Patent Publication Number: US-2010127299-A1

Title: Actively Cooled LED Lighting System and Method for Making the Same

Description:
FIELD OF THE INVENTION 
     The present invention relates to illumination systems that utilize light emitting diodes (“LEDs”) to provide light, and more specifically to LED illumination systems that incorporate active cooling, so the LEDs operate in a favorable temperature range. 
     BACKGROUND 
     LEDs offer benefits over incandescent, high energy discharge (“HID”) and fluorescent lights as sources of illumination. Such benefits include high energy efficiency and longevity. To produce a given output of light, an LED consumes less electricity than an incandescent or a fluorescent light. And, in general, the LED will last longer before failing. 
     The level of light that a typical LED outputs depends upon the amount of electrical current supplied to the LED and the operating temperature of the LED. Thus, the intensity of light emitted by an LED changes when electrical current is constant and the LED&#39;s temperature varies and when electrical current varies and temperature remains constant. Operating temperature also impacts the usable lifetime of most LEDs. Accordingly, an LED typically has a temperature range that can sustain efficient operation for many years without failure. 
     The conventional technologies available for maintaining an LED at a desired operating temperature are generally limited. Conventional technologies frequently involve inefficient manufacturing procedures, can be costly to implement, are often inflexible, and may lack sufficient finesse for maintaining an LED at optimal operating conditions. 
     Accordingly, to address these representative deficiencies in the art, what is needed is an improved technology for operating an LED at a desired temperature or within a specified range of temperatures. Moreover, a need exists for applying temperature control or thermal regulation to an LED in a manner that supports cost-effective manufacturing. Such need encompasses not only product architectures that promote manufacturability, but also processes for fabrication and manufacturing. Another need exists for processes and designs that tightly integrate thermal regulation or cooling with an LED. Yet another need exists for efficiently removing heat generated by an LED. Still another need exists for attaching a cooling circuit and an LED drive circuit to one substrate, for example to reduce size, to control cost, to minimize manufacturing steps, or to improve flexibility. A capability addressing one or more of the aforementioned needs, or some similar want in the field, would advance LED lighting. 
     SUMMARY 
     In one aspect of the present invention, a lighting system, apparatus, or device can comprise one or more LEDs. The LEDs can emit or produce visible light, for example light that is white, red, blue, green, purple, violet, yellow, multicolor, etc. Thus, the light can have a wavelength or frequency that a typical human being can perceive visually. Furthermore, the emitted light can have spectral content invisible to a human observer, for example in an ultraviolet or near-ultraviolet spectral range. The emitted light can comprise photons, luminous energy, electromagnetic waves, radiation, or radiant energy. 
     In addition to one or more LEDs, the lighting system can comprise a system that thermally regulates or controls at least one LED, for example via cooling or extracting heat from the LED. Accordingly, a thermal regulation system can provide the LED with a temperature or a thermal condition that benefits the LED&#39;s operation, for example enhancing efficiency, reducing risk of failure, providing desirable spectral content, or extending the LED&#39;s useful life. 
     The thermal regulation system can comprise a substrate, at least part of which is electrically insulative (or inhibits flow of electricity) and is thermally conductive (or promotes heat transfer). The term “substrate,” as used herein, generally refers to a material, or an integrated combination of materials, upon which circuits, circuit elements, LEDs, conductors, or components that are electrical (or optical, semiconductor, electronic, etc.) can be mounted. A substrate can comprise a plate, wafer, sheet, or material having at least one flat surface, to name a few possibilities. Moreover, a substrate can comprise a base material that is coated, plated, layered, deposited, or filmed with another material. The base material can comprise an electrically insulating material, while the coating can comprise a metallic plating, for example. Candidate base materials for the substrate of the thermal regulation system can comprise ceramic, alumina, aluminum oxide, aluminum nitride, boron nitride, diamond, silicon dioxide, or some other inorganic substance (not an exhaustive list). As an alternative to applying a coating on the base material, the substrate can be uncoated. 
     An electrical circuit that cools the substrate can be attached to one side (or face) of the substrate. That cooling electrical circuit can comprise at least two different materials, which may be dissimilar metals or semiconductors, cooperatively extracting heat from the substrate in response to a flow of electricity. The cooling electrical circuit, which can be viewed as a type of heat pump, can cool via thermal electric (“TE”) cooling or via the Peltier effect, for example. One of the two different materials, or some other portion of the cooling electrical circuit that conducts electricity, can adjoin, contact, or touch that side of the substrate. 
     The LED can be mounted to another side (or face) of the substrate (e.g. opposite the electrical cooling circuit), for example via soldering to a metal overcoat. In this configuration, the substrate can provide an electrical barrier or electrical insulation between the cooling electrical circuit and another circuit that supplies electrical power to the LED. Meanwhile, the substrate can exhibit low thermal resistance to provide sufficient transmission of heat or thermal conductivity. Via low thermal resistance, the cooling effect of the cooling circuit reaches the LED, and the LED can be cooled efficiently. That is, heat generated by the LED can transmit preferentially through the substrate to facilitate active heat removal by the cooling electrical circuit. 
     The discussion of cooling or thermally regulating LEDs presented in this summary is for illustrative purposes only. Various aspects of the present invention may be more clearly understood and appreciated from a review of the following detailed description of the disclosed embodiments and by reference to the drawings and the claims that follow. Moreover, other aspects, systems, methods, features, advantages, and objects of the present invention will become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such aspects, systems, methods, features, advantages, and objects are to be included within this description, are to be within the scope of the present invention, and are to be protected by the accompanying claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a line drawing of a lighting system comprising an LED and a capability for cooling the LED in accordance with certain exemplary embodiments of the present invention. 
         FIG. 2  is a cross sectional view of a lighting system, comprising an LED and a capability for cooling the LED, connected to a source of electrical power in accordance with certain exemplary embodiments of the present invention. 
         FIG. 3  is a line drawing of an exemplary cooling system for a lighting system in accordance with certain embodiments of the present invention. 
         FIG. 4  is functional block diagram of a thermally regulated lighting system that comprises an LED and a feedback loop, in accordance with exemplary embodiments of the present invention. 
         FIG. 5  is flowchart of a process for fabricating a lighting system comprising an LED and a capability for cooling the LED, in accordance with exemplary embodiments of the present invention. 
         FIG. 6  is flowchart of a method of operation of a lighting system comprising an LED and a capability for cooling the LED, in accordance with exemplary embodiments of the present invention. 
     
    
    
     Many aspects of the invention can be better understood with reference to the above drawings. The elements and features shown in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of exemplary embodiments of the present invention. Moreover, certain dimensions may be exaggerated to help visually convey such principles. In the drawings, reference numerals designate like or corresponding, but not necessarily identical, elements throughout the several views. 
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     An exemplary embodiment of the present invention supports operating an LED under conditions that provide efficient or reliable illumination. The LED can be mounted, for example via soldering, solder bumps, or bonding, to a surface of a generally flat piece of material, such as a plate or a sheet of ceramic material. The term “plate”, as used herein, generally refers to a piece or body of material having at least one side or area that is approximately flat or planar, and the term can encompass a piece of material that incorporates layered or laminated structures. Thus, the mounted LED can adjoin, contact, or touch the generally flat piece of material. An electrical circuit for removing heat generated by the LED can also adjoin, contact, or touch the generally flat piece of material, for example on a surface that is opposite the LED. The electrical circuit can comprise one or more components that cool the generally flat piece of material when the circuit is energized. 
     A lighting fixture will now be described more fully hereinafter with reference to  FIGS. 1-6 , which describe representative embodiments of the present invention.  FIGS. 1-4  generally describe an illustrative LED lighting system having a provision for LED cooling.  FIGS. 5 and 6  respectively show methods for manufacturing and operating an LED lighting system having a cooling provision. 
     The invention can be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those having ordinary skill in the art. Furthermore, all “examples” or “exemplary embodiments” given herein are intended to be non-limiting, and among others supported by representations of the present invention. 
     Turning now to  FIG. 1 , this figure illustrates a line drawing of an exemplary lighting system  100  comprising an LED  175  and a capability for cooling the LED  175  according to certain embodiments of the present invention. More specifically, the illustrated lighting system  100  comprises an array of LEDs, in six rows. (Other exemplary embodiments may have more or fewer LEDs, LEDs arranged in various arrayed and non-arrayed configurations, and various form factors.) In an exemplary embodiment, the lighting system  100  can be a module of a luminaire or a lighting fixture for illuminating a space or an area that people may occupy or observe. 
     The term “luminaire”, as used herein, generally refers to a system for producing, controlling, and/or distributing light for illumination. A luminaire can be a system that outputs or distributes light into an environment so that people can observe items in the environment. Such a system could be a complete lighting unit comprising one or more LEDs; sockets, connectors, or receptacles for mechanically mounting and/or electrically connecting components to the system; optical elements for distributing light; and mechanical components for supporting or attaching the luminaires Luminaires are sometimes referred to as “lighting fixtures” or as “light fixtures.” A lighting fixture that has a socket for a light source, but no light source installed in the socket, can still be considered a luminaires That is, a lighting system lacking some provision for full operability may still fit the definition of a luminaires 
     As discussed in further detail below, the LEDs  175  are mounted on a ceramic substrate  125  that is printed with electrical connections  130  and/or other electrical circuitry features that provide electrical power to the LEDs  175 . In addition to functioning as and LED circuit board, the ceramic substrate  125  is also an element of a thermal electric cooler (“TEC”)  150 . In terms of composition, the substrate  125 , as well as the substrate  120  can comprise alumina, aluminum nitride, boron nitride, diamond, ceramic materials, etc. 
     The term “ceramic” or “ceramic material”, as used herein, generally refers to an article or material comprising a crystalline or partially crystalline structure or glass that is produced from substantially inorganic, non-metallic substances and is either formed from a molten mass which solidifies on cooling, or is formed and simultaneously or subsequently matured by action of heat. Such non-metallic substances can comprise metal oxides, for example. A ceramic material can have a glazed or unglazed surface. A ceramic article having a coating of a pure metal or some other non-ceramic material would still be a ceramic article. By way of example, ceramic materials can comprise aluminum oxide, alumina, aluminum nitride, barium titanate, bismuth strontium calcium copper oxide, boron carbide, boron nitride, ferrite, lead zirconate titanate, magnesium diboride, sialons, silicon carbide, silicon nitride, steatite, magnesium silicate, titanium oxide, yttrium barium copper oxide, zinc oxide, zirconium dioxide, zirconia, etc. 
     Referring to  FIG. 1 , a electrical circuit that cools the substrate  125  (and the LEDs attached thereto) is sandwiched between the substrate  125  and another substrate  120 . That circuit will be discussed in further detail below with reference to  FIG. 2 . 
     As an optional feature, the lighting system  100  comprises two holes  115  extending through the TEC to facilitate mounting in a luminaire or some other lighting fixture or device. Each hole  115  can receive a fastener, such as a screw, that attaches to the luminaires 
     The TEC  150  receives electricity via the connectors  105 ,  110 , one comprising a positive lead and the other comprising a negative lead. In an exemplary embodiment, the connectors  105 ,  110  provide mechanical support in addition to electricity. The connectors  105 ,  110  can be rigidly attached to the TEC  150 . In this configuration, the connectors  105 ,  110  can plug into a female receptacle of a luminaire so the mounting holes  115  can be optional. Alternatively, the connectors  105 ,  110  can be flexible leads, wires, or pigtails that are coupled to an electrical supply line. 
     In the exemplary embodiment that  FIG. 1  illustrates, the connectors  105 ,  110  are dedicated electrically to powering the TEC  150 . Meanwhile, the LEDs  175  receive electricity via contact pads  130  printed, coated, plated, or otherwise attached to the substrate  125 . The lighting system  100  can slide into a groove or slot having associated conductive elements that touch the contact pads  130 . Accordingly, a luminaire can comprise spring-loaded, springy, elastic, flexible, or resilient members that contact the contact pads to power the LEDs  175  electrically. 
     In an alternative exemplary embodiment, the connectors  105 ,  110  can provide electrical power to both the TEC  150  and the LEDs  175 . In this situation, the contact pads  130  can be optional. Accordingly, in one exemplary embodiment, the connectors  105 ,  110  provide essentially full electrical and mechanical support for mounting and operating the lighting system  100  in a luminaire or some other support structure. 
     Turning now to  FIG. 2 , this figure illustrates a cross sectional view of an exemplary lighting system  100 , comprising an LED  175  and a capability for cooling the LED  175 , connected to a source of electrical power  235  according to certain embodiments of the present invention. In an exemplary embodiment,  FIG. 2  illustrates the lighting system  100  of  FIG. 1  connected to support facilities that include an electrical circuit  240  and a heatsink  205 . The electrical circuit  240  can be an exemplary embodiment of a cooling electrical circuit and will thus often be referred to as the cooling circuit  250  below. 
     Although the cross sectional view of  FIG. 2  illustrates a single LED  175 , exemplary embodiments can include either a single LED  175  or multiple LEDs  175 . Additional LEDs  175  can furthermore appear in other cross sectional views of the system  100 . Accordingly, it is appropriate to refer to the system  100  of  FIG. 2  as comprising “LEDs”, and the below discussion will sometimes make such reference. 
     The cooling power supply  235  supplies direct current (“DC”) voltage and current to a network or series of members, semiconductors, or conductors (also referred to as “TE elements”  210 ,  215  and interconnect  220 ) that cool the substrate  125  and the LEDs  175  attached thereto when electrically energized. The cooling circuit  250  comprises a system or circuit  250  of TE elements  210 ,  215  that extract heat from the substrate  125  to provide a beneficial thermal environment for the LEDs  175 . The circuit  250  is referred to herein as a “TE circuit”. The TEC  150  can function in a capacity of an active heat pump. 
     The TE elements  210 ,  215  can respectively comprise two different materials or dissimilar metals that are in the electricity&#39;s path. The cooling power supply  235  provides a voltage differential across the two TE elements  210 ,  215  of dissimilar metals, causing a temperature differential that is similar to operating a thermal couple in reverse. In an exemplary embodiment, the temperature differential is a result of the Peltier effect, Peltier cooling, Peltier-Seebeck cooling, or a thermal electric effect. The TEC  150  typically comprises numerous junctions between dissimilar metals. Those junctions are electrically in series with one another and thermally in parallel with one another. As an alternative to having an intervening conductor  220  disposed between the two dissimilar metals as shown in  FIG. 2 , those metals can directly contact one another. 
     As an alternative to dissimilar or different metals, the TE circuit  250  can provide thermal regulation via semiconductor-based cooling. The TE elements  210 ,  215  can respectively be N- and P-type semiconductors with high Seeback coefficients, high thermal conductivity, high figure or merit, and/or low thermal resistance. The TE elements can comprise bismuth telluride, lead telluride, silicon germanium, or cobalt lead (not an exhaustive list). In one embodiment, the semiconductor materials can be layered in thin-films to create micro-sized devices that enhance cooling density without sacrificing cooling capacity. 
     In the illustrated exemplary embodiment, the TE elements  210 ,  215  are attached to electrical interconnects  220  that attach to the substrates  120 ,  125 . In exemplary embodiments, the electrical interconnects  220  comprise metallic materials plated, coated, deposited, layered, or filmed on the substrates  120 ,  125 . For example, the full surfaces  201 ,  208  of the substrates  120 ,  125  facing the TE circuit  250  can be plated. Following plating, acid etching can selectively remove regions of the plating so the electrical interconnects  220  remain. The TE members  210 ,  215  can then be attached, for example via welding, soldering, or bonding, to the patches of interconnect material layer that remain. Via such a process, the TE circuit  250  is in electrical and physical contact with the substrates  120 ,  125 . More specifically, the TE circuit  250  touches and contacts the substrate surface  201 , both physically and electrically. In one exemplary embodiment, physical and electrical contact results from urging or pressing the TE elements  210 ,  215  to the electrical interconnects  220 , without necessarily incorporating permanent bonding. 
     In another exemplary embodiment, the TE circuit  250  can be formed as a separate structure that is attached to the substrates  120 ,  125 . More specifically, a series network can be fabricated by welding, bonding, or otherwise attaching the TE elements  210 ,  215  to the interconnection elements  220 , thus forming a stand-alone structure. That structure, which comprises the TE circuit  250 , can be sandwiched between the two substrates  120 ,  125 . The TE circuit  250 , so formed, can be bonded, glued, welded, soldered, or otherwise attached (chemically, metallically, via heat, etc.) to the substrates  120 ,  125 . Accordingly, the TE circuit  250  can adjoin, contact, or touch the substrates  120 ,  125  and specifically the substrate surface  201 . Electricity flowing in the TE circuit  250  can thereby adjoin, contact, or touch each of the substrates  120 ,  125 , and the substrates  120 ,  125  can electrically insulate the TE circuit  250 . The electrical insulation of the substrate  120  prevents electrical shorting or unwanted/uncontrolled flow of electricity while providing thermal conductivity to improve TEC efficiency and to lower the junction temperature of the LEDs  175 . 
     The heatsink  205  dissipates heat that the TEC  150  draws from the substrate  125  and the LEDs  175 . A system of fins, channels, or grooves  203  comprises open areas through which air flows and circulates to promote convection. In an exemplary embodiment, the heatsink  205  can be made of aluminum or another metal with reasonably high thermal conductivity. In certain exemplary embodiments, the heatsink  205  comprises one or more heat pipes, a water cooler, or some other appropriate heat management system. 
     The outer surface  200  of the substrate  125 , opposite the surface  201 , comprises facilities for attaching the LEDs  175  thereto. In one exemplary embodiment, that surface  202  comprises pads  202  to which LEDs  175  are attached. In an exemplary embodiment, the pads  202  comprise a metal plating, coating, or layer. The material of the pads  202  can comprise copper, nickel, silver, gold, etc. In one embodiment, the surface  200  comprises a coat of nickel or other material that promotes adherence of a copper film to the substrate  125 . The pads  202  can, in other words, comprise multiple layers of metal or other materials to support adhesion, bonding, etc. 
     The LEDs  175  can be soldered, bonded, or attached with electrically conductive adhesive, for example. With the LEDs  175  in “die” form, the die-to-substrate attachments and electrical connections can be implemented with eutectic bonds. The material of the eutectic bonds can comprise bismuth tin or some other material that supports low-temperature bonding. Epoxies can also be used to die bond the LED  175  to the substrate  125 . 
     In addition to the pads  202 , the surface  200  comprises electrical conductors in the form of electrical traces  275  that feed or provide electricity to the LEDs  175 . The feed traces  275  can be defined via photolithography or via essentially any other known process or procedure for imprinting a surface with electrical conductors or elements. 
     The LEDs  175  are wirebonded to the feed trace  275  via one or more microwires  204 . Wirebonding typically involves soldering each microwire, which can comprise gold, aluminum, or copper, for example. In certain exemplary embodiments, the LEDs  175  can be attached via flip-chip assembly. 
     The LEDs  175  of the lighting system  100  comprise semiconductor diodes emitting incoherent light when electrically biased in a forward direction of a p-n junction. In an exemplary embodiment, each LED  175  emits blue or ultraviolet light, and the emitted light excites a phosphor that in turn emits red-shifted light. The LEDs  175  and the phosphors emit blue and red-shifted light that essentially matches blackbody radiation and may approximate or emulate incandescent light to a human observer. In one exemplary embodiment, the LEDs  175  and their associated phosphors emit substantially white light that may seem slightly blue, green, red, yellow, orange, or some other color ting or tint. Exemplary embodiments of the LEDs  175  in the system  100  can comprise indium gallium nitride (“InGaN”) or gallium Nitride (“GaN”) for emitting blue light. 
     In an alternative embodiment, the system  100  can comprise LEDs  175  that individually produce distinct colors of light while collectively producing substantially white light or light emulating a blackbody radiator. Some of the LEDs  175  can produce red light, while others produce, blue, green, orange, or red, for example. 
     In certain exemplary embodiments, the lighting system  100  is controlled via RGB (Red-Green-Blue) and/or tri-stimulus methodology to create white or off-white light shifted to provide desired colors. For example, the lighting system  100  can support a range of desired colors, decorative lighting effects, theatrical light, or architectural aesthetics (not an exhaustive list). Furthermore, the lighting system&#39;s LEDs  175  can be controlled to provide color shifts for biological purposes, such as in support of day/night cycles. 
     In one exemplary embodiment, active and passive electrical circuit components can be attached to the surface  200  in addition to the LEDs  175 . For example, resistors, amplifiers, LED drivers, transistors, operational amplifiers, power supplies, sensors (including the sensor  405  illustrated in  FIG. 4  an discussed below), digital logic circuits, etc. can be soldered or solder-bumped to the surface  200 . Further, electrical or electronic components can be either surface mounted or attached to through-holes or vias of the substrate  125 . 
     In one exemplary embodiment, optically transparent or clear material encapsulates the LEDs  175 , either individually or collectively. Thus, one body of optical material can encapsulate the full LED array  175  illustrated in  FIG. 1 . The encapsulating material can comprise a conformal coating, a silicone gel, cured/curable polymer, acrylic, glass, adhesive, or some other material that protects the LEDs while transmitting light. Moreover, one body of such material can contact the surface  200 ; the electrical circuitry associated with the contact pad  130 , the mounting pad  202 , and the feed traces  275 ; the LEDs  175 ; and associated active electrical elements. In one exemplary embodiment, phosphors, for converting blue or ultraviolet light to light of another color, are coated onto or dispersed in the body of material. 
     Turning now to  FIG. 3 , this figure illustrates a line drawing of an exemplary cooling system  150  that a lighting system  100  can comprise according to certain embodiments of the present invention. In an exemplary embodiment, the cooling system  150  can be the TEC  150  of  FIGS. 1 and 2 . In other words,  FIG. 3  provides a perspective view of an example of the TEC  150  exemplarily illustrated in  FIGS. 1 and 2 . 
     In one exemplary embodiment, the TEC  150  of  FIG. 3  is formed as a distinct step in manufacturing the lighting system  100 . After fabricating the TEC  150 , the circuitry, for example the feed traces  275 , and LEDs  175  are applied to the surface  200 , thereby creating the lighting system  100 . In other words, LEDs  175  and other elements not shown in  FIG. 3  can be attached directly to the TEC  150  illustrated in  FIG. 3 . 
     In an alternative exemplary embodiment, the feed traces  275  and LEDs  175  are applied to the surface  200  of the substrate  125  prior to integrating an active cooling capability to the substrate  200 . Then, the TEC  150  is created from the substrate assembly.  FIG. 5 , discussed below, describes an exemplary embodiment of such a process. 
     Commercial suppliers of TEC components suitable for including in exemplary embodiments of the lighting system  100  and/or the TEC  150  include Custom Thermoelectic of Bishopville, Md.; Ferrotec (USA) Corporation of Santa Clara, Calif.; and Marlow Industries, Inc. of Dallas Tex. 
     Turning now to  FIG. 4 , this figure illustrates a functional block diagram of an exemplary thermally regulated lighting system  400  that comprises an LED  175  and a feedback loop  410  according to certain embodiments of the present invention. More specifically,  FIG. 4  describes outfitting the system  100 , discussed above, with a feedback loop  410  that controls the TEC  150  based at least in part on sensing light output by the LEDs  175 . Alternatively, the feedback look  410  controls the TEC  150  via a thermal sensor, such as a thermometer, a thermocouple, a thermistor, or an RTD. 
     In one exemplary embodiment, the sensor  405  detects the level or intensity of light emitted by the LEDs  175 , and the feedback loop  410  controls the TEC  150  to maintain LED intensity at a target level. In another exemplary embodiment, the sensor  405  detects the spectral content or color of the emitted light and adjusts the TEC  150  accordingly. Accordingly, the sensor  405  can comprise a simple light detector, an intensity meter, or a spectrometer. In one exemplary embodiment, the sensor  405  mounts on or otherwise attaches to the surface  125 . 
     In one exemplary embodiment, the feedback loop  410  feeds a temperature target (or “setpoint”) to the cooling power supply  235 , and the cooling power supply  235  supplies sufficient electricity to maintain the LEDs  175  at the target temperature. In an alternative exemplary embodiment, the feedback loop  410  adjusts the electrical output of the cooling power supply  235  based on sensed light, without direct temperature feedback. 
     In either case, the sensor  405  provides the feedback controller  415  with information about performance or operating status of the LEDs  175 . In one exemplary embodiment, the feedback controller  415  comprises a proportional-plus-integral-plus-derivative (“PID”) controller, which may be based on digital or analog circuitry. In one exemplary embodiment, the feedback controller  415  comprises a proportional-plus-integral (“PI”) controller, implemented via digital logic or an analog circuit. In one exemplary embodiment, the feedback controller  415  comprises a computer or microprocessor that controls the lighting system  100  according to programming instructions stored in memory. 
     The feedback controller issues instructions or prompts to the cooling power supply  235  that adjust the amount of electricity (e.g. current and/or voltage) delivered to the TEC  150 . The electrical adjustments control the temperature of the LEDs  175  so the LEDs operate in a temperature region that provides power efficiency and long life. 
     Dynamically controlling or regulating the operating temperature of the LEDs  175  can further compensate for variations in the LED power supply  420 . For example, a user may dim the LEDs  175  via modulating the time duration of current pulses delivered by the LED power supply  420  to the LEDs  175 , in a process that can be described as “pulse width modulation”. The dimmed LEDs  175  generate less heat than they would at their full brightness. The feedback controller  415  adjusts the amount of heat extracted from the substrate  200  so the LEDs  175  continue to operate in favorable temperature conditions. Accordingly, the feedback controller  415  can compensate for changes in the LEDs  175 , whether such changes are due to user adjustments, aging of the LEDs  175 , ambient light, random fluctuations in the LED power supply  420 , environmental influences due to seasonal or other changes, or some other variation. 
     Turning now to  FIG. 5 , this figure illustrates a flowchart of an exemplary process  500  for fabricating a lighting system  100  that comprises an LED  175  and a capability for cooling the LED  175  according to certain embodiments of the present invention. In an exemplary embodiment, the process  500 , which is entitled “Fabricate Cooled LED Lighting System”, comprises a method for mass producing the lighting system  100  depicted in  FIGS. 1 and 2 . Accordingly, reference will be made to the lighting system  100  while discussing the exemplary steps of process  500 . 
     As discussed above, one exemplary method for fabricating the lighting system  100  comprises attaching circuitry, for example the contact pads  130 , the feed traces  275 , and the mounting pad  202 , on top of a previously constructed TEC  150 . However, process  500  offers an alternative approach. Exemplary process  500  proceeds via first applying such circuitry to a ceramic substrate  125  and then applying an active cooling capability to the circuit-substrate assembly. 
     At step  505 , an electrical or electronic circuit is printed on or otherwise added to the ceramic substrate  125 , typically as a separate sheet or plate of ceramic material. 
     In an exemplary embodiment of step  505 , a manufacturer or a fabricator procures a flat piece of ceramic material that is suitable stock for creating a ceramic circuit board. To facilitate making multiple lighting systems  100 , the flat piece of ceramic material can comprise a ceramic wafer large enough to yield multiple lighting system substrates  125 . 
     The fabricator plates one side of the ceramic stock with a conductive material such as copper, gold, silver, etc. An application of photoresist, or other material that responds to light, readies the stock for photolithography and etching. An engineer creates a circuit layout using circuit-design software executing on a personal computer. The personal computer exports the circuit layout to a photolithographic system. The photolithographic system projects the circuit image (or a negative thereof) onto the metal-plated stock and the photoresist coating. Typically, the system projects multiple images, displaced from one another, onto the ceramic stock. 
     Submerging the ceramic stock in an acid bath etches selective areas of metal plating according to the projected images. When etching completes, the desired circuit pattern remains, in a metallic pattern. A solvent wash removes residual photoresist. Multiple instances of the desired circuitry are thereby patterned onto one wafer of the ceramic stock. 
     Dicing the stock, for example with a diamond saw, between each circuit pattern yields multiple copies of the desired circuit. Accordingly, one large wafer of ceramic stock produces numerous circuits. Each patterned piece of ceramic or “die” can be the substrate  125  incorporating the circuit patterns  130 ,  275 ,  202 . 
     At step  510  of process  500 , the fabricator attaches one or more LEDs  175  to each patterned ceramic substrate  200 . As discussed above with reference to  FIG. 2 , die bonding and wire bonding machinery attaches the LEDs  175  as well as supporting active and passive electronic components, to the surface  200 . In an alternative exemplary embodiment, manual or automatic soldering, or some other attachment technique known in the art, attaches the circuit elements to the surface  200  of the substrate. 
     At step  515 , the fabricator attaches TE circuit  250 , including the TE elements  210 ,  215 , to each ceramic substrate  125 , specifically on the side  201  opposite from the LEDs  175 . As discussed above, exemplary procedures for making this attachment can comprise soldering, gluing, applying ceramic adhesives or refractory bonding agents, welding, etc. 
     At step  520 , the fabricator attaches another ceramic substrate  120  to each TE circuit  250 , with the TE circuit sandwiched between the two ceramic substrates  120 ,  125 . This attachment can comprise applications of glue, ceramic adhesive, solders, brazes, or fasteners, for example. In one exemplary embodiment, the TE circuit  250  is pressed between the two ceramic substrates  120 ,  125  with compression force holding the assembly together. Thus, one or more mechanical fasteners hold the assembly together without glues or adhesives. 
     At step  525 , the fabricator attaches the heatsink  205  to each ceramic substrate  120  opposite from the TE circuit  250 . A intermediate layer of thermally conductive adhesive, thermal interface material (“TIM”), tape, or material can promote thermal transfer from the ceramic substrate  120  to the heatsink  205 . 
     Process  500  ends following step  525 . Via processing the substrates in batches, particularly at step  505 , process  500  yields numerous copies of the system  100  with a high level of manufacturing efficiency. 
     Turning now  FIG. 6 , this figure illustrates a flowchart of an exemplary process  600  of operation of a lighting system  100  that comprises an LED  175  and a capability for cooling the LED  175  according to certain embodiments of the present invention. In an exemplary embodiment, process  600  comprises a method for producing light with a lighting system  100  produced by process  500  as discussed above. 
     At step  605  of process  600 , the cooling power supply  235  delivers electrical power to the TEC  150 . In response to the electrical power, the TEC  150  actively extracts heat from the substrate  125 , effectively reducing the temperature of the substrate  125  and the LEDs  175  attached thereto. As discussed above, the heat extraction can comprise pumping heat, TE cooling, utilizing Peltier cooling, passing electricity through semiconductor materials that produce a cooling effect, or some other means for actively removing heat known in the art. 
     At step  610 , the LED power supply  420  delivers electrical current to the LEDs  175  via circuit traces (for example the contact pads  130 ) printed on the surface  200  at step  505  of process  500 . The current can be pulsed or continuous and can be pulse width modulated to support user-controlled dimming. In response to the applied current, the LEDs  175  emit or produce substantially white light or some color of light that a person can perceive. As discussed above, in one exemplary embodiment, at least one of the LEDs  175  produces blue or ultraviolet light that triggers photonic emissions from a phosphor. Those emissions can comprise green, yellow, orange, and/or red light, for example. 
     In response to the environmental conditions provided by the TEC  150 , the LEDs  175  operate efficiently and avoid premature failure. In an exemplary embodiment, the mean time before failure or average life of the LEDs  175  can exceed 50,000 hours in the thermal conditions provided by the TEC  150 . 
     At step  615 , the sensor  405  detects a portion of the light the LEDs  175  emit. In an exemplary embodiment, the sensor  405  determines light intensity from the LEDs  175  or light intensity in the vicinity of LEDs  175 . The sensor  405  feeds an electrical signal carrying the intensity information to the feedback controller  415 . 
     As an alternative to light intensity, the sensor  405  can detect another parameter that provides operational feedback about the LEDs  175 . In certain exemplary embodiments, the sensor  405  comprises an RTD, a thermistor, a thermocouple, or some other means for measuring or assessing temperature of the LEDs  175 . In certain exemplary embodiments, the sensor  405  comprises a component measuring a voltage associated with the LEDs  175  to provide an indication of operational state, temperature, performance, etc. of the LEDs  175 . For example, the sensor  405  can sense a secondary voltage V f  of the LEDs  175  as an indication of the LEDs&#39; operational temperature. 
     At step  620 , the feedback controller  415  prompts the cooling power supply  235  to output electrical power to the TEC  150  according to the sensor input. When ambient temperature drops in the winter, for example, the cooling power supply  235  may decrease the power output to compensate for increased ambient cooling. Similarly, the feedback controller  415  can set the cooling power supply  235  to compensate for age-related degradation, changes in the electrical characteristics of the power supply  420 , failure of one or more LEDs  175 , chromatic changes, etc. 
     More generally, at step  620 , the feedback control loop  410  regulates or manipulates the temperature of the LEDs  175  so that the LEDs  175  operate within a particular band of thermal conditions, despite fluctuating conditions, random events, and various perturbations. 
     Process  600  ends following step  620 . In an exemplary embodiment, the LEDs  175  provide efficient illumination for many years. 
     Technology for cooling an LED of an illumination system, for fabricating an illumination system that comprises a cooled LED, and for operating such an illumination system has been described. From the description, it will be appreciated that an embodiment of the present invention overcomes the limitations of the prior art. Those skilled in the art will appreciate that the present invention is not limited to any specifically discussed application or implementation and that the embodiments described herein are illustrative and not restrictive. From the description of the exemplary embodiments, equivalents of the elements shown therein will suggest themselves to those skilled in the art, and ways of constructing other embodiments of the present invention will appear to practitioners of the art. Therefore, the scope of the present invention is to be limited only by the claims that follow.