Abstract:
An LED bulb has a base, a shell connected to the base, and a thermally conductive liquid held within the shell. The LED bulb has a plurality of LEDs mounted on LED mounting surfaces disposed within the shell. The LED mounting surfaces face different radial directions, and the LED mounting surfaces are configured to facilitate a passive convective flow of the thermally conductive liquid within the LED bulb to transfer heat from the LEDs to the shell when the LED bulb is oriented in at least three different orientations. In a first orientation, the shell is disposed vertically above the base. In a second orientation, the shell is disposed on the same horizontal plane as the base. In a third orientation, the shell is disposed vertically below the base.

Description:
BACKGROUND 
     1. Field 
     The present disclosure relates generally to light emitting-diode (LED) bulbs, and more particularly, to the efficient transfer of heat generated by LEDs in a liquid-filled LED bulb. 
     2. Related Art 
     Traditionally, lighting has been generated using fluorescent and incandescent light bulbs. While both types of light bulbs have been reliably used, each suffers from certain drawbacks. For instance, incandescent bulbs tend to be inefficient, using only 2-3% of their power to produce light, while the remaining 97-98% of their power is lost as heat. Fluorescent bulbs, while more efficient than incandescent bulbs, do not produce the same warm light as that generated by incandescent bulbs. Additionally, there are health and environmental concerns regarding the mercury contained in fluorescent bulbs. 
     Thus, an alternative light source is desired. One such alternative is a bulb utilizing an LED. An LED comprises a semiconductor junction that emits light due to an electrical current flowing through the junction. Compared to a traditional incandescent bulb, an LED bulb is capable of producing more light using the same amount of power. Additionally, the operational life of an LED bulb is orders of magnitude longer than that of an incandescent bulb, for example, 10,000-100,000 hours as opposed to 1,000-2,000 hours. 
     While there are many advantages to using an LED bulb rather than an incandescent or fluorescent bulb, LEDs have a number of drawbacks that have prevented them from being as widely adopted as incandescent and fluorescent replacements. One drawback is that an LED, being a semiconductor, generally cannot be allowed to get hotter than approximately 120° C. As an example, A-type LED bulbs have been limited to very low power (i.e., less than approximately 8 W), producing insufficient illumination for incandescent or fluorescent replacements. 
     One potential solution to this problem is to use a large metallic heat sink attached to the LEDs and extending away from the bulb. However, this solution is undesirable because of the common perception that customers will not use a bulb that is shaped radically different from the traditionally shaped A-type form factor bulb. Additionally, the heat sink may make it difficult for the LED bulb to fit into pre-existing fixtures. 
     Another solution is to fill the bulb with a thermally conductive liquid to transfer heat from the LED to the shell of the bulb. The heat may then be transferred from the shell out into the air surrounding the bulb. However, current liquid-filled LED bulbs do not efficiently transfer heat from the LED to the liquid. Additionally, current liquid-filled LED bulbs do not allow the thermally conductive liquid to flow efficiently to transfer heat from the LED to the shell of the bulb. For example, in a conventional LED bulb having LEDs placed at the base of the bulb structure, the liquid heated by the LEDs rises to the top of the bulb and falls as it cools. However, the liquid does not flow efficiently because the shear force between the liquid rising up and the liquid falling down slows the convective flow of the liquid. Another drawback of current liquid-filled LED bulbs is that they do not efficiently dissipate heat when the bulb is not positioned in an upright orientation. When a conventional LED bulb is placed upside-down, for example, the heat-generating LEDs are flipped from the bottom of the bulb to the top of the bulb. This prevents an efficient convective flow within the bulb because the heated liquid remains at the top of the bulb near the LEDs. 
     Thus, an LED bulb capable of efficiently transferring heat away from the LEDs, while the LED bulb is in various orientations, is desired. 
     BRIEF SUMMARY 
     In one exemplary embodiment, an LED bulb has a base, a shell connected to the base, and a thermally conductive liquid held within the shell. The LED bulb has a plurality of LEDs mounted on LED mounting surfaces disposed within the shell. The LED mounting surfaces face different radial directions, and the LED mounting surfaces are configured to facilitate a passive convective flow of the thermally conductive liquid within the LED bulb to transfer heat from the LEDs to the shell when the LED bulb is oriented in at least three different orientations. In a first orientation, the shell is disposed vertically above the base. In a second orientation, the shell is disposed on the same horizontal plane as the base. In a third orientation, the shell is disposed vertically below the base. 
     In another exemplary embodiment, an LED bulb has a base, a shell connected to the base, and a thermally conducting liquid held within the shell. The LED bulb has a plurality of finger-shaped projections, disposed within the shell. The finger-shaped projections are separated by a plurality of channels formed between pairs of the plurality of finger-shaped projections for holding a plurality of LEDs. The plurality of finger-shaped projections and the plurality of channels are configured to facilitate a passive convective flow of the thermally conductive liquid through the plurality of channels, when the LED bulb is oriented in at least three different orientations. In a first orientation, the shell is disposed vertically above the base. In a second orientation, the shell is disposed on the same horizontal plane as the base. In a third orientation, the shell is disposed vertically below the base. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  illustrates an exemplary LED bulb. 
         FIG. 1B  illustrates a cross-sectional view of an exemplary LED bulb. 
         FIG. 2A  illustrates a cross-sectional view of an exemplary LED bulb in a first orientation. 
         FIG. 2B  illustrates a cross-sectional view of an exemplary LED bulb in a second orientation. 
         FIG. 2C  illustrates a cross-sectional view of an exemplary LED bulb in a third orientation. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is presented to enable a person of ordinary skill in the art to make and use the various embodiments. Descriptions of specific devices, techniques, and applications are provided only as examples. Various modifications to the examples described herein will be readily apparent to those of ordinary skill in the art, and the general principles defined herein may be applied to other examples and applications without departing from the spirit and scope of the various embodiments. Thus, the various embodiments are not intended to be limited to the examples described herein and shown, but are to be accorded the scope consistent with the claims. 
     Various embodiments are described below, relating to LED bulbs. As used herein, an “LED bulb” refers to any light-generating device (e.g., a lamp) in which at least one LED is used to generate the light. Thus, as used herein, an “LED bulb” does not include a light-generating device in which a filament is used to generate the light, such as a conventional incandescent light bulb. It should be recognized that the LED bulb may have various shapes in addition to the bulb-like A-type shape of a conventional incandescent light bulb. For example, the bulb may have a tubular shape, globe shape, or the like. The LED bulb of the present disclosure may further include any type of connector; for example, a screw-in base, a dual-prong connector, a standard two- or three-prong wall outlet plug, bayonet base, Edison Screw base, single pin base, multiple pin base, recessed base, flanged base, grooved base, side base, or the like. 
     As used herein, the term “liquid” refers to a substance capable of flowing. Also, the substance used as the thermally conductive liquid is a liquid or at the liquid state within, at least, the operating ambient temperature range of the bulb. An exemplary temperature range includes temperatures between −40° C. to +40° C. Also, as used herein, “passive convective flow” refers to the circulation of a liquid without the aid of a fan or other mechanical devices driving the flow of the thermally conductive liquid. 
       FIGS. 1A and 1B  illustrate a perspective view and a cross-sectional view, respectively, of exemplary LED bulb  100 . LED bulb  100  includes a base  112  and a shell  101  encasing the various components of LED bulb  100 . For convenience, all examples provided in the present disclosure describe and show LED bulb  100  being a standard A-type form factor bulb. However, as mentioned above, it should be appreciated that the present disclosure may be applied to LED bulbs having any shape, such as a tubular bulb, globe-shaped bulb, or the like. 
     Shell  101  may be made from any transparent or translucent material such as plastic, glass, polycarbonate, or the like. Shell  101  may include dispersion material spread throughout the shell to disperse light generated by LEDs  103 . The dispersion material prevents LED bulb  100  from appearing to have one or more point sources of light. 
     LED bulb  100  includes a plurality of LEDs  103  connected to LED mounts  107 , which are disposed within shell  101 . LED mounts  107  may be made of any thermally conductive material, such as aluminum, copper, brass, magnesium, zinc, or the like. Since LED mounts  107  are formed of a thermally conductive material, heat generated by LEDs  103  may be conductively transferred to LED mounts  107 . Thus, LED mounts  107  may act as heat-sinks for LEDs  103 . 
     In the present exemplary embodiment, thermal bed  105  is inserted between an LED  103  and an LED mount  107  to improve heat transfer between the two components. Thermal bed  105  may be made of any thermally conductive material, such as aluminum, copper, thermal paste, thermal adhesive, or the like. Thermal bed  105  may have a higher thermal conductivity than LED mount  107 . For example, LED mount  107  may be formed of aluminum and thermal bed  105  may be formed of copper. It should be recognized, however, that thermal bed  105  may be omitted, and LED mount  107  can be directly connected to LEDs  103 . 
     As depicted in  FIG. 1A , in the present exemplary embodiment, LED mounts  107  are finger-shaped projections with a channel  109  formed between pairs of LED mounts  107 . One advantage of such a configuration is increased heat dissipation due to the large surface-area-to-volume ratio of LED mounts  107 . It should be recognized that LED mounts  107  may have various shapes other than that depicted in  FIG. 1A  in order to be finger-shaped projections. For example, LED mounts  107  may be straight posts with a channel formed between pairs of posts. 
     As depicted in  FIG. 1B , in the present exemplary embodiment, top portions of LED mounts  107  may be angled or tapered at an angle  119 , which is measured relative to a vertical line when LED bulb  100  is in a vertical position. Exemplary angle  119  includes a range of −35° to 90°. Also, all the top portions of LED mounts  107  can be angled or tapered at the same angle, such as 9° or 15°. Alternatively, a combination of angles can be used, such as half at 18° and half at 30°, or half at 9° and half at 31°. As will be described in greater detail below with respect to  FIGS. 2A-2C , the angled top portions of LED mounts  107  may facilitate the passive convective flow of liquids within LED bulb  100 . 
     As also depicted in  FIG. 1B , in the present exemplary embodiment, LEDs  103  are connected to portions of LED mounts  107 , which serve as mounting surfaces for LEDs  103 , that are angled or tapered at an angle  121 , which is measured relative to a vertical line when LED bulb  100  is in a vertical position. Exemplary angle  121  includes a range of −35° to 90°. Also, the portions of LED mounts  107  to which LEDs  103  are connected can be angled or tapered at the same angle, such as 9° or 15°. Alternatively, a combination of angles can be used, such as half at 18° and half at 30°, or half at 9° and half at 31°. The particular angle or angles may be selected to create a desirable photometric distribution. 
     In the present embodiment, as depicted in  FIG. 1B , the angled or tapered portions on which LEDs  103  are connected (the mounting surfaces) are separate from the top portions of LED mounts  107 , which are also angled or tapered. It should be recognized, however, that LEDs  103  can be connected on the top portions of LED mounts  107 , which are angled or tapered. 
     In the present embodiment, LED bulb  100  is filled with thermally conductive liquid  111  for transferring heat generated by LEDs  103  to shell  101 . Thermally conductive liquid  111  may be any thermally conductive liquid, mineral oil, silicone oil, glycols (PAGs), fluorocarbons, or other material capable of flowing. It may be desirable to have the liquid chosen be a non-corrosive dielectric. Selecting such a liquid can reduce the likelihood that the liquid will cause electrical shorts and reduce damage done to the components of LED bulb  100 . 
     In the present embodiment, base  112  of LED bulb  100  includes a heat-spreader base  113 . Heat-spreader base  113  may be made of any thermally conductive material, such as aluminum, copper, brass, magnesium, zinc, or the like. Heat-spreader base  113  may be thermally coupled to one or more of shell  101 , LED mounts  107 , and thermally conductive liquid  111 . This allows some of the heat generated by LEDs  103  to be conducted to and dissipated by heat-spreader base  113 . 
     The size and shape of LED mounts  107  may affect the amount of heat conducted to conductive liquid  111  and heat-spreader base  113 . For example, when LED mounts  107  are formed to have a large surface-area-to-volume ratio, a large percentage of the total heat in LED mounts  107  may be conducted from LED mounts  107  to conductive liquid  111 , while a small percentage of the total heat in LED mounts  107  may be conducted from LED mounts  107  to heat-spreader base  113 . Where LED mounts  107  have a smaller surface-area-to-volume ratio, a small percentage of the total heat in LED mounts  107  may be conducted from LED mounts  107  to conductive liquid  111 , while a large percentage of the total heat in LED mounts  107  may be conducted from LED mounts  107  to heat-spreader base  113 . 
     In the present embodiment, base  112  of LED bulb  100  includes a connector base  115  for connecting the bulb to a lighting fixture. Connector base  115  may be a conventional light bulb base having threads  117  for insertion into a conventional light socket. However, it should be appreciated that connector base  115  may be any type of connector, such as a screw-in base, a dual-prong connector, a standard two- or three-prong wall outlet plug, bayonet base, Edison Screw base, single pin base, multiple pin base, recessed base, flanged base, grooved base, side base, or the like. 
       FIGS. 2A-2C  illustrate the passive convective flow of thermally conductive liquid  111  overlaid on a cross-sectional view of LED bulb  100 . In particular,  FIG. 2A  illustrates a cross-sectional view of the top portion of LED bulb  100  positioned in an upright vertical orientation in which shell  101  is disposed vertically above base  112 . The arrows indicate the direction of liquid flow during operation of LED bulb  100 . The liquid at the center of LED bulb  100  is shown rising towards the top of shell  101 . This is due to the heat generated by LEDs  103  and conductively transferred to thermally conductive liquid  111  via LEDs  103  and LED mounts  107 . As thermally conductive liquid  111  is heated, its density decreases relative to the surrounding liquid, thereby causing the heated liquid to rise to the top of shell  101 . 
     As described above with respect to  FIG. 1A , LED mounts  107  may be separated by channels  109 . Separating LED mounts  107  with channels  109  not only increases the surface-area-to-volume ratio of LED mounts  107 , but also facilitates an efficient passive convective flow of thermally conductive liquid  111  by allowing the flow of thermally conductive liquid  111  there between. For example, since the liquid along the surfaces of LED mounts  107  is heated faster than the surrounding liquid, an upward flow of thermally conductive liquid  111  is generated around LED mounts  107  and within channels  109 . In one example, channels  109  may be shaped to form vertical channels pointing towards the top of shell  101 . As a result, thermally conductive liquid  111  may be guided along the edges of channel  109  towards the top and center of shell  101 . 
     Once the heated, thermally conductive liquid  111  reaches the top portion of shell  101 , heat is conductively transferred to shell  101 , causing thermally conductive liquid  111  to cool. As thermally conductive liquid  111  cools, its density increases, thereby causing thermally conductive liquid  111  to fall. In one example, as illustrated by  FIGS. 1A-1B  and  FIGS. 2A-2C , the top portions of LED mounts  107  may be angled. The sloped surfaces of LED mounts  107  may direct the flow of the cooled, thermally conductive liquid  111  outwards and down the side surface of shell  101 . By doing so, thermally conductive liquid  111  remains in contact with shell  101  for a greater period of time, allowing more heat to be conductively transferred to shell  101 . In addition, since the downward flow of thermally conductive liquid  111  is concentrated along the surface of shell  101 , the shear force between the upward flowing liquid at the center of LED bulb  100  and the downward flowing liquid along the surface of shell  101  is reduced, thereby increasing the convective flow of thermally conductive liquid  111  within LED bulb  100 . 
     Once reaching the bottom of shell  101 , thermally conductive liquid  111  flows inwards toward LED mounts  107  and rises as heat generated by LEDs  103  heats up the liquid. The heated, thermally conductive liquid  111  is again guided through channels  109  as described above. The described convective cycle continuously repeats during operation of LED bulb  100  to cool LEDs  103 . It should be appreciated that the convective flow described above represents the general flow of liquid within shell  101 . One of ordinary skill in the art will recognize that some of thermally conductive liquid  111  may not reach the top and bottom of shell  101  before being cooled or heated sufficiently to cause the liquid to fall or rise. 
       FIG. 2B  illustrates two cross-sectional views of the top portion of LED bulb  100  positioned in a horizontal orientation in which shell  101  is disposed on the same plane as base  112 .  FIG. 2B  includes both a side view of LED bulb  100  and a front view looking into the top portion of LED bulb  100 . Similar to those in  FIG. 2A , the arrows indicate the direction of liquid flow during operation of LED bulb  100 . In the side view of  FIG. 2B , the liquid at the center of LED bulb  100  is shown rising towards the top (previously side) of shell  101 . This is due to the heat generated by LEDs  103  and conductively transferred to thermally conductive liquid  111  via LEDs  103  and LED mounts  107 . As thermally conductive liquid  111  is heated, its density decreases, thereby causing the heated liquid to rise to the top (previously side) of LED bulb  100 . 
     As described above with respect to  FIG. 1A , LED mounts  107  may be separated by channels  109 . Separating LED mounts  107  with channels  109  not only increases the surface-area-to-volume ratio of LED mounts  107 , but may also facilitate an efficient passive convective flow of thermally conductive liquid  111  by directing the flow of thermally conductive liquid  111 . For example, since the liquid along the surfaces of LED mounts  107  is heated faster than the surrounding liquid, a flow of thermally conductive liquid  111  is generated around LED mounts  107  and within channels  109 . In one example, as illustrated by the front view of  FIG. 2B , channels  109  may be shaped to point radially outward, from a top-down view. As indicated by the arrows representing the liquid flow, channels  109  may guide the heated, thermally conductive liquid  111  radially outwards along the edges of channels  109  towards shell  101 . This may generate an efficient convective flow of liquid as shown by  FIG. 2B . Additionally, channels  109  may further facilitate an efficient passive convective flow of thermally conductive liquid  111  by allowing thermally conductive liquid  111  to flow between LED mounts  107  rather than having to go around the entire mounting structure. 
     Once the heated, thermally conductive liquid  111  reaches the top (previously side) portion of shell  101 , heat is conductively transferred to shell  101 , causing thermally conductive liquid  111  to cool. As thermally conductive liquid  111  cools, its density increases, thereby causing thermally conductive liquid  111  to fall. In one example, as illustrated by  FIGS. 1A-1B  and  FIGS. 2A-2C , the top portion of LED mount  107  may be angled inwards towards the center of LED bulb  100 . As illustrated by the side view of  FIG. 2B , the sloped surface of LED mount  107  may direct the flow of the cooled, thermally conductive liquid  111  down the side (previously top) surface of shell  101 . By doing so, thermally conductive liquid  111  remains in contact with shell  101  for a greater period of time, allowing more heat to be conductively transferred to shell  101 . 
     As illustrated by the front view of  FIG. 2B , the top-view profile of LED mounts  107  may be similar to the shape of shell  101 . In the illustrated example, this shape is a circle. However, it should be appreciated that shell  101  and LED mounts  107  may be formed into any other desired shape. As depicted in  FIG. 2B , the LED mounting surfaces face different radial directions. As a result of LED mounts  107  conforming to the shape of shell  101 , the outer side surfaces of LED mounts  107  may guide the flow of the cooled, thermally conductive liquid  111  down the side surfaces of shell  101 . By doing so, thermally conductive liquid  111  remains in contact with shell  101  for a greater period of time, allowing more heat to be conductively transferred to shell  101 . Since the downward flow of thermally conductive liquid  111  is concentrated on the outer surface of shell  101 , the shear force between the upward flowing liquid at the center of LED bulb  100  and the downward flowing liquid along the surface of shell  101  is reduced, thereby increasing the convective flow of thermally conductive liquid  111  within LED bulb  100 . 
     Once reaching the bottom of shell  101 , thermally conductive liquid  111  flows towards LED mounts  107  and rises as heat generated by LEDs  103  heats up the liquid. The heated thermally conductive liquid  111  is again guided through channels  109  as described above. The described convective cycle continuously repeats during operation of LED bulb  100  to cool LEDs  103 . It should be appreciated that the convective flow described above represents the general flow of liquid within shell  101 . One of ordinary skill in the art will recognize that some of thermally conductive liquid  111  may not reach the top and bottom of shell  101  before being cooled or heated sufficiently to cause the liquid to fall or rise. 
       FIG. 2C  illustrates a cross-sectional view of the top portion of LED bulb  100  positioned in an upside-down vertical orientation in which shell  101  is disposed vertically below base  112 . The arrows indicate the direction of liquid flow during operation of LED bulb  100 . The liquid at the center of LED bulb  100  is shown rising towards the top (previously bottom) of shell  101 . This is due to the heat generated by LEDs  103  and conductively transferred to thermally conductive liquid  111  via LEDs  103  and LED mounts  107 . As thermally conductive liquid  111  is heated, its density decreases, thereby causing the heated liquid to rise to the top (previously bottom) of LED bulb  100 . 
     In one example, as described above with respect to  FIG. 1A , LED mounts  107  may be separated by channels  109 . Separating LED mounts  107  with channels  109  not only increases the surface-area-to-volume ratio of LED mounts  107 , but may also facilitate an efficient passive convective flow of thermally conductive liquid  111  by directing the flow of thermally conductive liquid  111 . For example, since the liquid along the surfaces of LED mounts  107  is heated faster than the surrounding liquid, an upward flow of thermally conductive liquid  111  is generated around LED mounts  107  and within channels  109 . In one example, channels  109  may be shaped to form vertical channels pointing towards the bottom (previously top) of shell  101 . As a result, thermally conductive liquid  111  may be guided along the vertical edges of channel  109  towards the top (previously bottom) of shell  101 . 
     Once the heated, thermally conductive liquid  111  reaches the top (previously bottom) portion of shell  101 , heat is conductively transferred to shell  101 , causing thermally conductive liquid  111  to cool. As thermally conductive liquid  111  cools, its density increases, thereby causing thermally conductive liquid  111  to fall. Since the heated, thermally conductive liquid  111  is forced up and outwards in an upside-down vertical orientation, the cooled, thermally conductive liquid  111  falls down the sides of shell  101 . This allows thermally conductive liquid  111  to remain in contact with shell  101  for a greater period of time, allowing more heat to be conductively transferred to shell  101 . In addition, since the downward flow of thermally conductive liquid  111  is concentrated along the surface of shell  101 , the shear force between the upward flowing liquid at the center of LED bulb  100  and the downward flowing liquid along the surface of shell  101  is reduced, thereby increasing the convective flow of thermally conductive liquid  111  within LED bulb  100 . 
     Once reaching the bottom (previously top) of shell  101 , thermally conductive liquid  111  may move towards the center of LED bulb  100  and rise as heat generated by LEDs  103  heats up the liquid. In one example, as illustrated by  FIGS. 1A-1B  and  FIGS. 2A-2C , the bottom (previously top) portions of LED mounts  107  may be angled inwards towards the center of LED bulb  100 . The sloped surface of LED mount  107  may direct the flow of the heated, thermally conductive liquid  111  outwards and upwards to the top (previously bottom) portion of shell  101 , as illustrated by  FIG. 2C . The heated, thermally conductive liquid  111  may be further guided through channels  109  towards the top (previously bottom) portion of shell  101 . The described convective cycle continuously repeats during operation of LED bulb  100  to cool LEDs  103 . It should be appreciated that the convective flow described above represents the general flow of liquid within shell  101 . One of ordinary skill in the art will recognize that some of thermally conductive liquid  111  may not reach the top and bottom of shell  101  before being cooled or heated sufficiently to cause the liquid to fall or rise. 
     In the examples described above with respect to  FIG. 2C , a passive convective flow of thermally conductive liquid  111  throughout shell  101  is improved by the inclusion of the central structure comprising LED mounts  107 . Providing LEDs  103  on LED mounts  107  near the center of shell  101  avoids the situation described above with respect to a conventional LED bulb where the heat-generating elements (LEDs) are positioned at the top of the bulb. 
     Although a feature may appear to be described in connection with a particular embodiment, one skilled in the art would recognize that various features of the described embodiments may be combined. Moreover, aspects described in connection with an embodiment may stand alone.