Abstract:
The present invention provides a light-emitting diode (LED) lamp ( 100, 100   a   , 100   b   , 100   c ). The LED lamp ( 100, 100   a , etc.) comprises a plug ( 110, 110   a   , 110   b ) having two contacts for electrical connections to two respective electric power supply conductors, a fixture ( 120, 120   a   , 120   b   , 120   c   , 120   d ) connected to the plug and a plurality of LEDs ( 11 ) mounted onto the fixture ( 120, 120   a , etc.), so that heat is conducted directly away from the LEDs ( 11 ) through the fixture and plug. When the LED lamp is connected to a lamp holder ( 20 ) and electric power is supplied from the power supply conductors, heat generated from operation of the LEDs ( 11 ) is conducted away through the fixture, plug and power supply conductors to the ambience.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. provisional application Ser. No. 61/611,014 filed on Mar. 15, 2012, the disclosure of which is herein incorporated in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to light emitting diode (LED) lamps. In particular, the present invention relates to LED lamps in which waste heat is dissipated away along a thermal conduction path from the LED junction, to the lamp holder and then to the electric power conductors. 
       BACKGROUND 
       [0003]    A light-emitting diode (LED) lamp uses solid-state light-emitting diodes as sources of illumination. For example, a LED light bulb is made to replace screw-in incandescent or compact fluorescent light bulbs, since LED light bulb is more power-efficient and has a longer life compared to the conventional light bulbs or light tubes. 
         [0004]    A LED lamp is typically assembled with a plurality of LEDs. The operation of a plurality of LEDs raises the temperature of the LEDs rapidly. The waste heat needs to be removed from the LEDs, as the temperature of the light-emitting junctions is higher, the faster the LEDs fail. Often, the life of a conventional LED lamp is less than the 50,000 hours a LED is expected to last. 
         [0005]    Various methods to dissipate waste heat of the LED light bulb are widely known in the art. Most common method used is by thermally conducting the waste heat generated to a special heat sink. Typically, the heat sink is being integrated into the LED lamp. The waste heat from the heat sink is accordingly dissipated to the atmosphere. 
         [0006]    Another method known for dissipating waste heat of LED lamp is by having the holder of the LED lamp filled with a heat transfer fluid. The heat transfer fluid conducts and convects the waste heat from the LEDs to the holder, and eventually transfers it to the atmosphere. 
         [0007]    Whether using a heat sink or heat transfer liquid to dissipate the waste heat, the transfer of the waste heat of the LED lamp to the atmosphere in a well-ventilated atmosphere is sufficiently effective for a low wattage LED lamp. However, problems arise when the LED lamp is operated in a poorly-ventilated atmosphere, such as, in an enclosed lighting fixture or concealed ceiling fitting. The waste heat transfer process in a poorly-ventilated atmosphere is undoubtedly inadequate, so the LED lamp cannot dissipate the waste heat effectively. Consequently, the lifespan of the LED lamp is significantly reduced. With the pull/push for higher energy efficiency, the reduced life of LED lamp for illumination using higher wattage LED lamps remains an issue. 
         [0008]      FIG. 1  shows a typical prior art LED lamp  10 . The LED lamp  10  comprises at least one light-emitting diodes  11 , a base  12  for electrical and mechanical connection to a lamp holder  20 , an electronic driver assembly (not shown) disposed in the base  12  for converting electric energy into a power suitable for the light-emitting diodes  11 , a mechanical and electrical assembly (not shown) disposed in the base  12  to hold and connect the light-emitting diodes  11  to the electronic driver assembly, a transparent enclosure  14  to protect the internal components of the LED lamp  10  and to enable light to emit into the environment, a housing  15  to connect the transparent enclosure  14  to the base  12  and, at the same time, to act as a heat-sink for waste heat transfer to the environment. 
         [0009]    Despite development of LED lamps, there is still a need to lower the junction temperature at the LED to achieve the 50,000 hours life expected of a LED. With improved heat dissipation, it is then possible to provide LED lamps with higher lumen for illumination. 
       SUMMARY 
       [0010]    In one aspect of the present invention, there is provided a light emitting diode (LED) lamp. The LED lamp comprises a plug having two contacts for electric connections to two respective electric power supply conductors; a fixture for mounting onto the plug; and a plurality of LEDs for mounting on the fixture, wherein the fixture conducts heat away from the plurality of LEDs to the plug. When the LED lamp is connected to a lamp holder and power is supplied from the electric power supply conductors, heat generated from operation of the plurality of LEDs is conducted away through the fixture, plug and electric power supply conductors to the ambience 
         [0011]    Preferably, the fixture comprises a heat conductive material, which includes a metal, such as copper or aluminium. 
         [0012]    Preferably, the fixture comprises an elongate member, which is thermal conductively and electrically connected directly to either of the electric power supply conductor. The associated plug is configured at an end of a long fluorescent tube with two terminal pins, and the elongate member is connected to either of the terminal pin. 
         [0013]    Preferably, the fixture comprises two elongate members, which are thermal conductively and electrically connected directly to either of the electric supply conductors. In another embodiment, each elongate member is thermal conductively and electrically connected directly to separate power supply conductors. 
         [0014]    When the plug is configured with a screw thread, bayonet or PL connection, a distal end (opposite the mounting end at the plug) of the elongate member is formed with one or more flat segments that is/are inclined at a predetermined angle, such that a LED is mountable on a flat segment. Preferably, the plug comprises a peripheral surface and a base tip, such that the peripheral surface is metallic and is connected to an AC neutral line of the electric power supply conductors, whilst the base tip is connected to an AC live line of the electric power supply conductors. 
         [0015]    When the plug is configured at an end of a long fluorescent tube with two terminal pins, each of the elongate members of the fixture is connected separately to the terminal pins. Preferably, each plug is associated with an electronic driver assembly that supplies DC power to the LEDs. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    This invention will be described by way of non-limiting embodiments of the present invention, with reference to the accompanying drawings, in which: 
           [0017]      FIG. 1  illustrates a typical prior art LED light bulb integrated with a heat sink; 
           [0018]      FIG. 2A  illustrates a LED lamp according to one embodiment of the present invention;  FIG. 2B  illustrates an exploded view of the LED lamp shown in  FIG. 2A  together with a matching lamp holder; whilst  FIG. 2C  illustrates a LED lamp with a parabolic reflector; 
           [0019]      FIGS. 3A-3C  illustrate schematics of internal fixtures of LED lamps according to other embodiments of the present invention; and 
           [0020]      FIGS. 4A and 4B  illustrate schematics of a LED lamp according to yet other embodiments of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    One or more specific and alternative embodiments of the present invention will now be described for a reader to understand the inventive features of the present invention. It shall be apparent to one skilled in the art, however, that this invention may be practiced without such specific details. Some of the details may not be described in length so as to not obscure the invention. For ease of reference, common reference numerals will be used throughout the figures when referring to same or similar features common to the figures. 
         [0022]    As outlined above, waste heat dissipation of LEDs is very crucial as it directly affects the lifespan of the LED lamp. For example, an increase of a few degree C. in the LED junction reduces the lifespan of a LED by several months, and a 20 degree C. increase will take years out of the lifespan. The present invention provides a LED lamp  100  with good heat dissipation capability, thus ensuring the designed lifespan of the LED lamp is not adversely reduced. Advantageously, the LED lamp of the present invention dissipates its waste heat along a continuous thermal conduction path from a fixture and lamp holder to the electric power supply conductors rather than to a heat sink. 
         [0023]      FIG. 2A  shows an external view of a LED lamp  100  according to an embodiment of the present invention, whilst  FIG. 2B  shows an exploded view of the LED lamp  100 . Referring to  FIGS. 2A and 2B , the LED lamp  100  comprises a plurality of LEDs  11  mounted at a free end of a fixture  120 , with an opposite end of the fixture being joined to a plug  110 . A lamp cover  150 , for connection with the plug  110 , is provided to fit over the fixture  120 . In use, the lamp cover  150  protects the fixture  120  and LEDs  11 , but allows light to radiate from the LEDs  11  to illuminate the ambience. 
         [0024]    Still referring to  FIG. 2A , the fixture  120  is shown to be made up of two elongate metallic legs  121  with the distal ends  122  being joined together and the proximal ends  124  are bent for mounting onto the plug  110 . The surface  123  at the distal end  122  is formed at an angle to the legs  121  thereby providing one or more flat segments. Each flat segment on the surface  123  is sized and dimension for mounting a LED  11  assembly. For illustration purposes, the surface  123  is shown with a flat sloping segment in  FIG. 2B . It is possible that the surface  123  is shaped like a pyramid with a polygonal base. Preferably, the segmented surfaces  123  are configured at various angles so that light from the plurality of LEDs  11  is projected out through the lamp cover  150  for optimal illumination. In one embodiment, the metallic legs  121  have a length L of about 34 mm, a width W of about 6 mm and a thickness T of about 1 mm. In another embodiment, the proximal ends  124  of the fixture  120  are mounted onto the plug  110  with screws; in another embodiment, the proximal ends  124  of the fixture  120  are mounted onto the plug with rivets. It is possible that the fixture  120  be mounted onto the plug  110  by other connection means, as long as the connection is reliable and it provides a continuous thermal conduction path to dissipate heat away from the fixture  120  to the plug  110 . As a reader will appreciate later, in use, this continuous thermal conduction path extends to the electric supply conductors from the lamp holder  20 . It is even possible to embed the proximal ends  124  in the plug  110  to form an integral sub-assembly. 
         [0025]    In  FIG. 2B , the lamp holder  20  is shown with the AC neutral line N being connected to a screw socket for receiving the screw plug  110 . The AC live line L is connected to a spring terminal  24 , which in use is electrically connected to a base tip  116  on a bottom side of the screw plug  110 . For illustration purposes, the insulator  22  around the lamp holder is not shown. 
         [0026]    In one embodiment of the present invention, the fixture  120  is made of metal or any other good thermal conductor materials. Preferably, the fixture  120  is made of copper or aluminium, as copper and aluminium are good thermal conductors. 
         [0027]    When the LED lamp  100  is configured for screw connection, as shown in  FIGS. 2B and 3A , a peripheral surface  111  of the plug  110  is metallic and is formed with a screw thread. In one embodiment, a proximal end  124  of the fixture  120  is in contact with the peripheral, metallic surface of the plug  110  so that the fixture  120  is in continuous thermal conduction with the metallic plug  110 . In use, when the LEDs  11  are powered up, heat generated at the LEDs  11  is conducted immediately away from the LEDs through the fixture  120  and the metallic surface  111  of the plug  110 . The heat energy is conducted to the lamp holder  20  through the plug  110  and is then dissipated away along the electric supply conductor N terminated at the lamp holder  20 . In this way, heat generated at the LEDs  11  is conducted away so that the designed life of the LEDs  11  is not adversely affected. In effect, the operating life of the LED lamp  100  according to the present invention is substantially at or exceeds the designed life; in other words, with the present invention, the long life of LED is not compromised. Also with this invention, long life of LEI) lamp with higher lumen or power, such as 100 W or more, is now made possible and there is an economic advantage for promoting more prevalent use of LED lamps. 
         [0028]    As shown in  FIG. 3A , an electronic driver assembly  114  is disposed inside the plug  110  with the AC neutral line N being connected to the peripheral, metallic screw surface  111  of the plug and the AC live line L being connected to a base tip  116  of the plug  110 . Also as shown, the DC output lines  118  from the electronic driver assembly  114  supply electric power to the plurality of LEDs  11 . The electronic driver assembly  114  controls and regulates power to the LEDs  11 . The DC output lines  118  of the electronic driver assembly  114  are electrically isolated from the fixture  120 . 
         [0029]      FIG. 3B  shows a fixture  120   a  according to another embodiment. The fixture  120   a  is similar to the above embodiment  120  except that the fixture  120   a  is thermally and electrically connected to the AC live line L via the base tip  116 , but the fixture  120   a  is electrically isolated from the peripheral, screw surface  111  of the plug  110 . In use, heat generated at the LEDs is conducted away directly through the fixture  120   a  and the electric supply conductor L, and indirectly through the plug  110 , the lamp holder  20  and the electric supply conductor N. 
         [0030]      FIG. 3C  shows a fixture  120   b  according to another embodiment. The fixture  120   b  is similar to the above fixtures  120 ,  120   a  except that the two elongate legs  121  are electrically isolated from each other at the distal ends  122  by an isolator  140 . The isolator  140  mechanically connects the distal ends  122  of the legs  121  together and provides rigidity to the fixture  120   b . In this embodiment, a leg  121  of the fixture  120   b  is connected to the peripheral surface  111  of the plug  110  whilst the other leg  121  is connected to the base tip  116  of the plug. In use, heat generated at the LEDs is conducted away along both the electric supply conductors N, L. 
         [0031]    Referring back to  FIG. 2C , it shows another LED lamp  100   a  of the present invention. This lamp embodiment  100   a  is similar to the above embodiment  100  except that the lamp cover  150   a  is of another shape and that there is a parabolic aluminium reflector  152  to provide homogeneous light output from the lamp. 
         [0032]      FIG. 4A  shows a LED lamp  1001 ) according to another embodiment of the present invention. As shown partially in  FIG. 4A , the LED lamp  100   b  is of the long fluorescent form factor and has a plug  110   b  at each of the two ends. As shown, each plug  110   b  has two terminal pins  111   a ,  116   a  for separate connection to the AC power supply conductors N, L and the LEDs  11  are thermally connected to a leg  121   c  of a fixture  120   c . In one embodiment, the leg  121   c  of the fixture  120   c  is connected to the terminal pin  111   a ; in another embodiment, the leg  121   c  of the fixture  120   c  is connected to the terminal pin  116   a . As in the previous embodiments, heat generated at the LEDs  11  is dissipated away through the fixture  120   c , terminal pin and either of the electric supply conductor N or L. In one embodiment, the electronic driver assembly  114  is connected to one of the plugs  110   b , whilst the plug at the opposite end is provided for only mechanical support with a lamp holder; in another embodiment, two electronic driver assemblies  114  are provided and each driver assembly is connected separately to each of the plugs  110   b  at the two ends so that each driver assembly  114  supplies power to a number of the LEDs  11 , preferably an equal number of LEDs to each driver assembly. 
         [0033]      FIG. 4B  shows a LED lamp  100   c  according to yet another embodiment. The LED lamp  100   c  is similar to the above LED lamp  100   b  except that fixture  121   d  is made up of two parallel legs  121   d  on which the LEDs are straddledly mounted. The two legs  121   d  are electrically isolated from each other by an isolator  140   d  but are separately connected to the terminal pins  111   a ,  116   a . In use, both the legs  121   d  of the fixture  120   d  conduct heat from the LEDs  11  through the terminal pins separately to both the electric supply conductors N, L. 
         [0034]    From the above description, a reader will appreciate that the LED lamps of the present invention rely on heat conduction as the primary mode of heat dissipation from the LED junctions. Heat dissipation from the LED lamp by conduction is found to be more effective than convection or radiation. For example, assuming a LED is heated to a temperature T 2  of 75 degreeC and the ambient temperature T 1  is 25 degreeC, the comparative amounts of heat power dissipation according to the conduction, convection and radiation are: 
       Conduction: 
       [0035]    
       
         
           
             
               
                 
                   Power 
                   = 
                   
                     k 
                     · 
                     
                       ( 
                       
                         
                           A 
                           1 
                         
                          
                         
                           / 
                         
                          
                         L 
                       
                       ) 
                     
                     · 
                     
                       ( 
                       
                         
                           T 
                           2 
                         
                         - 
                         
                           T 
                           1 
                         
                       
                       ) 
                     
                   
                 
               
             
             
               
                 
                   = 
                   
                     
                       380 
                       · 
                       
                         ( 
                         
                           0.006 
                           × 
                           0.001 
                            
                           
                             / 
                           
                            
                           0.034 
                         
                         ) 
                       
                     
                     × 
                     
                       2 
                       · 
                       
                         ( 
                         
                           75 
                           - 
                           25 
                         
                         ) 
                       
                     
                   
                 
               
             
             
               
                 
                   = 
                   
                     6.7 
                      
                     
                         
                     
                      
                     W 
                   
                 
               
             
           
         
       
     
         [0000]    where: 
         [0036]    k is the heat conductivity in W/mC for copper or aluminium; and 
         [0037]    A 1  is the cross-section area in m 2  (assuming, each leg  121  of the fixture shown in 
         [0038]      FIG. 2B  or  2 C is 6 mm wide, 1 mm thick and about 34 mm long.) 
       Convection: 
       [0039]    
       
         
           
             
               
                 
                   Power 
                   = 
                   
                     h 
                     · 
                     
                       A 
                       2 
                     
                     · 
                     
                       ( 
                       
                         
                           T 
                           2 
                         
                         - 
                         
                           T 
                           1 
                         
                       
                       ) 
                     
                   
                 
               
             
             
               
                 
                   = 
                   
                     100 
                     · 
                     
                       ( 
                       
                         0.034 
                         × 
                         
                           ( 
                           
                             0.001 
                             + 
                             0.006 
                           
                           ) 
                         
                         × 
                         2 
                         × 
                         
                           2 
                           · 
                           
                             ( 
                             
                               75 
                               - 
                               25 
                             
                             ) 
                           
                         
                       
                     
                   
                 
               
             
             
               
                 
                   = 
                   
                     4.76 
                      
                     
                         
                     
                      
                     W 
                   
                 
               
             
           
         
       
     
         [0000]    where: 
         [0040]    h is the convective heat transfer coefficient in W/m 2 C; and 
         [0041]    A 2  is the surface area of the fixture  120 . 
       Radiation: 
       [0042]    
       
         
           
             
               
                 
                   Power 
                   = 
                   
                     sigma 
                     · 
                     
                       A 
                       2 
                     
                     · 
                     
                       T 
                       2 
                       4 
                     
                   
                 
               
             
             
               
                 
                   = 
                   
                     5.67 
                     × 
                     
                       
                         10 
                         
                           - 
                           8 
                         
                       
                       · 
                       
                         ( 
                         
                           0.034 
                           × 
                           
                             ( 
                             
                               0.001 
                               + 
                               0.006 
                             
                             ) 
                           
                           × 
                           2 
                           × 
                           
                             2 
                             · 
                             
                               
                                 ( 
                                 
                                   75 
                                   + 
                                   273 
                                 
                                 ) 
                               
                               4 
                             
                           
                         
                       
                     
                   
                 
               
             
             
               
                 
                   = 
                   
                     0.79 
                      
                     
                         
                     
                      
                     W 
                   
                 
               
             
           
         
       
     
         [0000]    where: 
         [0043]    sigma is the Stefan-Boltzmann constant; 
         [0044]    A 2  is the surface area of the fixture  120 ; and 
         [0045]    T 2  is in degree Kelvin. 
         [0000]    In the above convective heat dissipation calculation, the result is reasonable if there is no lamp cover  150 ; with the lamp cover, the effective heat dissipation from the LED is much lower. From the above calculations, it is thus reasonable to conclude that heat dissipation by conduction is the most effective mode for reducing LED junction temperature. 
         [0046]    The heating effect on the electric supply conductors is now examined. From physical law, as a conductor becomes heated up, its resistance increases proportionally as follow: 
         [0000]      Delta  R/R   0 =alpha·( T   2   −T   1 )
 
         [0000]    Assuming, all the heat energy from the LEDs is conducted to the electric supply conductors and the electric supply conductors are heated to temperature T 2  of 75 degreeC, the ambient temperature T 1  remains at 25 degreeC, the resultant resistance is R and the initial resistance is R 0 , the above equation simplifies to: 
         [0000]        R=R   0 ·(1−alpha·( T   2   −T   1 ))
 
         [0000]    If the initial resistance R 0  is 100 ohms and the thermal temperature coefficient, alpha, is 3.9×10 −3 /C for copper or aluminium, then 
         [0000]    
       
         
           
             
               
                 
                   R 
                   = 
                   
                     100 
                     · 
                     
                       ( 
                       
                         1 
                         + 
                         
                           3.9 
                           × 
                           
                             
                               10 
                               
                                 - 
                                 3 
                               
                             
                             · 
                             
                               ( 
                               
                                 75 
                                 - 
                                 25 
                               
                               ) 
                             
                           
                         
                       
                       ) 
                     
                   
                 
               
             
             
               
                 
                   = 
                   
                     100 
                     · 
                     
                       ( 
                       
                         1 
                         + 
                         0.195 
                       
                       ) 
                     
                   
                 
               
             
           
         
       
     
         [0000]    From the above calculation, it is seen that a 50 degreeC increase in conductor temperature causes a resistance increase of only about 20%. It is thus reasonable to conclude that an increase in the electric supply conductor temperature results in a small increase in resistance; in contrast, a 50 degreeC increase in the LED junction temperature will adversely reduce the long life of a LED. 
         [0047]    From the above description, the LED lamp  100 ,  100   a ,  100   b ,  100   c  according to the present invention dissipates waste heat effectively through the electric power supply conductors, thereby giving it a lifespan that is longer than a conventional LED lamp. The LED lamp does not require any heat sink, thus the manufacturing cost of the same is accordingly lower; in addition, the lamp of the present invention can be used with existing luminaries and incandescent lamp holders, instead of lamp holders with heat-sinks. The LED lamp of the present invention is also usable in all environmental operation conditions, even in a very poor-ventilated environment or concealed fitting. Whilst the plug is shown with screw bulb form factor, it can be configured in other form factors, such as, the bayonet and PL forms. Other bi-pin form factors are also possible, such as those with two side or end prongs. Consequently, the LED lamp of the present invention with enhanced heat dissipation will allow wider use of higher lumen LED lamps for illumination in the future. 
         [0048]    The above description illustrates various embodiments of the present invention along with examples of how aspects of the present invention may be implemented. While specific embodiments have been described and illustrated it is understood that many charges, modifications, variations and combinations thereof could be made to the present invention without departing from the scope of the present invention. For example, the two elongate legs  121   d  of the fixture shown in  FIG. 4B  may be polished finished and orientated at an angle to each other to additionally act as reflectors. The above examples, embodiments, instructions semantics, and drawings should not be deemed to be the only embodiments, and are presented to illustrate the flexibility and advantages of the present invention as defined by the following claims: