Abstract:
A light source that utilizes light emitting diodes that emit white light is disclosed. The diodes are mounted on an elongate member having at least two surfaces upon which the light emitting diodes are mounted. The elongate member is thermally conductive and is utilized to cool the light emitting diodes. In the illustrative embodiment, the elongate member is a tubular member through which a heat transfer medium flows.

Description:
FIELD OF THE INVENTION 
     This invention pertains to lighting sources, in general, and to a lighting source that utilizes Light Emitting Diodes (LED&#39;s), in particular. 
     BACKGROUND OF THE INVENTION 
     LED&#39;s have many advantages as light sources. However, in the past LED&#39;s have found application only as specialized light sources such as for vehicle brake lights, and other vehicle related lighting, and recently as flashlights. In these prior applications, the LED&#39;s are typically mounted in a planar fashion in a single plane that is disposed so as to be perpendicular to the viewing area. Typically the LED planar array is not used to provide illumination, but to provide signaling. 
     Recent attempts to provide LED light sources as sources of illumination have been few, and generally unsatisfactory from a general lighting standpoint. 
     It is highly desirable to provide a light source utilizing LED&#39;s that provides sufficient light output so as to be used as a general lighting source rather than as a signaling source. 
     One problem that has limited the use of LED&#39;s to specialty signaling and limited general illumination sources is that LED&#39;s typically generate significant amounts of heat. The heat is such that unless the heat is dissipated, the LED internal temperature will rise causing degradation or destruction of the LED. 
     It is therefore further desirable to provide an LED light source that efficiently conducts heat away from the LED&#39;s. 
     SUMMARY OF THE INVENTION 
     In accordance with the principles of the invention, an improved light source is provided. The light source includes an elongate thermally conductive member having an outer surface. A plurality of light emitting diodes is carried on the elongate member outer surface. At least some of the light emitting diodes are disposed in a first plane and others of said light emitting diodes are disposed in a second plane not coextensive with the first plane. Electrical conductors are carried by the elongate thermally conductive member and are connected to the plurality of light emitting diodes to supply electrical power thereto. The elongate thermally conductive member conducts heat away from the light emitting diodes. 
     In accordance with one aspect of the invention, an illustrative embodiment of the invention utilizes light emitting diodes that emit white light. However, other embodiments of the invention may utilize light emitting diodes that are of different colors to produce monochromatic light or the colors may be chosen to produce white light or other colors. 
     In accordance with another aspect of the invention the elongate thermally conductive member transfers heat from the light emitting diodes to a medium within said elongate thermally conductive member. In the illustrative embodiment of the invention, the medium is air. 
     In accordance with another aspect of the invention, the elongate thermally conductive member has one or more fins to enhance heat transfer to the medium. 
     In accordance with another aspect of the invention the elongate thermally conductive member comprises a tube. In one embodiment of the invention, the tube has a cross-section in the shape of a polygon. In another embodiment of the invention, the tube has a cross-section having flat portions. 
     In accordance with another embodiment of the invention, the elongate thermally conductive member comprises a channel. 
     In accordance with the principles of the invention, the elongate thermally conductive member may comprise an extrusion, and the extrusion can be highly thermally conductive material such as aluminum. 
     In one preferred embodiment of the invention the elongate thermally conductive member is a tubular member. The tubular member has a polygon cross-section. However, other embodiments my have a tubular member of triangular cross-section. 
     In one embodiment of the invention, a flexible circuit is carried on a surface of said elongate thermally conductive member; the flexible circuit includes the electrical conductors. 
     In another aspect of the invention, the flexible circuit comprises a plurality of apertures for receiving said plurality of light emitting diodes. Each of the light emitting diodes is disposed in a corresponding one of the apertures and affixed in thermally conductive contact with said elongate thermally conductive member. 
     The elongate thermally conductive member includes a thermal transfer media disposed therein in a flow channel. 
     At least one clip for mounting the elongate thermally conductive member in a fixture may be included. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The invention will be better understood from a reading of the following detailed description of a preferred embodiment of the invention taken in conjunction with the drawing figures, in which like reference indications identify like elements, and in which: 
     FIG. 1 is a planar side view of a light source in accordance with the principles of the invention; 
     FIG. 2 is a top planar view of the light source of FIG. 1; 
     FIG. 3 is a perspective view of the light source of FIG. 1 with mounting clips; 
     FIG. 4 is a planar side view of the light source of FIG. 3 showing mounting clips separated from the light source; 
     FIG. 5 is a top view of the light source and mounting clips of FIG. 4; and 
     FIG. 6 is a partial cross-section of the light source of FIG.  1 . 
    
    
     DETAILED DESCRIPTION 
     A light source in accordance with the principles of the invention may be used as a decorative lighting element or may be utilized as a general illumination device. As shown in FIG. 1, a light source  100  in accordance with the invention includes an elongate thermally conductive member or heat sink  101 . Elongate heat sink  101  is formed of a material that provides excellent thermal conductivity. Elongate heat sink  101  in the illustrative embodiment of the invention is a tubular aluminum extrusion. To improve the heat dissipative properties of light source  100 , elongate heat sink  101  is configured to provide convective heat dissipation and cooling. As more clearly seen in FIG. 2, tubular heat sink  101  is hollow and has an interior cavity  103  that includes one or more heat dissipating fins  105 . Fins  105  are shown as being triangular in shape, but may take on other shapes. Fins  105  are integrally formed on the interior of elongate heat sink  101 . In the illustrative embodiment convective cooling is provided by movement of a medium  102  through elongate heat sink  101 . The medium utilized in the illustrative embodiment is air, but may in some applications be a fluid other than air to provide for greater heat dissipation and cooling. 
     The exterior surface  107  of elongate heat sink  101  has a plurality of Light Emitting Diodes  109  disposed thereon. Each LED  109  in the illustrative embodiment comprises a white light emitting LED of a type that provides a high light output. Each LED  109  also generates significant amount of heat that must be dissipated to avoid thermal destruction of the LED. By combining a plurality of LEDs  109  on elongate heat sink  101 , a high light output light source that may be used for general lighting is provided. 
     Conductive paths  129  are provided to connect LEDs  109  to an electrical connector  111 . The conductive paths may be disposed on an electrically insulating layer  131  or layers disposed on exterior surface  107 . In the illustrative embodiment shown in the drawing figures, the conductive paths and insulating layer are provided by means of one or more flexible printed circuits  113  that are permanently disposed on surface  107 . As more easily seen in FIG. 6, printed circuit  113  includes an electrically insulating layer  131  that carries conductive paths  129 . As will be appreciated by those skilled in the art, other means of providing the electrically conductive paths on the 
     Flexible printed circuit  113  has LED&#39;s  109  mounted to it in a variety of orientations ranging from 360 degrees to 180 degrees and possibly others depending on the application. Electrical connector  111  is disposed at one end of printed circuit  113 . Connector  113  is coupleable to a separate power supply to receive electrical current. Flexible printed circuit  113 , in the illustrative embodiment is coated with a non-electrically conductive epoxy that may be infused with optically reflective materials. Flexible printed circuit  113  is adhered to the tube  101  with a heat conducting epoxy to aid in the transmission of the heat from LEDs  109  to tube  101 . Flexible printed circuit  113  has mounting holes  134  for receiving LEDs  109  such that the backs of LEDs  109  are in thermal contact with the tube surface  107 . 
     Tubular heat sink  101  in the illustrative embodiment is formed in the shape of a polygon and may have any number of sides. Although tubular heat sink  101  in the illustrative embodiment is extruded aluminum, tubular heat sink  101  may comprise other thermal conductive material. Fins  105  may vary in number and location depending on particular LED layouts and wattage. In some instances, fins may be added to the exterior surface of tubular heat sink  101 . In addition, apertures may be added to the tubular heat sink to enhance heat flow. 
     Light source  100  is mounted into a fixture and retained in position by mounting clips  121 ,  123  as most clearly seen in FIGS. 3,  4 , and  5 . Each of the clips is shaped so as to engage and retain light source  100 . Each clip is affixed on one surface  122 ,  124  to a light fixture. 
     Although light source  100  is shown as comprising an elongate tubular heat sink, other extruded elongate members may be used such as channels. 
     In the illustrative embodiment shown, convection cooling by flow of air through tubular heat sink  101  is utilized such that cool or unheated air enters tubular heat sink  101  at its lower end and exits from the upper end as heated air. In higher wattage light sources, rather than utilizing air as the cooling medium, other fluids may be utilized. In particular, convective heat pumping may be used to remove heat from the interior of the heat sink. 
     In one particularly advantageous embodiment of the invention, the light source of the invention is configured to replace compact fluorescent lighting in decorative applications. 
     As will be appreciated by those skilled in the art, the principles of the invention are not limited to the use of light emitting diodes that emit white light. Different colored light emitting diodes may be used to produce monochromatic light or to produce light that is the combination of different colors. 
     Although the invention has been described in terms of illustrative embodiments, it is not intended that the invention be limited to the illustrative embodiments shown and described. It will be apparent to those skilled in the art that various changes and modifications may be made to the embodiments shown and described without departing from the spirit or scope of the invention. It is intended that the invention be limited only by the claims appended hereto.