Abstract:
An electrical device, preferably a light bulb having an electrical base, comprises a container having a sealed interior, an electrical component contained within the sealed interior; a liquid filling the sealed interior; and a pressure relief member. The pressure relief member has an interior tubular passage. The tubular passage has an inlet which is in fluid communication with the liquid. The tubular passage is filled with liquid from the inlet partially toward an outer end of the passage. The remainder of the passage is filled with gas. The pressure relief member provides relief from increases of pressure caused by heating the liquid. Preferably, a heat sink is provided for the electrical component and contacts the liquid coolant. The pressure relief member may be located either in the sealed interior or outside of the container.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims priority on U.S. provisional application No. 61/765,287, filed on Feb. 15, 2013. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to a lighting device and more particularly to an LED lighting device in which one or more LEDs are contained within a rigid, sealed container containing a liquid coolant. The container may be an Edison-type light bulb. 
         [0003]    For many LED applications, it is important to remove heat generated by the LED. For such reason, LEDs are typically mounted on a metal substrate and the substrate is mounted on a heat sink with cooling fins. A fan can then be used to blow air over the heat sink fins to cool the LED chip. 
         [0004]    However, due to the relatively large distance between the LED chip and the heat sink fins, the cooling efficiency is usually low. As a result, the LED junction operates at higher temperatures, which reduces the light output and lifetime of the LED chip. 
         [0005]    My prior U.S. patent application Ser. No. 13/092,112 discloses an LED lamp which includes a sealed housing containing an LED. The housing is filled with a liquid coolant which is in contact with the LED and the heat sink on which the LED package is mounted. When the lamp is turned on, the liquid coolant cools the LED element, thereby providing higher light output and increased lifetime of the LED element. 
         [0006]    As the LED continues to operate, the liquid heats up and expands in volume. In the case of a rigid housing such as a glass light bulb, such expansion could cause the bulb to crack or break. To compensate, my prior invention employs an enclosure containing compressible material, which is positioned within the bulb. The enclosure containing the compressible material compresses in response to expansion of the liquid coolant as the liquid absorbs heat from the LED element. 
       SUMMARY OF THE INVENTION 
       [0007]    A system, preferably a light bulb having an electrical base, comprises a container having a sealed interior, an electrical component contained within the sealed interior; a liquid coolant filling the sealed interior; and a pressure relief member. The pressure relief member has an interior tubular passage. The tubular passage has an inlet which is in fluid communication with the liquid coolant. The tubular passage is partially filled with liquid which extends from the inlet partially toward an outer end of the passage. The remainder of the passage is filled with gas when the end is enclosed. When the end is open to the air, the length of the passage is sufficient long such that the liquid will not escape at the highest operating temperature. 
         [0008]    The tubular passage is preferably engineered such that the liquid inside will form a meniscus at the liquid/air interface with sufficient adhesion that the interface will remain intact when the system is subjected to normal shock and vibration, which can occur, for example, during normal operation and shipment. 
         [0009]    The pressure relief member provides relief from increases of pressure caused by heating the liquid. Preferably, a heat sink is provided for the electrical component and contacts the liquid coolant. 
         [0010]    The pressure relief member may be located either in the sealed interior or outside of the container. In one embodiment, the pressure relief member is a expansion tube whose outer end is closed. In another embodiment, the expansion tube&#39;s outer end is open. The open end may be connected to an expansion chamber or left open without any connections. Without having the outer end closed or connected to an expansion chamber, the pressure inside the light bulb will remain at the outside atmospheric pressure. 
         [0011]    In an alternate embodiment, a phosphor material, which may be a powder phosphor or ceramic phosphor, is secured to the heat sink  5  in place of an LED. An external laser is provided, whose output is directed at the phosphor material. 
         [0012]    In a preferred embodiment, the light bulb is an Edison-type light bulb with a bulb portion and a neck. The expansion tube may be coiled around the neck. In yet another embodiment, the expansion tube may be a coil located inside the sealed bulb. 
         [0013]    In yet another embodiment, the pressure relief member is a frusto-conical member having a core and an outer shell. A helical groove is formed on the outside surface of the core and, when covered by the outer shell, forms the tubular passage for containing air and liquid. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is a side view of a first embodiment of a liquid-cooled LED light bulb according to the invention; 
           [0015]      FIG. 2  is a side view of a second embodiment of a liquid-cooled LED light bulb according to the invention; 
           [0016]      FIG. 3  is an exploded side view of an alternative embodiment of a pressure relief member for use with the liquid-cooled LED light bulb according to the invention; 
           [0017]      FIG. 4  is a side view of a third embodiment of a liquid-cooled LED light bulb according to the invention; 
           [0018]      FIG. 5  is a side view of a fourth embodiment of a liquid-cooled LED light bulb according to the invention; 
           [0019]      FIG. 6  is a side view of a fifth embodiment of a liquid-cooled light bulb; and 
           [0020]      FIGS. 7  ( a ) and ( b ) are side and front views of a sixth embodiment of a liquid-cooled light bulb. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0021]      FIG. 1  shows an LED lighting device according to one embodiment of the present invention. The LED lighting device includes a container  12  with a sealed interior, for example an Edison-type light bulb  12   a  having a screw-threaded base  17  for use in a standard electrical socket. Other type of sockets or other connectors may be used for other applications. The sealed bulb  12   a  can be made of plastic, glass or metal. The interior of the sealed container  12  includes an LED package  14 , a heat sink  5  in thermal communication with the LED  10 , and liquid coolant  9 . 
         [0022]    The LED package  14  includes at least one LED  10  which is typically an LED element having an emitting area that emits light and a substrate  13  on which the chip is mounted. The heat sink  5  is attached to the substrate  13  to carry heat away from the LED chip  10 . Such LED packages, for example, are available from Luminus Devices, Inc. of Billerica, Mass. 
         [0023]    Liquid coolant  9  fills the container  12  and either contacts the LED  10  or is in indirect contact therewith, so that any heat generated by the LED will be transferred by conduction into the liquid coolant. Preferably, the liquid coolant  9  has low thermal expansion and high heat conductivity, is chemically inert, and includes electrically insulating characteristics. One such liquid coolant is a perfluorinated liquid coolant called Fluorinert© available from 3M Company of St. Paul, Minn. Other lower cost liquid coolants can be mineral oil, paraffin, silicone oil, or the like. 
         [0024]    The LED lamp further includes a driver circuit  3  for driving the LED  10 . The LED package  14  can be a single chip  10  or multiple chips of white color, single color, or multiple colors. The LED elements  10  are preferably arranged in the same plane and closely positioned to minimize any space between any two emitting areas of the LED elements. The LED elements  10  can emit light of a single color such as red, green and blue or emit white light. The emission angle is typically 180 degrees or less. The LED can also be a DC LED, or an AC LED. 
         [0025]    An LED mount  28  is attached to the base  17  and provides a rigid support structure for attaching the control circuit  3 , heat sink  5 , substrate  13  and LED  10 . 
         [0026]    Although  FIG. 1  shows a light bulb having an Edison type threaded base connector, any other LED lighting devices such as one having MR-16 type base are also suitable for use with the present invention. 
         [0027]    The LED  10  generates heat when emitting light. The heat in turn heats the liquid coolant  9  which expands in volume. Since the liquid coolant  9  is sealed inside the bulb  12   a,  a relief member is provided to compensate for the expansion of the liquid coolant. As shown in  FIG. 1 , in this embodiment of the invention the relief member is an expansion tube  30  having a first end  32  which is in liquid communication with the interior of the bulb  12   a.  The tube  30  is preferably engineered such that the liquid inside the tube will form a meniscus at the liquid/air interface with sufficient adhesion that the interface will remain intact when the system is subjected to normal shock and vibration, such as can occur during shipping. 
         [0028]    The opposite end  34  of the expansion tube is closed. The expansion tube  30  is partly filled with liquid  36  and partly filled with air  38  or another gas. The expansion tube  30  may be made of any suitable material including glass, metal, or plastic, and may be formed with an elbow such that the tube  30  extends an initial distance perpendicular to the longitudinal axis of the bulb  12   a.  At the elbow  31 , the tube bends approximately 90 degrees to extend in a direction generally parallel to the axis. 
         [0029]    When the LED is turned on, the liquid  9  is heated up and expands. Excess volume of liquid coolant  9  will flow into the expansion tube  30  to compress the air  38  to control the increase in pressure and prevent the bulb from breaking. Alternately, the air  38  can be partially evacuated in a manner similar to that used in thermometers. As the light bulb is turned on and off, cycling through heated and cooled states, liquid will flow from the bulb  12   a  alternately into and back from the expansion tube  30 . The interior volume of the expansion tube  30  is determined by the volume of the bulb, and thereby the amount of liquid coolant  9  present. 
         [0030]    The improved heat sink provided by the liquid coolant  9  results in higher output from the LED  10  using the same power. It also allows the LED  10  to operate at a higher wattage, resulting in a brighter output. 
         [0031]    When used, the light bulb may have various orientations, depending upon the fixture in which it is used. Therefore, it is important that the meniscus  40  remain above the lower end  32  of the expansion tube  30  so that some liquid  36  always be present inside the expansion tube  30  and such that air inside the expansion tube  30  remains within the expansion tube  30 . In order to do so, the diameter of the expansion tube interior is made small enough that air  38  will not enter the light bulb  12   a  regardless of the orientation of the bulb when used. 
         [0032]    In a variation of the above embodiment, the outer end  34  of the expansion tube  30  may be connected to an expansion chamber  42  (shown schematically in broken lines). Also, for further cooling, a plurality of cooling fins  50  may be provided around the neck portion  60 . The fins  50  lie in planes perpendicular to the axis of the light bulb  12  and project radially from the neck portion  60  in all directions (except where the expansion tube  30  interferes). The fins  50  may be mounted on an annular collar  52  which surrounds the neck portion  60 . 
         [0033]      FIG. 2  shows a second embodiment in which the relief member is an expansion tube  30   a.  In  FIG. 2 , the expansion tube  30   a  is located on the outside of the neck portion  50  of the light bulb and wraps spirally around the neck portion  60 . One end  32   a  of the expansion tube  30   a  communicates with the interior of the light bulb  12   a.  The opposite end  34   a  of the expansion tube  30   a  is closed. 
         [0034]      FIG. 3  shows an alternative embodiment of a pressure relief member  30 ′ which may be used in place of the expansion tubes  30 ,  30   a  shown in connection with  FIGS. 1-2 . The pressure relief member  30 ′ contains an inner, frusto-conical core  60  and an outer, hollow, frustoconical shell  62 . The core  60  contains, on its outer surface, a helical groove  64  having an inlet  66  and an outlet  60  located on opposed faces  70 ,  72  which lie in planes perpendicular to the center axis  74  of the pressure relief member  30 ′. Thus, when the core  60  is inserted into the shell  62 , the resulting member  30 ′ will include a helical passage  64  whose inlet  66  and outer end  68  are open. If desired, however, the outer end  68  may be closed, as in  FIGS. 1 and 2 . Again, the helical passage  64  preferably has a diameter such that the liquid inside the passage will form a meniscus at the liquid/air interface with sufficient adhesion that the interface will remain intact when the system is subjected to normal shock and vibration, e.g., during shipment. 
         [0035]    In use, the inlet  66  of the pressure relief member  30 ′ is placed in fluid communication with the liquid  9  in the interior of the bulb  12   a  by any suitable means. Alternatively, the pressure relief member  30 ′ may be disposed within the bulb  12   a,  in a manner similar to that to be described in connection with  FIG. 5 . In such case, the outer end  68  would be closed. 
         [0036]    In the embodiment of  FIG. 4 , the expansion tube  30   c,  which is in fluid communication with the liquid  9 , has an outer end  34   c  which is open to the atmosphere. Thus, when the fluid  9  expands, there is no pressurization of the air inside the expansion tube  30   c  or the fluid  9 . 
         [0037]    The inside diameter “id” of the expansion tube  30   c  is kept small enough such that surface tension will keep the meniscus  40  intact such that air will not travel across the meniscus  40  and reach the liquid  9 . The length of the expansion tube  30   c  is sufficient such that liquid  36  inside the expansion tube  30   c  will not overflow beyond the open end  34   c  at steady state conditions at the highest-designed operating temperature. 
         [0038]      FIG. 5  shows an embodiment of an LED light bulb with LEDs  10  mounted on a heat sink  5 . An expansion tube  34   d  is coiled around the stem  28  (and may be supported by the stem  28 ) in the interior of the bulb  12   a.  The tube  34   d  has an open, lower end  32   d  and a closed upper end  34   d.  The interior of the expansion tube  34   d  is partly filled with air, and the interior diameter of the expansion tube  34   d  is small enough so that air remains inside the tube  34   d  and does not escape into the liquid  9  regardless of the orientation of the bulb. 
         [0039]      FIG. 6  shows another embodiment of the invention. In  FIG. 6 , a housing  110 , with an output aperture  112 , contains a light bulb  120  and a laser  154 . The light bulb  120  contains a light source  130 , which is mounted on a heat sink  5 , The light source  130  is a phosphor material, such as a powder phosphor or a ceramic phosphor in the form of a plate. The light bulb  120  of FIG.  6  is illuminated by the laser  154 , whose output beam  155  is directed onto the phosphor plate  130 . The bulb  130  also includes a mounting base  132  in order to be mounted on a fixture (not shown). 
         [0040]    As the light emission efficiency of the phosphor is temperature dependent, and as the phosphor can be damaged by exposure to high temperature, the liquid cooling of the phosphor provides a light source which is more efficient and has a longer life. The light emitted by the phosphor can be used for general lighting, or coupled into fiber optics or projection engines. The phosphor can be selected to emit a desired color depending on the intended application and the laser can be blue or other colors depending on the phosphor used. 
         [0041]      FIGS. 7   a  and  7   b  show another embodiment of the liquid cooled light bulb with the ceramic phosphor (in general, phosphor powder deposited on top of the heat sink by appropriate means) excited by an external laser beam. In this configuration, the ceramic phosphor  130  is mounted on top of a heat sink  143  having fins  143   a  and covered with a flat window  140  which is spaced from the phosphor by a spacer  142  such that the liquid will be covering the ceramic phosphor such that the phosphor can be cooled effectively. The expansion tube  144 , filled with liquid and air separated by a meniscus  146  is can be made part of the heat sink as shown such that the unit is self contained and if flat. Such configuration will be especially advantageous for use with projection engines. 
         [0042]    The foregoing description represents the preferred embodiments of the invention. Variations and modifications will be apparent to persons skilled in the art, without departing from the inventive concepts disclosed. For example, the bulb  12   a  can be made of glass or any other suitable transparent material such as plastic. The LED or LEDs may be blue or white or a combination of colors. In the case of using blue LEDs, the bulb may be coated with fluorescent materials of various colors producing colored light or white light. 
         [0043]    The expansion tube can be made of metal, plastic, or other materials that can be coiled tightly inside a chamber. If desired, the expansion tube can be made of metal and coiled such that it can function as a heat sink. 
         [0044]    The socket  17  can be a standard Edison bulb socket with screw threads, can be prongs like standard MR-16 bulbs, or can be other types of electrical connectors. 
         [0045]    Although the exemplary embodiments disclosed in applications for light bulbs, the same inventive features can be applied to provide an improved heat sink of electronic modules with electronic components that generate heat but do not emit light. All such modifications and variations are intended to be within the scope of the invention, as set forth in the following claims.