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. A cooling or fluid movement device coupled with the elongate thermally conductive member enhances cooling of the light emitting diodes.

Description:
RELATED APPLICATIONS  
       [0001]    This application is a continuation-in-part of my co-pending application Ser. No. 10/156,810 filed May 29, 2002. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    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  
         [0003]    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.  
           [0004]    Recent attempts to provide LED light sources as sources of illumination have been few, and generally unsatisfactory from a general lighting standpoint.  
           [0005]    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.  
           [0006]    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.  
           [0007]    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  
         [0008]    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 to a thermally conductive fluid medium. A cooling device is utilized to remove heat from the light emitting diodes. In one aspect of the invention, the cooling device comprises a fluid moving device utilized to cause the fluid medium to flow to cause cooling of the elongate thermally conductive member and therefore to dissipate heat from the light emitting diodes. In another aspect of the invention, the cooling device may be an electronic or solid state device such as a Piezoelectric device or a device that uses the Peltier effect, known as a Peltier device.  
           [0009]    In accordance with the principles of the invention, a temperature sensor is provided to determine the temperature of the light emitting diodes. The temperature sensor is coupled to a controller that monitors the temperature and controls the cooling device to vary the degree of cooling in accordance with the monitored temperature. In addition, the controller can be used to control the power provided to the light emitting diodes in response to the monitored temperature. Still further, the controller may be operated to control the light output provided by the light emitting diodes.  
           [0010]    In the illustrative embodiment of the invention, the fluid medium is air and the fluid moving device is an air moving device.  
           [0011]    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.  
           [0012]    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.  
           [0013]    In accordance with another aspect of the invention, the elongate thermally conductive member has one or more projections or fins to enhance heat transfer to the medium. The projections or fins may be disposed on the outer surface or inner surface of the elongate thermally conductive member or may be disposed on both the outer and inner surfaces.  
           [0014]    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.  
           [0015]    In accordance with another embodiment of the invention, the elongate thermally conductive member comprises a channel.  
           [0016]    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.  
           [0017]    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.  
           [0018]    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.  
           [0019]    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.  
           [0020]    The elongate thermally conductive member includes a thermal transfer media disposed therein in a flow channel.  
           [0021]    At least one clip for mounting the elongate thermally conductive member in a fixture may be included.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0022]    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:  
         [0023]    [0023]FIG. 1 is a planar side view of a light source in accordance with the principles of the invention,  
         [0024]    [0024]FIG. 2 is a top planar view of the light source of FIG. 1;  
         [0025]    [0025]FIG. 3 is a perspective view of the light source of FIG. 1 with mounting clips;  
         [0026]    [0026]FIG. 4 is a planar side view of the light source of FIG. 3 showing mounting clips separated from the light source;  
         [0027]    [0027]FIG. 5 is a top view of the light source and mounting clips of FIG. 4;  
         [0028]    [0028]FIG. 6 is a partial cross-section of the light source of FIG. 1;  
         [0029]    [0029]FIG. 7 is a top view of an alternate elongate thermally conductive member,  
         [0030]    [0030]FIG. 8 is a side view of the member of FIG. 7; and  
         [0031]    [0031]FIG. 9 is a block diagram of a control arrangement for the light source of the invention. 
     
    
     DETAILED DESCRIPTION  
       [0032]    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 surface discontinuities or heat dissipating protrusions  105 . In the illustrative embodiment the surface discontinuities or heat dissipating protrusions  105  are triangular shaped fins, but may take on other shapes. In yet other embodiments, the surface discontinuities may include apertures or blind bores either alone or in combinations with heat dissipation protrusions. Protrusions  105  are integrally formed on the interior of elongate heat sink  101 . In the illustrative embodiment movement of a medium  102  through elongate heat sink  101  provides cooling. Medium  102  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.  
         [0033]    Cooling device  199  is coupled to elongate thermally conductive member  101  to enhance cooling of the LED&#39;s. Cooling device in one embodiment of the invention is a medium moving device in fluid coupling with elongate thermally conductive member  101  to enhance the movement of medium  102 . Medium moving device  199  is utilized to enhance fluid medium  102  to flow to cause cooling of the elongate thermally conductive member and therefore to dissipate heat from the light emitting diodes. Medium moving device  199  in a first illustrative embodiment is a fan and may be an electromechanical fan, electronic fan, or solid-state device such as a piezoelectric fan. In a second embodiment of the invention, cooling device  199  may comprise one or more solid state cooling devices utilizing the Peltier effect, otherwise known as Peltier devices. Although cooling device  199  is shown at one end of the light source  100 , it will be appreciated by those skilled in the art that where solid state devices are utilized, a plurality of solid state devices may be positioned at locations other than on an end of the light source  100 . It will also be appreciated by those skilled in the art that solid state cooling devices such as Piezoelectric and Peltier devices are known.  
         [0034]    A controller  300  is provided in accordance with the principles of the invention. Controller  300  is coupled to a temperature sensor  301  that is disposed on light source  100  so as to monitor the temperature of the light emitting diodes  109 . Controller  300  is utilized to control the rate of cooling provided by cooling device  199 . It will be appreciated by those skilled in the art that although controller  300  and sensor  301  are shown separated from each other in the drawing, that such separation is provided merely for clarity in understanding the invention and controller  300  and sensor  301  may be fabricated as a single integrated device.  
         [0035]    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. As noted above cooling device  199  provides cooling to avoid thermal destruction. By combining a plurality of LEDs  109  on elongate thermally conductive member or heat sink  101 , a high light output light source that may be used for general lighting is provided.  
         [0036]    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 may be provided.  
         [0037]    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 .  
         [0038]    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, surface discontinuities such as heat dissipation protrusions or fins may be added to the exterior surface of tubular heat sink  101 . In addition, apertures may be added as surface discontinuities to the tubular heat sink to enhance heat flow.  
         [0039]    [0039]FIGS. 7 and 8 show an alternate elongate thermally conductive member  201  that has both exterior surface discontinuities or heat dissipation protrusions or fins  205  in addition to interior surface discontinuities or heat dissipation protrusions or fins  241 .  
         [0040]    Turning now to FIG. 9, controller  300  is advantageously utilized in accordance with the principles of the invention. Controller  300  may be any one of a number of commercially available controllers. Each such controller is programmable and includes a processor, and memory (which are not shown). Controller  300  memory is utilized to program operation of the microprocessor. It will be appreciated by those skilled in the art that controller  300  may be integrated into the same chip as sensor  301  and interface  303  that is utilized to interface controller  300  to the cooling device  199 . Controller  300  is programmed so that when temperature sensor  301  detects a temperature that is too high, cooling device  199  is activated or, if activated at less than full capacity, is activated to a higher cooling capacity. In addition, controller  300  is coupled to power supply  305 , which in turn provides power to LED&#39;s  109  at the appropriate voltage level and type via power bus  307 , so that the amount of power provided to LED&#39;s  109  may also be regulated to control the amount of power dissipated by LED&#39;s  109 . Controller  300  controls the amount of cooling provided by cooling device  199 . The amount of cooling provided by cooling device  199  is increased when temperature sensor  301  indicates a predetermined temperature. In addition, controller  300  will turn off all LED&#39;s  109  in the event that a second predetermined temperature threshold is reached or exceeded. Controller  300  also operates to increase the power provided to LED&#39;s  109  in the event that the temperature sensed is below another predetermined threshold. Controller  300  has control input  309  to receive control inputs to determine the on-off status of LED&#39;s  109  and to determine the brightness level output of LED&#39;s  109 . In addition, controller  300  is programmed to be  
         [0041]    responsive to control signals that will command controller  300  to brighten or dim the light output of LED&#39;s  109  Interface  303  is provides the appropriate interface between controller  300  and cooling device  199   
         [0042]    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.  
         [0043]    Although light source  100  is shown as comprising elongate tubular thermally conductive members or heat sinks  101 ,  201 , other extruded elongate members may be used such as channels.  
         [0044]    In the illustrative embodiment shown, cooling by flow of air through elongate thermally conductive members or tubular heat sinks  101 ,  201  is utilized such that cool or unheated air enters elongate thermally conductive members  101 ,  201  by fluid movement device  199 , passes over the surface discontinuities or heat dissipation protrusions, and exits from the opposite end of elongate thermally conductive member  101 ,  201  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.  
         [0045]    In one particularly advantageous embodiment of the invention, the light source of the invention is configured to replace compact fluorescent lighting in decorative applications.  
         [0046]    It will be appreciated by those skilled in the art that although the invention has been described in terms of light emitting diodes, the invention is equally applicable to other non-filament miniature lights sources such as organic light emitting diodes (OLED&#39;s) and polymer type light sources. It is intended that the term “light emitting diode” or “LED” as used in the claims is intended to not be limited to solid state light emitting diodes, but is intended to include such other miniature light sources.  
         [0047]    It has further been determined that the uniformity of light distribution of a light source having an elongate thermally conductive member with heat dissipation protrusions or fins  205  on the outer surface of the elongate thermally conductive member  201  is enhanced by utilization of an appropriately selected coating or treatment to the outer or exterior surfaces of elongate thermally conductive member  201 . In particular, in a comparison of various surface coatings or treatments, it has been found that the use of a non-reflective or black surface on the protrusions or fins  205  provides a more uniform light output. It has been determined that the use of reflective or white surfaces on protrusions results in the protrusions producing shadows in the light output.  
         [0048]    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.  
         [0049]    Controller  300  is programmable to be further responsive to control signals  309  to control which of different colored LED&#39;s are activated and the amount of power provided to the different colors such that the color output of lights source  100  is varied.  
         [0050]    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.