Patent Publication Number: US-7217006-B2

Title: Variation of power levels within an LED array

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application claims priority to pending U.S. patent application Ser. No. 60/629,856, filed Nov. 20, 2004 by inventors Stephen E. Trenchard and Alan Trojanowski and entitled “Variation of Power Levels within an LED 
   This application for patent is related to pending U.S. patent application Ser. No. 10/695,191, filed Oct. 28, 2003 by inventors Stephen E. Trenchard and Alan Trojanowski and entitled “High Flux LED Lighting Device.” 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates generally to a lighting device having high flux light emitting diodes, or LEDs, mounted on a heat sink and surrounded by a diffuser. The present invention further relates to an LED assembly having multiple layers of LEDs mounted on a heat sink and surrounded by a diffuser, wherein the LED assembly is positioned within a fresnel lens and individual power is provided to each layer of LEDs. 
   2. Description of the Related Art 
   Reliable safety lights are critical for the safety of boats to prevent accidental collisions during darkness and inclement weather. The vast majority of marine safety lights, such as the one disclosed in U.S. Pat. No. 5,711,591 issued to Jordan use incandescent light bulbs as the light source. 
   A number of attempts have been made to replace marine filament bulbs with LEDs in marine safety lights because of their relatively small power consumption and long life. Incandescent bulbs have a resistant tungsten filament suspended by support wires with a vacuum inside a glass bulb. As a result, they are highly susceptible to damage due to temperature variations and vibrations. The typical life of incandescent bulbs usually averages one or two thousand hours, so that they must be replaced several times a year. 
   LEDs, on the other hand, are more efficient than bulbs at converting electricity into light. LEDs are also durable and immune to filament breakage due to shock or vibration. Therefore, LEDs have a life span of approximately 50,000 hours versus one to two thousand hours for an incandescent bulb. This means that the bulbs do not have to be replaced nearly so often and do not require much maintenance. This is particularly important for marine lanterns that are difficult to get to. 
   However, LEDs are not without their problems. Several of these problems are discussed in a paper entitled  Design Considerations for Reliability and Optical Performance of LED Signal Lights  given by Paul F. Mueller at the XVth IALA Conference, March 2002. 
   A first problem is that typical low output 5 millimeter LEDs (currently available in lighting devices such as those used for marine and airport safety lights) only have a driving current ranging from about 50 to 70 milliwatts and put out insufficient lumens or candlepower to meet the 3–4 mile visibility requirement. Although it is possible to increase the optical output considerably by increasing the forward current above the nominal rated value, such an increase in forward current generally leads to premature failure due to overheating of the diode junction. Recently, however, high-output LEDs (driving current of about 1–5 Watt with a high lumens output) have become available. 
   A second problem is that LEDs have a poorly directed, non-uniform and excessively divergent pencil beam pattern. It is customary to produce a 360° beam pattern of superimposed pencil beams by arraying multiple LED sources in a circular, outward-directed pattern. While this provides an omni-directional beam pattern, lacking further optical enhancement, the result is energy inefficient and grossly non-uniform in horizon intensity. 
   There are several major manufacturers that produce marine lanterns with LEDs including: Carmanah Technologies, Inc., Zeni Buoy Light Company Limited, Vega Industries Limited, Tideland Signal Corporation, and Sabik Oy. All of the currently available marine lanterns using LEDs use low output LEDs. Thus, all of these lanterns require large numbers of, up to several hundred, LEDs to produce the minimal total flux (lumens or candlepower) necessary for a marine lantern. 
   Marine LED lanterns use multiple arrays of numerous LEDs that do not have a single point source of light and cannot use a fresnel lens to capture and focus the light from the LED arrays used. All five of the manufacturers mentioned above have been required to design new lenses to capture and focus the light from their LED arrays. 
   One approach to this problem has been to design a fine lens incorporated in front of the LEDs to converge the beam of light and increase the luminance thereof. For example, U.S. Pat. No. 5,224,773 discloses a thin fresnel lens made by rolling and welding the edges of a thin, transparent film of acrylic resin with a fine-pitched surface that is formed by heating and pressing a mold for a thin linear fresnel lens to form a cylinder. 
   Alternatively, U.S. Pat. No. 6,048,083 issued to McDermott describes an optic lens that is contoured to create a plurality of focal points which form a bent or crooked focal line cooperate with the orientation of the LED elements to project a composite light beam with limited divergence about a first reference plane. 
   Another approach has been to construct a small marine safety light that has a much lower candlepower. U.S. Pat. No. 6,086,220 issued to Lash et al. describes a marine safety light having six or more low output LEDs having a uniform star configuration. The inventors determined that such an LED array produced visible light over one nautical mile away from the vessel, whereas most marine lanterns must meet a 60 candela requirement for a three to four mile visibility. 
   There is an existing need for a marine lantern that replaces the incandescent bulb with LEDs that has sufficient candlepower and provides an omni-directional beam pattern. There is a further need to provide highly efficient LED lanterns to meet the 3–4 mile nautical visibility requirement and other performance specifications for various marine and aeronautical uses. 
   SUMMARY OF THE INVENTION 
   The present invention combines the use of high flux LEDs, configured in multi-level LED modules, with independently provided electrical power for each of the LED modules to meet differing performance specifications. 
   The LED assembly has at least three stacked levels of LED modules with each of the LED modules having an array of radially disposed LEDs around a central member which is made of thermally conductive material for transferring the heat from the LEDs to the outside environment. The power supply provides individual, independent electrical power for each of the LED modules to allow the LED modules to operate at different power levels. 
   One aspect of the present invention is a lighting device comprising: (a) a plurality of LEDs disposed in three stacked radial arrays about a vertical axis; (b) a central member having each LED mounted on a vertical surface thereof, the central member made of a thermally conductive material to conduct heat away from the LEDs; (c) a power supply for each level of LEDs to allow the application of different power levels to the different levels of LEDs; and (d) a hollow member having a dentated surface, wherein the dentated surface surrounds the LEDs to diffuse the light emitted from the LEDs. 
   Another aspect of the present invention is a lighting device comprising: (a) a lighting assembly having (i) a heat sink having at least three centralized right angle prisms, each with a square horizontal cross-section with a plurality of vertical surfaces, (ii) a plurality of equispaced LEDs, each LED mounted on a vertical surface of the heat sink, and (iii) a tubular diffuser having a frosted surface, wherein the frosted surface surrounds the LEDs to diffuse the light emitted from the LEDs; (b) an individual power supply for each level of LEDs; and (c) a fresnel lens surrounding the lighting assembly; whereby light emanating from the LEDs passes through the diffuser and the fresnel lens to provide a substantially uniform horizontal plane of light. 
   Yet another aspect of the present invention is a lighting assembly comprising: (a) a plurality of equispaced high flux LEDs; (b) a controller for conditioning electric power for the LEDs; (c) a heat sink for transferring heat from the LEDs, wherein each LED is secured to the heat sink; and (d) a tubular diffuser surrounding the LEDs having a roughened surface with a random pattern of microfaceted angles on the surface, wherein the microfaceted angles diffuse the light emitted from the LEDs. 
   The foregoing has outlined rather broadly several aspects of the present invention in order that the detailed description of the invention that follows may be better understood and thus is not intended to narrow or limit in any manner the appended claims which define the invention. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and the specific embodiment disclosed may be readily utilized as a basis for modifying or designing of the structures for carrying out the same purposes as the invention. It should be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: 
       FIG. 1  is a plan view in partial section of a typical installation of a lighting device of the present invention mounted on a marine piling; 
       FIG. 2  is a profile view, partially in section, showing the LED source module of the lighting device and its mounting base; 
       FIG. 3  is a partially exploded oblique view, partially in section, showing one embodiment of the mounting of the LED source module on the mounting base; 
       FIG. 4  shows a profile view showing details of the mounting of the controller assembly and the LED source assembly; 
       FIG. 5  is a partially exploded oblique view, partially in section, showing details of the mounting of the lighting device; 
       FIG. 6  is a partially exploded oblique view, partially in section, showing details of one embodiment of the LED source assembly; 
       FIG. 7  is a partially exploded oblique view, partially in section, showing details of another embodiment of the LED source assembly; 
       FIG. 8  is a polar coordinate diagram illustrating the circumferential variation in light output from the lighting device of the present invention with and without use of a diffuser; 
       FIG. 9  is an oblique exploded view of the LED assembly of the embodiment of the LED source assembly shown in  FIG. 6 ; 
       FIG. 10  is a profile view of the LED assembly of the LED source assembly shown in  FIG. 7 ; 
       FIG. 11  is a plan view of the LED assembly of the embodiment of the LED source assembly shown in  FIG. 7 ; 
       FIG. 12  is a transverse cross-sectional view, cut on the section line  12 — 12  shown in  FIG. 10 , of the LED assembly; 
       FIG. 13  is a transverse cross-sectional view, cut on the section line  13 — 13  shown in  FIG. 10 , of the LED assembly; 
       FIG. 14  is a transverse cross-sectional view, cut on the section line  14 — 14  shown in  FIG. 10 , of the LED assembly; 
       FIG. 15  is a partially exploded oblique view, partially in section, showing details of an alternative embodiment of the controller assembly of an LED source assembly; 
       FIG. 16  is a profile view showing details of the mounting of the LED source assembly of  FIG. 15 ; 
       FIG. 17  is a profile view of the LED assembly of the LED assembly of  FIG. 16 ; 
       FIG. 18  is a transverse cross-sectional view of the LED assembly of  FIG. 17 ; 
       FIG. 19  is a semi-schematic view that illustrates the preferred interwiring of the LEDs as a function of their color and required input voltages; 
       FIG. 20  is an oblique exploded view of another embodiment of the lighting device of the present invention; 
       FIG. 21  is a vertical cross-sectional view of the lighting device of the present invention of  FIG. 20 ; 
       FIG. 22  is a graph showing specification requirements versus the peak intensity and vertical divergence output of the lighting device when the outer levels of LED modules are at 0% of the middle LED module; 
       FIG. 23  is a graph showing specification requirements versus the peak intensity and vertical divergence output of the lighting device when the outer levels of LED modules are at 50% of the middle LED module; 
       FIG. 24  is a graph showing specification requirements versus the peak intensity and vertical divergence output of the lighting device when the outer levels of LED modules are at 100% of the middle LED module; and 
       FIG. 25  is a graph showing specification requirements versus the peak intensity and vertical divergence output of the lighting device when the outer levels of LED modules are at 150% of the middle LED module. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   One embodiment of the present invention relates to a lighting device using high flux light emitting diodes (LEDs) mounted on a heat sink in a conventional fresnel lens having a diffuser positioned between the LEDs and the fresnel lens. High flux LEDs are defined herein as LEDs with driving current of about 1–5 Watts and having a high output of lumens. This embodiment is described below. 
   Referring now to the drawings, it is noted that like reference characters designate like or similar parts throughout the drawings. The figures, or drawings, are not intended to be to scale. For example, purely for the sake of greater clarity in the drawings, wall thicknesses and spacings are not dimensioned as they actually exist in the assembled embodiments. 
   Several embodiments of the lighting device of the present invention are described in detail below. One preferred embodiment of a lighting device  10  of the present invention, shown in  FIGS. 1 and 2 , is often installed on bridges, offshore platforms, airport towers, marine beacons, and the like.  FIG. 1  illustrates an example of the lighting device  10  installed as a marine beacon. This type of installation is commonly used on remote channel markers for navigable waterways. A piling  2  of treated wood, concrete, pipe or other applicable material is driven into the soil below a mudline  4  to support the lighting device  10  high enough above a water surface  3  to prevent the lighting device  10  from being damaged by wakes, waves, and the like. 
   The lighting device  10  is optionally powered by batteries (not shown) contained in a tubular battery case  6  that has a closed bottom flange  12  and an annular top flange  13 . The lighting device  10  is mounted to the top of the battery case  6  with base attachment bolts  11  and the battery case  6  is attached to the top of the piling  2  with bolts  8 . In this embodiment, the batteries located in the interior of case  6  are recharged by electricity generated by a solar panel assembly  5  and transferred to the batteries via a solar collector cable  7  as shown in  FIG. 1 . The cable  7  penetrates into the side of case  6  through a sealing fitting  14 . The solar panel assembly  5  is mounted on the piling  2  or, alternatively (not shown), on battery case  6 . 
   A power cable  9  emerges from a sealing fitting  15  in the side of case  6  to transfer electricity from the battery case  6  to the lighting device  10 . In the embodiment shown in  FIG. 1 , the power cable  9  enters the side of a mounting base  20  of lighting device  10  through a sealing fitting  16 . As an alternative, the power cable  9  could be attached to a fitting  22  at the bottom of the lighting device  10  (as shown in  FIG. 2 ) to transfer electricity from the battery case  6  to the lighting device  10 . Without departing from the spirit of the invention, the electrical power also could be supplied by other configurations such as from a remote external source via a supply cable (not shown). In other configurations, the battery case  6  and/or the solar panel assembly  5  could be omitted or modified to work with a different exterior power supply (not shown). 
   Unless noted as being made of specific materials, the lighting device  10  of the present invention can be made of a variety of materials as long as the materials meet the desired performance specifications. The construction materials in the preferred embodiment are steel or aluminum alloy for structural items and insulated copper wire for wiring connections. 
     FIGS. 2–3  show general details of the lighting device  10  and specifically the interrelationship of the mounting base  20 , a lantern lens assembly  30  and a light-emitting diode (LED) source assembly  80  ( FIG. 3 ) which is the source of the light from the lighting device  10 . The mounting base  20  is a tubular, substantially right-circular cylinder with a right circular cylindrical lower transverse blind mounting flange  21  and a transverse annular top flange  27 . The mounting base  20  is typically a painted aluminum casting and its approximately cylindrical wall surfaces are slightly conical in shape to provide draft for the extraction of the casting patterns (not shown). A bolt circle of holes in the mounting flange  21  accommodate bolts  11  so that mounting base  20  can be bolted to corresponding tapped holes in the battery case  6  ( FIG. 1 ). 
   The mounting flange  21  has an axial tapped hole, which mounts a commercially available sealing cable fitting  22  so that a power cable (not shown) can enter the lighting device  10  through the bottom of the mounting base  20  instead of the side of the mounting base  20  as shown in  FIG. 1 . Annular gasketed sealing washers  23   a,b  seal the exterior and the interior respectively of the joint between fitting  22  and flange  21  ( FIG. 3 ). In the arrangement shown in  FIG. 2 , the sealing cable fitting  22  extends downwardly into the battery case  6  and serves to isolate the interior of the mounting base  20  from potentially corrosive conditions within the battery case  6 . 
   Mirror image hinge brackets  24 , extending outwardly from the exterior of mounting base  20  adjacent to top flange  27 , are symmetrically offset from a vertical plane through the axis of the mounting base  20  and have coaxial hinge holes (not shown) normal to the vertical plane. The axis of the hinge holes in hinge brackets  24  is approximately at the level of the upper surface of top flange  27 . A hinge pin  25  consists of a bolt and nut and is mounted through the hinge holes of hinge brackets  24 . 
   External threaded bosses  26   a,b,c,d  ( FIG. 2 ) on the approximately cylindrical outer wall of mounting base  20  are drilled and tapped for alternative power cable entry locations (such as shown in  FIG. 1 ), which are shown sealed with threaded plugs  28   a,b,c,d , but which could likewise be used to mount the sealing cable fitting  22 . 
   The upper transverse face of top flange  27  has a concentric O-ring groove  29  for mounting a face-sealing O-ring  31  ( FIG. 3 ). Additionally, top flange  27  is provided with a concentric bolt circle of tapped holes. 
   Mirror-image, inwardly projecting bosses  36  with transverse upper shoulders are located in the bore of mounting base  20 . These bosses  36  are provided with drilled and tapped mounting holes parallel to the axis of mounting base  20  in order to mount a controller assembly  40  of the lighting device  10 . 
   The lantern lens assembly  30  is positioned on top of and coaxially with mounting base  20 . A lens base  32  is an annular ring flange with a concentric bolt circle of holes corresponding to that of the top flange  27  of mounting base  20  and having a shallow counterbore on its under side. Radially projecting to one side of lens base  32  is a lens hinge  33 , which constitutes a rectangular tab having at its outer end a transverse eye hole formed in an outer end enlargement. The axis of the eye hole of lens hinge  33  is aligned with the transverse hinge holes in hinge bracket  24  of mounting base  20  when the lantern lens assembly  30  is aligned with and resting on the top flange  27  of the mounting base  20 . 
   A thin-walled lens body  35  has, from its lower end, an annular flange, a slowly tapering elongated large diameter frustro-conical main body portion, a short frustro-conical transition section of intermediate diameter, and a sharp small diameter conical bird spike  38  section at its top. All of the conical sections taper upwardly. The function of the bird spike  38  is to discourage birds from perching on and fouling the lens body  35 . 
   The exterior of the main portion of lens body  35  both above and below a central portion (termed the “bulls eye” and shown in  FIG. 2 ) is annularly grooved in a mathematically determined pattern which constitutes a standard fresnel lens  37  of the type conventionally used to focus light from a centrally located point or point source into a horizontal beam. The pattern of the annular grooves is approximately mirror imaged about the midplane of the bulls eye, but with slight modifications due to the conical pattern of the lens body  35 . 
   The lens body  35  is positioned coaxially with lens base  32  with the bottom flange of the lens body retained within the counterbore of the lens base  32  and held so that the bottom flange of the lens body  35  may be clamped against the top flange  27  of the mounting base  20 . O-ring  31  ( FIG. 3 ) is positioned in groove  29  of the mounting base  20  and seals between the lens body  35  and the mounting base  20 . After the lens body  35  is positioned against the top flange  27 , lens closure screws  34  are positioned in the bolt circle holes of lens base  32  and screwed into the threaded bolt circle holes of the top flange  27  of the mounting base  20 , so that the lantern lens assembly  30  is firmly mounted to the mounting base  20 . 
   In  FIGS. 4 and 5 , the structure of one embodiment of the controller assembly  40  is shown.  FIG. 4  is a profile view showing the details of the shock resistant mounting of the controller assembly  40 . The controller assembly  40  serves to provide appropriate, conditioned electrical power and, if desired, a programmable blinking pattern for the LEDs  91  and differing power amounts to the individual levels of LEDs (described below). 
   A base plate  41  in the preferred embodiment is a thin flat steel plate of hexagonal shape and dual symmetry with multiple mounting holes and access holes cut into it so that other components can be mounted to it and the mountings for other components can be accessed. A carrier plate  42  is similar to base plate  41 , but with a different pattern of mounting holes and access holes. The carrier plate  42  is positioned parallel to and above the base plate  41 . Three or more spring mount assemblies  43  with their axes not lying on a common line are positioned in mounting holes on corresponding corners of base plate  41  and carrier plate  42  to support the carrier plate  42 . Four spring mount assemblies are used in the preferred embodiment, two of which are shown in  FIG. 4 . The spring mount assembly  43  consists of a spring mount screw  44  with, in sequential order from the upper end, the head of the screw  44 , a flat washer  45 , the carrier plate  42 , a standoff spring  48 , the base plate  41 , a washer  46  and a nylon insert lock nut  47 . Washers  45  and  46 , spring  48  and nut  47  are concentric with screw  44 . The nut  47  is sufficiently threaded onto the screw  44  so that the spring  48  is preloaded in compression. 
   As shown in  FIG. 5 , a U-bracket  49  is formed from a strip of thin plate approximately 2 inches wide that has two outwardly projecting coplanar ears, each adjoining a symmetrical vertical leg, and a central horizontal section supported by the vertical legs. The outer ends of the ears of bracket  49  have similar but oppositely facing parallel slots transverse to the longitudinal mid-plane of the U-bracket  49 . This is to allow the U-bracket  49  to be readily slipped in and out of engagement with vertically projecting headed screws (not shown) mounted on the interior bosses  36  of mounting base  20  by rotating it about its vertical axis without removal and reinstallation of the screws. U-bracket  49  is in turn rigidly mounted to the interior bosses  36  in the bore of mounting base  20  by means of screws engaged in its slots. 
   Two sets of mounting holes for attaching the base plate  41  are located at either side of the central horizontal section of U-bracket  49 . Base plate  41  is rigidly mounted in its center to the lower side of U-bracket  49  by screws  52 , lock washers  53 , and nuts  54  at two sets of holes on opposed sides of its central portion corresponding to the mounting holes in the central portion of bracket  49 . 
   A printed circuit board (PCB) bracket  58  ( FIGS. 4 and 5 ), formed from a thin strip of plate, is symmetrical about its vertical mid-plane perpendicular to the plate strip longitudinal axis. The PCB bracket  58  has a horizontal central upper section  55  adjoined by two inclined segments  56 , which are in turn attached to vertical legs  57  that have inwardly projecting horizontal mounting tabs  61  on their bottom ends. The PCB bracket  58  is mounted in a central position to carrier plate  42  by means of two other sets of screws  52 , lock washers  53  and nuts  54 . 
   Three mounting holes (not shown) for the LED source assembly  80  are provided on the horizontal central upper section  55  of PCB bracket  58 . One hole is in the middle of the horizontal central upper section  55  and two others are symmetrically placed straddling the first hole. 
   Multiple PCB mounting tabs  59  are mounted in transverse slots pierced in the thin plate of bracket  58  and welded or soldered in place. A controller PCB  60  is a flat construction of conventional printed circuit board material having a shape that closely fits within the interior of the PCB bracket  58   
   If the incoming electrical power is AC, then it is rectified to DC on the controller PCB  60 . The input current and voltage are adjusted and regulated to provide appropriate polarities, voltages, current limits, power levels, and timing of any blinking functions desired for individual LED modules  90  in the LED source assembly  80 . 
   The controller PCB  60  is mounted to the tabs  59  by means of screws  63  and nuts  64 . A PCB controller terminal strip  66  is rigidly mounted onto the lower end of controller PCB  60  and the individual terminals of the PCB terminal strip  66  are attached to appropriate conductor paths on controller PCB  60 . Similarly, in the preferred embodiment, three light emitting diode (LED) power terminals  67  (each with two terminals for its respective LED module  90 ) are mounted at the upper end of the controller PCB  60  and interconnected to appropriate circuit conductor paths on the printed circuit board. 
   A base terminal strip  70  is rigidly mounted to the upper surface of base plate  41  by means of screws  63  engaged in tapped holes in the base plate  41 . Alternatively, base terminal strip  70  may be similarly mounted to carrier plate  42 . Main leads  71  are discrete insulated wires that are each connected at their first end to one of the terminals of the base terminal strip  70  and at the second end at its corresponding terminal on the PCB terminal strip  66 . 
   Multiple embodiments of the LED source assembly  80  are possible and several ( 80 ,  180 ,  380  and  480 ) are described below. The first embodiment of the LED source assembly  80 , shown in the exploded view of  FIG. 6 , consists primarily of housing elements for an LED assembly  89 . This embodiment is most suitable for use with one to two Watt high flux LED light sources, which generate less heat than the five Watt high flux LED sources. Generally when five Watt LEDs are used in this embodiment, some of the LEDs  91  are driven at a lower power level than the other LEDs  91  to save energy and to allow an overall cooler operation of the LED source assembly  80  as described in more detail below. 
   A bottom base  81   a  is a right circular disk having a central axial through hole and a concentric annular O-ring face seal groove  82   a  having a depth in excess of that necessary to properly house O-ring  83   a  ( FIG. 7 ) on its upper surface. Base  81   a  also has an equispaced array of multiple primary vent holes  84  located on a first radius, an equispaced array of multiple secondary vent holes  85  smaller than holes  84  and located on a smaller second radius, and two threaded holes  86  in diametrically opposed positions for the purpose of providing an optional mounting (not shown) of the LED source assembly  80 . All of the holes  84 ,  85 , and  86  are parallel to the axis of disk  82   a . The threaded holes  86  are spaced similarly to those straddling the central hole on the horizontal central upper section of bracket  58 . 
   An upper base  81   b , which is inverted relative to lower base  81   a , is substantially identical to the lower base  81   a  except for the optional omission of threaded holes  86 . An O-ring groove  82   b  of upper base  81   b  houses an O-ring  83   b  ( FIG. 7 ). 
   To neutralize the possibility of non-uniform light dispersion when using high flux LEDs  91  instead of very large numbers of lower power LEDs of prior designs, the present invention incorporates an optical diffuser  88  to redistribute the light emitted from the LEDs  91  in a more uniform manner in spherical coordinates. This feature of the present invention, in combination with the other aforementioned features, provides the characteristics necessary for enabling a compact LED lighting device  10  that can be used for new installations as well as for retrofitting the population of existing lighting devices designed for incandescent bulb sources. 
   The diffuser  88 , as shown in  FIG. 6 , is a right circular thin-walled tube made of plastic, glass or any other material that is clear, heat resistant and satisfies the structural and optical requirements of the diffuser  88 . In the preferred embodiment, the diffuser  88  is made of fused quartz or borosilicate or crown glass or a similar optically clear, heat resistant glass. The inner diameter of diffuser  88  is greater than the inside diameter of O-ring groove  82   a , and the outer diameter of the diffuser  88  is a close fit to the inner diameter of groove  82   a  so that the diffuser  88  may be positioned concentrically with the base  81   a.    
   The diffusion properties of the diffuser  88  result from a roughened microfinish (not shown) on at least one of the surfaces of the diffuser  88  that surrounds the LED assembly  89 . As the random lay pattern of one or more surfaces of the diffuser  88  is increased, the uniformity of the light emitted from the diffuser  88  also increases. For example, in one embodiment the inner bore of diffuser  88  is smooth, while the outer cylindrical surface of diffuser  88  is dentated (not shown), such as being uniformly frosted by sand blasting or other suitable means, so that the roughened outer surface has a statistically consistent random pattern of microfacet angles. Alternatively, the inner bore may be dentated or frosted (not shown) rather than the outer surface or both the inner and outer surfaces may be frosted. 
   The dentated surface of the diffuser  88  is able to refract incoming light emanating from the LEDs  91  in such a manner that the intensity of the light emitted from the diffuser  88 , as measured in spherical coordinates, is substantially uniformized for the angles of admissivity of the fresnel lens  37  ( FIG. 3 ) in combination with the LED source assembly  80 . This substantial uniformization is demonstrated by the measured results shown in  FIG. 8 , wherein the emitted light intensity on the horizontal midplane of the LED source assembly  80  is shown both without and with the diffuser  88 . 
   As an alternative (not shown), the inner bore of diffuser  88  may be frosted, rather than the outer surface, with the resultant diffusion and substantial uniformization of the emitted light being similar to that for the frosting on the outer surface. 
   The LED assembly  89 , used in the first embodiment of the LED source assembly  80 , is characterized by three LED modules  90  installed one atop the other as shown in exploded view in  FIG. 9 . Each LED module  90  contains a heat sink  87  and four outwardly projecting light source LEDs  91  at its mid height, with one of the LEDs  91  centrally positioned on each of the vertical sides of the LED module  90 . In the preferred embodiment, the heat sinks  87  are right angle prisms (made out of material such as aluminum alloy) with square horizontal cross-sections. 
   Each of the LEDs  91  is attached to its respective face of its heat sink  87  with an adhesive such as Loctite Product Output  315 , which is a high temperature thermally conductive one-part acrylic adhesive, or a one or two-part epoxy. If an epoxy is used it is preferably compounded with a filler such as aluminum nitride or silver to enhance the thermal conductivity of the adhesive bond so that it will readily conduct heat into the heat sink  87  of the LED module  90 . 
   Each of the LED modules  90  has a vertical through hole on its axis of symmetry. Filler blocks  92   a,b  are constructed identically to the heat sinks  87  of the LED modules  90  but do not have any LEDs  91  attached. Filler blocks  92   a  and  92   b  are respectively located below and above the three stacked LED modules  90  in this preferred embodiment. All of the LED modules  90  and the filler blocks  92   a,b  are aligned with their vertical sides parallel. 
   Each of the LED modules  90  is independently connected to a power supply (not shown) by two insulated wire jumpers  72  attached to the respective terminals of LED power terminal  67  on controller PCB  60  so that electric power can be transmitted individually to each LED module  90  and then to the LEDs  91  for the lighting device  10 . The jumpers  72  are passed through one of the primary vent holes  84  of base  81   a  ( FIG. 6 ). The four LEDs  91  within a given LED module  90  are electrically interconnected in series or in parallel serial pairs, all by small wires that are not shown in  FIG. 6  for reasons of clarity. One possible wiring scheme is shown in  FIG. 19 . The required wiring pattern depends on the operating voltages needed for the particular type and color of high flux LEDs  91  being used and the light outputs desired. 
   The entire LED source assembly  80  is arranged in the following pattern from the bottom to the top. The bottom base  81   a  has the LED assembly  89  concentrically placed with the bottom of filler block  92   a  in firm contact with the upper surface of base  81   a . Upper base  81   b  is then concentrically placed relative to lower base  81   a  where its grooved lower surface is in firm contact with the top of filler block  92   b  of the LED assembly  89 . The firm contact ensures good thermal conductivity across the connections and permits heat absorbed by the heat sinks  87  to flow to the bases  81   a,b . The firm contact is maintained by using a threaded rod  94  to clamp the entire LED source assembly  80  together. The threaded rod  94  is inserted through the central bore of bases  81   a,b  and LED assembly  89  and holds the LED assembly  89  together by tightening lower lock washer  95   a  and nut  96   a  onto rod  94  as it extends out the bottom of the LED source assembly  80 , and upper lock washer  95   b  and nut  96   b  onto rod  94  as it passes out the top of the LED source assembly  80 . 
   Before assembly, O-ring  83   a  ( FIG. 7 ) is placed in groove  82   a  of lower base  81   a , O-ring  83   b  ( FIG. 7 ) is placed in groove  82   b  of upper base  81   b . The diffuser  88  is then positioned between and concentric with the two bases  81   a,b . The length of diffuser  88  is selected such that the O-rings  83   a,b  are compressed sufficiently to provide sealing but are not over compressed whenever thread rod  94  and the nuts  96   a,b  are used to clamp the LED assembly  89  between the bases  81   a,b.    
   LED source assembly  80  is mounted to the center mounting hole of the horizontal central upper section of bracket  58  by means of a lock washer  95   c  and a nut  96   c  ( FIG. 4 ), which threadedly connect to the bottom end of thread rod  94  so that bracket  58  is clamped between the nut  96   a  and the nut  96   c.    
   High flux LEDs produce substantial heat compared to lower power LEDs used in earlier beacon devices and marine and airport safety devices. The present invention uses heat sinks  87  to transfer heat away from the LEDs  91 . This dissipation of the resultant heat buildup within the lighting device  10  prevents a precipitous reduction in service life for the LEDs  91 . The aluminum structures, upon which the LEDs  91  of the present invention are mounted, function as heat sinks  87  so that much of the heat is transferred by conduction to regions in the lighting device  10  that are remote from the LEDs  91  and then transferred to the environment by convection and radiation. 
   An optional air circulation path exists between the lower base  81   a  and bracket  58  due to the gap created by the presence of washer  95   a  and nut  96   a  (see  FIG. 4 ). Cooling air thus can circulate as a result of thermally induced convection in through vent holes  84  and  85  in the base  81   a , between LED assembly  89  and diffuser  88 , and out through vent holes  84  and  85  in upper base  81   b . Although an air circulation path is described in this embodiment, the LED source assembly  80  may be sealed to protect the LEDs  91  from moisture. Whenever the LED assembly  89  is sealed, the conduction of generated heat through the heat sinks  87  to the environment is even more important. 
   The preferred embodiment uses twelve LEDs  91  grouped into three LED modules  90  stacked vertically as shown in  FIG. 6 . Each LED module  90  contains four LEDs  91  facing 90° apart. One LED module  90  is at the focal height of the lens  37 , while the other two LED modules  90  are directly above and below the center level as shown in  FIG. 6 . 
   Because the LED array is grouped into three distinct LED modules  90  with each LED module  90  having all four of its LEDs  91  on the same plane, the design allows for each plane of LEDs  91  (each LED module  90 ) to be independently electrically powered. Therefore, each LED module  90  can be operated at a different power level than the other two LED modules  90 . 
   The middle LED module  90  is located at the focal height of the lantern lens assembly  30  ( FIG. 2 ) which produces the peak intensity. Because the outer two LED modules  90  are above and below the focal height, the light produced by these two LED modules  90  will add primarily to the vertical divergence and not to the peak intensity. 
   The usual combinations of power levels of the LED modules  90  are: (1) middle level higher power than outer levels; (2) middle level lower than outer levels; and (3) all levels equal. 
   The reason to power the LED modules  90  independently is to meet certain light output specifications. Some specifications require high peak intensity with a narrow divergence. In that case, only the middle LED module  90  is used. However, a specification often requires a wider divergence, in which case, the outer LED modules  90  are required. By having the ability to tailor how the power is applied in the LED source assembly  80  and specifically to the individual LED modules  90 , the present invention is able to meet a wide range of required specifications while achieving power efficiency. 
   Many applications where these lighting devices  10  will be used are solar powered and these LED source assemblies  80  make efficient use of that power. The following graphs show how the light output is tailored to a specification, whereby in the graphs, the target specification is indicated by a dashed line. 
   In the first graph ( FIG. 22 ), the example configuration (which powers only the middle LED module  90 ) exceeds the peak intensity requirements but does not meet the vertical divergence requirements. 
   By using a lower power level, the LEDs  91  generate less heat thereby increasing the life of the light. Using such power standards, as shown in the second graph ( FIG. 23 ), the lighting device  10  is configured such that the outer LED modules  90  are powered at 50% of the power of the middle LED module  90 . This configuration now exceeds the peak intensity and the vertical divergence requirements. Testing of the configuration indicates that 50% of the power of the middle LED module  90  is the minimum power required for the outer LED modules  90  to meet the specifications (peak intensity and vertical divergence requirements). 
   In the third graph ( FIG. 24 ), the lighting device is configured with all LED modules  90  having equal power (outer LED modules  90  at 100% of the power of the middle LED module  90 ) to meet a more demanding specification. 
   In the fourth graph ( FIG. 25 ), the outer LED modules  90  are configured at 150% power of the center LED module  90  to exceed the requirements of a specification that requires a very wide divergence at the peak intensity level. 
   A second embodiment of an LED source assembly  180 , shown in  FIG. 7 , is designed to be a direct replacement for that used in the first embodiment (element  80  in  FIG. 6 ), so that it can be directly mounted to the top of U-bracket  58  and be operated by the same controller assembly  40  and use the same mounting base  20  and lantern lens assembly  30 . The LED source assembly  180  of this embodiment utilizes the same lower and upper bases  81   a,b , O-rings  83   a,b , and diffuser  88  as were used in the first embodiment of the LED source assembly  80 . For the second embodiment, an LED assembly  189  has the same height as the LED assembly  89  of the first embodiment, but the construction differs as explained below. This embodiment provides an improved angular uniformity of light output in the horizontal midplane (middle LED module  190 ) of the lighting device  10  as a consequence of having one of at least twelve LEDs  91  emitting light in each of the 30° sectors of the horizontal plane of the LED module  90   
     FIGS. 10–14  show the construction details of the LED assembly  189 , which is made from a single piece of material, such as aluminum alloy, with LEDs  91  attached. The LED assembly  189  has identical, integral, concentric right circular heat sink disks  192   a,b  (at the bottom and top respectively) which have thicknesses equal to approximately one half the diameter of the disks  192   a,b . These disks  192   a,b  are similar to the filler blocks  92   a,b  of  FIG. 6 . The diameter of the heat sink disks  192   a,b  is approximately 75% to 80% of the inner diameter of diff-user  88  ( FIG. 7 ), so that when LED assembly  189  is assembled concentrically with the bases  81   a,b , the primary vent holes  84  of the bases  81   a,b  are not blocked by the LED assembly  189 . The-distal ends of the disks  192   a,b  each have coaxial holes drilled to less than the thickness of the disk and are then tapped. The interior ends of the disks  192   a,b  are chamfered. 
   The central portion of LED assembly  189  is composed of three different right angle prisms  187  (similar to heat sinks  87  in  FIG. 6 ) with identical square horizontal cross-sections. When viewed from above, the top right angle prism  187  is rotated 30° clockwise, as shown in  FIG. 12 , and the bottom right angle prism  187  is rotated 60° clockwise, as shown in  FIG. 14 , about the vertical axis of the LED assembly  189  relative to the middle prism  187 . The bottom end of the bottom right angle prism  187  adjoins the interior upper end of disk  192   a , while the top end of the upper right angle prism  187  adjoins the interior lower end of disk  192   b . Each of the twelve faces of the set of three right angle prisms  187  has a shallow, flat-bottomed blind hole  197  positioned in the center of its vertical face. 
   Each right angle prism  187  of the LED assembly  189  mounts an outwardly projecting light source LED  91  in each of the pockets formed by the holes  197 . As a result, one LED  91  projects radially every 30° about the vertical axis of LED assembly  189 . Each of the LEDs  91  is attached to its respective face of the LED assembly  189  with an adhesive such as Loctite Product Output  315 , which is a high temperature thermally conductive one-part acrylic adhesive or a one or two-part epoxy compounded with a filler such as aluminum nitride or silver to enhance the thermal conductivity of the adhesive bond. 
   The individual LEDs  91  on a given right angle prism  187  (together forming an LED module  190 ) are electrically interconnected in series or in parallel serial pairs. Each individual LED module  190  is connected separately to its respective power source (not shown) by two insulated wire jumpers  72  attached to the terminals of the LED power terminal  67  on controller PCB  60  so that electric power can be transmitted individually to the different LED modules  190  for the lighting device  10 . The jumpers  72  are passed through one of the primary vent holes  84  of base  81   a . The wiring pattern is dependent on the operating voltages needed for the particular type and color of high flux LED being used and the performance characteristics desired. 
   The LED source assembly  180  is assembled as shown in  FIG. 7 . Upper base  81   b  is concentrically placed relative to lower base  81   a . The grooved lower surface of the upper base  81   b  is in firm contact with the top of the LED assembly  189  and the grooved upper surface of the lower base  81   a  is in firm contact with the bottom of the LED module  189 . The firm contact between the bases  81   a,b  and the LED assembly  189  ensures good thermal conductivity across the connections and permits heat absorbed by the LED assembly  189  to flow to the bases  81   a,b . The firm contact is maintained by clamping the entire LED source assembly  180  by means of screws  193  and lock washers  195  inserted through the central bore of bases  81   a,b  and threadedly connected to the threaded holes on the lower and upper ends of LED assembly  189 . 
   The LED source assembly  180  then is mounted to the spaced-apart mounting holes of the horizontal central upper section  55  of bracket  58  ( FIG. 5 ) with pairs of screws  194  and lock washers  195 , which threadedly connect to the threaded holes clamping screw  193  the bottom face of base  81   a.    
   An optional air circulation path is created between the lower base  81   a  and bracket  58  due to the gap created by the presence of the screw  193  and the washer  195 . Cooling air thus may circulate as a result of thermally induced convection in through vent holes  84  and  85  in base  81   a , between LED assembly  189  and diffuser  88 , and out through vent holes  84  and  85  in upper base  81   b . Although an air circulation is described for this embodiment, the LED source assembly  180  may be sealed to protect the LEDs  91  from moisture. Whenever the LED source assembly  180  is sealed, the transference of the heat through the heat sinks  192   a,b  and away from the LEDs  91  becomes even more important. 
   Another embodiment of a lighting device  300  of the present invention is shown in an oblique, partially exploded, sectional view in  FIG. 15 . In this embodiment, the mounting base  20  and lantern assembly  30  which house the components and the sealing cable fitting  22  are the same as in the first embodiment shown in  FIGS. 1–2 . The lighting device  300 , in this embodiment, is mounted on a hat-shaped bracket  315  with the sealing cable fitting  22 , which is screwed into the bottom of the mounting base  20  by means of its central threaded hole and sealed by means of gasket  23   a  which closes the possible leak paths between the fitting  22 , the mounting base  20 , and the bracket  315 . The hat-shaped bracket  315  has an elevated horizontal central portion  316  with a central vertical axis hole  317  for the fitting  22 , symmetrical vertical legs  318 , and outwardly extending horizontal ears  319  with mounting holes  320  for attachment to a supporting piling (not shown). The input power cable (not shown) for the lighting device  300  enters the interior of the lighting device  300  via the sealing fitting  22 . This arrangement, without a battery box or solar collector, is typically used with a remote AC power source. 
   While a controller assembly  340  performs substantially the same functions as the controller assembly  40  in the first embodiment of the lighting device  10 , the controller assembly  340  is configured differently. A base plate  341  is a thin circular plate which is attached by screws in holes in plate  341  to coaxial threaded holes in multiple bosses  321  which are on the upper side of the bottom transverse bulkhead of the mounting base  20 . A carrier plate PCB  342  is a thin circular printed circuit board (PCB) similar in its geometry to plate  341 . It is mounted coaxially with and spaced apart above plate  341  by multiple identical standoffs  343 , screws  344  on the connection of the standoffs with plate  341 , and the screws of spring mount assemblies  43  for the connection of the standoffs with the carrier plate PCB  342 : Similar holes are provided on the same pattern on the periphery of each of plates  341  and  342  in order to accommodate the screws  344  attaching to the standoffs  343 . 
   The carrier plate PCB  342  mounts a power supply assembly  348  on its lower side for rectifying AC power to DC if necessary and conditioning the power output of the power supply  348  by providing voltage stepdown and regulation. The power supply  348  also provides appropriate polarities, current limits, surge protection as required and independent power to the individual LED modules  390 . The other individual components of the carrier plate PCB  342  are not shown, but are substantially similar to those employed in the control circuitry of the conventional incandescent light beacon device sold by Automatic Power, Inc., Houston, Tex. 
   The carrier plate PCB  342  also provides the timing of any typical blinking functions desired for the type of LED light source used. The PCB controller terminal strip  66  is rigidly mounted onto the upper side of the carrier plate PCB  342  on one side and the individual terminals of the PCB terminal strip  66  are attached to appropriate conductor paths on the carrier plate PCB  342 . Similarly, a light emitting diode (LED) power terminal  67  for each LED module  390  (each LED power terminal having two terminals), are mounted on the upper side of the carrier plate PCB  342  and interconnected to the appropriate circuit conductor paths on the carrier plate PCB  342 . The leads of the input power cable (not shown here) are connected to the appropriate terminals of terminal strip  66  in order to power the carrier plate PCB  342 . 
   A hat-section bracket  358  is centrally mounted above the carrier plate PCB  342  with spring mount assemblies  43  so that the bracket  358  is shock isolated from the rest of the controller assembly  340 . The bracket  358  has a horizontal central section  361 , two similar, parallel vertical sides  362 , and coplanar outwardly projecting mounting ears  363 . Multiple holes coaxial with similar holes in the carrier plate PCB  342  serve to provide mounting locations for the spring mount assemblies  43 . A tab  364  is cut out of the central portion of one of the vertical sides  362  by making cuts on the vertical sides and bottom of the tab  364 . The tab  364  is then bent upwardly so that it projects horizontally as a projection of the central horizontal section  361  of the bracket  358 . A hole is punched close to the hinge line for the tab  364  and a supercapacitor  365  is mounted therein. 
   Referring to  FIG. 16 , a pylon  378  is mounted to a centrally positioned hole in the horizontal central section  361  of the bracket  358  by means of a screw  356  and a lock washer  357 , which are threadedly engaged with a tapped axial hole on the bottom end of the pylon  378 . The pylon  378  has a short frustro-conical enlarged base  375  and an extended cylindrical shank  376 . The upper end of the pylon  378  is turned down and threaded to form a projecting coaxial screw end  379 . An LED source assembly  380  is supported on the pylon  378  by inserting the screw end  379  of the pylon  378  into the axial hole of base  81   a  and thence threading the screw end  379  into the axial tapped hole in the bottom of an LED assembly  389  ( FIG. 17 ). 
   The upper base  81   b  is then concentrically placed relative to lower base  81   a . The grooved lower surface of the upper base  81   b  is in firm contact with the top of an LED assembly  389  and the grooved upper surface of the lower base  81   a  is in firm contact with the bottom of the LED assembly  389 . The firm contact between the bases  81   a,b  and the LED assembly  389  ensures good thermal conductivity across the connections and permits heat absorbed by the LED assembly  389  to flow to the bases  81   a,b . The firm contact is maintained on the top side by clamping the entire LED source assembly  380  with screws  394   b  and lock washers  395   b  inserted through the central bore of bases  81   b  and threadedly connected to the threaded holes on the upper ends of the LED assembly  389 . The firm contact is maintained on the bottom side by screwing the screw end  379  into the axial hole of base  81   a  and into the bottom of the LED assembly  389 . 
   The LED source assembly  380 , as shown in  FIG. 16 , is designed to be a direct replacement for the first embodiment of the LED source assembly  80 . The LED source assembly  380  utilizes the same lower and upper bases  81   a,b , O-rings  83   a,b , and diffuser  88  as were used in the first embodiment of the LED source assembly  80 . For this embodiment, the LED assembly  389  has the same height as the LED assembly  89  of the first embodiment, but the construction differs as follows. 
     FIGS. 17–18  show the construction details of the LED assembly  389 , which is made from a single piece of material such as an aluminum alloy. The LED assembly  389  has at each distal end identical, integral, concentric right circular heat sink disks  392   a,b  (similar to the filler blocks  92   a,b  in the first embodiment) that have thicknesses equal to approximately 75% of the diameter of the disks  392   a,b . The diameter of the heat sink disks  392   a,b  is approximately 75% to 80% of the inner diameter of the diffuser  88 , so that when the LED assembly  389  is assembled concentrically with the bases  81   a,b , the primary vent holes  84  of the bases are not blocked by the LED assembly  389 . 
   The distal ends of the heat sink disks  392   a,b  have coaxial holes drilled to less than the thickness of the disks  392   a,b  and then tapped. The interior ends of the heat sink disks  392   a,b  are chamfered, with the minimum diameter of the chamfers equal to the diagonal dimension of the central portion of the LED assembly  389 . The central portion of the LED assembly  389  is composed of three cubic (or nearly cubic) right angle prisms  387  with square horizontal cross-sections ( FIG. 17 ). The upper-most prism  387  adjoins the chamfered interior upper end of disk  392   a , while the lower-most prism  387  adjoins the chamfered interior lower end of disk  392   b . Associated with each face of both the top of the upper-most prism  387  and the bottom of the lower-most prism  387  are a pair of horizontal arcuate flats (not shown), which are the transitions between the chamfered shoulders and the right angle prisms  387 . 
   Each of the four faces of each of the right angle prisms  387  has a shallow, flat-bottomed blind hole  397  positioned in the center of its vertical face for mounting an outwardly projecting light source LED  91 . As a result, at least one LED  91  projects radially every 90° about the vertical axis of the LED assembly  389 . Each of the LEDs  91  is attached to its respective face of the prisms  387  with an adhesive such as Loctite Product Output  315 , which is a high temperature thermally conductive one-part acrylic adhesive or a two-part epoxy compounded with a filler such as aluminum nitride or silver to enhance the thermal conductivity of the adhesive bond. An LED module  390  contains one of the prisms  387  and its associated LEDs  91 . 
   One of the LEDs  91  in each of the LED modules  390  is connected by two insulated wire jumpers  72  to the terminals of the LED power terminal  67  on the carrier plate PCB  342  so that electric power can be transmitted individually to the LED modules  390  for the lighting device  300 . The jumpers  72  are passed through one of the primary vent holes  84  of base  81   a . The individual LEDs  91  on the right angle prism  387  of an LED module  390  are electrically interconnected in series or in parallel serial pairs by small wires which are not shown in  FIGS. 15–16  for reasons of clarity. The wiring pattern depends on the operating voltages needed for the particular type and color of high flux LEDs  91  being used. 
   Alternatively, the LED source assembly  380  may be mounted on the PCB bracket  58 , similar to LED source assembly  80  as shown in  FIGS. 4–5 . The LED source assembly  380  is mounted to the spaced-apart mounting holes of the horizontal central upper section  55  of bracket  58  by means of pairs of screws and lock washers which threadedly connect to the threaded holes on the bottom end of base  81   a . When the LED source assembly  380  is mounted on the PCB bracket  58 , a firm contact between the bases  81   a,b  and the LED assembly  389  is maintained to ensure good thermal conductivity between the LED assembly  389  and the bases  81   a,b . The firm contact is maintained on the top side by clamping the entire LED source assembly  380  by means of a screw  394   b  and a lock washer  395   b  inserted through the central bore of the base  81   b  and threadedly connected to the threaded holes on the upper end of the LED assembly  389 . The firm contact is maintained on the bottom side by means of a screw and a lock washer inserted through the central bore of base  81   a  and threadedly connected to the central threaded hole on the lower end of the LED assembly  389 . 
   Referring to  FIGS. 20–21 , another embodiment of a lighting device  400  of the present invention is shown. This embodiment, which has its own (either open-frame or closed-frame) electrical power supply unit  478  for converting the input electric current, is configured to be mounted in a standard screw-in type socket base. A screw plug shell  410  is a substantially constant thickness, thin-walled, modified cylindrical shell. The screw plug shell  410  has, from its upper end, a short straight right circular cylindrical segment, a downwardly extending roll-formed righthand thread compatible with one of the standard sizes of screw-in sockets, and a frustro-conical end which is reduced in diameter on its lower end. The major diameter of the thread is the same as the outer diameter of the upper segment, while the minor diameter is the same as the largest diameter of the frustro-conical lower end. The top end of the screw plug shell  410  is open. 
   A first input power wire  412  is insulated except on its lower and upper ends. A solder contact button  411  is a highly ovaled ovate spheroid which has a relatively short axial length compared to its diameter. The contact button  411  is positioned coaxially at the lower end of the first wire  412 . The first wire  412  is positioned coaxially with the screw plug shell  410  such that the contact button  411  protrudes slightly beyond the lower end of the screw plug shell  410 . A second input power wire  414  is insulated except on its lower and upper ends and is soldered at its lower end to the interior lower end of the screw plug shell  410 . Although the lower portion of the second power wire  414  is bent slightly, most of the power wire  414  runs adjacent and parallel to the first power wire  412 . 
   A potting cup  420  is an annular cylinder having a thin wall of a constant thickness over most of its length and constructed of a nonconductive compound, such as a high molecular weight high density filled polyethylene or a phenolic resin. Starting from the upper end, the potting cup  420  has a short, right-circular, cylindrical annular section with an upwardly facing first internal transverse shoulder at approximately midlength, joined by a frustro-conical transition to a reduced diameter, an inwardly projecting second transverse shoulder section, and a straight cylindrical section. The length of the lower cylindrical section is equal to approximately half of the overall length of the potting cup  420 . The lower cylindrical section is penetrated by multiple radially oriented circular holes. The potting cup  420  is inserted into the larger, upper end of the screw plug shell  410  so that its downwardly facing second transverse shoulder abuts the upper transverse end of the screw plug shell  410 . 
   A lower end plate  481  is a short, right-circular, cylindrical disk (made of a material such as black anodized aluminum) with a larger diameter lower end which has a close slip fit to the upper inner diameter of the potting cup  420 , a transverse upwardly facing shoulder, and a smaller diameter upper end which is a close slip fit inside the bore of the diffuser  88 . The outer diameter of the lower end plate  481  is the same as that of the diffuser  88 . The lower transverse face of the lower end plate  481  rests against the upwardly facing first transverse shoulder of the potting cup  420 . The diameter of the upper end is reduced so that it and the upward facing transverse shoulder can serve as two sides of a face-seal O-ring groove for the mounting of O-ring  83   a . The inner diameter of the upper end of the potting cup  420  then serves as the third side of the face-seal O-ring groove. The disk  481  has an axial through hole for passage of wires  412  and  414  and a first pattern of four equispaced off-axis through holes located on a circle with a diameter equal to about one third of the lower end plate  481  outer diameter. Additionally, two other drilled and tapped-through holes in a second pattern are diametrically opposed and located at radii equal to about two thirds of the outer diameter of lower end plate  481 . 
   The lower end plate  481  is mounted with its axis vertical. Multiple panhead screws  494  are mounted in the first pattern of holes of lower end plate  481  with their threaded ends protruding upwardly above the upper transverse face of the plate to engage an LED assembly  489 , as described in a subsequent paragraph. The set screws  493 , as shown in  FIG. 21 , are mounted in the drilled and tapped holes of the second hole pattern and extend upwardly into the lower end plate  481 . 
   The LED assembly  489  is similar in many respects to the LED assembly  389  ( FIG. 16 ), described previously. The LED assembly  489  is made from a single piece of material such as a black anodized aluminum alloy and has at its upper distal end an integral, concentric right circular cylindrical heat sink disk  491  (similar to the upper base  81   b  in  FIG. 16 ). 
   The lower side of the disk  491  has a downwardly facing horizontal transverse shoulder that extends to a reduced diameter cylinder which in turn is a slip fit into the bore of the diffuser  88 . The LED assembly  489  has a coaxial through hole  495  for accommodating wires  412  and  414  and the wiring (not shown) for supplying power to the LEDs  91 . The lower transverse end of the LED assembly  489  is provided with a concentric circular pattern of drilled and tapped holes consistent with the pattern in the lower end plate  481  so that screws  494  can be used to attach the lower end plate  481  onto the bottom of the LED assembly  489 , as shown in  FIGS. 20–21 . The upper heat sink disk  491  is also provided with multiple off-axis drilled holes for the mounting of the power supply  478 . 
   The main portion of the LED assembly  489  is a right circular cylindrical shaft having symmetrical frustro-conical transitions to its reduced cross-section central section. The central section of the LED assembly  489  is composed of three cubic (or nearly cubic) right angle prisms  487  with square horizontal cross-sections. Associated with each face of both the top of the upper-most prism  487  and the bottom of the lower-most prism  487  are a pair of horizontal arcuate flats, which are the transitions between the frustro-conical transitions and the right angle prisms  487 . Indentations in each of the four faces of each of the right angle prisms  487  provide a mounting surface for LEDs  91 . Each of the three LED modules  490  contains one of the prisms  487  and the set of four LEDs  91  that are attached to the prism  487 . 
   The outwardly projecting light source LEDs  91  are attached to the faces of the prisms  487  with an adhesive such as Loctite Product Output  315 , which is a high temperature thermally conductive one-part acrylic adhesive or a two-part epoxy compounded with a filler such as aluminum nitride or silver to enhance the thermal conductivity of the adhesive bond. 
   One LED  91  for each LED module  490  is connected by two insulated wire jumpers (not shown) attached to the power supply  478  so that electric power can be independently transmitted to the LED modules  490  for the lighting device  400 . The jumpers are passed through either an off-axis vertical hole in the heat sink  491  or through a radial hole intersecting the axial through hole  495  in the LED assembly  489 . 
   A clamp ring  477  is a horizontal, nonconductive member (made of a material such as plastic) that serves to mount the diffuser  88  and the power supply module  478  to the lighting device  400  when the ring  477  is clamped to the heat sink disk (upper base)  491  of the LED assembly  489 . The clamp ring  477  is an annular flat ring with transverse upper and lower surfaces and a right circular cylindrical outer face with a large chamfer on its lower external corner. The clamp ring  477  has a concentric, circular, through-bore with a first downwardly facing counterbore on its lower side and a larger second counterbore on its upper side. The first counterbore is a close slip fit to the exterior of diffuser  88 , and the second counterbore is a slip fit to the outer diameter of the heat sink disk  491 . Both counterbores are adjoined to the central bore by transverse shoulders. Drilled and tapped vertical off-axis holes are provided on the same pattern as those of the off-axis holes in the heat sink disk  491  for engagement by pan head screws  471  and washers  472 , so that the clamping of the clamp ring  477  to the heat sink disk  491  can be accomplished. 
   A power supply printed circuit board (PCB)  470  is made of conventional nonconductive, printed circuit board material with structural and electrical attachments provided for the schematically shown power supply  478 . The wires  412  and  414  are attached to the power supply  478 , as are the leads conveying power to the LEDs  91 . The power supply  478  operates without use of a transformer and rectifies the input power if it is AC, provides power independently to each of the three LED modules  490 , and adjusts the voltage level of the output to conform to the needs of the set of LEDs  91  in each of the LED modules  490 . 
   A snap-on, protective cover  479  is a thin-walled structure (made of a material such as plastic) with a vertical right circular cylindrical side joined to a transverse upper diaphragm by a large chamfer. The lower opening of the cover  479  is slightly enlarged to provide sufficient interference fit to either or both of the outer diameters of the power supply PCB  470  and the clamp ring  477  that the cover can be retained thereon. 
   The lighting device  400 , as shown in  FIG. 20 , is assembled in two sequential steps. For the first step, before assembly, the clamp ring  477  is concentrically positioned against the lower side of the heat sink plate  491  of the LED assembly  489 . A first O-ring  83   b  is placed in the face seal O-ring groove formed between the heat sink plate  491  of the LED assembly  489  and the clamp ring  477 . The diffuser  88  is concentrically positioned with its upper end abutting the first O-ring  83   b  in the seal groove. A second O-ring  83   a  is placed concentrically around the reduced-diameter, upper cylindrical face of the lower end plate  481  and then screws  494  are used to connect the lower end plate  481  to the bottom transverse end of the LED assembly  489  using the tapped holes thereon. 
   The upper end of the potting cup  420  is engaged around the second O-ring  83   a , the diffuser  88 , and the lower end plate  481  so that the upper transverse interior shoulder of the potting cup  420  abuts the lower end of the lower end plate  481 . At this point, both O-rings  83   a,b  are sealingly engaged so that the volume enclosed by the diffuser  88  is isolated. The length of the diffuser  88  is selected such that the O-rings  83   a,b  are compressed sufficiently to provide sealing but at the same time are not over compressed whenever the LED assembly  489  is clamped together with the lower end plate  481  by the screws  494 . The first input power wire  412  and the second input power wire  414  are then inserted through the axial holes in lower end plate  481  and the LED assembly  489 , respectively, as the screw plug shell  410  is concentrically abutted with the intermediate downwardly facing transverse shoulder of the potting cup  420 . 
   For the second assembly step, the elements of the inverted plug base assembly  430  (consisting of the screw plug shell  410 , the potting cup  420 , the lower end plate  481 , wires  412  and  414 , and the screws  493  and  494 ) are potted together with insulative ceramic or plastic potting compound  417 , as shown in  FIG. 21 . The potting compound  417  completely fills the interior of the shell  410  to the bottom end of the screw plug shell  410  and interconnects the elements of the plug base assembly  430 . Specifically, the potting compound  417  firmly engages the interior threads of the screw plug shell  410 , the radial holes in the potting cup  420 , the wires  412  and  414 , and the downwardly protruding threaded ends of the set screws  493 , so that the assembly  430  is unitized. The contact button  411  protrudes outwardly beyond the end of the screw plug shell  410 . 
   The final assembly steps involve attaching the LED power leads (not shown) from one of the LEDs  91  in each of the LED modules  490  to the electrical power supply PCB  470 , along with the upper ends of the input power wires  412  and  414 . Screws  471  are then inserted through the provided holes in the PCB  470 , the nonconductive plastic tubular standoffs  473  and the off-axis holes in the heat sink disk  491 , and then threadedly engaged in the tapped holes provided in the clamp ring  477 . The standoffs  473  help isolate the PCB  470  from the head of the heat sink disk  491 . The snap-on cover  479  can then be axially engaged by forcing it onto the outer peripheries of the PCB  470  and the clamp ring  477  to complete the assembly of the LED source module  400 . 
   OPERATION OF THE INVENTION 
   The present invention is a compact, high intensity light source (lighting device), based upon high flux light emitting diodes (LEDs), which is configured in one embodiment to serve as a direct replacement for electrical single bulb incandescent light sources in existing lighting devices for marine, highway and airway traffic. The lighting device  10  of the present invention is particularly suited for marine and airway navigation aids. The lighting device  400  is suitable for a wider spectrum of devices such as standard traffic lights, roadway hazard lights and airport runway lights. 
   The lighting device  10  of the present invention avoids the need to replace existing lighting fixtures, especially the expensive fresnel lens used to focus the emitted light beam when converting from an incandescent to an LED light source. Prior LED light sources used large quantities of LEDs  91  to get sufficient light output and are physically too large to fit into existing fresnel lenses. Furthermore, prior LED light sources were unsuitable for retrofitting existing lighting fixtures due to the substantial deviation of location from the focal point of existing fresnel lenses. 
   Conventional single bulb light source filaments for typical navigation aids are very compact and hence closely resemble point sources. Consequentially, the light beam emitted when using the prior LED light sources with the single bulb fresnel lenses is sufficiently unfocused that the required light intensities cannot be obtained. The physical configurations of the LED patterns in the different embodiments of the present invention are sufficiently compact that existing fresnel lenses designed for single incandescent bulb sources can be used successfully. In addition, the compactness of the described LED assemblies allows them to be placed at appropriate positions within the lens of the lantern structure. The sizes and attachment points of the mounting U-bracket and base plate and controller assemblies are also compatible with the mounting base of the large number of existing units based upon commercially available lighting devices such as the marine beacon designs of Automatic Power, Inc., Houston, Tex. 
   Although the high flux LEDs provide sufficient candlepower, they introduce the necessity to convey heat away from the LEDs to avoid reducing the useful lifespan of the LEDs. This requirement is due to a rapid deterioration in LED useful life when exposed to temperatures elevated above a critical threshold. Since the LED assemblies of this invention are almost fully enclosed or fully enclosed and sealed, use of the thermally conductive support mountings for the LEDs as heat sinks to distribute the heat away from the LEDs increases the life expectancy of the LEDs and further enhances the practicality of the lighting devices of the present invention. This is particularly important for the high flux LEDs. The heat conducted away from the LEDs by the heat sink behavior of the support mountings of the LED assemblies  89 ,  189 , and  389  is conveyed to the bases  81   a,b  where it is radiated away. 
   Another means of reducing heat output during the operation of the multi-tiered LED source assemblies  80 ,  180 ,  380 ,  480  is to drive the center LED module  90 ,  190 ,  390 ,  490  at a higher power level than used to drive the two outer LED modules. Preferably, the center LED module that is positioned at the focal point of the fresnel lens  87  is run at 80%–100% full power, while the top and bottom tiers of LED modules are driven at 30%–60% of full power. The differential powering of the LED modules provide a lighting device  10 ,  300 ,  400  that operates more efficiently, produces less heat, and provides increased vertical divergence. The increased vertical divergence observed in these lighting devices (such as marine lanterns) is great for such lighter devices as marine and airway navigational lights, increasing their visibility to six or seven miles. 
   Furthermore, the high flux LEDs  91  offer the advantage of minimizing the number of LEDs required and thereby permit construction of a sufficiently compact light source to approximate a point source. The rather narrowly focused light output of the commercially available LEDs causes the light emitted by the LED assemblies  89 ,  189 ,  389 ,  489  of the present invention to be nonuniformly distributed in spherical coordinates. This poor light distribution of the unsupplemented LED assemblies precludes their usefulness in certain navigation aid lighting devices. This deficiency is substantially eliminated in the present invention by addition of the tubular glass diffuser  88 , having a dentated surface with a roughened microfinish, closely spaced in proximity around the LED source assemblies. 
   The resulting refractive redistribution by the diffuser  88  of the impinging light from the LEDs  91  (as measured in spherical coordinates for the range of emission angles possible with the assembled structure of the nontransparent components of each of the LED source assemblies  80 ,  180 ,  380 ,  480 ) results in a more uniformly reemitted light pattern. The approximation to uniformity of the reemitted light from the diffuser  88  is sufficient to permit using the embodiments of the present invention as a substitute for existing navigation aid incandescent bulb light sources. 
   The general operation of the lighting device is mounted on a supporting structure, such as the marine piling  2  that is shown in  FIG. 1 . The mounting base  20  and lantern assembly  30  are generally common to the various embodiments of lighting device  10 , since the controller assembly  40  and LED source assemblies  80 ,  180 ,  380 ,  480  are all designed to be retrofits into existing units in the field. 
   The mounting base  20  provides a housing for the controller assembly  40  and serves as a base for stable support of the lantern lens assembly  30 . The controller assembly  40  and  478  serves to condition the power provided to operate the LCD assembly  89 ,  189 ,  389 ,  489  of the lighting device  10 ,  300 ,  400  so that it is delivered at the proper voltage, has current limiters, and other desirable features. Since many navigation aids are required to flash in a prescribed, regular pattern, the controller assembly  40  or  478  provides power level, control and timing functions to cause its output power to the light source to turn on at the desired power level and only when it is required (such as during darkness) and to cycle on and off in order to cause flashing in any prescribed pattern. All of these functions are standard requirements for beacons and marine lighting devices used in existing navigation aids. 
   The structure of the LED source assemblies all have certain key features in common, in that all use a diffuser  88  mounted in the same manner with O-rings  83   a,b  in grooves  82   a,b  in the end bases  81   a,b ,  381   ab ,  481  and  491 . The primary differences in LED mounting construction lie in the number of LEDs required and the arrangement of the LEDs  91  and the structural supports for the LEDs so that construction of the LED source assemblies is eased and the LED assemblies can properly reject the heat produced by the LEDs  91 . Besides providing structural support for mounting and aligning the LEDs  91 , each of the LED modules  90 ,  190 ,  390 ,  490  provides a heat sink  87 ,  187 ,  387 ,  487  and a path for conductive heat transfer to the end bases  81   a,b ,  381   a,b ,  481  and  491  of the LED source assemblies so that the excess heat load from the LEDs  91  can be released through radiation. Whenever the LED source assemblies are not sealed and an air circulation path is provided, the heat is also removed via convection with the circulating air within the lantern lens assembly  30 . The heat is then released to the walls of the lantern lens assembly  30  and housing (mounting base)  20  and, in turn, to the external environment. The required size of the LED modules is related to the heat generated by its set of LEDs  91 , with higher heat fluxes requiring larger heat sinks in order to hold the LED temperature below the critical threshold at which LED life is precipitously reduced. 
   The construction of the LED source assemblies is sufficiently compact to permit their use with preexisting fresnel lenses  37 , since the LEDs  91  in the array for the different types of LED assemblies are positioned closely enough to the focal point of the lenses  37  to avoid excessive divergence of the emitted light from the lenses  37 . 
   The provision of the diffuser  88  smoothes and tends to uniformize the spherical distribution of output light reradiated from the diffuser  88  relative to the input closely focused narrow beam outputs directly from the LEDs  91 . This critical feature removes the need to provide a very large array of LEDs so that their overlapping patterns of radiated light will closely approximate a uniform light source. Without provision of the diffuser  88  of the present invention, it would be impractical to use a lighting device having as few as 12 equispaced LEDs, since the distribution in the horizontal plane of light emitted from the lens  37  with such an array would have an insufficient intensity in the arc segments between the LED projection centerlines. 
   The lighting device  400  with its threaded base offers a convenient unitized light source which can be installed by simply screwing it into a standard threaded socket. Because the power supply  478  is not based upon use of a transformer, the power supply can operate on any AC input voltage over a broad range of, say, between 85 VAC and 265 VAC. This permits the same LED source module to work in both Europe and the United States, thereby simplifying stocking of inventory. 
   Although the lighting device  400  can be used in a lighting fixture with a fresnel lens, it is anticipated that it will more commonly be used in applications without the fresnel lens. However, the use of the diffuser  88  and the resultant uniform distribution of light make the lighting device  400  particularly suitable for a wide variety of applications, such as aviation runway lights, marker lights for marine bridges and piers, hazard lights, marker lights for towers and buildings, and traffic lights. The LED assembly  489  uses a similar but integral heat sink disk for conducting heat away from its LEDs  91 . Its relatively low construction cost and long life can permit the sealed LED source module  400  to be employed economically on a throw-away basis 
   As can be seen by the above described embodiments, the ability to independently adjust the power for different levels of LEDs allows a single lighting device to be set up for differing specifications. Additionally, existing lanterns (not shown) can be retrofitted with the multiple-level, independent power technology to provide independent, adjustable power to each of the LED assemblies. 
   Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.