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.
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.
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.
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.
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In the present embodiment, as depicted in
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.
As described above with respect to
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
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.
As described above with respect to
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
As illustrated by the front view of
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.
In one example, as described above with respect to
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
In the examples described above with respect to
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.
Number | Date | Country | |
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Parent | 13984022 | US | |
Child | 13963943 | US |