Abstract:
Techniques for light emitting diode (LED) lighting with heat spreading in illumination gaps. Inexpensive structural aluminum may be suitably employed to form a passive heat spreading mount for plural LEDs whose illumination collectively combines to provide the light needed by a particular lighting fixture, such as a pendant chandelier, by way of example, by angling fins of the passive heat spreading mount to correspond to illumination gaps of the LEDs.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates generally to improvements in light emitting diode (LED) lighting methods and apparatus, and more particularly to advantageous arrangements for locating heat spreading components in illumination gaps of LEDs mounted in lighting fixtures. 
       BACKGROUND OF THE INVENTION 
       [0002]    LED lighting systems are becoming more prevalent as replacements for existing lighting systems. LEDs are an example of solid state lighting and are superior to traditional lighting solutions such as incandescent and fluorescent lighting because they use far less energy, are far more durable, operate longer, can be combined in red-blue-green arrays that can be controlled to deliver virtually any color light, and contain no lead or mercury. As LEDs replace the typical incandescent and fluorescent light fixtures found in many homes and workplaces, the present invention recognizes that it is important to cost effectively dissipate the heat generated by the LEDs used in these systems while maintaining the aesthetically pleasing look of existing lighting hardware. 
         [0003]    As illustrated by  FIGS. 1A ,  1 B and  1 C, a common prior art LED mounting arrangement results in a substantial portion of the light output going outwardly in the direction of a normal to the top surface of a semiconductor photonic chip  12  as seen in  FIG. 1B . As seen in  FIG. 1A , a top view of an LED  10 , the semiconductor photonic chip  12  is mounted on a substrate  14  which is in turn mounted on a bonding pad  16 . The chip  12  is encapsulated beneath an optical lens  18  which focuses the light emitted by the chip  12 . 
         [0004]      FIG. 1B  shows a side view of LED  10  with a plurality of light rays relative to a normal, N, to the top surface of chip  12  illustrating the light emitted by chip  12  as it passes out of lens  18 . LED  10  is an XLaamp™ from Cree, Incorporated. 
         [0005]      FIG. 1C  shows an illustrative plot of the light emitted by LED  10  with the y-axis representing the intensity, I, and the x-axis representing the angle, θ, of the emitted light with respect to the normal, N, of  FIG. 1B . As illustrated in  FIG. 1C , a substantial portion of the light emitted from the LED is along or near the normal, N. Conversely, only a small percentage is emitted transverse to the normal. Angle α, the angle of intensity, is equal to 2*θ. 
         [0006]    One common lighting fixture is a ceiling mounted lighting fixture such as a pendant chandelier  200  shown illustratively in  FIG. 2A . Fixture  200  may suitably comprise a cord  202  including electrical wires connecting to electrical circuitry located in a ceiling  240 , a mounting socket  204 , a light bulb  206  which may suitably be an incandescent or fluorescent bulb, and a decorative glass shade  208 . Many other variations on ceiling mounted lighting fixtures are common, such as multiple light units with a wide variety of mounts. Similarly, a wide variety of floor and wall mounted lighting fixtures are available. With incandescent bulb and fluorescent bulb versions of pendant chandelier  200 , heat from bulb  206  is dissipated into the ambient air around the bulb  206 . 
         [0007]      FIG. 2B  shows one prior art attempt at an LED based chandelier fixture  250 . In  FIG. 2B , circle  252  represents the diameter of the glass of chandelier fixture  250 . In the fixture  250 , a first plurality of LEDs  253 ,  254 ,  255  and  256  were mounted on a mount  260  having three fins at each corner of the mount  260 . A second plurality of LEDs (not shown) was spaced vertically on the mount  260  from the first plurality. All of the LEDs were Nichia LEDs. 
       SUMMARY OF THE INVENTION 
       [0008]    Among its several aspects, the present invention recognizes that in replacing an incandescent or fluorescent bulb or bulbs with multiple LEDs capable of providing a comparable amount of room light in a lighting fixture such as a pendant chandelier, it is necessary to redesign the fixture to provide adequate heat dissipation while maintaining the overall aesthetic appeal of the fixture. With such multiple LED fixtures, the present invention recognizes that a balance must be struck to avoid hot spots while satisfactorily dissipating the heat generated by multiple LEDs. To such ends, the present invention addresses advantageous methods and apparatus for LED lighting with heat spreading in illumination gaps. 
         [0009]    In one aspect of the invention, a heat spreading light emitting diode (LED) mounting arrangement comprises a heat spreading base unit having plural flat mounting areas with each of said plural flat mounting areas having one or more associated angled fins; and at least two LEDs mounted on at least two of the plural flat mounting areas, said at least two LEDs having an angle of intensity so that in operation a substantial majority of emitted light from said at least two LEDs is within a viewing angle in which the intensity of emitted light is 50% of the maximum intensity or higher. Said one or more associated angled fins have an angle so that said fins are located in illumination gaps of said at least two LEDs, a gap for purposes of this application being outside the viewing angle, or in other words, in a location in which the intensity of emitted light is less than or equal to 50% of the maximum intensity of emitted light. In this heat spreading LED mounting arrangement, the heat spreading base unit may suitably be formed of structural aluminum. The heat spreading LED mounting arrangement may further comprise an end cap unit supporting a further LED mounting arrangement thereon. In the heat spreading LED mounting arrangement, said at least two LEDs may be spaced along a length of said base unit. 
         [0010]    In a further aspect, the heat spreading LED mounting arrangement comprises four LEDs which are mounted about a central axis of the base unit and eight angled fins are angled at an angle γ of approximately 45° with respect to normals, N, to four flat mount areas on which the four LEDs are mounted. In this heat spreading LED mounting arrangement wherein four LEDs are employed, these LEDs collectively operate to provide 360° illumination. 
         [0011]    These and other advantages and aspects of the present invention will be apparent from the drawings and Detailed Description which follow. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1A  illustrates a top view of a mounting arrangement for a prior art LED; 
           [0013]      FIG. 1B  shows a side view of the LED of  FIG. 1A ; 
           [0014]      FIG. 1C  shows an illustrative plot of light emitted by the LED of  FIGS. 1A and 1B  with intensity, I, plotted versus angle, θ. 
           [0015]      FIG. 2A  illustrates an exemplary prior art chandelier fixture with an incandescent or fluorescent bulb providing illumination; 
           [0016]      FIG. 2B  illustrates a prior art attempt at an LED based chandelier fixture; 
           [0017]      FIG. 3  illustrates an exemplary embodiment of an LED chandelier lighting fixture in accordance with the present invention; 
           [0018]      FIGS. 4A ,  4 B,  4 C,  4 D,  4 E and  4 F illustrate further aspects of LED mounting arrangements in accordance with the present invention; 
           [0019]      FIG. 5  illustrates an alternative LED mounting embodiment in accordance with the present invention; 
           [0020]      FIG. 6A  illustrates an arrangement not in accordance with the present invention in which heat sink fins are not located in illumination gaps and hot spots result; 
           [0021]      FIG. 6B  illustrates aspects of how an embodiment in accordance with the present arrangement avoids hot spots; and 
           [0022]      FIG. 7  is a flowchart of a method of mounting LEDs in accordance with the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0023]      FIG. 3  illustrates a first embodiment of an LED lighting fixture, a pendant chandelier  300 , in accordance with the invention. Chandelier  300  includes a power cord  302 , an aluminum heat spreading LED mount  304 , a plurality of LEDs  306  and a glass or plastic shade  308 . A mounting cap  310  fits over electrical cord  302  and covers most of an opening  312  which allows insertion of the heat spreading LED mount  304  and LEDs  306  into the interior of the shade  308  upon assembly of the chandelier  300 . 
         [0024]    The mounting cap  310  covers the opening  312  with the exception of an air gap or air gaps  314  to allow airflow as follows. When hung from a ceiling and in normal operation, heat from the LEDs  306  is transferred to the heat spreading LED mount  304  and to the surrounding air inside the glass shade  308 . The heated air rises escaping from the air gap  314 . Cooler air is drawn into the bottom of the glass shade so that a flow of heat dissipating air as represented by dashed lines  316  cools the fins of the mount  304  and the LEDs  306 . In  FIG. 3 , heat sink fins for the LEDs and an LED facing the viewer are not shown to better illustrate the overall chandelier  300 . Further details of the fins and the mounting of LEDs  306  are shown in  FIGS. 4A-4E  and described below. 
         [0025]      FIGS. 4A ,  4 B,  4 C,  4 D,  4 E and  4 F illustrate details of embodiments of a mount  450  suitable for use as the mount  304  in  FIG. 3 . Effective heat dissipation and a cost effective price are two design criteria for selecting the materials for the mount  450 . While pure aluminum has a conductivity of approximately 200° C./watt, a more affordable and readily available structural aluminum T bar has a conductivity of approximately 160° C./watt and provides a cost effective choice for the mount  450 . 
         [0026]    After cutting about 0.5″ from bases  402  and  404  of three inch pieces  406  and  408  of T-shaped aluminum 6061, the two pieces  406  and  408  can be joined together as shown in  FIG. 4A  with a layer of thermal gap filler  419 , such as a thermal epoxy, sandwiched between the two bases  402  and  404  to form a preform  400  utilized to make the mount  450  shown in  FIG. 4D . 
         [0027]    As seen in  FIG. 4B  a base unit  420  is formed by bending ends  412  and  414  of piece  406  at fold lines  413  and  415 , respectively, and ends  416  and  418  of piece  408  at fold lines  417  and  419 , respectively, at an angle β of approximately 45°. 
         [0028]    As further seen in  FIG. 4B , LEDs  456  and  458  are mounted on base  402  and on the face of piece  408 .  FIG. 4D  shows the mount  450  rotated 180° so that base  404  and piece  406  are exposed to the viewer and it is seen that further LEDs  460  and  462  are mounted on base  404  and piece  406 , respectively. As seen from  FIGS. 4B and 4D , the LEDs  456 ,  458 ,  460  and  462  are spaced along the length of the mount  450  to improve the heat dissipation of mount  450 . They may also be mounted at the same vertical position along the length of unit  420  or with different spacings than the one shown. Different numbers of LEDs may also be employed. For example, a module like the module  450  might be modified to have two bands of four LEDs along the length of the module as illustrated in  FIG. 4F , for example. For a corner wall unit two or three LEDs might be employed with no LED on a surface or surfaces of the module facing the wall. 
         [0029]      FIG. 4C  shows a further end cap unit  440  formed from a further piece of T-shaped aluminum  6061 . The width w of end cap unit  440  is substantially the same as the length of the bases  402  and  404  of pieces  406  and  408 . Ends  442  and  444  are bent up at an angle β of approximately 45° and an LED  464  is mounted on surface  446  of unit  440 . 
         [0030]    As seen in  FIG. 4D , the base unit  420  of  4 B and the end cap unit  440  of  FIG. 4C  are combined to form mount  450  by inserting leg  448  of preform  440  between bases  402  and  404  and securing the base unit  420  and end unit  400  together. 
         [0031]    As seen in  FIG. 4E  which shows a top view of base unit  420 , the bending described above results in angled heat sink fins which are advantageously located in illumination gaps for the LEDs  456 ,  458 , 460  and  462  as discussed further below in connection with  FIGS. 6A and 6B . Thus, a large and effective heat dissipating surface area is provided without substantial interference with the bulk of the illumination provided by the LEDs  456 ,  458 ,  460  and  462 . For four LEDs driven with a current of 350 mA, the module  450  provides each LED with a cooling surface area of more than 4 square inches/watt thereby providing adequate passive thermal protection so that the LEDs do not run away. 
         [0032]      FIG. 4F  shows an alternative arrangement  480  in which two bands of four LEDs  480 - 483  and  484 - 487 , respectively, are spaced apart along the vertical length of a mounting module  492 . As seen for LED  483  on face  498 , additional heat fins  497  and  499  may be provided so that heat fins are located in illumination gaps in both the x- and y-dimensions. 
         [0033]      FIG. 5  shows an alternative mount arrangement  550  formed from two T-shaped pieces  506  and  508  with a thermal gap filler  512  between them and angled mount supports  522 ,  524 ,  526  and  528  arranged as follows. Taking mount support  522  by way of example, it is seen that heat dissipating fins or legs  523  and  525  are angled with respect to a normal N to an LED chip  506  mounted thereon at an angle γ so that these heat dissipating fins are located in illumination gaps for the LED chip  505  and the neighboring LED chips  507  and  509 . 
         [0034]      FIG. 6A  illustrates a mounting arrangement  600  not in accordance with the present invention As illustrated in  FIG. 6A , a plurality of pairs of heat sink fins  602  and  604 ,  606  and  608 ,  610  and  612 , and  614  and  616  are not located in the illumination gaps of multiple LEDs  622 ,  624 ,  626  and  628 , respectively. As a result, they result in reflection of substantial amounts of illumination from the LEDs  622 ,  624 ,  626  and  628  resulting in hot spots  632   634 ,  636  and  638 , respectively, which are generally not pleasing to a typical observer and thus arrangement  600  while providing an adequate heat sink does not provide an acceptable lighting fixture. 
         [0035]    By contrast,  FIG. 6B  illustrates how a mounting arrangement  650  in accordance with the present arrangement provides a much more diffuse lighting output without unacceptable hot spots. With fins  652 ,  654 ,  664  and  666 , angled at 45°, the bulk of the illumination from the LEDs  656 ,  658 ,  660  and  662 , such as the LED  10  of  FIGS. 1A-1C  having a viewing angle of 90°, passes directly to glass  670 . Rays such as ray  680  have substantially reduced intensity at the angle shown and add with other reduced intensity rays to make the fall off at the corners less noticeable. Similarly, rays such as ray  682  hit fin  652  at a shallow angle and are reflected so as to add with other reduced intensity rays to again reduce the fall off at the corners. Thus, the fins  652 ,  654 ,  664  and  666  are effectively in illumination gaps in which intensity of illumination from the LEDs  656 - 660  is less than 50% and hot spots are avoided. 
         [0036]      FIG. 7  illustrates a method  700  of mounting heat spreading light emitting diodes (LEDs) to avoid hot spots in accordance with the present invention. In step  702 , a heat spreading base unit having plural flat mounting areas with each of said plural flat mounting areas having one or more associated angled fins is utilized. In step  704 , at least two LEDs are mounted on at least two of the plural flat mounting areas, said at least two LEDs having a viewing angle so that in operation a substantial majority of emitted light from said at least two LEDs is within the viewing angle, wherein said one or more associated angled fins have an angle so that said fins are located in illumination gaps of said at least two LEDs. In step  706 , an end cap unit supporting a further LED is mounted on an end of the base unit. Optionally, in step  708 , two or more LEDs are spaced along a length of said base unit and heat sink fins are provided in illumination gaps in two dimensions. 
         [0037]    In step  704 , four LEDs may be mounted about a central axis of the base unit and eight angled fins then are angled at an angle γ of approximately 45° with respect to normals, N, to four flat mount areas on which the four LEDs are mounted. Further, portions of said base unit contacting said at least two LEDs may suitably have a conductivity of at least approximately 160° C./watt. 
         [0038]    The method  700  may further comprise the step of forming said base unit from two T-shaped bars with their bases secured together, and a layer of thermal gap material may be advantageously clamped between said bases of the T-shaped bars. 
         [0039]    In step  704 , said at least two LEDs may suitably have a viewing angle of 90°. Further, in said illumination gaps, the intensity of light emitted by said LEDs is less than or equal to 50% of the maximum intensity of light emitted thereby. 
         [0040]    While the present invention has been disclosed in the context of various aspects of presently preferred embodiments, it will be recognized that the invention may be suitably applied to other environments consistent with the claims which follow. By way of example, while the present invention has been disclosed primarily in the context of a pendant chandelier embodiment, it will be recognized that the present teachings may be readily adapted to floor, wall and other mountings of lighting fixtures. While presently preferred materials and arrangements of exemplary numbers of LEDs are described herein, other materials and arrangements may be adapted to particular lighting environments. For example, a material or materials other than or in addition to aluminum may be employed to dissipate heat. As a further example, for LEDs having a viewing angle of 120°, three LEDs on a triangular mount with fins at 120° might be employed consistent with the teachings herein.