Patent Publication Number: US-11029015-B1

Title: Submersible light fixture with multilayer stack for pressure transfer

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of and claims priority to co-pending U.S. Utility patent application Ser. No. 15/069,953, entitled SUBMERSIBLE LIGHT FIXTURE WITH MULTILAYER STACK FOR PRESSURE TRANSFER, filed Mar. 14, 2016, which is a continuation of and claims priority to U.S. Utility patent application Ser. No. 13/930,511, now U.S. Pat. No. 9,285,109, entitled SUBMERSIBLE LED LIGHT FIXTURE WITH MULTILAYER STACK FOR PRESSURE TRANSFER, filed Jun. 28, 2013, which is a continuation of and claims priority to co-pending U.S. Utility patent application Ser. No. 12/844,759, entitled SUBMERSIBLE LED LIGHT FIXTURE WITH MULTILAYER STACK FOR PRESSURE TRANSFER, filed Jul. 27, 2010, which claims priority under 35 U.S.C. § 119(e) to U.S. Provisional Patent Application Ser. No. 61/229,693, entitled SUBMERSIBLE LED LIGHT FIXTURE WITH LAMINATE STACK FOR PRESSURE TRANSFER, filed Jul. 29, 2009. The content of each of these applications is incorporated by reference herein in its entirety for all purposes. 
     This application is also related to co-assigned U.S. patent application Ser. No. 12/036,178, entitled LED ILLUMINATION SYSTEM AND METHODS OF FABRICATION, filed Feb. 22, 2008 and to co-assigned U.S. patent application Ser. No. 12/185,007, entitled DEEP SUBMERSIBLE LIGHT WITH PRESSURE COMPENSATION, filed Aug. 1, 2008. The content of each of these applications is incorporated by reference herein in its entirety for all purposes. 
    
    
     FIELD 
     This disclosure relates generally to light fixtures for use in underwater applications or other applications subject to high pressures. More particularly, but not exclusively, the disclosure relates to deep submersible light fixtures that incorporate light emitting diodes (LEDs) as illumination elements. 
     BACKGROUND 
     Semiconductor LEDs have largely replaced conventional incandescent, fluorescent and halogen lighting sources in many applications due to their long life, ruggedness, color rendering, efficacy, and compatibility with other solid state devices. 
     In marine applications, LEDs are becoming more widely accepted for their energy efficiency, instant on-off, color purity, and vibration resistance. However, the underwater environment presents problems for lighting devices due to high pressures, especially at depth. 
     SUMMARY 
     In accordance one aspect, the disclosure relates to a submersible luminaire including a housing and a transparent pressure bearing window positioned at a forward end of the housing. Window supporting structure is mounted in the housing behind the transparent window. A water-tight seal is located between the window and the housing. A circuit element is configured and positioned within the housing behind the window supporting structure to bear at least some of the pressure applied to the transparent window. At least one solid state light source is mounted on the circuit element behind the transparent window. 
     Various additional aspects, features, and functions are further described below in conjunction with the appended drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure may be more fully appreciated in connection with the following detailed description taken in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is an isometric view of the exterior of an embodiment of the present invention in the form of an underwater multilayer LED light fixture. 
         FIG. 2  is a vertical sectional side view of the underwater multilayer LED light fixture of  FIG. 1  taken along line  2 - 2  of  FIG. 1 . 
         FIG. 3  is an enlarged fragmentary view of a light head subassembly of  FIG. 2  illustrating the details of one embodiment of a multilayer stack. 
         FIG. 4  is an enlarged fragmentary section view of a portion of  FIG. 3 . 
         FIG. 5  is an isometric exploded view of the light head subassembly of  FIG. 3 . 
         FIG. 6  is an enlarged fragmentary portion of  FIG. 5 . 
         FIG. 7  is an enlarged section view of an alternate embodiment of the present invention incorporating a floating groove ring in the light head subassembly. 
         FIG. 8  illustrates an enlarged section view of an alternate embodiment of the present invention incorporating a radial seal O-ring installed in the light head subassembly window. 
         FIG. 9  illustrates an enlarged section view of an alternate embodiment of the present invention incorporating a radial seal O-ring installed in the light head subassembly body. 
         FIG. 10  is an isometric view of the exterior of an embodiment of the present invention in the form of a single multilayer LED light fixture. 
         FIG. 11  is a vertical section view of the single multilayer LED light fixture of  FIG. 10  taken along the line  11 - 11  of  FIG. 10 . 
         FIG. 12  is a vertical section view of the single multilayer LED light fixture of  FIG. 10  rotated 45° to  FIG. 11 . 
         FIG. 13  is an enlarged fragmentary view of a portion of  FIG. 11  illustrating details of the embodiment of the invention using a plurality of lenses within the multilayer stack. 
         FIG. 14  is an enlarged fragmentary view of a portion of  FIG. 13  illustrating the function of the titanium ring with a plurality of flexible titanium ring tangs. 
         FIG. 15  is an enlarged fragmentary view of a portion of  FIG. 10  illustrating installation of the titanium ring with the plurality of flexible titanium ring tangs. 
         FIG. 16  is an illustration of an alternate embodiment of the present invention using a reflector plate within the multilayer stack. 
         FIG. 17  is an isometric exploded view of the single multilayer LED light fixture of  FIG. 10 . 
         FIG. 18  is an isometric view of the exterior of an alternate embodiment of the present invention in the form of a remote single multilayer LED light fixture. 
         FIG. 19  is a vertical section view of a remote single multilayer LED light head taken along line  19 - 19  of  FIG. 18 . 
         FIG. 20A  is an enlarged fragmentary view of a portion of  FIG. 19  illustrating a slip ring subassembly of the remote single multilayer LED light head with an integral thermal sensing circuit. 
         FIG. 20B  is a block diagram of the LED driver circuit of the light head of  FIG. 18 . 
         FIG. 21  is a vertical section view of the remote single multilayer LED light head rotated 30° to  FIG. 19 . 
         FIG. 22  is an enlarged fragmentary view of a portion of  FIG. 21 , illustrating a slip ring subassembly. 
         FIG. 23  is an enlarged fragmentary view of a portion of  FIG. 19  illustrating one embodiment of the multilayer stack. 
         FIG. 24  is an isometric exploded view of the remote single multilayer LED light head of  FIG. 19 . 
         FIG. 25  is a vertical section view of the remote electronic driver assembly taken along line  25 - 25  of  FIG. 18 . 
         FIG. 26  is a vertical section view of the remote electronic driver assembly rotated 45° to  FIG. 25 . 
         FIG. 27  is an isometric view of the exterior of an embodiment of the present invention in the form of a triple multilayer LED light fixture. 
         FIG. 28  is a vertical section view of the interior of the triple multilayer LED light fixture taken along line  28 - 28  of  FIG. 27 . 
         FIG. 29  is a vertical section view of the triple multilayer LED light fixture rotated 60° relative to  FIG. 28 . 
         FIG. 30  is an isometric view of the exterior of an alternate embodiment of the present invention in the form of a remote triple multilayer LED light fixture. 
         FIG. 31  is a vertical section view of the remote triple light head taken along line  31 - 31  of  FIG. 30 . 
         FIG. 32  is a vertical section view of the remote triple electronic driver assembly taken along line  32 - 32  of  FIG. 30 . 
         FIG. 33  is an isometric view of the exterior of an alternate embodiment of the present invention in the form of a mid-size LED light. 
         FIG. 34  is a vertical section view of the mid-size LED light fixture taken along line  34 - 34  of  FIG. 33 . 
         FIG. 35  is an enlarged fragmentary view of a portion of  FIG. 34  illustrating one embodiment of the multilayer stack. 
         FIG. 36  is an enlarged fragmentary view of a portion of  FIG. 35 . 
         FIG. 37  is an isometric exploded view of the mid-size LED light fixture of  FIG. 33 . 
         FIG. 38  is an isometric view of the exterior of an alternate embodiment of the present invention in the form of a boat thru-hull light fixture. 
         FIG. 39  is a vertical section view taken along line  39 - 39  of  FIG. 38 . 
         FIG. 40  is an enlarged fragmentary section view of a portion of  FIG. 39  illustrating one embodiment of the multilayer stack. 
         FIG. 41  is an isometric exploded view of the boat thru-hull light fixture of  FIG. 38 . 
         FIG. 42  is an enlarged fragmentary section view of a portion of  FIG. 40  illustrating a window assembly utilizing a press fit ring. 
         FIG. 43  is an enlarged fragmentary section view of a portion of  FIG. 40  illustrating the double electrical isolation of the LED electrical circuit and the boat thru-hull light fixture housing. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Overview 
     Light emitting diodes (LEDs) are now the most efficient light source widely available, having surpassed High Intensity Discharge (HID) lamps in lumens/watt. For underwater application, a design must use either a pressure-protected housing to isolate the LEDs from ambient pressure, or immerse the LEDs in an inert, non-conductive fluid-filled pressure compensation environment. There are disadvantages to fluid-filling an LED light, notably with light beam control and contamination of the LED phosphor coating. Thus, a preferred embodiment protects the LEDs from external pressure rather than using a fluid-filled pressure compensation design. 
     LEDs project light from the front while heat must be conducted from the back. LED light fixtures as described in U.S. patent application Ser. No. 12/036,178 of Mark S. Olsson, et al., filed 22 February, 2008 entitled “LED Illumination System and Methods of Fabrication,” provide for such conductive dissipation. The entire disclosure of said application is hereby incorporated by reference. Use of a sapphire window, as illustrated in alternate embodiments of the present invention, provides high light transmissivity as well as high thermal conductivity. The sapphire window allows excess heat to be drawn out of the front of the fixture as well as through the rear metallic housing, and into a surrounding cooler environment, such as the deep ocean. A specific advantage of the present invention is the ability to draw additional heat away from a printed circuit board (PCB) by conductive transfer of heat through a multilayer stack overlaying the front of the PCB and optionally connected by a plurality of metallic screws to the rear heat sink. This effectively creates a second path for heat transfer away from the LEDs, as heat is then passed both forward through the sapphire window, and to the rear to exit through the metallic light body into the surrounding cooler environment. This design innovation will allow brighter lights in smaller packages. 
     Recent manufacturing developments reduce the size of the LED package to only a few times the die footprint itself. Examples of suitable solid state light sources for use in underwater laminate include Cree Incorporated&#39;s XP series, Philips Lumileds Lighting Company&#39;s Luxeon Rebels, and OSRAM Opto Semiconductor&#39;s OSLON. A subtle, but important implication of the LED package miniaturization is that the respective size of the open land area around the LEDs is increased and may be used for structural support of a clear window with a minor unsupported aperture over the plurality of LEDs. 
     The present invention provides a light fixture wherein a multilayer stack provides a waterproof and pressure resistant barrier for an LED array mounted to one side of a PCB. As will be illustrated, each layer within the stack provides a clear and distinct function, and together comprises a unique solution to underwater lighting design. 
     Under increasing external pressure, the clear window presses on a multilayer stack which distributes that load around the LEDs and onto the surface area of the PCB located between the LEDs. This PCB rests on an underlying light head that is structurally able to bear the full compressive pressure load of the deep ocean environment. 
     According to one embodiment of the present invention, a surface mount LED light fixture includes a metal core printed circuit board (MCPCB) having a rear side and a front side. A plurality of LEDs is mounted to the front side of the MCPCB. A flat LED pacer made of an electrically non-conductive high compressive strength material is placed over the MCPCB with apertures cut to fit around the ceramic bases of each individual LED. Above this is a flat window support spacer made of high compressive strength material with apertures cut to fit around the silicone domes of each individual LED. The height of the window support spacer may be reduced by manually trimming the silicone dome on each LED if desired. Alternately, the height of the window support spacer may be lengthened and the apertures increased in size to allow the use of beam forming apparatus such as reflectors or lenses. The use of one or more thin layers of Kapton plastic sheet within the multilayer stack allows for the compliant and uniform distribution of pressure over the full area by eliminating point loading, and additional electrical isolation of the LED electrical circuit. The clear window is supported by the multilayer stack. An O-ring between the window and the light head body seals the light fixture interior from the exterior environment. Alternate embodiments of the present invention may use a radial seal, a face seal, or any other seal type without restriction. 
     The ability of the clear window of any material to survive high external pressures with a non-pressure compensated interior volume comes from its ability to resist the stress imposed by the external pressure. Designers can optimize combinations of material strength, thickness, geometric shape, and aperture size to provide the strength and rigidity to resist maximum design pressure. The clear windows may be made from any one of several clear materials including borosilicate glass (Pyrex®), sapphire, or clear plastic sheet, such as acrylic (Plexiglas®), polycarbonate (Lexan®), or transparent nylons. Clear plastic window materials whose yield strength is reduced by exposure to heat are still useful in LED light fixtures which have adequate ability to conductively dissipate heat into the local environment thereby keeping the window from reaching its Vicat softening point or heat deflection temperature. The advantages of the sapphire window were mentioned earlier. 
     The LED light fixtures of the present invention are able to conduct excess heat through the metallic light head body, to the surface of the light head body, then into the surrounding fluid or gas environment in which the LED light fixture is immersed. LEDs may be mounted to the PCB with a substrate of flexible circuit material, thermally conductive plastic, metal, ceramic, diamond, or other material with a high heat transfer coefficient. One embodiment uses an MCPCB made with copper, aluminum, steel, or other thermally conductive ferrous or non-ferrous metal as the central core. Ceramic and synthetically grown diamonds are alternative materials that would function as a central core. An alternate embodiment incorporates LEDs mounted to substrate of flexible circuit material that is held in firm and uniform contact with the light head body, which acts as the heat sink. 
     An alternate embodiment of this invention incorporates a self-adjusting face seal groove that permits manufacturing variation in the multilayer stack-up height, maintaining the optimum O-ring groove depth dimension, while allowing the multilayer stack to take the full compressive load. 
       FIG. 1  illustrates an embodiment of the present invention in the form of an underwater multilayer LED light fixture  102 . A cowl  104  surrounds and protects a light head subassembly  106  which is slightly recessed below the level of the front opening of the cowl  104 . An underwater electrical connector  108  is mounted on the rear of a housing  110 , permitting connection to an electrical power supply (Not illustrated). A mounting bracket  112  grips the exterior of the housing  110 . 
     Illustrated in  FIG. 2  are the cowl  104 , the light head subassembly  106 , the underwater electrical connector  108 , the housing  110 , the mounting bracket  112 , and an electronics driver circuit board  114  to convert and condition input electrical power and supply constant current to the LEDs. 
     Referring to  FIG. 3 , the light head subassembly  106  includes a multilayer stack  146  comprised of a window support spacer  130 , a front Kapton sheet  136 , an LED spacer  138 , a light engine printed circuit board  140 , and a rear Kapton sheet  142 . The light engine printed circuit board  140  is populated with a plurality of LEDs  128 . The window support spacer  130 , the front Kapton sheet  136 , and the LED spacer  138  have a plurality of apertures  125  through which the plurality of LEDs  128  may protrude. Other elements illustrated include a generally cylindrical housing in the form of a light head body  116 , a retaining ring  122 , an O-ring retainer  124 , a window front O-ring  120  used for initial compressive loading of a window  126 , a window face seal O-ring  118 , a plurality of recessed flat head screws  132 , a plurality of flat head screw insulating sleeves  134 , and an electrical connector  144  for connecting the electronics driver circuit board  114  in  FIG. 2 , to the plurality of LEDs  128 . 
     The window support spacer  130  and the LED spacer  138  are first a high compressive strength material to resist the compressive force of ambient pressure at depth, such as, but not limited to, PEEK plastic, ULTEM, ceramic, or a common metal such as aluminum, steel, copper, or zinc. The window support spacer  130  may be machined, injection molded or die cast. In one embodiment, the light head body  116  is machined from a thermally conductive metal, such as an aluminum alloy, that will assist with heat transfer away from the plurality of LEDs  128  and the light engine printed circuit board  140 . In alternate embodiments, the light head body  116  may be made by one of several alloys of beryllium-copper alloy, stainless steel, titanium alloy, cupronickel alloy, or any other metal or metal alloy, or a thermally conductive plastic. The window  126  may be made from clear plastic, borosilicate glass, sapphire, or other transparent materials. A sapphire window is particularly desirable since its hardness will resist scratching and its high coefficient of heat transfer will help dissipate heat from the plurality of LEDs  128 . 
     The window face seal O-ring  118  rests in a groove in the light head body  116 , and provides a water tight, pressure resistant seal to the window  126 . The window front O-ring  120  provides a compliant pre-load to compress and energize the window face seal O-ring  118 , but does not serve a sealing function. The O-ring retainer  124  holds the window front O-ring  120  in position. The multilayer stack  146  is compressed and retrained by a window and retainer subassembly  148  comprised of the retaining ring  122 , the O-ring retainer  124 , the window front O-ring  120 , the window  126 , and the window face seal O-ring  118 . Under increasing external pressure found at deeper ocean depths, the window  126  is pressed inwards, through the multilayer stack  146 , but around the plurality of LEDs  128  which are within the plurality of apertures  125 , and directly to the light head body  116 . 
       FIG. 4  illustrates the window sealing approach in the light head subassembly  106 . 
     The window face seal O-ring  118  is in a compressed state due to compressive pre-load pressure from the window front O-ring  120 , the O-ring retainer  124 , and the retaining ring  122 . The window  126  is in full contact with the multilayer stack  146  in this view. There is a gap  147  between the window  126  and the light head body  116  in the area between the inside diameter (ID) of the window face seal O-ring  118  and the outside diameter (OD) of the multilayer stack  146 . The gap  147  is exaggerated to illustrate the embodiment of the invention in which the multilayer stack  146  takes the full compressive load of the window  126  pressing on it, with no support of the window  126  provided directly by the light head body  116 . The gap  147  between the window  126  and the area between the ID of the window face seal O-ring  118  and the OD of the multilayer stack  146  is controlled to be within industry accepted O-ring high pressure seal gap tolerances. While under increasing external pressure with increasing depth, the additional compressive load is transferred through the multilayer stack  146  to the light head body  116 . The plurality of LEDs  128  and the plurality of recessed flat head screws  132  are recessed below the top surface of the multilayer stack  146  and do not bear any of the load induced by external pressure. The plurality of recessed flat head screws  132  are thermally-conductive to provide additional pathways for excess heat from the light head body  116 , to pass through the multilayer stack  146 , and be conducted out through the window  126 . In the full assembly, the multilayer stack  146  is supported by the light head body  116  which takes the compressive force generated by high external pressure on the window  126 . 
       FIG. 5  illustrates the longitudinal relationship of the components of the light head subassembly  106 . The three principle groups are the window and retainer subassembly  148 , the multilayer stack  146 , and a light head body subassembly  150 . The window and retainer subassembly  148  includes the retaining ring  122 , the O-ring retainer  124 , the window front O-ring  120 , the window  126 , and the window face seal O-ring  118 . The multilayer stack  146  includes the window support spacer  130 , the front Kapton sheet  136 , the LED spacer  138 , the light engine printed circuit board  140 , and the rear Kapton sheet  142 . The light engine printed circuit board  140  is populated with the plurality of LEDs  128 . Additionally, the multilayer stack  146  contains within its structure the plurality of recessed flat head screws  132 , and the plurality of flat head screw insulating sleeves  134 . The light head body subassembly  150  includes a plurality of spring loaded electrical contacts  152 , a plurality of flanged insulating washers  154 , a plurality of insulated copper wires signifying polarity, black wires for negative  156 , and red wires for positive  158 , a plurality of shrink tubing segments  160 , the light head body  116  and the electrical connector  144 . 
     Referring to  FIG. 6 , the light head body subassembly  150  includes the plurality of spring loaded electrical contacts  152 , each passing through the plurality of flanged insulating washers  154 , to the plurality of insulated copper wires signifying polarity, the black wires for negative  156 , and the red wires for positive  158 . The plurality of shrink tubing segments  160  provides a second layer of insulation. The wires pass through the light head body  116  and terminate in the electrical connector  144 . The arrangement brings electrical power from the electronics driver circuit board  114  (not illustrated) to the LED light engine circuit board  140  (not illustrated). 
       FIG. 7  illustrates an alternate embodiment of the present invention, incorporating a spring or wave washer  162 , in a grooved light head body  163  used to energize a floating groove ring  164  as part of the window seal. In the full assembly, the spring or wave washer  162  presses the floating groove ring  164  against the interior face of the window  126 , creating the interior wall of a standard O-ring groove for the window face seal O-ring  118 . The floating groove ring  164  provides minimal, if any, support to the window  126 , and substantially all of the full compressive load is carried solely by the multilayer stack  146 . 
       FIG. 8  illustrates an alternate embodiment of the present invention that uses a light head body  165 , incorporating a radial seal O-ring  166  installed in a groove cut into a window  167 . This construction eliminates the tight tolerance of the multilayer stack  146  with respect to the window face seal O-ring  118  illustrated in  FIG. 3 , providing a simple machined bore. 
       FIG. 9  illustrates an alternate embodiment of the present invention that uses a light head body  169 , incorporating a radial seal O-ring  168  installed in a groove cut into the light head body  169  to eliminate the tight height tolerance of the multilayer stack  146  with respect to the window face seal O-ring  118  illustrated in  FIG. 3 . The window  126  can thereby be a simpler cylindrical shape. 
       FIG. 10  illustrates an alternate embodiment of the present invention that uses a single multilayer LED light fixture  170 . A single light head subassembly  172  is attached to a driver subassembly  174 , and held by a coupling collar  176 , using a plurality of ball tipped glassfilled nylon screws  178 . The underwater electrical connector  108  connects the single multilayer LED light fixture  170  to an electrical power source. A mount  180  is attached to the coupling collar  176  by a large centering screw  182 , a large centering screw flat washer  183 , a plurality of retaining screws  184 , and a plurality of retaining screw flat washers  185 . A range of angular adjustment of the light head is permitted by loosening the plurality of retaining screws  184 , and rotating the single multilayer LED light fixture  170  around the large centering screw  182  within the range of the slots cut into the mount  180 . A plurality of sacrificial anodes  186 , made of a material galvanically less noble than the single light head subassembly  172  and the driver subassembly  174 , provides galvanic corrosion protection. 
     Referring to  FIG. 11 , the single multilayer LED light fixture  170  is comprised of the driver subassembly  174 , and the single light head subassembly  172 , held together by the coupling collar  176 , and sealed against outside pressure by the pressure resistant housing O-ring  206 . The driver subassembly  174  is comprised of a pressure resistant driver housing  190 , to which is mounted the underwater electrical connector  108 . The underwater electrical connector  108  brings electrical power to an electronic driver subassembly  192 . 
     An outside groove  196  cut into the outside diameter of the electronic driver subassembly  192  holds a circular beryllium-copper spring  194 . The circular beryllium-copper spring  194  functions as a positioning and retaining device, locating the electronic driver subassembly  192  inside the pressure resistant driver housing  190  which has an inside groove  198  cut into the inside diameter. The circular beryllium-copper spring  194  further functions to absorb vibrations imposed on the electronic driver subassembly  192 , and improves thermal coupling to remove excess heat from the electronic driver subassembly  192  to the surrounding cold ocean. The circular body of the electronic driver subassembly  192  further functions as an internal ring to support the pressure resistant driver housing  190 , which allows the housing to function to a greater depth. A grounding tap  200  provides for a common electrical ground. A thermal sensor board  201  measures the temperature of the single light head subassembly  172  as part of the electronic driver subassembly  192 . If an overheat condition were to occur as detected by the thermal sensor board  201 , the electronic driver subassembly  192  rolls back the current delivered to the plurality of LEDs  128 , thereby lowering the heat of the single light head subassembly  172 . The electronic driver subassembly  192  also contains a thermal sensor integrated within its circuitry to self-monitor its own temperature. If an overheat condition occurs as detected by the thermal sensor integrated into the electronic driver subassembly  192 , it rolls back the current delivered to the plurality of LEDs  128 , thereby lowering the heat developed by the driver itself. The response of the electronic driver subassembly  192  to an overheat condition can be one of linear rollback, where gradual increasing temperature is cause for uniform reduction of current. In the case of rapid overheat, where the rate of change of increasing heat appears to be exponential, the electronic driver subassembly  192  can roll back at a compounded higher rate to prevent thermal overshoot or thermal runaway. 
     The single light head subassembly  172  includes a pressure resistant housing end cap  204 , which is aligned and held to the pressure resistant driver housing  190  by the coupling collar  176 . The pressure resistant housing O-ring  206  seals the housing, and prevents seawater from entering the interior space. A plastic bumper guard  208  is attached to the pressure resistant housing end cap  204  by means of a plurality of machine screws  210 . The plurality of machine screws  210  may be made from either marine grade metal or high strength plastic. An optional light tube  212  provides for a sharp light beam edge cut-off. The mount  180  allows for attachment of the light to a larger underwater structure. 
       FIG. 12  illustrates the plurality of ball tipped glass-filled nylon screws  178 , used in the coupling collar  176 , to align and restrain the single light head subassembly  172  to the driver subassembly  174 . The plurality of ball tipped glass-filled nylon screws  178  are designed to shear should the interior pressure of the light housing exceed a predetermined maximum pressure, e.g. 100 psi (nominal), as can occur if the pressure resistant housing O-ring  206  fails at depth, the housing partially floods, and the pressure resistant housing O-ring  206  seals high internal pressure on return to the surface. 
       FIG. 13  illustrates details of the single multilayer LED light fixture  170 . The light tube  212 , illustrated in  FIG. 11 , is removed to improve the clarity of this fixture. The multilayer LED light fixture  170 , a multilayer stack  214  is comprised of a window support plate  218 , a front Kapton sheet  219 , an LED spacer  220 , a middle Kapton sheet  222 , a light engine printed circuit board  224 , and a rear Kapton sheet  226 . Load imposed by external pressure on a sapphire window  216  is transferred directly through the multilayer stack  214  to the pressure resistant housing end cap  204 . Pressure is carried around the plurality of LEDs  128  which is centered inside a plurality of apertures  221  in the window support plate  218 , the front Kapton sheet  219 , the LED spacer  220 , and the middle Kapton sheet  222 . 
     The window support plate  218  is preferably made from a material with a high compressive strength, including but not limited to: stainless steel, aluminum, PEEK, FR-4 and G-10 fiberglass reinforced epoxy, and ceramic. The LED spacer  220  is preferably made from a non-conductive high compressive strength material, including but not limited to: PEEK, FR-4 and G-10 fiberglass reinforced epoxy, and ceramic. A plurality of lenses  228  is pressed into the window support plate  218 , which focus the light of the plurality of LEDs  128  into a narrow beam. A light assembly may outfit some or all of the plurality of LEDs  128  with focusing lenses to provide different beam characteristics. The plurality of LEDs  128  is soldered to the light engine printed circuit board  224 . The thin layer of the rear Kapton sheet  226  electrically isolates but thermally connects the light engine printed circuit board  224  to the pressure resistant housing end cap  204 . This permits heat to be drawn off the back of the plurality of LEDs  128  and routed to the cold surrounding environment. A center screw  230  holds the multilayer stack  214  together during assembly. A plurality of indexing screws  232  provides anti-rotation and alignment of the layers. The center screw  230  and the plurality of indexing screws  232  are surrounded by a plurality of flanged electrically insulating washers  234 . The multilayer stack is pre-loaded in compression by a titanium ring  236  that engages the pressure resistant housing end cap  204  by means of machined threads. A group of four slots  237  on the face of the titanium ring  236 , better illustrated in  FIG. 15 , create a plurality of four flexible titanium ring tangs  242 , a feature better illustrated in  FIG. 14 . As the titanium ring  236  is tightened, this plurality of titanium ring tangs  242  engage the sapphire window  216  and create a pre-load compressive force on the multilayer stack  214 . A sealing O-ring  238  is compressed by the titanium ring  236 , pressing on a tapered sealing wedge  240 , which is forced to engage the outer edge of the sapphire window  216 , thus acting as a compression seal. The plastic bumper guard  208  provides impact resistance. 
       FIG. 14  illustrates the titanium ring  236 , and the titanium ring tang  242  flexing in contact with the sapphire window  216 . The degree of flexure is illustrated by the titanium ring tang  242  in its unflexed (dotted) and flexed (solid line) positions. This flexure provides positive initial compressive force for the multilayer stack  214  illustrated in  FIG. 13 . 
       FIG. 15  illustrates the installation of the titanium ring  236  with the plurality of flexible titanium ring tangs  242  as installed in the single light head assembly  172 . The light tube  212 , referred to in  FIG. 11 , and illustrated in  FIG. 10 , is removed to improve the clarity of this view. The four slots  237  on the face of the titanium ring  236  create the four flexible titanium ring tangs  242  illustrated in  FIG. 14  that flex to engage the sapphire window  216 , and preload the multilayer stack  214  illustrated in  FIG. 13 . Additionally, the four slots  237  serve as spanner wrench drive points for ease of installation. 
       FIG. 16  illustrates of an alternate embodiment of the present invention which utilizes a window support plate  244  for wide beam illumination, and an anodized aluminum spacer plate  246 . A multilayer stack  247  is comprised of the window support plate  244  into which are cut a plurality of apertures  249  which function as reflectors, the front Kapton sheet  219 , the LED spacer  220 , the middle Kapton sheet  222 , the light engine printed circuit board  224 , and a rear Kapton sheet  226 . Load imposed by external pressure on a sapphire window  216  is transferred directly through the multilayer stack  247  to the pressure resistant housing end cap  204 . Pressure is carried around the plurality of LEDs  128  which are centered inside the plurality of apertures  249  in the window support plate  244 , and also centered inside the plurality of apertures  221  in the front Kapton sheet  219 , the LED spacer  220 , and the middle Kapton sheet  222 . 
       FIG. 17  illustrates the single multilayer LED light fixture  170 , illustrating the single light head subassembly  172 , the electronic driver subassembly  192 , the pressure resistant driver housing  190 , and the underwater electrical connector  108 . An exterior top label  248 , an exterior bottom label  250 , and a plurality of exterior rear labels  252  are also illustrated. 
       FIG. 18  illustrates an embodiment of the present invention in the form of a remote single multilayer LED light fixture  253 , comprised of a remote single multilayer LED light head  254 , a remote electronic driver assembly  256 , and a connecting electrical cable  258 . The remote single multilayer LED light head  254  is comprised of a remote light head body  260 , a cowl  262 , and a remote light head underwater electrical connector  264 . A mounting bracket  266  is fastened to the remote single multilayer LED light head  254  by a plurality of small centering screws  188  and a plurality of small centering screw flat washers  189 . A range of angular adjustment for pointing the light can be made by loosening the plurality of small centering screws  188 , rotating the remote single multilayer LED light head  254  in the mounting bracket  266  to the desired angle, and then re tightening the plurality of small centering screws  188 . The remote electronic driver assembly  256  is comprised of the pressure resistant driver housing  190 , the underwater electrical connector  108  for power input and control, the coupling collar  176 , the plurality of ball tipped glass-filled nylon screws  178 , and a pressure resistant housing blank end cap  271 . 
     The pressure resistant housing blank end cap  271  ( FIG. 18 ) is fitted with a remote driver underwater electrical connector  268 . Also illustrated in  FIG. 18  are the plurality of sacrificial anodes  186  which use a plurality of nylon washers  273  to provide an isolating spacer with the pressure resistant housing blank end cap  271 . The mount  180  is attached to the coupling collar  176  by the large centering screw  182 , the large centering screw flat washer  183 , the plurality of retaining screws  184 , and the plurality of retaining screw flat washers  185 . Internal to the remote electronic driver assembly  256  is the electronic driver subassembly  192 , illustrated in  FIG. 17 . 
       FIG. 19  illustrates the remote single multilayer LED light head  254  taken along line  1919  of  FIG. 18 . The construction of the plurality of sacrificial anodes  186  is clearly illustrated. A galvanically active material, such as anode grade zinc or magnesium, that makes the plurality of sacrificial anodes  186 , is fixed to a short segment of threaded rod  270  made of an electrically conductive metal such as stainless steel. The threaded rod  270  screws into a bare tapped hole  272  made into the side of the remote light head body  260 . The plurality of nylon washers  273  acts as a compression gasket to seal the interface between the plurality of sacrificial anodes  186  and the remote light head body  260 , keeping seawater from entering the electrical contact interface between the two when installed with grease. The remote light head underwater electrical connector  264  is mounted to the rear of the remote light head body  260 . 
       FIG. 20A  illustrates a slip ring subassembly  281  that permits a shortened light head assembly. A central slip ring printed circuit board  286  holds a plurality of inner spring contacts  282 , a plurality of outer spring contacts  284 , and a temperature cut-off sensor  285 , which is part of an FET based thermal cut-out switch circuit  202  that provides a solid state thermal cut-out safety feature in the event of a defined overheat condition inside the remote single multilayer LED light head  254  illustrated in  FIG. 18 . In addition, the central slip ring printed circuit board  286  provides reverse voltage protection for the LEDs  128 , in the event the connecting electrical cable  258  is plugged in backwards. The central slip ring printed circuit board  286  is prevented from shorting to the housing by a set-back of the copper trace from the edge of the central slip ring printed circuit board  286 , and by an upper plastic ring  288 , and a lower plastic ring  290 . The slip ring subassembly  281  is held together by a plurality of retaining screws  292  that is threaded into the remote light head body  260 . The remote light head underwater electrical connector  264  has a bulb socket into which is screwed an assembly consisting of a center tap  274 , an insulating ring  276 , an outer tap  278 , and a locking O-ring  280  used to hold the assembly from rotating loose. The plurality of inner spring contacts  282  engage the center tap  274 , while the plurality of outer spring contacts  284  engage the outer tap  278  as the remote light head underwater electrical connector  264  is screwed into the remote light head body  260 . 
     An alternate embodiment of the FET based thermal cut-out switch circuit  202 , illustrated as a block diagram in  FIG. 20B , provides a power line communications (PLC) scheme from the remote single multilayer LED light head  254  to the remote electronic driver assembly  256  of  FIG. 18 , creating an automatic dimming control capability for thermal protection. The scheme uses either a modulated or digitally superimposed signal generated in the remote single multilayer LED light head  254  to control a dimming circuit within the remote electronic driver assembly  256 . Temperature sensing devices, control logic, and data encoding circuitry located within the remote single multilayer LED light head  254 , monitor the local operating temperature and convert that measurement into digital data. The digital data is then encoded into a digital waveform suited for transmission from the remote single multilayer LED light head  254  along the power lines back to the remote electronic driver assembly  256  of  FIG. 18 . 
     Modulation of the encoded digital temperature data is accomplished through a power switching technique where the control logic in the remote single multilayer LED light head  254  switches a load rapidly on-and-off in a specific pattern. The power shift pattern signals the encoded temperature. At the electronic driver subassembly  192  the modulated data is received and a de-modulation device retrieves the encoded digital data derived from the power shift pattern. The encoded digital data is then decoded and the temperature data retrieved by the electronic driver subassembly  192 , the closed loop thermal rollback is complete, and power to the remote light is decreased or increased in order to maximize light output while maintaining safe operating temperatures. This modulation communication technique can be used to tell the ballast when preset thermal limits are crossed (for example, 50% rated temperature, 80% rated temperature, etc.) or to simply report temperature data at regular intervals. 
     An alternate dimming control solution uses a digital overlay technique to transmit encoded temperature data as a signal superimposed on the DC power carried through the electrical wires supplying power to the remote single multilayer LED light head  254 . This relays data to the driver dimming control circuit in the remote electronic driver assembly  256 . The closed loop thermal rollback is now complete and power to the remote light can be decreased or increased in order to maximize light output while maintaining safe operating temperatures. 
     Either of these methods establishes a closed loop thermal roll back control in the remote light head configuration without additional wires for data transfer between the remote single multilayer LED light head  254  and the remote electronic driver assembly  256 . The digital overlay technique has the advantages that its transmitted temperature measurement data are more precise, and does it not use the power shift pattern of the modulation technique, which cause the remote single multilayer LED light head  254  to toggle on-and-off. 
       FIG. 20B  illustrates the manner in which the LED driver circuit of the remote single multilayer LED light fixture  253  follows the power flow from an AC/DC power source  255 , through an input rectifier/filter  257 , through a power regulator  269 , through a closed-loop switch mode power regulator  275 , through a hysteretic thermal switch/temperature transmitter  277 , to an LED light engine  279 . The power regulator  269  additionally provides power to a microcontroller system  283 , which controls the closed-loop switch mode power regulator  275 , based on measurements sent from the hysteretic thermal switch/temperature transmitter  277 . The microcontroller system  283  provides timing to a ballast interconnect and sync circuit  289 . The microcontroller system  283  incorporates such elements as conduction angle decoder, line bleed circuitry, temperature compensation, LED regulation command, remote interface host, and real time parameter monitor. The power regulator  269  additionally provides power to an isolated 5 volts DC excitation supply  291  which powers a manual dimming control interface  287 , whose function is to interpret signals (such as isolated RS-485 half-duplex, isolated analog 0-15 volts DC, 0 10 volts DC, or 0-20 mA) received from an external control input  293 . 
       FIG. 21  illustrates the remote single multilayer LED light head  254 . This view illustrates the relative position of the interior components which connect the light engine printed circuit board  224  of the remote single multilayer LED light head  254  to the central slip ring printed circuit board  286 , better illustrated in  FIG. 22 . 
       FIG. 22  illustrates the means that connect the light engine printed circuit board  224  to the central slip ring printed circuit board  286 . A plurality of copper washers  300  are held in place by a plurality of copper rivets  298 , which are individually insulated from the core of the light engine printed circuit board by a plurality of plastic flanged washers  296 . A plurality of electrical contact pins  294  are soldered into each of the plurality of copper rivets  298 . The plurality of copper washers  300  are likewise soldered to the top conductive traces of the light engine printed circuit board  224 . The plurality of electrical contact pins  294  engage a plurality of sockets  295  that are part of the central slip ring printed circuit board  286 . The plurality of sockets  295  are electrically insulated using a short segment of heat shrink tubing  297 . 
       FIG. 23  illustrates the composition of the multilayer stack  214  which is comprised of the window support plate  218 , the front Kapton sheet  219 , the LED spacer  220 , the middle Kapton sheet  222 , the light engine printed circuit board  224 , and the rear Kapton sheet  226 . The plurality of LEDs  128  is soldered to the light engine printed circuit board  224 . The load imposed by external pressure on the sapphire window  216  is transferred directly through the multilayer stack  214 , through an anodized aluminum puck  302  to the remote light head body  260 . The anodize coating of the anodized aluminum puck  302  acts as the primary electrical insulator. The anodized aluminum puck  302  is secondarily electrically insulated by a Kapton collar  306 . Pressure is carried around the plurality of LEDs  128  which is centered inside the plurality of apertures  221  in the window support plate  218 , the front Kapton sheet  219 , the LED spacer  220 , and the middle Kapton sheet  222 . The plurality of lenses  228  are pressed into the plurality of apertures  221  in the window support plate  218 , which individually focus the light of the plurality of LEDs  128  into a narrow beam. The window support plate  218  may outfit some or all of the plurality of apertures  221  with the plurality of lenses  228  to provide different light beam characteristics. 
     The rear Kapton sheet  226  electrically isolates but thermally connects the light engine printed circuit board  224  to the remote light head body  260 . This permits heat to be drawn off the back of the plurality of LEDs  128  and routed to the cold surrounding environment. The center screw  230  holds the multilayer stack together during assembly. The plurality of indexing screws  232  provides anti-rotation and alignment of the layers. The plurality of indexing screws  232  and the center screw  230  are electrically isolated by the plurality of flanged electrically insulating washers  234 . 
     The multilayer stack  214  is pre-loaded in compression by a titanium convex flat spring  310  ( FIG. 23 ) that engages the sapphire window  216  on its inside diameter, and rests on a plastic galvanic insulator  308  on its outer diameter, and is pressed on a circle midway between its inside diameter and outside diameter by the cowl  262  creating a compressive force on the sapphire window  216 . As the cowl  262  is tightened, the pre-load compressive force on the multilayer stack  214  is increased by the downward force imposed by the titanium convex flat spring  310 . In addition, the titanium convex flat spring  310  presses downward on the plastic galvanic insulator  308 , which then compresses the sealing O-ring  238  and the tapered sealing wedge  240  below that. The tapered sealing wedge  240  is forced to engage the outer edge of the sapphire window  216 , acting as a secondary compression seal. An anti-rotation O-ring  312  locks the cowl from rotating loose. 
     Referring to  FIG. 24 , the remote single multilayer LED light head  254  includes the cowl  262 , the anti-rotation O-ring  312 , the titanium convex flat spring  310 , the plastic galvanic insulator  308 , the sealing O-ring  238 , the tapered sealing wedge  240 , and the sapphire window  216 . The LED light head  254  further includes the center screw  230 , the plurality of indexing screws  232 , the plurality of lenses  228 , the window support plate  218 , the front Kapton sheet  219 , the LED spacer  220 , and the middle Kapton sheet  222 . The LED light head  254  further includes the plurality of flanged electrically insulating washers  234 , the plurality of copper washers  300 , and the light engine printed circuit board  224  populated with the plurality of LEDs  128 . The LED light head  254  further includes the rear Kapton sheet  226 , the plurality of plastic flanged washers  296 , the plurality of copper rivets  298 , the plurality of electrical contact pins  294 , and the Kapton collar  306 . The LED light head  254  further includes the anodized aluminum puck  302 , the upper plastic ring  288 , the central slip ring printed circuit board  286 , the lower plastic ring  290 , the plurality of retaining screws  292 , and the center tap  274 . The LED light head  254  further includes the insulating ring  276 , the outer tap  278 , the locking O-ring  280 , the remote light head body  260 , a plurality of exterior labels  261 , and the remote light head underwater electrical connector  264 . The LED light head  254  further includes the mounting bracket  266 , the plurality of small centering screws  188 , a mount washer  187 , the small centering screw flat washers  189 , the sacrificial anode  186 , the threaded rod  270 , and the nylon washer  273 . 
     Referring to  FIG. 25 , the remote electronic driver assembly  256  includes the pressure resistant driver housing  190 , to which is mounted the underwater electrical connector  108 . This brings power to the electronic driver subassembly  192 , which is retained inside the pressure resistant driver housing  190  by use of the circular beryllium-copper spring  194  that seats in the outside groove  196  machined into the outside diameter of the electronic driver subassembly  192 , positioning it in the inside groove  198  machined into the interior diameter of the pressure resistant driver housing  190 . The circular beryllium-copper spring  194  functions as a positioning and retaining device, absorbing vibrations imposed on the electronic driver subassembly  192 , and improves thermal coupling to remove excess heat from the electronic driver subassembly  192  to the surrounding cold environment. The circular body of the electronic driver subassembly  192  further functions as an internal ring to support the pressure resistant driver housing  190 , which allows it to function to a greater depth. The grounding tap  200  provides for a common electrical ground. The thermal sensor board  201 , measures the temperature of the remote electronic driver assembly  256  as part of the electronic driver subassembly  192 . As fully described in  FIG. 11 , the electronic driver subassembly  192  also contains a thermal sensor integrated within its circuitry to self-monitor its own temperature. If an overheat condition were to occur as detected by the thermal sensor integrated into the electronic driver subassembly  192 , it would roll back the current delivered to the remote single multilayer LED light head  254  (Not illustrated), thereby lowering the heat developed by the remote electronic driver assembly  256  itself. 
     The pressure resistant housing blank end cap  271  is aligned and held to the pressure resistant driver housing  190  by the coupling collar  176 . The pressure resistant housing O-ring  206  prevents seawater from entering the interior space. The remote driver underwater electrical connector  268  brings power for the remote light head through the pressure resistant housing blank end cap  271  and connects to the connecting electrical cable  258 . The mount  180  allows for attachment of the light to a larger underwater structure. 
     Referring to  FIG. 26 , the plurality of ball tipped glass-filled nylon screws  178  is used in the coupling collar  176  to align and restrain the pressure resistant housing blank end cap  271  to the pressure resistant driver housing  190 . The plurality of ball tipped glass-filled nylon screws  178  are designed to shear should the interior pressure of the light housing exceed 100 psi (nominal), as may occur if the pressure resistant housing O-ring  206  fails at depth, the housing partially floods, and the pressure resistant housing O-ring  206  seals high internal pressure on return to the surface. 
       FIG. 27  illustrates the exterior of an alternate embodiment of the present invention in the form of a triple multilayer LED light fixture  314  incorporating three multilayer stack  214  assemblies as illustrated in  FIG. 13 . The triple multilayer LED light fixture  314  is comprised of a triple multilayer LED light head  316  attached to a triple driver assembly  318 , and held by the coupling collar  176 , using the plurality of ball tipped glass-filled nylon screws  178 . The underwater electrical connector  108  connects the triple multilayer LED light fixture  314  to an electrical power source. The mount  180  is attached to the coupling collar  176  by the large centering screw  182 , the large centering screw flat washer  183 , the plurality of retaining screws  184 , and the plurality of retaining screw flat washers  185 . The second mount  180  is placed near the rear of the triple multilayer LED light fixture  314  near the underwater electrical connector  108  for additional support. The second mount  180  is similarly attached to the triple multilayer LED light fixture  314 . 
     Referring to  FIG. 28 , the triple multilayer LED light fixture  314  includes the triple multilayer LED light head  316  attached to the triple driver assembly  318 , and held by the coupling collar  176 , using the plurality of ball tipped glass-filled nylon screws  178  as illustrated in  FIG. 27 . In this embodiment of the invention, the three multilayer stack  214  assemblies, which are individually described in  FIG. 13 , are incorporated into a triple light head body  320 . The triple multilayer LED light fixture  314  includes a pressure resistant driver housing  321 , to which is mounted the underwater electrical connector  108 . This brings power to the three electronic driver subassemblies  192 , bolted together in a manner illustrated in  FIG. 29 . The circular berylliumcopper spring  194  seats in the outside groove  196  machined into the outside diameter of each of the three electronic driver subassemblies  192 . 
     The sub-assembly of the three electronic driver subassemblies  192  is retained inside the pressure resistant driver housing  321  by use of the single inside groove  198  machined into the inside diameter of the pressure resistant driver housing  321 . The single inside groove  198  captures one of the circular beryllium-copper springs  194 , thus functioning as a means for positioning and retaining the three electronic driver subassemblies  192 . In addition, the circular beryllium-copper springs  194  absorb vibrations imposed on the three electronic driver subassemblies  192 , and improve thermal coupling to remove excess heat from the driver to the surrounding cold environment. The circular bodies of the three electronic driver subassemblies  192  secondarily function as internal rings to support the pressure resistant driver housing  321 , allowing the housing to operate at greater depths. The grounding tap  200  provides for a common electrical ground. The thermal sensor board  201  measures the temperature of the triple multilayer LED light fixture  314  as part of the plurality of electronic driver subassemblies  192 . As fully described in  FIG. 11 , the plurality of electronic driver subassemblies  192  each contain an integrated thermal sensor to self-monitor their individual temperatures. If an overheat condition were to occur in any single electronic driver subassembly  192 , it would roll back the current delivered to the triple multilayer LED light head  316 , thereby lowering the heat developed by the plurality of electronic driver subassemblies  192 . 
     The triple multilayer LED light head  316  is aligned and held to the pressure resistant driver housing  321  by the coupling collar  176 . The pressure resistant housing O-ring  206  provides a seal, preventing seawater from entering the interior. A plastic bumper guard  322  is attached to the triple light head body  320  by means of the plurality of machine screws  210 , better illustrated in  FIG. 29 . The pair of mounts  180  allows for attachment of the light to a larger underwater structure, as described in  FIG. 27 .  FIG. 29  illustrates the manner in which the three electronic driver subassemblies  192  are held together as a single module within the triple driver assembly  318  by a plurality of threaded rods  193  passing through the three electronic driver subassemblies  192  and screwing into a lower end ring  199 . A plurality of shrink tubing segments  197  are used on the plurality of threaded rods  193  to prevent electrical contact with the three electronic driver subassemblies  192 . A plurality of hex nuts  195 , tighten onto the plurality of threaded rods  193 , securely holding the three electronic driver subassemblies  192  together. The plastic bumper guard  322  is attached to the triple light head body  320  by means of the plurality of machine screws  210 . The plurality of machine screws  210  may be made from either marine grade metal or high strength plastic. As described in connection with  FIG. 12 , the plurality of ball tipped glass-filled nylon screws  178  are used with the coupling collar  176  to align and restrain the triple multilayer LED light head  316  to the triple driver assembly  318 . The pressure resistant housing O-ring  206  provides a seal, preventing seawater from entering the interior. The pair of mounts  180  allows for attachment of the triple multilayer LED light fixture  314  to a larger underwater structure, in the manner described connection with in  FIG. 27 . 
       FIG. 30  illustrates an alternate embodiment of the present invention in the form of a remote triple multilayer LED light fixture  323 , comprised of a remote triple light head  324 , and a remote triple electronic driver assembly  326 , which are connected by a connecting electrical cable  328 . The underwater electrical connector  108  connects the remote triple electronic driver assembly  326  to an electrical power source (not illustrated). 
     Referring to  FIG. 31 , the remote triple light head  324  includes the triple light head body  320  attached to a rear pressure housing  329 , held together by the coupling collar  176 , and sealed by the pressure resistant housing O-ring  206 . A remote light head underwater electrical connector  330  connects the remote triple light head  324  to the remote triple electronic driver assembly  326  through the connecting electrical cable  328 , as illustrated in  FIG. 30 . Power is brought into the interior of the remote triple light head  324  through the remote light head underwater electrical connector  330  and delivered to an interface control board  332 . The interface control board  332  distributes power to each of the three multilayer stack  214  assemblies, which are illustrated in  FIG. 13 . The interface control board  332  also contains the FET based thermal cut-out switch circuit  202  which monitors the temperature of the remote triple light head  324 , and shuts off the power if an over-temperature threshold has been exceeded. Interface control board  332  may contain three separate FET based thermal cut out switch circuits  202  separately controlling each of the three multilayer stack  214  assemblies. The temperature cut out point for each of these thermal cut out circuits  202  may be set to cascade turning off one after another as the temperature rises. For example, the first cut out switch might operate at 60 C, the next at 65 C and third at 70 C, allowing at least partial sustained operation at elevated temperatures. As described in connection with  FIG. 20A , an alternate embodiment of the FET based thermal cut-out switch circuit  202  provides a power line communications (PLC) scheme from the remote triple light head  324  to the remote triple electronic driver assembly  326  inside the remote triple electronic driver assembly  326 , thus creating a remote automatic dimming control capability. The scheme uses either a modulated or digitally superimposed signal generated in the remote triple light head  324  to control a dimming circuit within the remote triple electronic driver assembly  326 . In addition, the interface control board  332  provides reverse voltage protection for the LEDs  128 , in the event the connecting electrical cable  328  is plugged in backwards. As described in connection with  FIG. 29 , the plastic bumper guard  322  is attached to the triple light head body  320 . 
       FIG. 32  illustrates the pressure resistant housing blank end cap  271  mated to the pressure resistant driver housing  321 . The remote light head underwater electrical connector  330  connects the three electronic driver subassemblies  192  to the remote triple light head  324  of  FIG. 31  through the connecting electrical cable  328 . The underwater electrical connector  108  connects the remote triple electronic driver assembly  326  to an electrical power source (Not illustrated). The pair of mounts  180  allows for attachment of the remote triple electronic driver assembly  326  to a larger underwater structure, in the manner described in connection with  FIG. 27 . As described in connection with  FIG. 12 , the plurality of ball tipped glass-filled nylon screws  178  (not illustrated) are used with the coupling collar  176  to align and restrain the pressure resistant housing blank end cap  271  to the pressure resistant driver housing  321 . The pressure resistant housing O-ring  206  provides a seal, preventing seawater from entering the interior. The thermal sensor board  201 , measures the temperature of the remote triple electronic driver assembly  326  as part of the plurality of electronic driver subassemblies  192 . As fully described in  FIG. 11 , the plurality of electronic driver subassemblies  192  each contain an integrated thermal sensor to self-monitor their individual temperatures. If an overheat condition were to occur in any single electronic driver subassembly  192 , it would roll back the current delivered to the remote triple light head  324 , thereby lowering the heat developed by the plurality of electronic driver subassemblies  192 . 
       FIG. 33  illustrates an alternate embodiment of the present invention in the form of a mid-size LED light fixture  334 , which is comprised of a light head subassembly  336 , an electronics driver subassembly  338 , the underwater electrical connector  108 , a mount  340 , a housing clamp  342 , the plurality of retaining screws  184 , and the plurality of retaining screw flat washers  185 . Angular adjustment of the mid-size LED light fixture  334  with respect to the mount  340  is accomplished by loosening the plurality of retaining screws  184 , rotating the mid-size LED light fixture  334  within the angular range possible by the slots cut into the mount  340 , then retightening the plurality of retaining screws  184 . A plurality of circular openings  371  is visible in a cowl  370 , which are used to improve water flow for cooling. 
       FIG. 34  illustrates further details of the mid-size LED light fixture  334 . These include the light head subassembly  336  and the electronics driver subassembly  338 . The light head subassembly  336  is attached to an interior mounting flange  350  by a plurality of light head interior screws  352 . An electronic driver printed circuit board  354  is attached to the interior mounting flange  350  by means of a PCB screw  356 . The opposite end of the electronic driver printed circuit board  354  is fastened to a support ring  357  by a long screw  358  and a hex nut  360 . A cushion O-ring  362  is used as a compliant interface between the support ring  357  and a driver pressure housing  348 . The underwater electrical connector  108  provides an attachment to an external electrical power supply. The housing clamp  342  provides attachment to a larger structure as described in connection with  FIG. 33 . 
       FIG. 35  illustrates an alternate embodiment of the present invention in the form of a multilayer stack  386  in the light head subassembly  336 . The cowl  370  presses a light head body  364  against the driver pressure housing  348 . A face seal O-ring  366  provides the primary seal, while a radial seal O-ring  368  provides a secondary seal, preventing seawater from entering the interior of the light body. A friction O-ring  372  is used to prevent the cowl  370  from rotating loose from the driver pressure housing  348 . 
     Referring to  FIG. 36 , the cowl  370  engages the light head body  364 . The multilayer stack  386  consists of a window support plate  384 , an LED spacer  388 , a front Kapton sheet  390 , a light engine printed circuit board  392 , a rear Kapton sheet  394 , and an anodized aluminum spacer  396 . A recessed flathead screw  400  holds the multilayer stack  386  in the light head body  364 . The light engine printed circuit board  392  is populated with the plurality of LEDs  128 . Load imposed by external pressure on a sapphire window  382  is transferred directly through the multilayer stack  386  to the light head body  364 . Pressure is carried around the plurality of LEDs  128  which is centered inside the plurality of apertures  125  in the window support plate  384 , the LED spacer  388 , and the front Kapton sheet  390 . 
     The multilayer stack  386  ( FIG. 36 ) is pre-loaded in compression by a titanium convex flat spring  378  that engages the sapphire window  382  on its inside diameter, and rests on a plastic galvanic insulator  380  on its outer diameter. The titanium convex flat spring  378  is pressed on a circle midway between it&#39;s inside diameter and outside diameter by a front retainer ring  376  energized by a plurality of head screws  374 . As the plurality of head screws  374  are tightened, the compressive force on the multilayer stack  386  is increased by the downward force imposed by the titanium convex flat spring  378 . In addition, the titanium convex flat spring  378  captures and compresses a window sealing O-ring  402  and a tapered sealing wedge  404  behind the sealing O-ring  402 . The tapered sealing wedge  404  is forced to engage the outer edge of the sapphire window  382 , and acts as a compression seal. A Kapton collar  398  and an air gap  399  provide two additional layers of electrical insulation between the anodized light head body  364  and the light engine printed circuit board  392 . 
     Referring to  FIG. 37 , the mid-size LED light fixture  334  includes the light head subassembly  336  and the electronics driver subassembly  338 . Additionally illustrated are the plurality of head screws  374 , the front retainer ring  376 , the titanium convex flat spring  378 , and the plastic galvanic insulator  380 .  FIG. 37  also illustrates the window sealing O-ring  402 , the tapered sealing wedge  404 , the sapphire window  382 , and the recessed flathead screw  400 .  FIG. 37  also illustrates the window support plate  384 , the LED spacer  388 , the front Kapton sheet  390 , and a plurality of copper washers  406 .  FIG. 37  also illustrates the light engine printed circuit board  392  populated with the plurality of LEDs  128 .  FIG. 37  also illustrates the Kapton collar  398 , the rear Kapton sheet  394 , a plurality of plastic flanged washers  408 , and a plurality of copper rivets  410 .  FIG. 37  also illustrates a plurality of electrical contact pins  412  jacketed in an extra layer of heat shrink tubing  414 , the anodized aluminum spacer  396 , the light head body  364 , the face seal O-ring  366 , and the radial seal O-ring  368 .  FIG. 37  also illustrates the cowl  370 , the light head interior screws  352 , the interior mounting flange  350 , and the PCB screw  356 .  FIG. 37  also illustrates the electronic driver printed circuit board  354 , the long screw  358 , the hex nut  360 , the support ring  357 , the cushion O-ring  362 , and the friction O-ring  372 .  FIG. 37  also illustrates the driver pressure housing  348 , the mount  340 , the housing clamp  342 , the plurality of retaining screws  184 , the plurality of retaining screw flat washers  185 , and the underwater electrical connector  108 . 
     The embodiments described above are well suited for use on manned and unmanned submersible vehicles that can descend to significant depths, e.g. 1,500 meters and more. At these depths there is no ambient light, the ambient water temperature is near 32 degrees F. and pressures exceed 3,000 PSI. The submersibles may rest on the deck of a ship traveling in icy waters where the ambient air temperature may be well below 32 degrees F. 
       FIG. 38  illustrates an alternate embodiment of the present invention in the form of a boat thru-hull light fixture  415 , comprised of a driver electronics module  416 , and a remote thru-hull light head  418  connected by a light head electrical cable  420 . A thru-hull flanged threaded housing  427  is a single piece, but functionally comprised of a threaded body  428 , and a thru-hull flanged light head  430 . Electrical power is delivered to the driver electronics module  416  by a power input electrical cable  422 . Both the power input electrical cable  422  and the light head electrical cable  420  pass through a waterproof compression fitting  424  that is fitted to one end of a driver electronics module housing  426 . A plurality of brackets  429  allows the driver electronics module  416  to be conveniently restrained inside a vessel. 
     Referring to  FIG. 39 , the thru-hull flanged threaded housing  427  is illustrated as a single piece, functionally divided into the threaded body  428 , and the thru-hull flanged light head  430 , made of a material possessing a high coefficient of heat transfer. Such materials include, but are limited to, copper, brass, aluminum, aluminum alloy and some plastics which incorporate specific fillers and modifiers that permit high heat transfer. The thru-hull flanged light head  430  contains a multilayer stack  461 , better described in  FIG. 40 . The center of the thru-hull flanged threaded housing  427  is hollow. A thermal sensing printed circuit board  432  is inserted into this space, and connects the thru-hull flanged light head  430 , described in detail in connection with  FIG. 40 , to the light head electrical cable  420 . The thermal sensing printed circuit board  432  contains a forward thermal sensor  434  immediately behind the thru-hull flanged light head  430 , and a rear thermal sensor  436 , positioned in the middle of the threaded body  428 . The design of the thru-hull light fixture  415  permits the driver electronics module  416 , illustrated in  FIG. 38 , to constantly monitor temperature at both the thru-hull flanged light head  430 , where heat is largely generated, and inboard, where excess radiant heat may pose a hazard to personnel. The driver electronics module  416  can determine safe levels at these independent locations, and reduce electrical current to the thru-hull flanged light head  430  to achieve a safe operating condition. A layer of electrically insulating shrink tubing  438  protects the thermal sensing printed circuit board  432  from electrically shorting to the thru-hull flanged threaded housing  427 . The light head electrical cable  420  passes from the rear of the thru-hull flanged threaded housing  427  through a portion with a smaller inside diameter  442 . This region then flares outward to form a conic section  444 . Epoxy (not illustrated) is pumped into the center of the thru-hull flanged threaded housing  427  through a fill port  446  located on the threaded body  428  just behind the thru-hull flanged light head  430 . The epoxy is forced through the center of the thru-hull flanged threaded housing  427  until it exits out the back of the fitting, past the portion of the housing with the smaller inside diameter  442  and filling the conic section  444 . A flat head fill port screw  448  seals the fill port  446  after the epoxy fill operation is complete. This action seals the thermal sensing printed circuit board  432  from the damaging effects of moist marine air, inadvertent splash or shallow water immersion, and additionally provides a strain relief between the light head electrical cable  420  and the thru-hull flanged threaded housing  427 , the light head electrical cable  420  and the thermal sensing printed circuit board  432  internal to the thru-hull flanged threaded housing  427 . 
     The thru-hull flanged threaded housing  427  is mounted to a boat hull by first drilling a hole through the boat hull (not illustrated) of a diameter large enough to pass the threaded body  428  of the thru-hull flanged threaded housing  427 . A compressible rubber gasket  450  seals the thru-hull flanged light head  430  to the outside surface of the boat hull. Alternately a marine adhesive may be used. On the inside of the boat hull, an internally threaded jacking ring  454  is fitted with a plurality of jacking screws  456 , that pass through and engage a jacking plate  452 . The jacking ring  454  is installed on the threads of the thru-hull flanged threaded housing  427  from the inside of the vessel and screwed down until the jacking plate  452  engages the interior surface of the boat hull. A socket wrench (not illustrated) is used to drive the plurality of jacking screws  456  in a direction that presses down on the jacking plate  452 . The jacking ring  454  cannot rotate with this axial application of force. An increasing clamping force is applied until a watertight seal is achieved. A bonding screw  460  and a bonding wire  458  are supplied to properly attach the remote thru-hull light head  418  to the vessel&#39;s corrosion protection system. 
     Referring to  FIG. 40 , the multilayer stack  461  of the remote thru-hull light head  418  includes a window support plate  464 , a double-sided metal core printed circuit board (DSMCPCB)  498 , and a rear phase change material (PCM) sheet  468 . The DS-MCPCB  498  is preferentially a copper or an aluminum metal core, with both the front and rear faces clad first in a thin electrical dielectric and then with copper clad, better illustrated in  FIG. 43 . The DS-MCPCB  498  is populated with the plurality of LEDs  128 . The multilayer stack  461  is positioned within the thru-hull flanged light head  430 . A sapphire window  462  presses the multilayer stack  461 , forcing it into contact with the interior of the thru-hull flanged light head  430 . The sapphire window  462  and the multilayer stack  461  are held firmly by a press fit ring  470  with a flexible inner rim  490  that contacts the sapphire window  462 , better illustrated in  FIG. 42 . The press fit ring  470  additionally energizes a front sealing O-ring  472  by compressing it under the sapphire window  462 . A plurality of electrical contacts  474  pass through a foam block  476  to connect the DS-MCPCB  498  populated with the plurality of LEDs  128 , to the thermal sensing printed circuit board  432  and power from the driver electronics module  416  carried by the light head electrical cable  420  as illustrated in  FIG. 39 . The shrink tubing  438  protects the thermal sensing printed circuit board  432  from electrically shorting to the thru-hull flanged threaded housing  427 . 
     The rear PCM sheet  468  electrically isolates but thermally connects the DSMCPCB  498  to the thru-hull flanged threaded housing  427 . This permits heat to be drawn off the back of the plurality of LEDs  128  and routed to the cooler surrounding environment. Additionally, the rear PCM sheet  468  seals any gaps between the DS-MCPCB  498  and the thru-hull flanged light head  430 , and prevents the epoxy fill described in  FIG. 39  from entering into the space where the plurality of LEDs  128  are located. An outer groove  478 , machined into the interior face of the thru-hull flanged light head  430 , together with the plastic window support plate  464 , provide an air gap electrical insulator around and under the DS-MCPCB  498  and the thruhull flanged threaded housing  427 , better illustrated in  FIG. 43 . Load imposed by external pressure or wave slap on the sapphire window  462  is transferred directly through the multilayer stack  461  to the thru-hull flanged light head  430 . 
     Referring to  FIG. 41 , the remote thru-hull light head  418  includes the press fit ring  470 , the sapphire window  462 , the front sealing O-ring  472 , the window support plate  464 , the DS-MCPCB  498  populated with the plurality of LEDs  128 . The rear PCM sheet  468 , the plurality of electrical contacts  474 , and the foam block  476  are also illustrated in  FIG. 41 . This figure also illustrates the thermal sensing printed circuit board  432  with the forward thermal sensor  434  and the rear thermal sensor  436 . Also visible in  FIG. 41  are the shrink tubing  438 , the light head electrical cable  420 , the fill port  446 , the fill port screw  448 , and the thru-hull flanged threaded housing  427 . The thru-hull flanged threaded housing  427  is a single piece, functionally divided into the threaded body  428 , and the thru-hull flanged light head  430 . In an alternate embodiment, the threaded body  428  and the thru-hull flanged light head  430  may be separate pieces that are welded or brazed to create the single thru-hull flanged threaded housing  427 . 
       FIG. 42  illustrates an undercut snap edge  480  and a chamfer  484  of the press fit ring  470 . The chamfer  484  provides a means to align the press fit ring  470  within the inside diameter of a stepped inside edge  482  that is part of the thru-hull flanged light head  430 . On assembly, the press fit ring  470  is forced axially inward until the undercut snap edge  480  is forced past the stepped inside edge  482 . Upon release the two square edges of the undercut snap edge  480  and the stepped inside edge  482  engage and lock, creating a strong snap fit that captures the press fit ring  470  in position. This design creates a very flat, low profile structure that is advantageous to the function of the remote thru-hull light head  418  illustrated in  FIG. 38 . The flexible rim  490  of the press fit ring  470  is illustrated in its unflexed (solid line) and flexed positions (dotted line). The press fit ring  470  is preferentially made of a hard or half hard copper alloy. The flexible rim  490  is flexed within its elastic limit and will maintain the clamping pressure indefinitely. The flexible rim  490  also allows for stack height tolerances of the multilayer stack  461 , as detailed in  FIG. 40 . The window  462  is positioned within a window centering ring  492  of the press fit ring  470 . The window  462  compresses and energizes the O-ring  472  on assembly. 
       FIG. 43  illustrates the construction and application of the double-sided metal core printed circuit board (DS-MCPCB)  498  in an embodiment of the present invention. The DSMCPCB  498  is seen to be comprised of a top copper circuit  500 , a top dielectric layer  502 , a metal core of copper or aluminum  504 , a bottom dielectric layer  506 , and a bottom copper clad  508 . The plurality of LEDs  128  are made with a plurality of electrically conductive pads  494  to permit the devices to be attached the top copper circuit  500  by means of a plurality of solder junctions  496  for electrical power and heat dissipation. As fully described in  FIG. 40 , the rear Phase Change Material (PCM) sheet  468  electrically isolates but thermally connects the DSMCPCB  498  to the thru-hull flanged light head  430 . 
     Turning again to  FIG. 43 , a means of providing multiple layers of electrical insulation between the top copper circuit  500  and the thru-hull flanged threaded housing  427  is illustrated. The top copper circuit  500  carries electrical current to the plurality of LEDs  128 . The DS-MCPCB  498  is centered within the thru-hull flanged threaded housing  427  by a DS-MCPCB centering ring  514 , a feature of the window support plate  464 , which is molded from a non-electrically conductive high strength plastic. The DS-MCPCB centering ring  514  captures the edge of the DS-MCPCB  498 , preventing it from contacting the interior wall of the thru-hull flanged light head  430 . The top copper circuit  500  and the bottom copper clad  508  are recessed from the edge of the DS-MCPCB  498  by a set-back  510 . The set-back  510  prevents the top copper circuit  500 , which carries electrical power, from contacting the interior face of the thru-hull flanged light head  430  by both the insulation properties of the plastic DS-MCPCB centering ring  514 , and an air gap caused by the set-back  510 . In addition, the set-back  510  increases the isolation distance between the edge of the top copper circuit  500 , the edge of the bottom copper clad  508 , and the edge of the metal core  504 . 
     Triple electrical isolation from the plurality of LEDs  128  to the back wall of the thru-hull flanged light head  430  is achieved by the top dielectric layer  502 , the bottom dielectric layer  506 , and the rear Phase Change Material (PCM) sheet  468 . The bottom copper clad  508  provides improved thermal connection to the thru-hull flanged light head  430 . Additionally, the groove  478  creates an air gap that provides electrical isolation of the DS-MCPCB  498  from the interior wall of the thru-hull flanged light head  430 . This double insulation increases the operational safety of the remote thru-hull light head  418  of  FIG. 38 . Additionally, the bottom copper clad  508  extends slightly into groove  478  to avoid pressing the edge of the bottom copper clad  508  through the bottom dielectric layer  506  and into the metal core  504 , creating a more reliable structure. 
     While various embodiments of the present multilayer LED light fixture have been described in detail, it will be apparent to those skilled in the art that the present invention can be embodied in various other forms not specifically described herein. The innovative structures described herein are applicable to a wide variety of submersible luminaries besides deep submersible LED light fixtures. Therefore, the protection afforded the present invention should only be limited in accordance with the following claims and their equivalents.