Abstract:
A deep submersible light may include a body defining a hollow interior and a solid state light source such as a plurality of high brightness LEDs mounted in the interior of the body. A transparent window may be mounted over the LEDs. The space between the transparent window and the LEDs may be filled with an optically transparent fluid, gel, or grease, which allows light to pass through and ambient water pressure to pass in, thus pressure compensating the LEDs by allowing them to see ambient water pressure. The transparent window may be mounted in the body for reciprocation in both a forward direction and a rearward direction to accommodate volumetric changes in the compensating fluid, gel, or grease caused by changes in temperature and water pressure as the manned or remotely piloted submarine travels from the sea surface to deep ocean depths.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of and claims priority to U.S. Utility patent application Ser. No. 12/185,007, filed Aug. 1, 2008 now U.S. Pat. No. 8,033,677 entitled DEEP SUBMERSIBLE LIGHT WITH PRESSURE COMPENSATION, the content of which is incorporated by reference herein in its entirety for all purposes. 
    
    
     FIELD 
     The present invention relates generally to lighting fixtures used on manned and remotely piloted submarines. More particularly, but not exclusively, the invention relates to lights of for use at great depths that are configured to be subjected to very high ambient water pressure. 
     BACKGROUND 
     Prior art underwater lighting fixtures have used gas discharge or incandescent filaments housed in thin glass envelopes as the light source. These glass envelopes collapse at depths as shallow as 100-ft, and cannot operate in contact with any liquids. To go any deeper, these glass envelopes must be protected from direct ocean pressure to prevent them from imploding. Typical designs use a glass dome or flat window, with a metal or heavy plastic housing. A pressure proof underwater electrical bulkhead connector brings electrical power across the interface. 
       FIG. 1  illustrates a Multi SeaLite® light fixture  102  commercially available from DeepSea Power &amp; Light of San Diego, Calif., assignee of the instant application. The light fixture  102  utilizes a halogen gas-filled glass envelope lamp that must be protected from direct exposure to high ocean pressure. More particularly, referring to  FIG. 2 , a halogen lamp  204  is included in the light fixture  102 . The halogen lamp  204  includes a thin inert gas-filled glass envelope that is only designed to survive atmospheric pressure differences found in typical applications from sea level to mountain tops. In order to survive at great ocean depths, e.g. 3,000 meters, the light fixture  102  includes a pressure protected housing is comprised of a glass hemisphere  202 , metal back shell  206 , cowl  212 , and bulkhead connector  210 . An internal reflector  214  redirects lights from the halogen lamp  204  forward through the glass hemisphere  202 . A mount  208  permits the light assembly to attach to a manned or remotely piloted submarine. See U.S. Pat. Nos. 4,683,523 and 4,996,635 both of Mark S. Olsson et al. for further details regarding the construction of light fixture  102 . 
     Recently, high brightness light emitting diodes (LEDs) have begun to be used in terrestrial markets as a reliable, efficient solid state light source capable of narrow or wide chromatic bandwidth.  FIG. 3A  illustrates an individual Cree XRE high brightness LED  302 . It comprises light-emitting die  306  ( FIG. 3B ) illustrated centrally situated above a ceramic base  312 , encapsulated with silicone gel  310 , contained by a metallic ring  308 , that supports a transparent dome-shaped lens element  304 . Electrical contacts  314  and  320  are placed on top of the ceramic base  312 , and a duplicate pair  316  and  322  are placed on the underside. A thermal-transfer pad  318  is also located in the center of the underside of the ceramic base to aid in drawing heat away from the die  306 . 
     It would be desirable to provide a deep submersible light that takes advantage of the new high brightness LEDs that have become commercially available. LEDs in such a light can accommodate very high ambient water pressures directly, but due to the electrical nature of the LEDs requires that they be isolated from seawater, which is electrically conductive. 
     SUMMARY 
     In accordance with one aspect, a deep submersible light includes a body defining a hollow interior and a solid state light source such as a plurality of high brightness LEDs mounted in the interior of the body. A transparent window may be mounted over the LEDs. The space between the transparent window and the LEDs may be filled with an optically transparent fluid, gel, or grease, which allows light to pass through and ambient water pressure to pass in, thus pressure compensating the LEDs by allowing them to see ambient water pressure. The transparent window may be mounted in the body for reciprocation in both a forward direction and a rearward direction to accommodate volumetric changes in the compensating fluid, gel, or grease caused by changes in temperature and water pressure as the manned or remotely piloted submarine travels from the sea surface to deep ocean depths. 
     Various additional aspects, details, and functions are further described below in conjunction with the appended Drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an isometric view of a prior art deep submersible light fixture that incorporates a halogen gas-filled glass envelope lamp that must be protected from direct exposure to high ocean pressure. 
         FIG. 2  is a sectional side view of the light fixture of  FIG. 1  taken along line  2 . 
         FIG. 3A  is an isometric view of a prior art high intensity LED. 
         FIG. 3B  is a sectional view of the LED of  FIG. 3A  taken along line  3 B- 3 B. 
         FIG. 3C  is an isometric view of a metal core printed circuit board (MCPCB) assembly populated with eighteen LEDs. 
         FIG. 3D  is a section view of the LED assembly of  FIG. 3C  taken along line  3 D- 3 D. 
         FIG. 3E  is an isometric view of a molded reflector. 
         FIG. 3F  is a section view of the molded reflector of  FIG. 3E  taken along line  3 F- 3 F. 
         FIG. 4  is an isometric view of a deep submersible light incorporating an embodiment of the present invention. 
         FIG. 5  is a section view of the light of  FIG. 4  taken along line  5 - 5 . 
         FIG. 6A  is an enlarged portion of  FIG. 5  illustrating details of the LED light head of the light of  FIG. 4 . 
         FIG. 6B  is an enlargement of the portion of  FIG. 6A  circled in phantom lines illustrating details of the high pressure puck sub-assembly of the light of  FIG. 4 . 
         FIGS. 7A ,  7 B, and  7 C are similar sectional views illustrating the range of motion of the pistoning front window of the light of  FIG. 4 . 
         FIG. 8  is an exploded view of the light of  FIG. 4  illustrating its thermal sensor. 
         FIG. 9  is a block diagram of the LED driver circuit of the light of  FIG. 4 . 
         FIGS. 10A and 10B  illustrate the manner in which the prior art light fixture of  FIG. 1  can be retrofitted with the LED light head that forms a portion of the light of  FIG. 4 . 
         FIG. 11  is a section view illustrating an alternate embodiment of the present invention in which the interior window centering O-ring is replaced by a spring engaging the perimeter of the window. 
         FIG. 12  is a section view illustrating an alternate embodiment of the present invention in which the interior window centering O-ring is replaced by six short springs located on the reflector. 
         FIG. 13  is an exploded view illustrating construction details of the embodiment of  FIG. 12 . 
         FIG. 14  is an isometric view illustrating the light head and retaining collar of the  FIG. 4  embodiment fitted to an alternate embodiment of the back housing and light mount. 
         FIG. 15  is a section view taken along line  15 - 15  of  FIG. 14 . 
         FIG. 16  is a section view rotated ninety degrees relative to  FIG. 15 . 
         FIG. 17  illustrates an alternate embodiment of the light head of the  FIG. 4  embodiment, mounted to the back housing illustrated in  FIG. 14 . 
         FIG. 18  is a section view taken along line  18 - 18  of  FIG. 17 . 
         FIG. 19  is a section view rotated ninety degrees relative to  FIG. 18 . 
         FIGS. 20A ,  20 B,  20 C and  20 D illustrate four alternate miniature reflector shapes for redirecting the edge light of the LEDs. 
         FIGS. 21A ,  21 B,  21 C and  21 D illustrate in diagrammatic fashion the resultant light patterns from the four alternate miniature reflector shapes embodied in  FIGS. 20A ,  20 B,  20 C and  20 D, respectively. 
         FIG. 22  is a section view of an alternate embodiment of a deep submersible light in accordance with the present invention illustrating the use of a piggyback circuit board to dim the light output of the LED driver board by external control. 
         FIG. 23  is an isometric view of an alternate embodiment of a deep submersible light in accordance with the present invention incorporating a cast soft elastomeric window and an in-line driver circuit. 
         FIG. 24  is a section view of the light of  FIG. 23  taken along line  24 - 24 . 
         FIG. 25  is an enlarged exploded section view of the light head assembly of the light of  FIG. 23 . 
         FIG. 26A  is an alternate embodiment similar to the light of  FIG. 23  in which the shape of the cast soft elastomeric window blends to match the adjacent hydrodynamic shape of an underwater control surface of a deep submersible vehicle. 
         FIG. 26B  is a section view of  FIG. 26A  taken along line  26 B- 26 B. 
         FIG. 27  is a partially exploded view of  FIG. 26   
         FIG. 28A  is an alternate embodiment similar to the light of  FIG. 26A . 
         FIG. 28B  is a section view of  FIG. 28A  taken along line  28 B- 28 B. 
         FIGS. 29A and 29B  illustrate an alternate embodiment of the LED/reflector sub-assembly for the light of  FIG. 4 . 
         FIG. 30  is a section view of the alternate light head embodiment for the light of  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     The entire disclosure of co-pending U.S. patent application Ser. No. 12/036,178 filed Feb. 22, 2008 of Mark S. Olsson et al. is hereby incorporated by reference. That application is entitled “LED Illumination System and Methods of Fabrication.” 
       FIGS. 3C ,  3 D,  3 E and  3 F illustrate structure that is incorporated into the deep submersible light of  FIGS. 4 and 5 . More particularly,  FIG. 3C  illustrates an array of eighteen Cree XRE high brightness LEDs  302  combined with a metal core printed circuit board (MCPCB)  332  in an assembly  330 , which may referred to as a light engine.  FIG. 3D  illustrates a section view of the assembly  330 .  FIG. 3E  illustrates a metalized molded plastic multiple-reflector plate  340 , which is designed such that the light-emitting parts of the LEDs  302  ( FIG. 3C ) protrude through the reflector openings when aligned for placement above the LED/MCPCB assembly  330  ( FIG. 3C ).  FIG. 3F  illustrates a section view of the multiple-reflector plate  340 . 
     Referring to  FIGS. 4 and 5 , in accordance with an embodiment of the present invention a deep submersible light  402  includes a cylindrical light head sub-assembly  502 , a hemispherical back shell  206 , a cylindrical cowl  504 , a bulkhead connector  210 , an electronic LED driver  506 , a miniature candelabra lamp screw base  508 , and a mount  208 . The volume inside the back shell  206  is protected from high exterior ambient water pressure, e.g. that which would be encountered at depths of 1,400 meters and greater. At 1,400 meters, the ambient water pressure is approximately 2,000 PSI. The light head subassembly  502  functions as a pressure resistant forward bulkhead, while the bulkhead connector  210  seals the rear of the back shell  206 . The screw base  508  adapts the screw socket plug of the bulkhead connector  210  to allow wires to pass to the electronic LED driver  506 . The interior volume of the light head sub-assembly  502  is filled with an optically transparent dielectric fluid, grease, or gel  510  in sufficient volume to allow for volumetric change due to a combination of the cold temperature and high pressure of the deepest ocean depths. Examples of suitable fluids include Dow Corning 200, Dow 705, Dow 710, and 3M FC-70. Optical Gels include Dow Optical Coupling Gel, OE-4000. Optical Greases that are suitable include Saint-Gobain BC-630. 
     Referring to  FIG. 6A  the LED light head sub-assembly  502  includes a generally cylindrical ribbed metal body  602 , a cylindrical pistoning transparent plastic window  604  extending across and sealing one end of the metal body  602 , a radially sealing O-ring  614 , two longitudinal centering O-rings  612  and  616 , and an upper spiral retaining ring  610  to hold the window  604  in position. The metal body  602  defines a hollow interior in which the LED/MCPCB sub-assembly  330  is mounted. The plastic window  604  is substantially rigid and may be made from Acrylic, polycarbonate, Trogamid, or other materials combining suitable qualities for use at deep underwater depths. Alternatively, the window  604  could be made of various suitable non-plastic transparent materials such as glass and sapphire. The window  604  is sealed using the single radial O-ring  614  seated in a groove cut into the metal body  602 . The window  604  is capable of moving axially relative to the longitudinal center line of the generally cylindrical light head sub-assembly  502  as the ambient water pressure varies during descent and ascent of a deep submersible vehicle carrying the light of  FIG. 4 . The forward and rearward edges of the window  604  are beveled where they engage the centering O-rings  612  and  616  to facilitate such longitudinal or reciprocal pistoning movement of the window  604 . The O-ring  614  provides a water-tight seal between the window  604  and the metal body  602 . This water-tight seal need not be provided by an O-ring, but could instead be provided by other means including a bellows or a flat clamp gasket. 
     The reciprocal transparent window  604  allows light generated by the LEDs  302  ( FIG. 3C ) to pass through the window outward and ambient water pressure to pass inward, thus pressure compensating the LEDs  302  ( FIG. 3C ). In fluid mechanics, “ambient pressure” refers to the pressure of the surrounding fluid medium, either gas or liquid, which comes into contact with an apparatus. As a submarine dives deeper into the sea, pressure increases due to the increased weight of water above it. This increase in pressure can cause materials to compress if exposed to that pressure. Systems can either be built strong enough to resist that pressure, and thus “pressure protected”, or allowed to equalize to that pressure, and thus “pressure compensated.” In the embodiment of this invention, the fluid, gel, or grease is the material that compresses according to pressure, and the reciprocal transparent window  604  is the mechanism that allows the volume to change as necessary. Since the fluid, gel, or grease is in direct contact with the LEDs  302  ( FIG. 3C ), the ambient pressure is thereby transmitted directly to the LEDs  302  ( FIG. 3C ). 
     Referring still to  FIG. 6A , the LED/MCPCB sub-assembly  330 , is thermally connected to a thick rear wall of the generally cylindrical metal body  602  using a Phase Change Material (PCM)  622 , such as Laird Technologies T-pcm 583, and restrained and clamped by a centering collar  620  and a wave spring  618 . By way of example, the metal body  602  may be made of 6061-T6 aluminum, with a Type III hard anodize conversion coating on its interior surface that provides an additional electrical isolation layer between the metal core board and the aluminum housing. The multiple-reflector plate  340  is held in position by a hex nut  624 . The construction of the high pressure puck sub-assembly  630  is described below in conjunction with  FIG. 6B . The interior open volume surrounding the LED/MCPCB sub-assembly  330  is filled with an optically clear, dielectric fluid, gel, or grease  510 . The two longitudinal centering O-rings  612  and  616  are useful in keeping the pistoning clear plastic window  604  axially aligned down the center of the cylindrical interior of the metal body  602 , eliminating the danger of tipping and wedging. A large thickness-to-bore diameter ratio would otherwise be needed. 
     Referring still to  FIG. 6A , a seal screw  606  extends through a bore in the center of the window  604  and allows for installation of the window  604  and subsequent fluid filling during final assembly. The screw  606  is screwed into a threaded segment of a through-bore formed in the center of the window  604 . An unthreaded outer extension of the through-bore in the window  604  is sealed beneath a cast-in-place, or injection molded and pressed in place, clear elastomeric plug  608 . Alternatively, a pair of seal screws (not illustrated) may be inserted through bores in opposite sides of the metal body  602 , to permit fluid insertion and air extraction. 
     Referring to  FIG. 6B , the high pressure puck sub-assembly  630  includes a high pressure puck  642  made of high strength thermosetting epoxy with molded insert electrical contacts  644 , installed in a matching bore machined or otherwise formed in the metal body  602 . The electrical contacts  644  are made with pins on one end and sockets on the other. The sockets are positioned to face the LED/MCPCB sub-assembly  330 . The puck  642  is sealed by use of a radial O-ring  638 , centered between two Teflon® back-up rings  636  and  640 . The rings  636  and  640  are squeezed into position by an upper O-ring  634 , which itself is held in position by a spiral retaining ring  632 . Electrical pins  652  pass from the LED/MCPCB sub-assembly  330 , through an insulating centering plate  654 , and into the electrical sockets in the puck  642 . The electrical pins  652  are held against the LED/MCPCB sub-assembly  330  and prevented from rotating by an insulating top cap  650 . This stack-up is sandwiched together by use of a through-bolt  648 , and a hex nut  646 . The multiple-reflector plate  340  is then added to this stack-up and held by a hex nut  624 . 
       FIGS. 7A ,  7 B and  7 C illustrates the range of motion of the pistoning transparent plastic window  604 .  FIG. 7A  illustrates the position of the window  604  at average sea level conditions (72 degrees F. at 14.70 psi.), centered in the bore or hollow interior of the light head sub-assembly  502  with a starting volume of dielectric fluid, grease, or gel  510 .  FIG. 7B . illustrates the position of the window  604  centered in the bore of the light head sub-assembly  502  after it has moved axially forward as heat generated by the illumination of the LEDs causes the dielectric fluid, grease, or gel  510  inside the light to expand.  FIG. 7C  illustrates the position of the window  604  centered in the bore of the light head sub-assembly  502  after it has moved axially rearward due to the influence of deep ocean ambient high water pressure and cold temperatures (40 degrees F. at 10,000 psi) on the dielectric fluid, grease, or gel  510 . 
       FIG. 8  is an exploded view of the deep submersible light  402  showing the thermal sensor  802  on the electronic LED driver  506  and thermal conductive pad  804  that thermally connects the thermal sensing component of the LED electronic driver  506  to the light head sub-assembly  502 . 
       FIG. 9  is a block diagram of the LED driver circuit illustrating the power flow from an AC/DC power source  902 , through input filter elements  904  (over voltage clamp, current limit, and inrush current limit), to an input voltage rectifier  906 , switch mode current regulator  908 , to an LED Light engine  910 . The LED driver circuit further includes circuit feedback and self-regulating control elements in the form of a temperature monitor  912  to test for overheating, a dimming interface  914  to reduce heat by lowering power, and an AC line monitor  916  to test for under voltage conditions. 
     An important aspect of the embodiment of  FIG. 4  is that its LED light head sub-assembly  502  can be retrofitted into the body  206  of existing prior art Multi SeaLite® lights  102  manufactured for many years by DeepSea Power &amp; Light, Inc., the assignee of the subject application, in place of the halogen light head sub-assembly, creating the LED Multi SeaLite®  402 . This retrofit capability is illustrated by the side-by-side views of  FIGS. 10A and 10B . 
       FIG. 11  illustrates an alternate embodiment  1102  of light head sub-assembly  502  ( FIG. 5 ) in which the interior window centering O-ring  616  ( FIG. 6 ) is replaced by a single coil or wave spring  1104  that engages the rear face of the window  604  and rests on an internal land or flange of the metal body  602 . 
       FIG. 12  illustrates an alternate embodiment  1202  of light head sub-assembly  502  ( FIG. 5 ) in which the interior window centering O-ring  616  ( FIG. 6 ) is replaced by six compression springs  1204  that press on the multiple-reflector plate  340 , and push against the rear side of the window  604 . The springs  1204  provide uniform force to keep the window  604  aligned axially within the bore or hollow interior of the metal body  602 . 
     The exploded view of  1202  in  FIG. 13  further illustrates the relationship of the window  604 , the six compression springs  1204 , the multiple-reflector plate  340 , a hex nut  646 , and the metal body  602 . In the event of maximum inward movement of the window  604 , the hex nut  646  fits within a recess in the backside of the window  604 , precluding mechanical interference. 
     Referring to  FIG. 14  in an alternate embodiment  1402  a back housing  1404  replaces the back shell  206  ( FIG. 2 ). The light is centered in a U-shaped light mount  1412  using a shoulder bolt  1408 , and secured with two cap screws  1410 .  FIG. 15  is a section view taken along line  15 - 15  of  FIG. 14 , and illustrates the increased volume of  1402  with the larger back housing  1404 , permitting more LED drive circuitry to be placed inside the same.  FIG. 16  is a section view of the alternate embodiment  1402  rotated ninety degrees about the axial centerline relative to  FIG. 15 .  FIG. 16  illustrates a fiber or rubber washer  1602  that functions as a friction element of the mounting mechanism, allowing the light mount  1412  to positively clamp to the back housing  1404 , with all three structures held in alignment by the shoulder bolt  1408 . 
       FIG. 17  illustrates an alternate embodiment  1702  in which the light head  1704  is mounted to the back housing  1404 . The embodiment  1702  uses the same light mount  1412  as the embodiment  1402  ( FIG. 14 ).  FIG. 18  is a section view of the embodiment  1702  of  FIG. 17  along the line  18 - 18 , illustrating the alternate embodiment  1702 , composed of the light head  1704  mounted to the back housing  1404 . An O-ring  1802  is used to keep sea water and debris out of the mating threads to prevent corrosion, fouling, and galling.  FIG. 19  is a section view of the alternate embodiment  1702  rotated ninety degrees about the axial centerline relative to  FIG. 18 , showing details of the same light mount  1412  as the embodiment  1402  ( FIG. 14 ). 
       FIG. 20A . illustrates an alternate miniature smooth parabolic spot pattern reflector  2000  for use with the multiple-reflector plate  340  ( FIG. 3 ). The resultant light pattern with substantially parallel rays is illustrated in  FIG. 21A . 
       FIG. 20B  illustrates an alternate miniature parabolic flood pattern reflector  2002  with circumferentially extending convex or concave stepped rings  2004  for use with the multiple-reflector plate  340  ( FIG. 3 ). The resultant light pattern with spread rays is illustrated in  FIG. 21B . 
       FIG. 20C  illustrates an alternate miniature parabolic flood pattern reflector  2006  with micropeened surface made up of a plurality of miniature convex or concave surfaces  2008  for use with the multiple-reflector plate  340  ( FIG. 3 ). The resultant light pattern with spread rays is illustrated in  FIG. 21C . 
       FIG. 20D  illustrates an alternate miniature isoradiant flood pattern reflector  2010  for use with the multiple-reflector plate  340  ( FIG. 3 ). A Cree four-die MCE LED  2012  is mounted so that its transparent dome-shaped lens element  2014  extends within the reflector cavity, and the four dies are at an optimal position with respect to the focal point of the reflector, either congruent with or offset from said focal point. The resultant even flood light pattern is illustrated in  FIG. 21D . 
     By way of example, the Cree four die MCE LED  2012  are illustrated in  FIGS. 21A ,  21 B,  21 C, and  21 D mounted in its operative position relative to the reflectors  2000 ,  2002 ,  2006 , and  2010  respectively, with resultant light patterns. 
       FIG. 22  illustrates the use of a piggyback circuit board  2202  with the alternate embodiment  1702  to dim the light output of the electronic LED driver  506  by external control. The modular piggyback circuit board  2202  may be selected based on the type of dimming interfaces encountered, including isolated and non-isolated control voltage (0-10 VDC), current loop (4-20 mA), pulse width modulated (PWM), and serial communications. 
       FIG. 23  illustrates an alternate embodiment  2302  of LED light head sub-assembly  502  ( FIG. 5 ) that incorporates a cast soft elastomeric transparent window  2306  for pressure compensation. The light illustrated in  FIG. 23  also incorporates an in-line LED driver assembly  2304 , wherein a circuit board is encapsulated within a cylindrical elastomeric housing providing similar pressure compensation. 
       FIG. 24  is a section view of  FIG. 23  along the lines  24 - 24 , showing the alternate embodiment of the light head  2302 , composed of a metal housing  2402  that encloses the LED/MCPCB sub-assembly  330  that is thermally connected to the metal housing  2402  using a phase change material (PCM)  622 . Machine screws  2506  (illustrated in  FIG. 25 ) hold the LED/MCPCB sub-assembly  330  to the metal housing  2402 . A center screw  2508  (shown in  FIG. 25 ) holds the multi-cavity reflector plate  340  over the LED/MCPCB sub-assembly  330 . An optically transparent, high dielectric, non-hygroscopic, soft durometer, castable elastomer  2306  fills all voids. The two-part castable elastomer  2306  preferably has a low viscosity and a one-hour minimum pot life during its working phase in order to fill every small crevice and void. After it cures, the compliance of this material to external pressure provides the means of compensation to the LEDs. One suitable commercially available material for the elastomer  2306  is NuSil LS-6143. The LED driver assembly  2304  is shown remote from the LED light head sub-assembly  2302 , separated by an appropriate length of underwater electrical cable  2408 , here shown at minimum length. The cable entry to the LED light head  2302  is sealed with a low cost compression fitting  2406 , such as a Heyco Liquid Tight Cordgrips (p/n M3210). The LED driver assembly  2304  is comprised of an LED driver electronics  2410  encapsulated by a thermally conductive, non-hygroscopic, soft durometer castable elastomer  2412 , which has no requirement for optical clarity. One suitable commercially available material for the elastomer  2412  is Dow Corning Thermally Conductive Elastomer SYLGARD Q3-6632. An additional length of underwater electrical cable  2414  connects the LED driver electronics  2410  to electrical power. The cables  2408  and  2414  are cast in place and sealed watertight within the body of  2304  by the castable elastomer  2412 , requiring no additional seal fitting such as  2406 . The principal advantage of the embodiment of  FIGS. 23 and 24  is that the light head is placed where light is needed, but minimum profile is required, such as the inside wrist of a vehicle manipulator (robotic arm) on a deep submersible vehicle. 
       FIG. 25  further illustrates the mounting relationship of the components of the LED light head assembly  2302  and the metal housing  2402 , LED/MCPCB sub-assembly  330 , phase change material (PCM)  622 , held by three machine screws  2506 , multiple-reflector plate  340 , held by machine screw  2508 , and the optically clear, high dielectric, non-hygroscopic, soft durometer, castable elastomer window  2306 . A rib extends around the perimeter to help seal and retain the window  2306 . The compression fitting  2406  is shown as part of the LED light head assembly  2302 . 
       FIG. 26A  illustrates an alternate embodiment  2602  of castable elastomer window  2306  ( FIG. 23 ). The shape of the cast soft elastomeric window  2604  is blended to match or conform to the adjacent hydrodynamic shape of a control surface  2610  of an underwater vehicle. The control surface  2610  could either be a fixed dive plane, active dive plane, or a rudder. The LED driver assembly  2304  and underwater electrical cable  2408  are shown recessed within the leading edge of the dive plane. 
       FIG. 26B  is a section view of  2602  in  FIG. 26A  taken along line  26 B- 26 B, showing the LED driver assembly  2304  remote from the LED light engine  2606 , separated by an appropriate length of underwater electrical cable  2408 , here shown at minimum length, and sealed through a low cost compression fitting  2406 . This allows placement of the driver electronics  2410  at any distance convenient to the submarine builder. The elastomeric window  2604  is shown as a functional mechanical part of the control surface  2610 . An appropriate length of underwater electrical cable  2414  connects the LED driver assembly  2304  to electrical power. 
       FIG. 27  illustrates a partially exploded view of the castable window  2604  and LED light engine  2606  removed from its recessed pocket in the control surface  2610 . Though shown separated, the castable window  2604  fully encapsulates the LED light engine  2606 . LED driver assembly  2304  with underwater electrical cables  2408  and  2414 , is shown removed from the recess inside the leading edge of the control surface  2610 , and separated from the compression fitting  2406 . 
       FIG. 28A  is an alternate embodiment similar to  2602  of  FIG. 26A , showing the cast soft elastomeric window  2604  blended to match or conform to the adjacent hydrodynamic shape of a control surface  2610  of an underwater vehicle. The LED driver assembly  2304  and underwater electrical cable  2414  are shown extending from the recess pocket within the leading edge of the control surface  2610 . An appropriate length of underwater electrical cable  2414  connects the LED driver assembly  2304  to electrical power. 
       FIG. 28B  is a section view of  FIG. 28A  taken along line  28 B- 28 B, showing the LED driver assembly  2304  remote from the LED light engine  2606 , separated by an appropriate length of underwater electrical cable  2408 , here shown at minimum length, bonded to an underwater in-line connector pair  2608  rated for depth and power. An in-line underwater electrical connector  2608  allows simple assembly of the LED driver assembly  2304  and LED light engine  2606 , and allows placement of the LED driver assembly  2304  at any distance convenient to the submarine builder. The elastomeric window  2604  is shown as a functional mechanical part of the control surface  2610 . An appropriate length of underwater electrical cable  2414  connects the LED driver assembly  2304  to electrical power. 
       FIG. 29A  illustrates the assembly of an LED light engine subassembly  2902  using LED/MCPCB sub-assembly  330 , electrical pins  652  ( FIG. 6 ), insulating centering plate  654  ( FIG. 6 ), insulating top cap  650  ( FIG. 6 ), through-bolt  648  ( FIG. 6 ), and a hex nut  646  ( FIG. 6 ). The multiple-reflector plate  340  is then added to this stack-up and held by a hex nut  624  ( FIG. 6 ). This entire sub-assembly is then encapsulated in an optically clear, high dielectric, non-hygroscopic, soft durometer castable elastomer  2306 , which fills all voids between the front of LED light engine  330 , and the entirety of the multiple-reflector plate  340 . The back of the LED light engine  330  is left bare, as is its edge, and a small land area on the front for final assembly in the same manner illustrated in  FIG. 6A . The elastomer  2306  provides pressure compensation, reduces the volume of compensating dielectric fluid, grease, or gel  510  ( FIG. 5 ) required, and eliminates any undesirable chemical affects of the compensating dielectric fluid, grease, or gel  510  ( FIG. 5 ) on the LED dies  306  ( FIG. 3 ). 
       FIG. 29B  is a section view of the light engine subassembly  2902  of  FIG. 29A  taken along line  29 B- 29 B. This subassembly is shown in a full light assembly in  FIG. 30 . 
       FIG. 30  illustrates an alternate embodiment of the invention  3002  that incorporates the cast light engine sub-assembly  2902  as part of a hybrid pressure compensation technique. The cast light engine sub-assembly  2902  is constrained in the same manner illustrated in  FIG. 6A . A pressure compensating dielectric fluid, grease, or gel  510  fills the remaining void between the cast light engine sub-assembly  2902 , and the pistoning clear plastic window  604 . 
     While several embodiments of deep submersible lights and light head assemblies have been described and illustrated in detail, it should be apparent to those skilled in the art that our invention can be modified in arrangement and detail. For example, other solid state sources of illumination could be used besides LEDs. The relatively thick, substantially rigid window  604  could be replaced with a thinner flexible, but otherwise hard window, as taught in the Ser. No. 12/036,178 application incorporated by reference above. Therefore, the protection afforded our invention should only be limited in accordance with the scope of the following claims.