adapted to alter illumination, such as optical elements (e.g., lenses, shrouds, filters, polarizers), can be combined with the respective circuit card assemblies  42 ′. 
     Also shown are a power supply  34 ′ and control circuitry  44 ′ provided within a separate, power supply housing  14 ′. In the illustrative example, an interior cavity of the power supply housing  14 ′ is physically isolated from the LED array housing  12 ′, such that replacement, reconfiguration, or more generally, physical access to the lighting circuit card assemblies  42 ′ can be accomplished without disturbing either the power supply  34 ′ or the control circuitry  44 ′. In at least some embodiments, the two separate housings  12 ′,  14 ′ are interconnected by cabling  18 ′ providing one or more of electrical power and control signals between the LED array housing  12 ′ and the power supply housing  14 ′. Such physical isolation of the different elements of the lighting unit  11  can be advantageous in controlling access, for example, allowing maintenance personnel to access the LED array housing  12 ′ without disturbing or otherwise exposing such personnel to higher voltages that may be present within the power supply housing  14 . 
     Although the illustrative example includes different beamwidths, it is understood that other aspects affecting illumination provided by the solid-state lighting unit  11  can be controlled by selection and/or combination of various lighting elements  30 ′ with differing features within the multiple solid-state lighting circuit card assemblies  42 ′. Such features can include one or more of illumination color and illumination color temperature. It is also understood that in some embodiments, substantially all of the lighting elements  30 ′ of a particular lighting circuit card assembly  42 ′ can be substantially identical; whereas, in other embodiments, the lighting elements  30 ′ of a particular lighting circuit card assembly  42 ′ may differ. An example of such differences may be a particular combination of different color and/or different color temperature LED lighting elements  30 ′ on one lighting circuit card assembly  42 ′ that differs from a combination of LED lighting elements  30 ′ of any of the other lighting circuit card assemblies  42 ′. 
     As known by those of skill in the relevant art, the color or the color temperature output of the LED array  28  may include any desired color combination of LEDs  30  and may be controlled by a dimmer control for the LEDs  30 , forming the LED array  28 , so that the relative illumination level output of, the individual LEDs  30  in the array, combine to provide the desired color or color temperature for the lighting unit output. According to the present invention, the dimming control of the individual LEDs  30 , forming the LED array  28 , can be provided by one or more control circuits  44 , which are controlled by signals transmitted to each LED lighting unit  10  through the control/power cable  18  according to industry standard protocols, such as and for example, the industry standard DMX512 protocol, the DALI protocol, the digital signal interface (DSI), or the remote device management (RDM) protocol. Such control circuits  44  can be integrated, for example, in the one or more circuit boards  38  of the LED array assembly  13 . 
     As generally illustrated in  FIG. 3A , the control circuits  44  for the LEDs  30  of the LED array  28  are mounted on the front surface  36  of the circuit board  38  and are generally disposed circumferentially about the LED array  28 . The control leads (not shown), which connect the control outputs of the control circuits  44  to the individual LEDs  30 , can also be formed on the front surface  36  of the printed circuit board  38 . The power leads (not shown), which connect the power output of the power supply  34  in power supply housing  14  to the control circuits  44  and the LEDs  30 , are also coupled to the front surface  36  of the printed circuit board  38  for suitable powering of the various that the LEDs  30 . 
     According to the present invention, the rear surface  26  of the LED array housing  12  generally includes a thermally conductive heat transfer element  50 . A rear surface  52  of the printed circuit board  38  is generally provided in intimate contact with the heat transfer element  50  so as to facilitate conduction of the heat, generated by the LEDs  30 , from the circuit board  38  and into the heat transfer element  50  for subsequent transferred to surrounding air, as will be discussed below in further detail. During operation of the LED lighting unit  10 , the printed circuit board  38 , supporting the LED array  28 , generally absorbs, transfers and/or otherwise carries away the heat which is generated by the LEDs  30 . Accordingly, in such embodiments it is important that the rear surface  52  of the printed circuit board  38  be in thermally conductive contact with the adjacent surface of the heat transfer element  50 . 
     To facilitate the desired heat transfer from the printed circuit board  38 , the heat transfer element  50  is preferably manufactured from a thermally conductive material, such as aluminum or similar material or metal which readily conducts heat. When printed circuit board  38  is mounted within the LED array housing  12 , an adjacent surface of the heat transfer element  50  is thus located in thermally conductive contact with the rear surface  52  of the printed circuit board  38  and thereby forms a continuous thermally conductive path from the LEDs  30  through the printed circuit board  38  into the heat transfer element  50  to facilitate conduction thereto of heat generated from the LEDs  30 . 
     Referring now to the assembly of the LED array housing  12  and the power supply housing  14 , as illustrated in  FIGS. 3A and 3B , the LED array housing  12  is mounted to the power supply housing  14  via three or more perimeter support posts  54 , e.g., typically between three and eight and preferably about 4 to 6 support posts  54 , that extend between and interconnect the LED array housing  12  with the power supply housing  14 . Each support post  54  of the example embodiment has a threaded recess, in a free remote end thereof, while the power supply housing  14  as a mating aperture, which permits a conventional threaded fastener to pass through the mating aperture to threadedly engage the threaded recess of the support post  54 , thereby fixedly connecting the two housings to one another. Typically the support posts  54  are spaced about the periphery of the heat transfer element  50  so as not to hinder, as will be discussed below in further detail, the airflow through and along the heat transfer element  50 . 
     It should be appreciated that support posts  54  generally mechanically connect and secure the LED array housing  12  to the power supply housing  14  while also preventing the direct conduction of heat from the LED array housing  12  to the power supply housing  14 , or vice versa. That is, the support posts  54  of the LED lighting unit  10  are designed to minimize the transfer of heat from the LED array housing  12  to the power supply housing  14 . Accordingly, the support posts  54  include one or more conventional thermally isolating elements or components, for example, and/or may have a reduced diameter end which minimizes the heat transfer capacity along the support post  54  to the power supply housing  14 . Minimum lengths of the one or more support posts  54  are generally sufficient to maintain at least some degree of physical separation between the LED array housing  12  and the power supply housing  14 . 
     In at least some embodiments, a cable conduit  56  also extends between the LED array housing  12  and the power supply housing  14 . Such a cable conduit  56  generally includes a hollow internal passage, which facilitates the passage of associated leads or electrical wires between the power supply  34  and/or the control circuitry of LED array  28 . 
     As best shown in  FIGS. 3B ,  7 ,  7 A,  7 B and  7 C, the rear surface  26  of the LED array housing  12  is provided with multiple generally parallel extending heat dissipation elements  60 , e.g., generally twelve spaced apart elongate members or ridges, which project into an airflow space  62  formed between the rear surface  26  of the LED array housing  12  and the front surface  58  of the power supply housing  14 . As shown in  FIG. 7 , the two outer most heat dissipation elements  60  are both continuous and extend generally parallel to one another, from one lateral side to the opposite lateral side of the LED lighting unit  10 , while the inner heat dissipation elements  60 , located therebetween, are each discontinuous and generally extend radially inward and toward a central axis A of the LED lighting unit  10  which extends normal to the rear surface  26  of the LED array housing  12 . Such arrangement of the inner heat dissipation elements  60  has a tendency of channeling and/or directing air radially inwardly and toward the central region of the airflow space  62 , i.e., toward the central axis A, between the rear surface  26  of the LED array housing  12  and the front surface  58  of the power supply housing  14 . 
     Each of the heat dissipation elements  60  of the illustrative example generally has the shape of a rectangular member or ridge, which extends radially inward into and provides access to the airflow space  62 . Each generally rectangular shaped heat dissipation element  60  is thickest at its base where it is integrally connected with the rear surface  26  of the LED array housing  12  but becomes gradually thinner as the heat dissipation element  60  projects away from the base, extending upwards toward the power supply housing  14 . It is to be appreciated that the heat dissipation elements  60  generally do not contact, but are each spaced from, the front surface  58  of the power supply housing  14  so as to avoid transferring or conducting heat thereto. The exposed peripheral edges of the heat dissipation elements  60  are generally smooth and/or rounded so as to allow the air to flow around and by those edges without causing undue turbulence to the air which, in turn, assists with increasing the airflow through the airflow space  62  and dissipation or removal of heat from heat dissipation elements  60  of the heat transfer element  50 . 
     As illustrated, the heat dissipation elements  60  each generally extend from the rear surface  26  of the LED array housing  12  and toward the front surface  58  of the power supply housing  14  but are slightly spaced from the front surface  58  of the power supply housing  14 , e.g., are spaced therefrom by a distance of about 0.25 inches or less, thereby forming a thermal isolation gap which thermally isolates the LED array housing  12  from the power supply housing  14  and significantly reduces the direct transfer of heat from the LED array housing  12 , supporting the electrically powered LED array  28 , to the power supply housing  14  containing the power supply  34 . 
     It should be noted that the thermal conductivity between the heat dissipation elements  60  and the power supply housing  14  may also be reduced while allowing the heat dissipation elements  60  to be in contact with the power supply housing  14  by, for example, minimizing the surface contact area between each heat dissipation element  60  and the power supply housing  14  or by interposing a thermal isolation element, such as a thermally non-conductive spacer, between the leading edge of each heat dissipation element  60  and front surface  58  of the power supply housing  14 . 
     In addition to providing heat dissipation areas for transferring heat from the LED array housing  12  to the surrounding air, the heat dissipation elements  60 , the rear surface  26  of the LED array housing  12  and the adjacent front surface  58  of the power supply housing  14  together form multiple convective inlet passages  66  which allow inlet of convective airflow into the airflow space  62 , which can remove heat from by the heat dissipation elements  60  during operation of the LED lighting unit  10 , as will be discussed below. 
     The effectiveness and efficiency of this convective heat transfer is, as is well understood by those of skill in the relevant art, a function of the interior dimensions, the lengths and the number of convective circulation passages  66 , as well as the surface characteristics of the heat dissipation elements  60 , the rear surface  26  of the LED array housing  12  and the front surface  58  of the power supply housing  14 . For example, the interior dimensions and the lengths and the characteristics of the interior surfaces of the convective inlet passages  66  as well as the shape or contour of the airflow space  62  determines the type, the velocity and the volume of the convective airflow that is allowed to flow into the convective inlet passages  66 . As such, these features are significant factors in determining the overall efficiency and the rate of heat transfer from the heat dissipation elements  60  to the air flowing into the convective inlet passages  66  and contacting with and remove heat from the exposed surfaces of the heat dissipation elements  60  of the heat transfer element  50 . 
     This example embodiment generally defines a total of  22  convective inlet passages  66  with  11  convective inlet passages  66  being located along each oppose lateral side of the LED lighting unit  10 . That is, each convective inlet passage  66  is generally defined by a pair of adjacent heat dissipation elements  60  located on either side thereof as well as the rear surface  26  of the LED array housing  12  and the front surface  58  of the power supply housing  14 . Accordingly, each heat dissipation passage  66  generally has a width of between approximately 0.3 to 1.5 inches preferable about 0.75 inches, a height of between approximately 1.0 to 2.0 inches preferable about 1.5 inches, and a length ranging between approximately 1.0 to 4.5 inches preferable about 3.25 inches or so, depending upon the location of the passage  66 . 
     The heat dissipation elements  60  thereby provide a desired heat dissipation area for dissipating heat generated by the LED array  28  and transferred to the rear surface  26  of the LED array housing  12  while the non-conductive thermal isolation gaps  64 , between the remote free ends of the heat dissipation elements  60  and the front surface  58  of the power supply housing  14 , significantly reduce the transfer of any heat directly from the LED array housing  12  to the power supply housing  14  and thereby significantly reducing adverse mutual heating effects of the LED array  28  to the power supply  34 . 
     In some embodiments, the rear surface  26  of the LED array housing  12  also accommodates multiple spaced apart generally cylindrical or conical pins  68  in addition to the generally rectangular shaped heat dissipation elements  60 . For example, the rear surface  26  accommodates typically between 20 and 500 pins, more preferably between 100 and 300 pins, preferably about 206 pins (see  FIG. 7 ), which extend generally normal to the rear surface  26  of the LED array housing  12 . Each one of these cylindrical or conical pins  68  is generally uniformly spaced from each adjacent pin  68  and cooperates with the heat dissipation elements  60  to maximize a random convection airflow through the airflow space  62  as well as heat transfer from the cylindrical or conical pins  68  to the air so as to maximize cooling of the LED lighting unit  10 . Typically each pin  68  is generally cylindrical in shape and has a diameter of between approximately 0.3 to 0.65 inches preferable about 0.35 inches and a height of between approximately 0.6 to 1.75 inches, preferable between about 0.9 and 1.5 inches. It is to be appreciated that the somewhat thinner pins  68  tend to provide more efficient transfer of the heat from the LED array housing  12  to the air than thicker pins  68  which tend to be less efficient. 
     Each of the heat dissipation elements  60  has an approximate height of between approximately 0.6 to 1.75 inches, preferable between about 0.9 and 1.5 inches, measured relative to the rear surface  26  of the LED array housing  12 , a width or thickness of approximately 0.25 to 0.45 inches, preferably about 0.4 inches, of an inch tapering or narrowing in a direction away from the rear surface  26 , for example, with the taper being approximately 6°, and a length ranging from about 2 to 10 inches, depending upon their location across the diameter of the LED array housing  12 , and may be spaced apart by a distance on the order of 1.0 to 1.5, preferably about 1.35 inches or so. As generally shown in  FIG. 7A , the rear wall of the LED housing  12  may be domed or otherwise crowned so as to be located slightly closer to the front surface of the power source housing  14 , i.e., decrease the height of the airflow space, and this configuration facilitates accelerating of the air as the air flows through the airflow space  62 . 
     With reference now to  FIG. 8 , a detailed discussion concerning a chimney  70 , which is formed in and extends through the power supply housing  14 . As shown, the chimney  70  extends from the front surface  58  of the power supply housing  14  to the rear surface of the power supply housing  14  and thus forms a through opening  72  through a central region of the power supply housing  14 . In the illustrative example, the chimney  70  includes first and second conically shaped sections  74 ,  76  which join with one another at a generally narrower throat section  78 . That is, each one of the first and second conically shaped sections  74 ,  76  generally has a wider diameter at either the front surface  58  (e.g., having a diameter of between 1.0 inches to 2.5 inches, preferably about 2.12 inches) or the rear surface of the power supply housing  14  (e.g., having a diameter of between 1.0 inches to 2.5 inches, preferably about 1.94 inches) and a narrower diameter at the throat section  78  (e.g., having a diameter of between 0.75 inches to 1.5 inches, preferably about 1.0 to 1.2 inches). The chimney  70  is generally concentric with the central axis A of the LED lighting unit  10  as such positioning generally improves the airflow into and through the LED lighting unit  10 . 
     In some embodiments, a central region of the heat transfer element  50  includes three arcuate walls  80  to assist with directing airflow into the chimney. These three arcuate walls  80  generally are arranged in an interrupted circle and are generally concentric with both the longitudinal axis A and the chimney  70 . Six centrally located pins  68  are located within a region defined by the three arcuate walls  80  and these six pins  68  are generally separated from the remaining pins  68  by the three arcuate walls  80 . These six centrally located pins  68  are in intimate communication with air for such air is directed into the chimney  70 . 
     During operation of the LED lighting unit  10 , the LEDs  30  generate heat which is conducted to and through the printed circuit board  38  and into the rear surface  26  of the LED array housing  12 . As the heat transfer element  50  absorbs heat, ambient air naturally begins to flow into and through each one of the convective inlet passages  66  and into the airflow space  62  located between the rear surface  26  of the LED array housing  12  and the front surface  58  of the power supply housing  14 . As this ambient air flows in through each one of the convective inlet passages  66  from a peripheral space between the rear surface  26  of the LED array housing  12  and the front surface  58  of the power supply housing  14 , the air generally directed radially inwardly toward the central axis A of the LED lighting unit  10 . As the cooler ambient air flows along this radially inward path, the air contacts with the exterior surface of the rectangular heat dissipation elements  60  and the heat is readily transferred from the rectangular heat dissipation element  60  to the air. Such heat transfer in effect cools the rectangular heat dissipation element  60  so that such elements may in turn conduct additional heat away from the LEDs  30 . 
     For embodiments including pins  68 , the air continues to flow radially inward, the air contacts one or more of the pins  68  and, as a result of such contact, additional heat is transferred from the pins  68  to the air which further increases the temperature of the air while simultaneously cooling the pins  68 . Once the heated air generally reaches the central axis A, the heated air communicates with the three accurate walls and the six centrally located pins  68  before flowing into the chimney  70  and thus flowing axially along the central axis A and through the chimney  70  and out through the rear surface of the power supply housing  14 . This airflow pattern, from the convective inlet passages  66  through the airflow space  62  and out through the chimney  70  maximizes convection airflow through the LED lighting unit  10  and thus achieves maximum cooling of the LED lighting unit  10 . 
     As described, heat is transferred from the exterior surface of the rectangular heat dissipation elements  60  to air located within the airflow space  62 , between the LED array housing  12  and the power supply housing  14 . Such heating of air within the airflow space  62  reduces its density, also increasing its buoyancy. The heated air being more buoyant naturally rises. For arrangements in which the power supply housing  14  is located above the LED array housing  12 , as would be for downward directed illumination, the rising heated air encounters the front surface  58  of the power supply housing  14 . When configured with a chimney  70 , at least a portion of the heated air is directed upward through the chimney  70 , exiting the LED lighting unit  10 . This creates an upward draft removing heated air from the airflow space  62  and creating a relative pressure drop within the airflow space  62  compared to ambient air. As a result of the relative pressure difference, ambient air is drawn into the airflow space  62 , for example, through the inlet passages  66 , heated and directed through the chimney  70  resulting in a continual natural draft-driven cooling process. 
     With reference now to  FIG. 9 , the average temperature readings for four (4) different locations of the LED lighting unit  10 , according to the first embodiment discussed above, are shown. For example, the average temperature for the rear surface of the LED lighting unit  10  is typically about 96.0° C., the average temperature at the outer edge of one of the rectangular heat dissipation element  60  of the LED lighting unit  10  is typically about 102.3° C., the average temperature for the front surface  36  of the circuit board of the LED lighting unit  10  is typically about 80.7° C., while the average temperature for the outer circumference edge of the front surface  24  of the LED array housing  12  is typically about 98.4° C. It is to be appreciated that this arrangement generally provides particularly efficient cooling of the LEDs  30  as well as the internal circuitry of the LED lighting unit  10 . Nevertheless, the following discusses a couple of alternative arrangements for the rear surface  26  of the LED array housing  12 . Moreover, it is to be appreciated that other modifications and/or alterations of the rear surface  26  of the LED array housing  12 , in accordance with the teachings of the invention discussed above, would be readily apparent to those of ordinary skill in the art. 
     Turning now to  FIGS. 10 ,  10 A and  10 B, a second alternative embodiment of a heat transfer element  50 ′ will now be described. As this second embodiment is similar to the first embodiment in many respects, only the differences between the second embodiment and the first embodiment will be discussed in detail. 
     As best shown in  FIG. 10 , a rear surface  26 ′ of the LED array housing  12 ′ is provided with multiple generally parallel extending heat dissipation elements  60 ′, e.g., generally twelve spaced apart elongate members  60 ′, which project into elongated airflow spaces  62 ′ disposed between the rear surface  26 ′ of the LED array housing  12 ′ and the front surface  58  of the power supply housing  14 . Each one of the heat dissipation elements  60 ′ generally extends parallel to one another from one lateral side to the opposite lateral side. In the illustrative embodiment, each one of the heat dissipation elements  60 ′ is interrupted at mid section, thus forming an elongate channel  82 . This elongate channel  82  extends normal to each one of the heat dissipation elements  60 ′ and is coincident with a diameter of the LED lighting unit  10  which is also coincident with the central axis A of the LED lighting unit  10 . Such arrangement of the heat dissipation elements  60 ′ has a tendency of directing air radially inwardly and toward the elongate channel  82  where the air can then be directed radially outwardly along the elongate channel  82 , i.e., in both directions along the elongate channel  82  away from the central axis A, and thus out of the airflow space  62 ′ defined between the rear surface  26 ′ of the LED array housing  12 ′ and the front surface  58  of the power supply housing  14 . This arrangement is somewhat useful in the event that a chimney  70  is not provided in the rear surface of the power supply housing  14 . Alternatively, if so desired, this embodiment of the heat transfer element  50 ′ can be used in combination with a chimney  70  so that the air enters along both lateral sides of the LED lighting unit  10 , flows along the heat dissipation elements  60 ′ and is eventually exhausted up through the chimney  70  provided in the power supply housing  14 . 
     Turning now to  FIG. 11 , a third alternative version of the heat transfer element  50 ′ will now be described. As this third embodiment is similar to the second embodiment in many respects, only the differences between the third embodiment and the second embodiment will be discussed in detail. 
     As shown in  FIG. 11 , the rear surface  26 ″ of the LED array housing  12 ″ is provided with multiple generally parallel extending heat dissipation elements  60 ″, e.g., generally twelve spaced apart elongate members, which project into the airflow space  62 ″ formed between the rear surface  26 ″ of the LED array housing  12 ″ and the front surface  58  of the power supply housing  14 . Each one of the heat dissipation elements  60 ″ generally extends parallel to one another from one lateral side to the opposite lateral side. Such arrangement of the heat dissipation elements  60 ″ has a tendency of directing air from one lateral side to the opposite lateral side where the air can then be directed outward from the airflow space  62 ″ defined between the rear surface  26  of the LED array housing  12 ″ and the front surface  58  of the power supply housing  14 . This arrangement is somewhat useful in the event that a chimney  70  is not provided in the rear surface of the power supply housing  14 . Alternatively, if so desired, this embodiment of the heat transfer element  50 ″ can be used in combination with a chimney  70  so that the air enters from both lateral sides of the LED lighting unit  10 , flows along the heat dissipation elements  60 ″ and is eventually exhausted up through the chimney  70  provided in the power supply housing  14 . 
       FIGS. 12A and 12B  are respectively cross sectional schematic views of an embodiment of the LED lighting unit  100  positionable between downward ( FIG. 12A ) lighting and lateral ( FIG. 12B ) lighting applications. Such positioning can be accomplished, for example, with the standard mounting bracket can allow for vertical rotation of the lighting unit  100  about a horizontal axis HA (e.g.,  FIG. 1B ). The LED lighting unit  100  includes an LED array housing  112  projecting illumination  102  in a preferred direction as shown. A heat transfer element  150  is mounted to a rear surface of the LED array housing  112 , configured to draw heat away from internal lighting elements. The LED lighting unit  100  also includes a separate power supply housing  114  positioned in an overlapping, spaced-apart arrangement with the LED array housing  112 . An airflow space  162  is defined between overlap of the two separate housings  112 ,  114 . The power supply housing  114  includes a centrally located lumen, or chimney  70  extending through the power supply housing  114 . 
     When positioned for downward illumination as shown in  FIG. 12A , the heat transfer element  150  heats air within the airflow space  162 , creating an upward draft through the chimney  170 , as shown. The upward draft draws cooler ambient air laterally into the airflow space  162 , which results in a continual cooling of the LED lighting unit  100 . 
     When positioned for lateral illumination as shown in  FIG. 12B , the heat transfer element heats air within the airflow space  162 , creating an upward draft. Instead of being directed through the chimney  170 , however, the heated air exits the airflow space  162  from a top portion of the void between the LED array housing and the power supply housing  114 . In at least some embodiments, the heat transfer element  150  includes vertical passageways, such as flutes or openings between ridges and/or pins that are largely unobstructed to promote a draft according to the direction indicated by the arrows. When positioned between downward and lateral lighting, cooling can be enhanced by a combination of a portion of air heated within the airflow space  162  exiting through the chimney  170  and a portion exiting at an upper lateral region or edge of the airflow space  162 . As the warm air naturally rises, the heated air will rise creating a draft drawing in cooler, ambient air at least through a lower lateral region or edge of the airflow space  162 . 
       FIG. 13  is a cross sectional schematic view of an alternative embodiment of an LED lighting unit  200  for upward illumination. The LED lighting unit  200  includes an LED array housing  212  projecting illumination  202  in a preferred direction as shown. A heat transfer element  250  is mounted to a rear surface of the LED array housing  212 , configured to draw heat away from internal lighting elements. The LED lighting unit  200  also includes a separate power supply housing  214  positioned in an overlapping, spaced-apart arrangement with the LED array housing  212 . An airflow space  262  is defined between overlap of the two separate housings  212 ,  214 . The LED array housing  212  includes a centrally located lumen, or chimney  272  extending through the LED array housing  212 . The chimney  272  can take on any of various shapes, such as cylindrical, frusto-conical, and the other various chimney configurations described herein in relation to the power supply housing  14 . 
     When positioned for upward illumination as shown, the heat transfer element  250  heats air within the airflow space  262 , creating an upward draft through the chimney  272 , as shown. The upward draft draws cooler ambient air laterally into the airflow space  262 , which results in a continual cooling of the LED lighting unit  200 . 
       FIG. 14  is a cross sectional schematic view of another alternative embodiment of an LED lighting unit  300  including two chimneys  370 ,  372 . A heat transfer element  350  heats air within an airflow space  362  located between a rear surface of the LED array housing  314  and a front surface of the power supply housing  314 . A first chimney  370  is provided through the power supply housing  314  as described in relation to  FIG. 12A . A second chimney  372  is provided through the LED array housing  312  as described in relation to  FIG. 13 . When combined with a standard mounting bracket that allows for vertical rotation of the lighting unit  300  about a horizontal axis HA (e.g.,  FIG. 1B ), the LED lighting unit  300  can provide unassisted cooling in either upward, downward or lateral illumination positions. 
     Since certain changes may be made in the above described high power light emitting diode (LED) lighting unit for indoor and outdoor lighting functions, without departing from the spirit and scope of the invention herein involved, it is intended that all of the subject matter of the above description or shown in the accompanying drawings shall be interpreted merely as examples illustrating the inventive concept herein and shall not be construed as limiting the invention. 
     Whereas many alterations and modifications of the present invention will no doubt become apparent to a person of ordinary skill in the art after having read the foregoing description, it is to be understood that the particular embodiments shown and described by way of illustration are in no way intended to be considered limiting. Further, the invention has been described with reference to particular preferred embodiments, but variations within the spirit and scope of the invention will occur to those skilled in the art. It is noted that the foregoing examples have been provided merely for the purpose of explanation and are in no way to be construed as limiting of the present invention. 
     While the present invention has been described with reference to exemplary embodiments, it is understood that the words, which have been used herein, are words of description and illustration, rather than words of limitation. Changes may be made, within the purview of the appended claims, as presently stated and as amended, without departing from the scope and spirit of the present invention in its aspects. 
     Although the present invention has been described herein with reference to particular means, materials and embodiments, the present invention is not intended to be limited to the particulars disclosed herein; rather, the present invention extends to all functionally equivalent structures, methods and uses, such as are within the scope of the appended claims.