Abstract:
An LED bulb, which includes a shell, a heat dispersing apparatus, at least one LED attached to an upper surface of one of a plurality of fins; and a thermally conductive material within the shell of the bulb. The heat dispersing apparatus includes a plurality of fins, and a body, wherein the body separates the plurality of fins from one another.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to U.S. Patent Provisional Application No. 60/942,751, filed Jun. 8, 2007, which is incorporated herein by this reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to replacement of bulbs used for lighting by light emitting diode (LED) bulbs, and more particularly, to the efficient removal of the heat generated by the LEDs in order to permit the replacement bulb to match the light output of the bulb being replaced. 
       BACKGROUND OF THE INVENTION 
       [0003]    An LED consists of a semiconductor junction, which emits light due to a current flowing through the junction. At first sight, it would seem that LEDs should make an excellent replacement for the traditional tungsten filament incandescent bulb. At equal power, they give far more light output than do incandescent bulbs, or, what is the same thing, they use much less power for equal light; and their operational life is orders of magnitude larger, namely, 10-100 thousand hours vs. 1-2 thousand hours. 
         [0004]    However, LEDs have a number of drawbacks that have prevented them, so far, from being widely adopted as incandescent replacements. Among the chief of these is that, although LEDs require substantially less power for a given light output than do incandescent bulbs, it still takes many watts to generate adequate light for illumination. Whereas the tungsten filament in an incandescent bulb operates at a temperature of approximately 3000K, an LED, being a semiconductor, cannot be allowed to get hotter than approximately 120° C. The LED thus has a substantial heat problem: If operated in vacuum like an incandescent, or even in air, it would rapidly get too hot and fail. This has limited available LED bulbs to very low power (less than approximately 3 W), producing insufficient illumination for incandescent replacements. 
         [0005]    More recently, a means for cooling LEDs in light bulbs has had the LEDs immersed in a fluid, a gel or a plastic (International Patent Application No. PCT/US07/10470 entitled “Heat Removal Design for LED Bulbs” and International Patent Application No. PCT/US07/10469 entitled “All-Plastic LED Bulb”). The fluid, gel or plastic provides a high thermal conductivity path from the LED heat sources to the bulb&#39;s surface and the ambient. 
         [0006]    In some cases, however, the thermal conductivity of the fluid, gel or plastic may still not be high enough to maintain the LEDs at their desirable operating temperature given their small area of contact with the fluid, gel or plastic. This is true especially when using individual high-power LEDs as opposed to using many low-power LEDs since their power density is higher. For these applications, then, it would be desirable to find a means to even better connect the LEDs to the fluid, gel or plastic, and that at the same time maintained the desirable characteristics of the fluid, gel or plastic, that is, optical transparency or controlled optical scattering characteristics, and potentially electrical insulation. 
       SUMMARY OF THE INVENTION 
       [0007]    This invention has the object of developing a light emitting apparatus utilizing light emitting diodes (LEDs), such that the above-described primary problem is effectively solved. It aims at providing a replacement bulb for incandescent lighting having a plurality of LEDs with a light output equal in intensity to that of an incandescent bulb, and whose dissipated power may be effectively removed from the LEDs in such a way that their maximum rated temperature is not exceeded. The apparatus includes a bulb-shaped shell, preferentially formed of a plastic such as polycarbonate. The shell may be transparent, or may contain materials dispersed in it to disperse the light, making it appear not to have point sources of light, and may also contain materials dispersed in it to change the bluish color of the LED light to more yellowish color, more closely resembling the light from normal incandescent bulbs. 
         [0008]    The shell is filled with a thermally conductive fluid, gel or plastic, such as water or a hydrogel. This fluid, gel or plastic acts as the means to transfer the heat power generated by the LEDs to the shell, where it may be removed by radiation and convection, as in a normal incandescent bulb. The fluid, gel or plastic may be transparent, or may contain materials dispersed in it to disperse the light, making it appear not to have point sources of light, and may also contain materials dispersed in it to change the bluish color of the LED light to more yellowish color, more closely resembling the light from normal incandescent bulbs. The fluid, gel or plastic is preferentially electrically insulating. 
         [0009]    The LEDs are attached to an apparatus designed to increase the surface area of contact of the LEDs with the fluid, gel or plastic. Although similar apparatuses are often referred to as ‘heatsinks’, it can be appreciated that the apparatus is not a heatsink in the sense known to those skilled in the art because it does not function to increase the available convection cooling (although there may be some additional convection cooling in the case of the fluid). In accordance with one embodiment, the apparatus designed to increase the surface area of contact increases the effective surface area of the LED(s) and thus increase the contact area of the fluid, gel or plastic with the heat source. The fundamental reason this works is because the limited thermal conductivity of the fluid, gel or plastic results in a relatively high thermal gradient away from the LEDs. This results in inefficient usage of the fluid, gel or plastic. Enhancing the contact area of the LEDs with the fluid, gel or plastic results in greater net transfer of heat power. 
         [0010]    In accordance with one embodiment, the apparatus designed to increase the surface area of contact may be constructed of any of various high-thermal conductivity materials such as aluminum. The apparatus designed to increase the surface area of contact may be preferentially designed with fins in order to maximize contact area with the fluid, gel or plastic. However, the fins are preferentially spaced apart in such a way that there is sufficient fluid, gel or plastic between them that there is a significant temperature drop through the material at that distance. That is, the fins cannot be arbitrarily close together because no additional contact with lower temperature fluid, gel or plastic would be achieved; the minimum distance between the fins is set by a balance between the gain of additional surface area and the loss of additional material with which to be in contact, due to the limited thermal conductivity of the surrounding fluid, gel or plastic. The particular geometry described, although optimal, is not necessary. More or fewer fins may also be used; the fins may be further apart or closer together; or there may be no fins at all. The LEDs may be mounted to the apparatus designed to increase the surface area of contact through known methods providing high thermal conductivity but electrical insulation, such as thermal epoxy. 
         [0011]    The LEDs and the apparatus designed to increase the surface area of contact are installed in the fluid, gel or plastic in such a way as to prevent them from being shorted. If the fluid, gel or plastic is electrically insulating, no special measures need to be taken. If the fluid, gel or plastic is not electrically insulating, the electrically conductive portions of the LEDs may be electrically insulated to prevent shorting. 
         [0012]    With the LEDs installed in the fluid, gel or plastic, the shell is sealed with a watertight seal, which is preferentially constructed of the same material as the shell. Electrical contacts for powering the LEDs are brought out through the seal before the sealing is accomplished. These leads are connected to the power source for the LEDs, which will typically be included inside the remainder of the bulb. The power source is preferentially designed to be compatible with pre-existing designs, so that the bulb may directly replace traditional bulbs without requiring any change in the pre-existing fixture. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. In the drawings, 
           [0014]      FIG. 1  is a cross-sectional view of an LED bulb showing the light-emitting portion of the LED mounted in a fluid, gel or plastic. 
           [0015]      FIG. 2  is a perspective view of an apparatus for cooling LEDs in a bulb with the LEDs mounted to the apparatus and power wires coming from the LEDs. 
           [0016]      FIG. 3  is a cross-sectional view of an LED replacement bulb showing the apparatus for cooling LEDs in a bulb mounted inside the bulb. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0017]    Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts. 
         [0018]    According to the design characteristics, a detailed description of the current practice and a preferred embodiment is given below. 
         [0019]      FIG. 1  is a cross-sectional view of an LED replacement bulb  10  showing LEDs mounted in a fluid, gel or plastic. As shown in  FIG. 1 , the LED replacement bulb includes a screw-in base  20 , a shell  30 , an inner portion  40  containing a fluid, plastic or gel material  60 , and at least one LED  50 . The screw-in base  20  includes a series of screw threads  22  and a base pin  24 . The screw-in base  20  is configured to fit within and make electrical contact with a standard electrical socket. The electrical socket is preferably dimensioned to receive an incandescent or other standard light bulb as known in the art. However, it can be appreciated that the screw-in base  20  can be modified to fit within any electrical socket, which is configured to receive an incandescent bulb. The screw-in base  20  makes electrical contact with the AC power in a socket through its screw threads  20  and its base pin  24 . Inside the screw-in base  20  is a power supply (not shown) that converts the AC power to a form suitable for driving the at least one LED  50 . 
         [0020]    As shown in  FIG. 1 , the at least one LED  50  is connected by wires  56  to the power supply. The connecting wires  56  may be stiff enough to function as support for the at least one LED  50 , and may also form the interconnects between the LEDs  50  when there are multiple devices. The shell  30  also encases at least the light-emitting portion of the at least one LED  50 , with the connecting wires  56  coming out through the shell  30  through a sealed connection to the power supply. 
         [0021]      FIG. 2  is a perspective view of an apparatus  80  for cooling LEDs  50  in a bulb showing the LEDs  50  mounted to the apparatus  80  in accordance with one embodiment. The apparatus  80  may include one or more fins  82  having a relatively flat surface or top  81 , and a body (or body portion)  83  having at least one slot or groove  84 . The body  83  of the apparatus  80  provides separation for one or more fins  82 . It can be appreciated that the body  83  of the apparatus  80  can be a hollow cylinder or other suitable hollow member. In accordance with an exemplary embodiment, the one or more fins  82  can have a circular disk-like body or other suitable shape having a large surface area. Alternatively, in accordance with another exemplary embodiment, the body  83  of the apparatus  80  can be designed without the one or more fins  82 . 
         [0022]    The body  83  also permits the one or more fins  82 , if any, to have optimal contact with a surrounding fluid, gel or plastic material. In accordance with one embodiment, the apparatus  80  is preferably constructed of a high-thermal conductivity material such as aluminum. In accordance with a preferred embodiment, the at least one LED  50  is mounted to the flat surface or top  81  of the at least one fin  82 . Alternatively, in accordance with another exemplary embodiment, the at least one LED  50  is mounted to the body  83 . 
         [0023]    The at least one LED  50  is preferably attached to the apparatus  80  by means of a material, which is preferably a material with high-thermal conductivity, but electrically insulating, so that the apparatus  80  is in good thermal contact with the at least one LED  50 , but electrically isolated from them. The at least one groove or slot  84  allows the connecting wires  56  to run the length of the apparatus  80 , without protruding out beyond the side of the apparatus  80 . 
         [0024]      FIG. 3  is a cross-sectional view of an LED replacement bulb  10  showing the LEDs mounted in a fluid, gel or plastic according to the design of this invention. As shown in  FIG. 3 , the LED replacement bulb includes a base  20 , a shell  30 , an inner portion  40  containing a fluid, plastic or gel material  60 , and at least one apparatus  80  for cooling LEDs in a bulb, and including at least one LED  50 . The base  20  is preferably a screw-in base having a series of screw threads  22  and a base pin  24 . The screw-in base  20  is configured to fit within and make electrical contact with a standard electrical socket. The electrical socket is preferably dimensioned to receive an incandescent or other standard light bulb as known in the art. However, it can be appreciated that the base  20  can be modified to fit within any electrical socket, which is configured to receive an incandescent bulb or other suitable bulb. The screw-in base  20  makes electrical contact with the AC power in a socket through its screw threads  20  and its base pin  24 . Inside the screw-in base  20  is a power supply (not shown) that converts the AC power to a form suitable for driving the at least one LED  50 . 
         [0025]    As shown in  FIG. 3 , the at least one LED  50  attached to the apparatus  80  is connected by wires  56  to the power supply. The connecting wires  56  may be stiff enough to function as support for the apparatus  80  and the at least one LED  50 , and can also form the interconnects between the LEDs  50  when there are multiple devices. The shell  30  encases the apparatus  80  and at least the light-emitting portion of the least one LED  50 , with the connecting wires  56  coming out through the shell  30  through a sealed connection to the power supply. 
         [0026]    It will be apparent to those skilled in the art that various modifications and variation can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.