Abstract:
A device has a plurality of light emitting diodes (LEDs), heat conducting structure that includes a heat pipe and that carries heat from the region of the LEDs to a further location spaced therefrom, and heat dissipating structure that accepts heat from the heat conducting structure at the further location and that discharges the heat externally of the device. In a different embodiment, a device has a radiation generator, a thermal spreader that receives heat emitted by the radiation generator, heat conducting structure that carries heat from the thermal spreader to a location spaced therefrom, and heat dissipating structure that accepts heat at the location from the heat conducting structure and that discharges the heat externally of the device.

Description:
FIELD OF THE INVENTION 
     This invention relates in general to devices that emit electromagnetic radiation and, more particularly, to devices that use light emitting diodes or other semiconductor parts to produce the electromagnetic radiation. 
     BACKGROUND 
     Over the past century, a variety of different types of lightbulbs have been developed. The most common type of lightbulb is the incandescent bulb, in which electric current is passed through a metal filament disposed in a vacuum, causing the filament to glow and emit light. Another common type of lightbulb is the fluorescent light. 
     Recently, bulbs have been developed that produce illumination in a different manner, in particular through the use of light emitting diodes (LEDs). Pre-existing LED lightbulbs have been generally adequate for their intended purposes, but they have not been satisfactory in all respects. 
     As a first aspect of this, above a temperature of about 25° C., an LED operates less efficiently and produces less light than at lower temperatures. In particular, as the operating temperature progressively increases above 25° C., the light output of the LED progressively decreases. One approach to heat dissipation is to simply provide a heat sink. But although a heat sink can spread the heat, it does not remove the heat effectively from the vicinity of the LEDs, which reduces the brightness of the LEDs and shortens their operational lifetime. Consequently, efficient dissipation of the heat produced by the LEDs is desirable in an LED lightbulb. 
     A further consideration is that an LED lightbulb typically needs to contain some circuitry that will take standard household electrical power and convert it to a voltage and/or waveform that is suitable to drive one or more LEDs. Consequently, a relevant design consideration is how to package this circuitry within an LED lightbulb. 
     In this regard, it can be advantageous if the LED lightbulb has the size and shape of a standard lightbulb, including a standard base such as the type of base commonly known as a medium Edison base. However, due to spatial and thermal considerations, existing LED lightbulbs have not attempted to put the circuitry in the Edison base. Instead, the circuitry is placed at a different location, where it alters the size and/or shape of the bulb so that the size and/or shape differs from that of a standard lightbulb. For example, the bulb may have a special cylindrical section that is offset from the base and that contains the circuitry. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A better understanding of the present invention will be realized from the detailed description that follows, taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a diagrammatic elevational side view of an apparatus that is a lightbulb, and that embodies aspects of the present invention. 
         FIG. 2  is a diagrammatic exploded perspective view of the lightbulb of  FIG. 1 . 
         FIG. 3  is a diagrammatic sectional side view of the lightbulb of  FIG. 1 . 
         FIG. 4  is a diagrammatic elevational front view of a heat transfer assembly that is part of the lightbulb of  FIG. 1 . 
         FIG. 5  is a diagrammatic elevational side view of the heat transfer assembly of  FIG. 4 . 
         FIG. 6  is a diagrammatic bottom view of the heat transfer assembly of  FIG. 4 . 
         FIG. 7  is a diagrammatic top view of a heat spreader plate that is a component of the heat transfer assembly of  FIG. 4 . 
         FIG. 8  is a diagrammatic elevational side view that shows, in an enlarged scale, a power supply unit that is a component of the lightbulb of  FIG. 1 . 
         FIG. 9  is a diagrammatic top view of the power supply unit of  FIG. 8 . 
         FIG. 10  is a diagrammatic elevational side view of a flexible circuit carrier that is a component of the power supply unit of  FIG. 8 , before circuit components are mounted thereon, and before the carrier is bent to its operational configuration shape. 
         FIG. 11  is a schematic diagram of the circuitry of the power supply unit of  FIG. 8 . 
         FIG. 12  is a diagrammatic elevational side view of a lightbulb that embodies aspects of the invention, and that is an alternative embodiment of the lightbulb of  FIG. 1 . 
         FIG. 13  is a diagrammatic perspective exploded view of the lightbulb of  FIG. 12 . 
         FIG. 14  is a diagrammatic sectional side view of the lightbulb of  FIG. 12 . 
         FIG. 15  is a diagrammatic elevational front view of a heat transfer assembly that is a component of the lightbulb of  FIG. 12 . 
         FIG. 16  is a diagrammatic elevational side view of the heat transfer assembly of  FIG. 15 . 
         FIG. 17  is a diagrammatic bottom view of the heat transfer assembly of  FIG. 15 . 
         FIG. 18  is a diagrammatic exploded sectional side view of a lower portion of a further alternative embodiment of the lightbulb of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a diagrammatic elevational side view of an apparatus that is a lightbulb  10 , and that embodies aspects of the present invention. The lightbulb  10  includes a threaded base  11 , the exterior of which conforms to an industry standard known as an E26 or E27 type base, or more commonly a medium “Edison” base. Alternatively, however, the base could have any of a variety of other configurations, including but not limited to a candelabra, mogul or bayonet base. The base  11  serves as an electrical connector, and has two electrical contacts. In particular, the metal threads on the side of the base serve as a first contact, and a metal “button”  13  on the bottom of the base serves as a second contact. The two contacts are electrically separated by an insulating material  1 S. 
     Above the base  11  is a frustoconical cover  12 , and above the cover  12  is a heatsink  16 . A frustoconical bezel  17  is provided at the upper end of the heatsink  16 , and a circular lens  18  is coupled to the upper end of the bezel  17 . These parts are each discussed in more detail below. 
       FIG. 2  is a diagrammatic exploded perspective view of the lightbulb  10 , and  FIG. 3  is a diagrammatic sectional side view of the lightbulb  10 . With reference to the central portion of  FIG. 2 , the lightbulb  10  includes a heat transfer assembly  26 , of which the heatsink  16  is a component part. 
       FIG. 4  is a diagrammatic elevational front view of the heat transfer assembly  26 ,  FIG. 5  is a diagrammatic elevational side view of the heat transfer assembly  26 , and  FIG. 6  is a diagrammatic bottom view of the heat transfer assembly  26 . In addition to the heatsink  16 , the heat transfer assembly  26  includes a heat spreader plate  27 , and two heat pipes  28  and  29 . The heatsink  16  is made from a thermally conductive material. In the disclosed embodiment, the heatsink  16  is made from extruded aluminum. However, it could alternatively be made of any other suitable material that is thermally conductive. 
     With reference to  FIG. 6 , the heatsink  16  has a hub  36  with a central cylindrical opening  37  extending vertically therethrough. A plurality of fins extend radially outwardly from the hub  36 , and three of these fins are designated by reference numerals  41 ,  42  and  43 . The fins  42  and  43  are disposed on diametrically opposite sides of the hub  36 , and are wider than the other fins. The fins  42  and  43  each have a respective hole  38  or  39  extending vertically therethrough. The holes  38  and  39  each receive one end of a respective one of the heat pipes  28  and  29 , as discussed later. The fins  42  and  43  each have a further vertical hole extending a short distance thereinto from the bottom surface of the heatsink. The holes  46  and  47  are each internally threaded. 
     As best seen in  FIGS. 4 and 5 , the heatsink  16  has at its upper end, immediately above the radial fins, a circular plate-like portion  51 . A circumferentially extending annular groove  52  is provided in the radially outer edge of the plate-like portion  51 . 
     Still referring to  FIGS. 4 and 5 , the heat pipes  28  and  29  each have approximately the shape of a question mark. More specifically, each heat pipe has a horizontally-extending top end portion  56  or  57 , a curved central portion  58  or  59 , and a vertically-extending bottom end portion  61  or  62 . The bottom end portions  61  and  62  are each disposed in a respective one of the vertical openings  38  and  39  ( FIG. 6 ) through the heatsink  16 . As evident from  FIGS. 4 and 5 , the bottom end portions  61  and  62  each project a short distance below the bottom surface of the heatsink  16 . 
     The heat pipes  28  and  29  have an internal structure that allows them to operate properly in any orientation. Moreover, as discussed earlier, an LED operates less efficiently and produces less light at temperatures higher than about 25° C. More specifically, above 25° C., as the operating temperature of an LED progressively increases, the light output of the LED progressively decreases. Consequently, in the disclosed lightbulb  10 , it is a goal to keep the internal temperature below about 60° C. Accordingly, the heat pipes  28  and  29  need to be capable of operating at ambient temperatures below 60° C., and thus below the boiling point of water (100° C.). Heat pipes having a suitable internal structure and operation can be obtained commercially under the trade name Therma-Charge™ from Thermacore International, Inc. of Lancaster, Pa. Alternatively, however, the heat pipes  28  and  29  could have any other suitable internal structure. For example, and without limitation, the heat pipes  28  and  29  could include or be replaced with parts that include carbon nanotubes, fabric, micro spun metals, or some other suitable type of material. 
     The heat spreader plate  27  is made from a thermally conductive material that, in the disclosed embodiment, is cast aluminum. However, the heat spreader plate  27  could alternatively be made of any other suitable material that is thermally conductive. With reference to  FIGS. 5 and 6 , the underside of the heat spreader plate  27  has two spaced, parallel grooves  71  and  72  therein. The grooves  71  and  72  each receive the top end portion  56  or  57  of a respective one of the heating pipes  28  and  29 . The heat spreader plate  27  also has four notches  73  provided at circumferentially spaced locations along the lower outer edge thereof. 
       FIG. 7  is a diagrammatic top view of the heat spreader plate  27 . With reference to  FIGS. 2 and 7 , a shallow hexagonal recess  76  is provided in the top side of the heat spreader plate  27 . Three threaded holes  77 - 79  extend vertically through the spreader plate  27  at locations that are equally angularly spaced from each other. The holes  77 - 79  are offset laterally from each of the grooves  71  and  72 , and the upper ends of the holes  77 - 79  open into the shallow recess  76 . With reference to  FIGS. 6 and 7 , two further holes  82  and  83  also extend vertically through the spreader plate  27 . The holes  82  and  83  are spaced from each other, are offset angularly from the holes  77 - 79 , open into the shallow recess  76  at their upper ends, and are provided at locations that are offset from each of the grooves  71  and  72 . 
     With reference to  FIG. 2 , a hexagonal sheet  87  is disposed in the shallow hexagonal recess  76  of the spreader plate  27 . The sheet  87  has five holes therethrough, and each of these five holes is aligned with a respective one of the holes  77 - 79  and  82 - 83  in the plate  27 . The sheet  87  is made from a material that is thermally conductive and electrically insulating. In the disclosed embodiment, the sheet  87  is made from a material that is available commercially under the trade name HI-FLOW™ from The Bergquist Company of Chanhassen, Minn. However, the sheet  87  could alternatively be made of any other suitable material. 
     Still referring to  FIG. 2 , the lightbulb  10  includes a hexagonal circuit board  91  that is disposed in the shallow recess  76  of the spreader plate  27 , just above the sheet  87 . The circuit board  91  and the sheet  87  are secured in place on the spreader plate  27  by three screws  92 , which each extend through aligned holes in the circuit board  91  and the sheet  87 , and which each threadedly engage a respective one of the holes  77 - 79  in the spreader plate  27 . Since the sheet  87  is thermally conductive, it facilitates an efficient transfer of heat from the circuit board  91  to the spreader plate  27 . And since the sheet  87  is electrically insulating, it prevents the aluminum spreader plate  27  from creating electrical shorts between different portions of the circuitry on the circuit board  91 . 
     Seven radiation generators  93  are mounted on the circuit board  91 . In the disclosed embodiment, the radiation generators  93  are each a light emitting diode (LED) that emits visible light. However, the radiation generators  93  could alternatively be other types of devices, or could emit electromagnetic radiation at some other wavelength, such as infrared radiation or ultraviolet radiation. As another alternative, one subset of the illustrated radiation generators  93  could emit radiation at one wavelength, and another subset could emit radiation at a different wavelength. For example, one subset could emit visible light, and another subset could emit ultraviolet light. As still another alternative, some or all of the radiation generators  93  could be coated with a phosphor, so that they emit a multiplicity of wavelengths. 
       FIG. 2  depicts a spacer  96 . The spacer  96  is a circular ring that has four downwardly projecting tabs  97  at equally angularly spaced intervals. The tabs  97  are each resiliently flexible, and each have an inwardly projecting ridge  98  at the lower end thereof. The ridges  98  can each snap into a respective one of the notches  73  ( FIG. 4 ) provided in the spreader plate  27 , in order to releasably secure the spacer  96  to the spreader plate  27 . In the disclosed embodiment, the spacer  96  is made from a commercially available plastic of a known type. However, it could alternatively be made of any other suitable material. 
     The circular lens  18  is disposed above the spacer  96 . In the disclosed embodiment, the lens  18  is made from a clear plastic material, for example the same plastic material used to make the spacer  96 . However, the lens  18  could alternatively be made from any other suitable material. In  FIG. 2 , a broken line  101  encircles a center portion of the lens  18 . An opaque coating may optimally be provided on an annular portion of the inner surface of the lens  18  that lies outside the circle  101 , for example a white coating. 
     With reference to  FIG. 2 , the cover  12  has two spaced openings  106  and  107  that extend vertically therethrough, on opposite sides of a central vertical axis thereof. Two screws  108  and  109  each extend through a respective one of the openings  106  and  107 , and threadedly engage a respective one of the openings  46  and  47  ( FIG. 6 ) that are provided in the bottom of the heatsink  16 . The screws  108  and  109  thus fixedly secure the cover  12  to the underside of the heatsink  16 . 
     The cover  12  has a cylindrical upward projection  112  in the center thereof. The projection  112  extends into the central opening  37  ( FIG. 6 ) in the hub  36  of the heatsink  16 . A cylindrical vertical opening  113  is provided in the projection  112 , and extends completely through the cover  12 . The underside of the cover  12  has a short downward projection  114  of cylindrical shape. In the disclosed embodiment, the cover  12  is made from a plastic material, which may for example be the same plastic material used for the spacer  96  and the lens  18 . However, the cover  12  could alternatively be made from any other suitable material. 
     The base  11  is a cup-shaped part, with an upwardly-open cylindrical recess  121  therein. The upper end of the recess  121  receives the downward projection  114  on the cover  12 , and these parts are fixedly secured to each other in any suitable matter, for example by a suitable adhesive. The recess  121  in the base  11  contains a potting or overmolding material  122  of a known type, and a power supply unit  126  is embedded within the potting material  122 . The power supply unit  126  is discussed in more detail later. 
     In the disclosed embodiment, the bezel  17  is made from a plastic material, which may for example be the same plastic material used for the cover  12 , the spacer  96  and the lens  18 . However, the bezel  17  could alternatively be made of any other suitable material.  FIG. 2  shows an O-ring  131 , which is received in the annular groove  52  at the upper end of the heatsink  16 . The lower end of the bezel  17  has a radially inwardly facing annular surface portion  136  that sealingly engages the outer side of the O-ring  131 . At its upper end, the bezel  17  has an upwardly-facing annular surface portion  137  that engages the peripheral edge of the lens  18 . The annular surface portion  137  on the bezel  17  is fixedly secured to the peripheral edge of the lens  18 . In the disclosed embodiment, the bezel  17  and the lens  18  are each made of a plastic material, and are fixedly secured together by an ultrasonic weld that extends around the entire circumferential edge of the lens  18 . Alternatively, however, the bezel  17  and the lens  18  could be fixedly secured together in any other suitable manner. 
       FIG. 8  is a diagrammatic elevational side view showing the power supply unit  126  of  FIG. 2  in an enlarged scale. Two wires  141  and  142  each have one end electrically coupled to the power supply unit  126 , and each extend away from the underside of the unit  126  through the potting compound  122  ( FIG. 2 ). One of the two wires  141  and  142  has its outer end electrically coupled to the contact  13  ( FIG. 1 ) on the bottom of the base  11 , and the other wire has its outer end coupled to the threaded metal sidewall of the base  11 . 
     Two further wires  143  and  144  each have a lower end that is coupled to the power supply unit  126 , and each extend upwardly away from the power supply unit. In particular, the wires  143  and  144  each extend through the opening  113  in the cover  12 , and through the opening  37  in the heatsink  16 . Each of the wires  143  and  144  then extends through a respective one of the two openings  82  and  83  in the thermal spreader plate  27 , and through a respective one of the two corresponding openings in the sheet  87 . The upper ends of the wires  143  and  144  are each soldered to the circuit board  91 . 
       FIG. 9  is a diagrammatic top view of the power supply unit  126 . The power supply unit  126  includes a flexible circuit carrier  148 , which is a type of component that is often referred to in the art as a flexible circuit board, or a flex circuit. In the illustrated embodiment, the carrier  148  is made of a polyimide or mylar material, but could alternatively be made of any other suitable material.  FIG. 10  is a diagrammatic elevational side view of the flexible circuit carrier  148 , before circuit components are mounted thereon, and before it is bent to its operational configuration shape. It will be noted from  FIG. 10  that the flexible circuit carrier  148  is elongate, has a slot  151  near one end, and has a tab  152  at the other end. After circuit components have been mounted on the flexible circuit carrier  148 , the carrier  148  is bent to form approximately a loop or ring, as best seen in  FIG. 9 . The tab  152  is then inserted through the slot  151 , in order to help maintain the carrier in this configuration. It would alternatively be possible to omit the slot  151  and tab  152  from the carrier  148 , and to couple the adjacent ends of the carrier to each other in some other manner, for example, by placing a piece of double-sided tape between the adjacent ends of the carrier. As discussed above in association with  FIG. 2 , the power supply unit  126 , including the carrier  148 , is at least partially embedded in the potting material  122 , in order to prevent the power supply unit  126  from moving around within the base  11 , and to help maintain the flexible carrier  148  in its configuration as a loop or ring. Although the carrier  148  in the illustrated embodiment is bent to form a loop or ring, it would alternatively be possible for it to have any of a variety of other configurations, including but not limited to a folded configuration, a coiled configuration. As still another alternative, it could be a molded part with a ring-like cylindrical shape, or some other suitable shape. 
       FIG. 11  is a schematic diagram of the circuitry  156  of the power supply unit  126 , or in other words the circuitry that is mounted on the flexible circuit carrier  148 . Details of the configuration and operation of the circuitry  156  are not needed in order to understand of the present invention, and are therefore not described here in detail. Instead, the circuitry  156  is depicted in  FIG. 11  primarily for the purpose of completeness. With respect to how the circuitry  156  is depicted in  FIG. 11 , the wires  141  and  142  connect to the circuitry on the left side, and the wires  143  and  144  connect to the circuitry on the right side. 
     In operation, electrical power is received through the base  11 , and is carried through the wires  141  and  142  to the circuitry  156  of the power supply unit  126  ( FIG. 11 ). The carrier  148  and potting material  122  serve as electrical insulators that electrically isolate the circuitry from the metallic base  11 , while simultaneously serving as thermal conductors that carry heat from the circuitry to the metallic base  11 , so that the heat can be dissipated through the base and other parts of the bulb housing. The carrier  148  also provides signal and power paths for the circuitry. 
     The circuitry  156  produces an output signal that is supplied through the wires  143  and  144  to the circuit board  91 , where it is applied to the LEDs on the circuit board  91 . The LEDs emit radiation, for example in the form of visible light, and this radiation is transmitted out through the lens  18  to a region external to the lightbulb  10 . 
     In addition to emitting radiation, the LEDs  93  also give off heat. Since the sheet  87  is thermally conductive and electrically insulating, it efficiently transfers heat from the LEDs  93  and the circuit board  91  to the thermal spreader plate  27 , but without shorting out any of the circuitry on the circuit board  91 . The spreader plate  27  then transfers the heat to the upper end portions of the two heat pipes  28  and  29 . The heat then travels through the heat pipes  28  and  29  from the upper end portions thereof to the lower end portions thereof. The heat pipes  28  and  29  move heat away from the LEDs efficiently and without the aid of gravity, and thus without regard to the current orientation of the lightbulb. The heat is then transferred from the lower end portions of the heat pipes to the heatsink  16 , and after that the heatsink  16  dissipates the heat by dispersing it into the air or other ambient atmosphere surrounding the lightbulb  10 . 
       FIG. 12  is a diagrammatic elevational side view of a lightbulb  210  that embodies aspects of the invention, and that is an alternative embodiment of the lightbulb  10  of  FIG. 1 . Portions of the lightbulb  210  are similar or identical to corresponding portions of the lightbulb  10 . Accordingly, they are identified with the same or similar reference numerals, and are not described below in detail. Instead, the following discussion focuses primarily on differences between the lightbulb  210  of  FIG. 12  and the lightbulb  10  of  FIG. 1 . 
       FIG. 13  is a diagrammatic perspective exploded view of the lightbulb  210  of  FIG. 12 , and  FIG. 14  is a diagrammatic sectional side view of the lightbulb  210 . With reference to  FIG. 13 , the lightbulb  210  has a heat transfer assembly  226  which differs in some respects from the heat transfer assembly  26  of the lightbulb  10 . In this regard,  FIG. 15  is a diagrammatic elevational front view of the heat transfer assembly  226 ,  FIG. 16  is a diagrammatic elevational side view of the heat transfer assembly  226 , and  FIG. 17  is a diagrammatic bottom view of the heat transfer assembly  226 . 
     With reference to  FIG. 15 , the heat transfer assembly  226  has at the upper end thereof the plate-like portion  51  with the annular groove  52 . However, the portion of heatsink  216  located below the plate-like portion  51  is different from the heatsink  16  of  FIG. 1 . More specifically, with reference to  FIGS. 15 and 17 , the heatsink  216  includes two spaced, semi-cylindrical hub portions  235  and  236 . Each of the hub portions  235  and  236  has thereon a plurality of radially outwardly extending fins, some of which are identified by reference numerals  241 - 244 . Two spaced and parallel slots  238  and  239  extend vertically through the plate-like portion  51 . As best seen in the bottom view of  FIG. 17 , the slots  238  and  239  each have one edge that is aligned with the inner surface of a respective one of the semi-cylindrical hubs  235  and  236 . The heatsink  216  has two vertical threaded openings  246  and  247  that are each disposed between an adjacent pair of radially extending fins. In addition, the semi-cylindrical hub portions  235  and  236  each have a respective opening  248  or  249  extending vertically therethrough, and the openings  248  and  249  also extend vertically through the plate-like portion  51 . 
     With reference to  FIG. 15 , the heat transfer assembly  226  includes a single heat pipe  228 , which is different from the two heat pipes  28  and  29  in the embodiment of  FIGS. 1-11 . In particular, the heat pipe  228  has a cross-sectional shape that is thin and wide. The heat pipe  228  has a horizontally-extending central portion  256  at its upper end. On each side of the central portion  256  are curved portions  257  and  258  that lead to respective vertical end portions  261  and  262 . In particular, with reference to  FIGS. 15 and 17 , the end portions  261  and  262  each extend through a respective one of the vertical slots  238  and  239 , and each have a vertical surface on one side that engages the vertical surface on the inner side of a respective one of the semi-cylindrical hub portions  235  and  236 . As evident from  FIGS. 15 and 16 , the end portions  261  and  262  project a small distance below the bottom surface of the heatsink  216 . In the disclosed embodiment, the internal structure and operation of the heat pipe  228  is equivalent to that discussed above in association with the heat pipes  28  and  29 , and is therefore not described again in detail here. But any other suitable internal structure could alternatively be used. 
     With reference to  FIGS. 15 and 16 , the upper end of the heat transfer assembly  226  is defined by a heat spreader plate  227 , which has one significant difference from the heat spreader plate  27  in the embodiment of  FIGS. 1-11 . In particular, the heat spreader plate  227  has a single wide groove  271  in the underside thereof, rather than two spaced grooves. The central portion  256  of the heat pipe  228  is disposed in the groove  271 . 
     With reference  FIG. 13 , the lightbulb  210  includes a cover  212  that is slightly different from the cover  12  in the embodiment of  FIGS. 1-11 . In particular, the cover  212  has in the center thereof an upward projection of rectangular shape. As shown in  FIG. 14 , when the cover  212  is fixedly secured to the heatsink  216  by the screws  108  and  109 , the rectangular projection  274  is disposed between and engages the lower end portions  261  and  262  of the heat pipe  228 , in order to help hold them in position. With reference to  FIG. 13 , a vertical hole  276  extends through the cover  212  at a location between the projection  274  and the opening  106 . As shown in  FIG. 14 , the wires  143  and  144  extend upwardly from the power supply unit  126 , pass through the opening  276  in the cover  212  ( FIG. 13 ), and then extend through the vertical opening  249  in the heatsink  216 . 
     The operation of the lightbulb  210  is generally similar to that of the lightbulb  10 . In this regard, the LEDs  93  emit heat that is transferred through the circuit board  91  and the thermally conductive sheet  87  to the heat spreader plate  227 , and then to the central portion  256  of the heat pipe  228  ( FIGS. 14 and 15 ). The heat then travels downwardly through the curved portions  257  and  258  of the heat pipe  228 , to the lower end portions  261  and  262  thereof. From the lower end portions  261  and  262 , the heat is transferred to the heatsink  216 , and the heatsink  216  then dissipates the heat by dispersing it into the air or other ambient atmosphere surrounding the lightbulb  210 . 
       FIG. 18  is a diagrammatic exploded sectional side view of a lower portion  310  of an alternative embodiment of the lightbulb  10  of  FIGS. 1-11 . Parts that are equivalent to parts in the lightbulb  10  are identified in  FIG. 18  with the same reference numerals, and are not described again in detail. Instead, the following discussion will focus primarily on differences between the embodiment of  FIG. 18  and the embodiment of  FIGS. 1-11 . 
     The lower portion  310  includes a base  11  that is identical to the base  11  shown in  FIG. 1 . The base  11  in  FIG. 18  does not contain any of the potting compound  122  ( FIG. 2 ). Since the metal material of the base  11  is bent to form the external threads thereon, the inner surface of the base  11  has a similar shape and defines corresponding internal threads. 
     The lower portion  310  includes a cover  312  with a central recess  314  that opens downwardly, and that is internally threaded. The diameter of the recess  314  is less than the diameter of the recess  121  in the base  11 . The upper end of the recess  314  communicates with the lower end of the central opening  113  that extends vertically through the cover  312 . the top of the cover  312  has two spaced, upward projections located on opposite sides of the opening  113 , and one of these two projections is visible at  315 . 
     Between the base  11  and the cover  312  is a power supply unit  326 . The power supply unit  326  has a member or body  331  that is made from an electrically non-conductive material. In the disclosed embodiment, the member  331  is made from a relatively hard and durable plastic. However, it could alternatively be made from any other suitable material. A radially outwardly projecting annular flange  332  is provided approximately at the vertical center of the member  331 . The member  331  has a lower end portion  336  below the flange  332 , and an upper end portion  337  above the flange  332 . The diameter of the upper end portion  337  is less than the diameter of the lower end portion  336 . The lower end portion  336  and the upper end portion  337  are each externally threaded. Fixedly embedded and encapsulated within the material of the member  331  is a not-illustrated power supply unit that, in the disclosed embodiment, is effectively identical to the power supply unit shown at  126  in  FIG. 8 . In  FIG. 18 , it will be noted that the wires  143  and  144  extend outwardly through the top of the upper end portion  337 . 
     A first cylindrical electrode has one end fixedly secured in the lower end of the member  331 , and projects downwardly along the central vertical axis of the member  331 . A second cylindrical electrode  342  has one end fixedly secured in the annular flange  332 , and projects radially outwardly from the lower edge of the flange  332 . Within the member  331 , the wires  141  and  142  ( FIG. 8 ) of the power supply unit are each electrically coupled to a respective one of the electrodes  341  and  342  ( FIG. 18 ). 
     The threaded upper portion  337  of the member  331  engages the threaded recess  314  provided in the cover  312 . The threaded lower portion  336  engages the threaded recess  121  provided in the base  11 . The lower end of the electrode  341  engages the top of the button electrode  13 , so that they are in electrical contact. The electrode  342  slidably engages the top edge of the metal sidewall of the base  11 , so that they are in electrical contact. 
     Although selected embodiments have been illustrated and described in detail, it should be understood that a variety of substitutions and alterations are possible without departing from the spirit and scope of the present invention, as defined by the claims that follow. For example, the shapes and structural configurations of many of the parts described above can be varied without departing from the invention. Also, references in the foregoing discussion to various directions, such as up, down, in and out, are used in relation to how the disclosed embodiments happen to be oriented in the drawings, and are not intended to be limiting.