Patent Publication Number: US-7588351-B2

Title: LED lamp with heat sink optic

Description:
TECHNICAL FIELD 
     The invention relates to electric lamps and particularly to electric lamps with LED light sources. More particularly the invention is concerned with an electric lamp with an LED light source and a heat sinking optic. 
     BACKGROUND ART 
     Efficient LED lamp designed to replace the standard incandescent lamp are rapidly moving to commercial production. An essential problem is heat sinking the LED&#39;s to increase the lumen output and to preserve the potentially very long life of the LEDs. Heavy metal heat sinks have been used along expensive and sometime awkward air cooled structures. These are heat sinks are impractical in ordinary use and add additional cost to the lamp for material and manufacturing costs. LED lamps are frequently being assembled by hand, which limits their reasonable market volume. 
     DISCLOSURE OF THE INVENTION 
     An LED lamp may be made with a heat sink optic. The assembly includes a base having a first electrical contact and a second electrical contact for receiving current. At least one LED is mounted on a thermally conductive LED support. The LED support has at least one electrical connection for the at least one LED and provides thermal conduction of heat from the at least one LED. The LED support is mounted in the base and electrically coupled through the first electrical contact to electrical current. A light transmissive, and heat diffusing optic has an external wall and an internal wall defining a cavity. The at least one LED is positioned in the cavity. The optic is in thermal contact with the LED support, and the optic is mechanically coupled to the base. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a schematic cross sectional view of an LED lamp. 
         FIG. 2  shows a schematic cross sectional view of a further alternative LED lamp 
         FIG. 3  shows a schematic cross sectional view of a further alternative LED lamp. 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     An LED lamp with a heat sink optic may be constructed from a base, an LED light source, an LED support, and a heat sinking optic. 
     The base may be constructed as a thread metal shell having a wall defining an interior volume. The base may be similar to those typically used in thread mounted incandescent lamp bulbs. The base includes a first electrical contact and a second electrical contact for receiving line current, and mechanical contacts for coupling to a corresponding electrical socket. In a preferred embodiment, the base includes three or more coupling points, such as indentations, defining a location plane against which the LED support may be positioned. A ledge, groove or step may also be formed in the base, against which an edge of the LED support may be positioned. The base may also include formed features to press against the LED support to position the LED support in tight thermal contact with the base or with heat sinking optic. The base may also be formed with positioning or latching features to securely mate with the heat sinking optic. For example, the base wall may include a ledge, step or groove or similar shaped portion to mate the base with an end edge, or side wall of the optic to accurately and securely locate the base with respect to the optic. The base may include a wall portion that over laps a portion of the optic where the optic includes an indentation or protuberance, so that the base wall may be correspondingly indented or protruded to mechanically mate with the optic. For example, the wall portion of the base may be include a step that axial mates with and locates on an edge end of the optic. An exteriorly over lapping portion of the base wall may then be pressed into a recess formed in the optic to secularly latch the base to the optic. 
     At least one LED is mounted on a LED support. The LED has electrical connections that may be powered to cause the emission of light from the LED. The LED may be a light emitting semiconductor chip for “chip on board” mounting or may be a typical LED assembly with a supporting lead frame, electrical connections, and an optional optic, such as a covering lens. It is understood that two or more LEDs may be alternatively used, and that the LEDs may provide the same or different colors. In general the at least one LED produces light which is optically guided by the optic to a field to be illuminated and heat which is thermally conducted by conduction and radiation away from the LED. It is only important that the LED light source, whether it is a LED chip or an LED assembly be thermally coupled to the support structure for thermal conduction away from the LED light source. 
     In the preferred embodiment, the at least one LED comprises one or more pairs of a first LED and a second LED. Each first LED and each second LED having a preferred direction of current operation, and each being electrically coupled in series with respect at least one other LED of a pair. One LED of each pair of LEDs is electrically coupled to a first electrical contact in a first current orientation with respect to line current and while the second LED of each pair of LEDs is electrically coupled in a second current orientation, opposite the first current orientation, to a second electrical contact. The second electrical contact is opposite to that of the first LED of the respective LED pair. In this way, the first LED and second LED pair may act as mutually rectifying current diodes for each other. 
     The LED support has at least one electrical connection for the at least one LED. The LED support is well coupled mechanically to the LED for good thermal conduction from the LED to the LED support. The preferred LED support includes one or more electrical connections for the LED. The electrical connection(s) may in fact be the mechanical connections providing the thermal connection to the LED support. The LED support may be a printed circuitry board, a metal plate with conductive traces, a thermally conductive ceramic or other thermally conductive support structure, generally planar in form supporting the LED or LEDs (chips or assemblies) as the case may be. The LED support may also support circuit features such as alternating to direct current conversion, voltage reduction, ballasting, over current or over voltage protections, switching, timing, or similar electrical features. The leads for the LED(s) may pass along the surface or may pass through formed holes in the LED support for electrical connection. The LED support may further include one or more positioning and coupling features such as a peripheral flange extending radially, or a peripheral wall extending axially that may be snuggly positioned against the optic or the base or both. For example, a peripheral wall may be radially extended as a disk to mate against a circular end wall edge of an optic. A peripheral wall may be radially extended as a disk to mate against a circular ledge formed on the optic. The peripheral wall may extend axially in a forward direction or a rearward direction to closely mate to the interior diameter of an inner wall of the optic. The peripheral wall may extend to mate with the end wall edge of the optic and overlap an exterior portion outside diameter of the optic exterior. A latch may be formed in the LED support, such as a protuberance or a recess, and the optic may be correspondingly formed, so the LED support and the optic may be snapped, latched or otherwise fitted and coupled one to the other. In these ways, the LED light source and LED support maybe easily and accurately inserted into, covered across or coupled around an end of the optic respectively as a plug insert, an end plate or snapped on cap. The preferred coupling provides accurate optical alignment of the LED with respect to the optic and secure thermal coupling to the optic for thermal conduction. 
     The LED support may alternatively be mounted in the base and electrically coupled through the first electrical contact to line current. For example, the LED support may be mounted on a step, ledge, spring clip or similar positioning feature formed on an interior side of the base wall. In this way the LED and LED support may be inserted into an open end of the base and electrically and mechanically coupled to the base. Heat may then be conducted from the LED support to the base wall. At the same time the base wall may be formed with a groove, step, ledge, guide wall, or other coupling feature to mechanically and thermally mechanically latched, snapped or otherwise coupled to the optic. The base may then be mounted to an interior wall of the optic, and end edge wall of the optic or an outer wall of the optic. In this way the base may be mechanically coupled to the optic, and heated may be conducted from the LED through the LED support to the base and optic. 
     In a preferred embodiment, the LED support includes a first contact in mechanical and electrical contact with the interior of an electrically conductive base wall. In a preferred embodiment, the LED support has a plurality of LEDs arranged in rows or rings on a LED support with a first electrical connection on one side of a first row or ring of LEDS, and an intermediate connection between the first row or ring of LEDs and a second row or ring of LEDs. A second electrical connection from a second side of the second row or ring of LEDS is made with the first row of LEDs and the second row of LEDs. The LEDs may be electrically oriented in reverse polarity. 
     A light transmissive, and heat diffusing optic is mechanically supported by the base and positioned to optically span the at least one LED. The preferred optic is formed from glass, quartz, polycarbonate, or a thermally conductive ceramic. There are a number of preferred light transmissive ceramics. Some have thermal conductivities greater than 30 watts per meter-Kelvin. These include aluminum nitride (AlN) (200 W/mK), which may be regular grained AlN (15-30 micrometer grains), submicron-grained AlN or nano-grained AlN. Sapphire (35 W/mK); alumina (Al 2 O 3 ) (30 W/mK), submicron alumina (30 W/mK), or nanograined alumina (30 W/mK) may be used. Magnesium oxide (MgO) (59 W/mK) is also useful. There are advantages and disadvantages to each of these materials. Some have high transmissivities in the infrared range from 3 to 5 microns, which is approximately the peak radiation point of the typical LED chip&#39;s operating temperature of 300 K to 400 K. The better IR transmitters include aluminum nitride (AlN), alumina (Al 2 O 3 ), and magnesium oxide (MgO). Spinel, AlON, YAG, and yttria are also transparent in the 3 to 5 micron range. Other ceramics such as spinel, AlON, YAG and Yttria are transparent in the visible, but have low thermal conductivity (less than 30 W/mK) and therefore are not as desirable as aluminum nitride (AlN), alumina (Al 2 O 3 ), and magnesium oxide (MgO). Also, some materials such as YAG are not very transmissive (80% or less) in the IR range from 3 to 5 microns. The light transmissive heat sink further adds to cooling by radiating heat from the LED junction, which is absent, or limited in the case of a plastic or glass optic. The preferred light transmissive heat sink materials are therefore good at further reducing self-heating by allowing enhanced IR radiation, and in particular have a transmission greater than 80 percent in the IR region of from 3 to 5 microns. Other materials have lower indexes of refraction than the associated dies have, and thereby encourage light extraction from the LED die. The Applicants prefer aluminum nitride for thermal conductivity and for a thermal coefficient of expansion well matched to that of many LED chips. Nano-grained or submicron grained alumina is preferred for thermal conductivity and for transparency. Alumina in differing forms is preferred for manufacturing cost. Magnesium oxide is preferred for optical transmission and for a low refractive index. 
     The optic may include an input window at a first end, an intermediate light guide portion with an internally reflective surface, and an output window at a second end. The input window and output windows may include refractive features to develop a preferred distribution of the emitted light. The ends may be axially opposed one to the other. The optic may include a light diffusing exterior surface on some or the entire surface. The optic may include a light reflecting coating, such as a metallization, or interference coating, on some or the entire exterior surface to shape or direct the output light pattern. The optic may include a light filtering coating, such as a thin metallization, absorption coating or interference coating, on some or the entire exterior surface to filter or color or color pattern the output light. The optic may include on an interior surface, an end edge wall or exterior wall, one or more recesses or protuberances to mechanically mate with either the LED support or the base or both to mechanically align the LED with the optic, to thermally couple the LED through the LED support to the optic and to mechanically couple the base to the optic to enable threading of the whole assembly in to a socket. In one preferred embodiment, the optic includes a formed core recess to enclose the LED. The volume of the core recess may be filled with a light transmissive potting material, such as a silicone material as known in the art thereby providing further thermal coupling from the LED to the optic. The potting material; may include diffusion materials or colorant materials. 
     In one preferred embodiment, the optic includes a mechanical coupling for mating with the base. For example an interior surface or the exterior surface of the optic may include a ledge, groove or recess, to which a correspondingly shaped piece of the support or base may be tightly fitted by spring fitting, peening, gluing or similarly joining the fitted pieces. 
     In one preferred embodiment, the optic includes a formed recess mechanically coupled to a mechanical protrusion of the support of the LED. In one preferred embodiment, the optic includes a formed protrusion, mechanically coupled to a mechanical recess of the support of the LED. 
     In one preferred embodiment, the optic includes at least one light refractive element. The refractive elements may be a smooth single surface, a plurality of lenticules, or facets, or Fresnel edges, ribs or arranged circularly, axially or diffusely. 
     In one preferred embodiment, the optic includes at least one refractive band extending around the optic. In one preferred embodiment, the optic includes at least one refractive facet on the end of the optic. In one preferred embodiment, the optic includes at least one refractive band extending axially along the optic. 
     In one preferred embodiment, the optic has a diffusing surface intermediate the at least one LED and the optic. In one preferred embodiment, the diffusing surface is formed as a portion of the optic. The diffusing surface may be mechanically formed by etching, grinding or similar abrading or altering the surface or by coating the surface with a diffusing material. In one preferred embodiment, the diffusing surface is a separate body intermediate the optic and the at least one LED. For example a diffusing plate, diffusing filler, or diffusing potting may be inserted intermediate the LEDs and the optic. For example, a diffusing plate may be mechanically or frictionally engaged with an interior surface of the optic to intercept all or most of the light transmitted form the LED toward the optic. In the same fashion, a coloring layer may be inserted intermediate the LED and the optic to filter or color the emitted light. Alternatively the diffusing layer may be suspended over the LED from the LED support. It is understood the intermediate layer may be diffusing, coloring (e.g. phosphor coated), filtering or any combination thereof. In a preferred embodiment, the diffusing surface is formed as a portion of the least one LED. It is understood that in an LED assembly the exterior cover lens may be diffusing, coloring (e.g. phosphor coated), or filtering. 
     In a preferred embodiment, the optic comprises a cylindrical light guide optically coupled at a first end to the one or more LEDs and having a second end including a refractive element facing a field to be illuminated. In a preferred embodiment, the optic is formed from a light transparent ceramic selected from the group including: glass, quartz, polycarbonate, and acrylic. There are a number of preferred light transmissive ceramics that have thermal conductivities of 30 watts per meter-Kelvin or more. These include aluminum nitride (AlN) (200 W/mK), including regular grained AlN (15-30 micrometer grains), submicron-grained AlN or nano-grained AlN; sapphire (35 W/mK); alumina (Al2O3) (30 W/mK), submicron alumina (30 W/mK), or nanograined alumina (30 W/mK); or magnesium oxide (MgO) (59 W/mK). Each of these materials has advantages and disadvantages. Some of the light transmissive heat sink materials are also highly transmissive in the infrared range from 3 to 5 microns, which happens to be the approximate peak radiation point of the usual LED chip temperature operating range of 300 K to 400 K. The better IR transmitters include aluminum nitride (AlN), alumina (Al2O3), and magnesium oxide (MgO). Spinel, AlON, YAG, and yttria are also transparent in the 3 to 5 micron range. Other ceramics such as spinel, AlON, YAG and Yttria are transparent in the visible, but have low thermal conductivity (less than 30 W/mK) and therefore are not as desirable as aluminum nitride (AlN), alumina (Al2O3), and magnesium oxide (MgO). Also, some materials such as YAG are not very transmissive (80% or less) in the IR range from 3 to 5 microns. The light transmissive heat sink then adds an additional cooling mechanism by radiating heat from the junction, which is absent in the case of a plastic or glass, lens or window. The preferred light transmissive heat sink materials are therefore good at further reducing self-heating by allowing enhanced IR radiation, and in particular have a transmission greater than 80 percent in the IR region of from 3 to 5 microns. Other materials have lower indexes of refraction than the associated dies have, and thereby encourage light extraction from the LED die. The Applicants prefer aluminum nitride for thermal conductivity and for a thermal coefficient of expansion well matched to that of many LED chips. Nano-grained or submicron grained alumina is preferred for thermal conductivity and for transparency. Alumina in differing forms is preferred for manufacturing cost. Magnesium oxide is preferred for optical transmission and for a low refractive index. 
     In one preferred embodiment, light transmissive coupling material is in intimate contact with the at least one LED and with the optic. In one preferred embodiment, the LED support includes a center contact in electrically contact with a center contact of the base. 
     In one preferred embodiment, the optic includes an internal ledge to position the LED support. In one preferred embodiment, the optic includes a curved face radial of the plane of the LED positions. The curved surface has a reflective exterior coating and an optical curve to reflect light emitted radially from the LED(s) in a forward direction, substantially parallel to the lamp axis. Alternatively the reflective exterior coating reflects the radially emitted light at an angle to the lamp axis providing a cone of emitted light. In one preferred embodiment, the optic includes an internal coupling to latch with the base. 
       FIG. 1  shows a schematic cross sectional view of an LED lamp  10 . The lamp  10  comprises a threaded base  12  formed from a tubular metal shell similar to the typical Edison lamp base. As shown, the base  12  may include a first latch  14  and a second latch  16  formed along upper end of the metal side wall. The preferred first latch  14  comprises one or more indentations. The second latch  16  may similarly comprise one or more indentations. It is understood the latches described here may be male/female inverted to be protrusions. Alternatively a groove and rib or spline type couplings may be used. Other latching structures may also be used. The optic  20  comprises a heat conductive, light transmissive material with an external wall  22  and an internal wall  24  defining a cavity  26 . The external wall  22  may be formed to be smooth, or curved so as to provide a desired refractive aspect or detailed with facets, lenticules, frosted or similar refracting or diffusing features. As show, optic  20  includes an upper portion with a cylindrical side wall  21  with total internal reflection, and convex lens  23  formed on the axial end. The exterior wall  22  is formed with latch features to couple with indentations designed to mate with the first latch  14  of the base  12 . The base  12  and optic  20  may then be snuggly mated to together. Alternatively glue may be used to bond the base  12  to the optic  20 . The support  30  may be a cylindrical metal platform having a skirt  32  including latching indentations that mate with the second latch  16  of base  12 . The skirt  32  also includes a ledge  34  and sidewall  36  portion that snuggly mate to the end faces of the optic  20 . The support  30  may be in the form of a tube with an open upper end supporting an LED light source  42  in the open end as a plugged in element or the support  30  may be a closed end tube supporting the LED light source  42  along the top (upper) face of the closed end tube. The side wall  36  of the support  30  and the interior wall of the optic  20  are sized and shaped to snuggly fit together, for example as tubular sections with closely telescoping respective inner and outer diameters. The close fit enables good heat conduction from the support  30  to the optic  20 . The LEDs  40  may be mounted on an LED light source  42  that comprises a thermally conductive plate mounted in the end of the support  30 . The skirt  32  and side wall  36  of the support  30  are sized to enable proper depth insertion of the support  30  into the cavity  26 . The ledge  34  of the skirt  32  then blocks the end wall of the optic  20 . The LED light source  42  may be a thermally conductive ceramic, a printed circuit board, a metal body with appropriate electrically insulating layers or similarly appropriate mechanical support for enabling electrical connection of the LEDs  40  while providing good thermal conduction from the LEDs  40  to the support  30 , and optic  20 . The LED support  42  may include circuitry for controlling or operating the LEDs  40 . The LEDs  40  are mounted to face outwards to direct light through the optic  20 . In the preferred embodiment the LEDs  40  are extended into the cavity  26  to be at or above the level (dotted line) of the end of the side wall of the base  12  so that light emitted sideways from the LEDs  40  is not blocked by the first latch  14  or the adjacent end portion of the side wall of the base  12 . The lamp  10  may optionally include additional circuitry to electrically operate the LEDs  40 . For example, a circuit plate  50  may be positioned in the base  12  cavity  26  between the LED light source  42  and the end contact  60  of the base  12 . As shown, a circular second circuit plate  50  may be positioned, for example pinched or clipped, between the lower side of the skirt  32  and the second latch  16 . The lamp  10  may be assembled by joining the LED light source  42  and the support  30 . The second circuit board  50 , if any may be snapped in place on the bottom side of the support  30 . The LED light source  42  and support  30  may then be loaded into the cavity  26  of the optic  20 . The base  12  is then applied by latching the first  14  and second  16  latches. Electrical connections are made as in Edison lamps. The side wall of the base  12  is electrically coupled through the support  30  (or the second circuit board  50 ) to LED light source  42  (or directly to the LED  40  connections). The end contact  60  of the base  12  is electrically coupled through a center lead  62  to the LED light source  42  (or indirectly through the second circuit  50 .) The snug snap fit of the assembly enables rapid assembly and good heat conduction from the LEDs  40  and LED light source  42  to the optic  20  and base  12 . 
       FIG. 2  shows a schematic cross sectional view of an alternative LED lamp  100 . The LED support  110  need not latch to the base  112 . The support  110  may be fitted in the cavity  114  formed in the optic  116  and substantially retained in place by the friction of a snug fit. Instead of a second latch, the base  112  may be formed with spring tabs  118 . The spring tabs  118  extend from the side wall of the base  112  to contact the support  110  and press the support  110  into position with the optic  116 . The spring tabs  118  may simultaneously form one of the electrical contacts between the base  112  and the support  110 . The base  112  is otherwise latched the exterior of the optic. A light altering element  120  may also be placed in the cavity  114  between the LED light source  122  and light exit path through the optic  116 . The light altering element  120  may be a phosphor doped or coated glass, plastic or similar optical element or similarly colored optical element. Alternatively the light altering element  120  may be a light diffuser. Alternatively the light altering element  120  may be a phosphor or similar light color altering or light diffusing coating. It is convenient to have replaceable colored inserts or coatings placed in or formed on inner surface of the optic  116 . The same standard components may then be used to make a variety of differently color lamps. It is understood the interior surface of the optic may be etched, or coated to form the light altering element  120 . The optic  116  may also be formed with facets, or similar refractive elements  117  on the exterior surfaced. 
       FIG. 3  shows a schematic cross sectional view of a further alternative LED lamp  200 . The LED support need not latch to the base. The LED support  210  may include latch features  212  to mate with the interior of the optic  230 . For example, indentations  232  may be formed on the interior wall of the optic  230 , and the side wall of the support  210  may include corresponding features  212  to couple the support  210  to the interior wall of the optic  230 . The optic  230  as shown may include an outer end with a surface coating  231  that may be a filter, colored or diffusing and a side deflecting end reflector  233 . It is again convenient to use a skirt  214  and ledge  216  structure to properly locate the LED light source  240  optically in the depth of the cavity. The skirt  214  may extend to electrically contact the side wall of the base  220  for one of the LED electrical connections and of course for thermal conduction from the support  210  to the base  220 . The optional second circuit plate  250  may be positioned in the lower skirt  214  region. Intermediate the LEDs  260  and the optic  230  an optional side optic  270  may be included on the support, such as ring shaped prism or reflector. Where the side emission of LEDs  260  is adequately intercepted by the side optic  270 , the side wall  222  of the base  220  may be extended farther up the side of the optic  230  for thermal conduction. The interior of the cavity in the optic  230  may also optionally include a light refracting element  280 , such as an inserted Fresnel lens positioned intermediate the LEDs  260  and the light exit path through the optic  230 . The cavity in the optic  230  may also be filled with a sealant  290  intermediate the LEDs  260  and the interior wall of the optic  230 . Silicone fills are known in the art for this purpose. The sealant  290  may include phosphors, other colorants or light diffusing materials. 
     The snap together construction allows for rapid manufacture while addressing heat sinking and the need for numerous variations in color, diffusion, and beam spread. While there have been shown and described what are at present considered to be the preferred embodiments of the invention, it will be apparent to those skilled in the art that various changes and modifications can be made herein without departing from the scope of the invention defined by the appended claims.