Abstract:
A plurality of disc-shaped substrates carry light emitters and are axially stacked, spaced apart, in a metal housing to dissipate the heat produced by the light emitters. The housing comprises mutually connected elongate planar ribs that abut the light emitters or substrates for thermally connecting the light emitters to the housing. The ribs have shoulders. The substrates are received between the ribs and abut the shoulders. The shoulders are positioned proximate each light emitter in intimate contact with the substrate for efficient heat dissipation.

Description:
PRIOITY CLAIM 
   This patent claims priority from the earlier filed Hong Kong Patent Application No. 06112953.4 filed Nov. 24, 2006, by inventors Kai Chiu Wu, Ming Lu, and Chak Hau Pang. 
   TECHNICAL FIELD 
   This invention relates to light emitting assemblies having heat dissipating supports for reducing the operating temperature of the assembly. 
   BACKGROUND OF THE INVENTION 
   Light sources comprising assemblies of light emitters such as light emitting diodes (LEDs) are finding increasing application in mass production applications because of their high efficiency and long life. One such application is light sources for replacing florescent and incandescent lights and the like. 
   High output LEDs, particularly when a large number are used on a common support, produce a significant amount of heat. If elevated temperatures are then produced, the life of the LEDs is reduced. In practice, it is desirable that the LED be placed into contact with heat dissipation surfaces to effectively cool the LED. One such arrangement is described in the applicant&#39;s pending application No. 60/830,110. While this device performs satisfactorily, it will be appreciated that there is an ongoing need for an improved assembly capable of mounting a large number of light emitters and one which can be produced economically. The assembly should include a great deal of heat transfer potential in addition to providing a means for further incorporating the light emitter into the circuitry of an overall lighting assembly. 
   DISCLOSURE OF THE INVENTION 
   According to one aspect of the invention there is provided a light emitter assembly, comprising: 
   a substrate carrying a plurality of light emitters, and 
   a housing including mutually connected thermally conductive ribs spaced apart for air flow therebetween, the substrate supported generally transversely between the ribs, the ribs abutting the light emitters or substrate for thermally connecting the light emitters or substrate to the housing. 
   In another aspect the invention provides a light emitter assembly, comprising: 
   first and second substrates carrying first and second pluralities of light emitters respectively, 
   a housing including mutually connected metal ribs spaced apart for air flow therebetween, both substrates extending generally transversely between the ribs with the second substrate spaced apart from the first substrate for air flow therebetween, the ribs having shoulders abutting the light emitters or substrates and thermally connecting the light emitters to the housing. 
   Preferably the substrates are formed of sheet material, each substrate having a respective peripheral edge and respective planar inner and outer faces, the outer faces being aligned generally parallel, the ribs surrounding the peripheral edges of the substrates, the first substrate having a recess such that light emitted outward from each of the second plurality of light emitters in a direction perpendicular to the outer faces passes through the recess and is not occluded by the first substrate. 
   Preferably a mounting portion of each outer face abuts each light emitter, and one of said shoulders abuts a portion of the inner face opposite each mounting portion. 
   Preferably the ribs extend radially relative to a central axis of the housing and are mutually connected at the longitudinally inner ends thereof. In a preferred embodiment the ribs are also mutually connected by a ring portion at the longitudinally outer ends thereof. 
   The first and second pluralities of light emitters are preferably mounted substantially upon respective first and second pitch circles centred on the central axis, the diameter of the first pitch circle exceeding the diameter of the second pitch circle, the light emitters of the first plurality being circumferentially offset relative to the light emitters of the second plurality. 
   The substrates are preferably ring shaped, most preferably being formed from planar sheet material. 
   The assembly preferably further includes at least one generally transversely extending metal heat dissipation member connected to the ribs intermediate the inner and outer ends. Preferably the heat dissipation member is slotted to receive and engage each of the ribs. 
   The housing preferably has a substantially frustoconical periphery defined by the circumferentially spaced radially outermost edges of the ribs. 
   In another aspect the invention provides a light emitter assembly, comprising: 
   first and second substrates carrying first and second pluralities of light emitters respectively, 
   a housing including mutually connected metal ribs spaced apart for air flow therebetween and extending between an inner and an outer end of the housing, wherein 
   the substrates extend generally transversely between the ribs, the second substrate being spaced apart inwardly from the first substrate for air flow therebetween, the first substrate having a recess such that light emitted outward from each of the second plurality of light emitters in the longitudinal direction faces passes through the recess and is not occluded by the first substrate, and the ribs abutting the light emitters or substrates for thermally connecting the light emitters to the housing. 
   This invention provides an light emitter assembly having satisfactory light dispersion or radiation pattern and a simple design with a reduced number of parts to minimize manufacturing costs. Heat is efficiently dispersed into the housing and the spacings between the ribs of the housing, as well as between the substrates themselves, enhance the heat transfer rate through natural convection in different orientations of the assembly. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Preferred forms of the present invention will now be described by way of example with reference to the accompanying drawings, wherein: 
       FIG. 1  is a pictorial view of an light emitter assembly of the present invention; 
       FIG. 2  is an exploded view of the assembly of  FIG. 1 ; 
       FIGS. 3-5  are outer end views of substrates of the assembly of  FIG. 1 ; 
       FIG. 6  is an end view of the housing of the assembly of  FIG. 1 ; 
       FIG. 7  is an enlarged section illustrating the connection between a rib and substrate; 
       FIG. 8  is a section along line AA of  FIG. 6  showing an outer substrate in dashed outline; 
       FIG. 9  is a section along line BB of  FIG. 6  showing an inner substrate in dashed outline; 
       FIG. 10  is a section along line CC of  FIG. 6  showing an intermediate substrate in dashed outline, and 
       FIG. 11  is detail of the electrical connection between the substrates. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring to  FIGS. 1 and 2 , a light emitter assembly  100  includes three light emitter substrates  1 ,  2 ,  3  and two heat dissipating members  4 ,  5  which are stacked in a housing  6 . The components  1 - 5  are substantially parallel, extending transversely relative to a central longitudinal axis  7 . In the embodiment illustrated the LED substrates  1 ,  2 ,  3  and heat dissipating members  4 ,  5  are in a generally planar ring shape, but it will be understood that different shapes will be equally applicable depending upon the required application of the assembly. 
   Each LED substrate  1 ,  2 ,  3  has an outer surface  1   a ,  2   a ,  3   a  and an opposing inner surface  1   b ,  2   b ,  3   b . Four LEDs  8 ,  9 ,  10  are mounted on the respective outer surfaces  1   a ,  2   a ,  3   a  equally angularly spaced on respective pitch circles  11 ,  12 ,  13  centred on the central axis  7  and emitting light substantially parallel to the axis  7 . 
   The LEDs on the three substrates  1 ,  2 ,  3  are offset radially, the pitch circle diameter  11  exceeding pitch circle diameter  12 , and pitch circle diameter  12  exceeding pitch circle diameter  13 . The LEDs of adjacent pairs of substrates  1 ,  2  and  2 ,  3  are circumferentially offset by 45°. Substrate  1  has a central recess  14  with four indentations  14   a - 14   d  circumferentially offset by 45° from the LEDs  8  for registration with the LEDs  9 , such that light emitted outward from each of the LEDs  9  is not occluded by the substrate  1 . Likewise, substrate  2  has a recess  15  with four equally angularly spaced indentations  15   a - 15   d  for axial registration with the LEDs  10 . In this manner the LEDs  8 ,  9 ,  10  are not blocked by each other or the substrates. Alternatively, transparent windows or substrates may be used for enhancing light emission efficiency in alternate embodiments. 
   In the embodiment shown, each substrate  1 ,  2 ,  3  is formed with a thermally conductive material such as metal-core printed circuit board (MC-PCB) or ceramic based substrate, for assisting heat distribution in each substrate. The MC-PCBs or ceramic based substrates are patterned to provide electrical paths (not shown) thereon for powering the LEDs as generally understood by those skilled in the art. 
   Referring to  FIGS. 6-10 , the housing  6  is a one-piece metal component, for example, of die-cast aluminium or magnesium for good thermal conductivity. The housing  6  generally comprises substantially planar and radially aligned ribs  16 ,  17 ,  18  elongated to join a disc-shaped inner portion  19  to an outer ring  20 . 
   Four ribs  16  are equally angularly spaced, each having a radially outermost edge  21 , an inner shoulder  22  and an outer shoulder  23 . Each of the shoulders  22 ,  23  has a respective transversely aligned shoulder surface  22   a ,  23   a . The substrate  1  abuts the shoulder surface  23   a  below the LEDs  8  and the substrate  3  abuts the shoulder surfaces  22   a  below the LEDs  10 . 
   Angularly offset from ribs  16  by 45° are four ribs  17  that are also are equally angularly spaced. Each rib  17  has a radially outermost edge  24 , an inner shoulder  25  and an outer shoulder  26 . Each of the shoulders  25 ,  26  has a respective transversely aligned shoulder surface  25   a ,  26   a . The substrate  1  abuts the shoulder surfaces  25   a  and the substrate  2  abuts the shoulder surfaces  26   a  below the LEDs  9 . 
     FIG. 7  illustrates the mounting portion  27  of outer face  2   a  which abuts each LED  9 , by way of an illustration of the way all the heat dissipating ribs  16 ,  17  are fixed adjacent a respective LED. The shoulder surface  25   a  abuts the inner face  2   b  opposite each mounting portion  27  and is fixed by a thermally conductive adhesive for allowing efficient thermal connection between the ribs and the substrates. Optionally mechanical fasteners may also be used for joining the substrates and ribs. 
   Eight ribs  18  are equally angularly spaced, each having a radially outermost edge  35 , and shoulders  30 - 34 . The shoulders  30 ,  31 ,  32  abut the substrates  1 ,  2 ,  3  respectively and the shoulders  33 ,  34  abut the metal members  4 ,  5  and are likewise preferably fixed by thermally conductive adhesive. Each member  4 ,  5  extends transversely and is radially notched for receiving the ribs  16 ,  17 ,  18 . With the substrates  1 ,  2 ,  3  and members  4 ,  5  physically spaced apart by a gap, more efficient thermal dissipation from the substrate to the environment, for example air surrounding the substrates, can be achieved. With the substrates thermally connected, heat will be transferred from a substrate of a higher temperature to a substrate of a lower temperature, and therefore more even thermal distribution among the substrates can be achieved. 
   The ribs  16 ,  17 ,  18  are splayed apart in the longitudinal direction, the housing  6  having a substantially frustoconical periphery defined by the circumferentially spaced radially outermost edges  21 ,  34 ,  35  of the ribs  16 ,  17 ,  18 . Fixed to the inner portion  19  is a hollow mounting fitting  37  which receives the electrical circuit  38  for supplying power to the LEDs  8 ,  9 ,  10 . 
   Apertures  38 ,  39  in the substrate  1  are positioned between each LED  8  and are axially aligned with recesses  40 ,  41  in the substrate  2  for enhancing air flow through the substrates. The apertures  38 - 14  and the spacing between the ribs  16 - 18  provides satisfactory air flow and consequently enhance the thermal dissipation efficiency, regardless of the orientation of the assembly  100 . 
   With the axial assembly of the substrates  1 ,  2 ,  3  into the housing, axially aligned pin-and-socket type connectors  42 ,  43 , as shown in  FIG. 11  may provide the electrical connection between the substrates  1 ,  2 ,  3 . 
   Aspects of the present invention have been described by way of example only and it should be appreciated that modifications and additions may be made thereto without departing from the scope thereof.