Abstract:
A modular light emitting diode (LED) mounting configuration is provided including a light source module having a plurality of pre-packaged LEDs arranged in a serial array. The module includes a heat conductive body portion adapted to conduct heat generated by the LEDs to an adjacent heat sink. As a result, the LEDs are able to be operated with a higher current than normally allowed. Thus, brightness and performance of the LEDs is increased without decreasing the life expectancy of the LEDs. The LED modules can be used in a variety of illumination applications employing one or more modules.

Description:
RELATED APPLICATIONS  
       [0001]     This application is a continuation of copending U.S. application Ser. No. 11/542,072, which was filed on Oct. 3, 2006, which is a continuation of U.S. application Ser. No. 10/789,357, which was filed on Feb. 27, 2004, which is a continuation of U.S. application Ser. No. 09/693,548, which was filed on Oct. 19, 2000, now U.S. Pat. No. 6,712,486, which claims the benefit of U.S. Provisional Patent Application Nos. 60/160,480, which was filed on Oct. 19, 1999 and 60/200,351, which was filed on Apr. 27, 2000. The entirety of each of these related applications is hereby incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention is in the field of light emitting diode (LED) lighting devices and more particularly in the field of an LED lighting module having heat transfer properties that improve the efficiency and performance of LEDs.  
         [0004]     2. Description of the Related Art  
         [0005]     Light emitting diodes (LEDs) are currently used for a variety of applications. The compactness, efficiency and long life of LEDs is particularly desirable and makes LEDs well suited for many applications. However, a limitation of LEDs is that they typically cannot maintain a long-term brightness that is acceptable for middle to large-scale illumination applications. Instead, more traditional incandescent or gas-filled light bulbs are often used.  
         [0006]     An increase of the electrical current supplied to an LED generally increases the brightness of the light emitted by the LED. However, increased current also increases the junction temperature of the LED. Increased juncture temperature may reduce the efficiency and the lifetime of the LED. For example, it has been noted that for every 10° C. increase in temperature, silicone and gallium arsenide lifetime drops by a factor of 2.5-3. LEDs are often constructed of semiconductor materials that share many similar properties with silicone and gallium arsenide.  
       SUMMARY OF THE INVENTION  
       [0007]     Accordingly, there is a need in the art for an LED lighting apparatus having heat removal properties that allow an LED on the apparatus to operate at relatively high current levels without increasing the juncture temperature of the LED beyond desired levels.  
         [0008]     In accordance with an aspect of the present invention, an LED module is provided for mounting on a heat conducting surface that is substantially larger than the module. The module comprises a plurality of LED packages and a circuit board. Each LED package has an LED and at least one lead. The circuit board comprises a thin dielectric sheet and a plurality of electrically-conductive contacts on a first side of the dielectric sheet. Each of the contacts is configured to mount a lead of an LED package such that the LEDs are connected in series. A heat conductive plate is disposed on a second side of the dielectric sheet. The plate has a first side which is in thermal communication with the contacts through the dielectric sheet. The first side of the plate has a surface area substantially larger than a contact area between the contacts and the dielectric sheet. The plate has a second side adapted to provide thermal contact with the heat conducting surface. In this manner, heat is transferred from the module to the heat conducting surface.  
         [0009]     In accordance with another aspect of the present invention, a modular lighting apparatus is provided for conducting heat away from a light source of the apparatus. The apparatus comprises a plurality of LEDs and a circuit board. The circuit board has a main body and a plurality of electrically conductive contacts. Each of the LEDs electrically communicates with at least one of the contacts in a manner so that the LEDs are configured in a series array. Each of the LEDs electrically communicates with corresponding contacts at an attachment area defined on each contact. An overall surface of the contact is substantially larger than the attachment area. The plurality of contacts are arranged adjacent a first side of the main body and are in thermal communication with the first side of the main body. The main body electrically insulates the plurality of contacts relative to one another.  
         [0010]     For purposes of summarizing the invention and the advantages achieved over the prior art, certain objects and advantages of the invention have been described herein above. Of course, it is to be understood that not necessarily all such objects or advantages may be achieved in accordance with any particular embodiment of the invention. Thus, for example, those skilled in the art will recognize that the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein.  
         [0011]     All of these embodiments are intended to be within the scope of the invention herein disclosed. These and other embodiments of the present invention will become readily apparent to those skilled in the art from the following detailed description of the preferred embodiments having reference to the attached figures, the invention not being limited to any particular preferred embodiment(s) disclosed. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]      FIG. 1  is a perspective view of an LED module having features in accordance with the present invention.  
         [0013]      FIG. 2  is a schematic side view of a typical pre-packaged LED lamp.  
         [0014]      FIG. 3  is a top plan view of the LED module of  FIG. 1 .  
         [0015]      FIG. 4  is a side plan view of the apparatus of  FIG. 3 .  
         [0016]      FIG. 5  is a close-up side view of the apparatus of  FIG. 3  mounted on a heat conductive member.  
         [0017]      FIG. 6  is another sectional side view of the apparatus of  FIG. 3  mounted onto a heat conductive flat surface.  
         [0018]      FIG. 7  is a side plan view of an LED module having features in accordance with another embodiment of the present invention.  
         [0019]      FIG. 8  is a side plan view of another LED module having features in accordance with yet another embodiment of the present invention.  
         [0020]      FIG. 9  is a perspective view of an illumination apparatus having features in accordance with the present invention.  
         [0021]      FIG. 10  is a side view of the apparatus of  FIG. 9 .  
         [0022]      FIG. 11  is a bottom view of the apparatus of  FIG. 9 .  
         [0023]      FIG. 12  is a top view of the apparatus of  FIG. 9 .  
         [0024]      FIG. 13  is a schematic view of the apparatus of  FIG. 9  mounted on a theater seat row end.  
         [0025]      FIG. 14  is a side view of the apparatus of  FIG. 13  showing the mounting orientation.  
         [0026]      FIG. 15  is a side view of a mounting barb.  
         [0027]      FIG. 16  is a front plan view of the illumination apparatus of  FIG. 9 .  
         [0028]      FIG. 17  is a cutaway side plan view of the apparatus of  FIG. 20 .  
         [0029]      FIG. 18  is a schematic plan view of a heat sink base plate.  
         [0030]      FIG. 19  is a close-up side sectional view of an LED module mounted on a mount tab of a base plate.  
         [0031]      FIG. 20  is a plan view of a lens for use with the apparatus of  FIG. 9 .  
         [0032]      FIG. 21  is a perspective view of a channel illumination apparatus incorporating LED modules having features in accordance with the present invention.  
         [0033]      FIG. 22  is a close-up side view of an LED module mounted on a mount tab.  
         [0034]      FIG. 23  is a partial view of a wall of the apparatus of  FIG. 21 , taken along line  23 - 23 .  
         [0035]      FIG. 24  is a top view of an LED module mounted to a wall of the apparatus of  FIG. 21 .  
         [0036]      FIG. 25  is a top view of an alternative embodiment of an LED module mounted to a wall of the apparatus of  FIG. 21 .  
         [0037]      FIG. 26A  is a side view of an alternative embodiment of a lighting module being mounted onto a channel illumination apparatus wall member.  
         [0038]      FIG. 26B  shows the apparatus of the arrangement of  FIG. 26A  with the lighting module installed.  
         [0039]      FIG. 26C  shows the arrangement of  FIG. 26B  with a lens installed on the wall member.  
         [0040]      FIG. 26D  shows a side view of an alternative embodiment of a lighting module installed on a channel illumination apparatus wall member. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0041]     With reference first to  FIG. 1 , an embodiment of a light-emitting diode (LED) lighting module  30  is disclosed. In the illustrated embodiment, the LED module  30  includes five pre-packaged LEDs  32  arranged on one side of the module  30 . It is to be understood, however, that LED modules having features in accordance with the present invention can be constructed having any number of LEDs  32  mounted in any desired configuration.  
         [0042]     With next reference to  FIG. 2 , a typical pre-packaged LED  32  includes a diode chip  34  encased within a resin body  36 . The body  36  typically has a focusing lens portion  38 . A negative lead  40  connects to an anode side  42  of the diode chip  34  and a positive lead  44  connects to a cathode side  46  of the diode chip  34 . The positive lead  44  preferably includes a reflector portion  48  to help direct light from the diode  34  to the lens portion  38 .  
         [0043]     With next reference to  FIGS. 1-5 , the LED module  30  preferably comprises the five pre-packaged LED lamps  32  mounted in a linear array on a circuit board  50  and electrically connected in series. The illustrated embodiment employs pre-packaged aluminum indium gallium phosphide (AlInGaP) LED lamps  32  such as model HLMT-PL00, which is available from Hewlett Packard. In the illustrated embodiment, each of the pre-packaged LEDs is substantially identical so that they emit the same color of light. It is to be understood, however, that nonidentical LEDs may be used to achieve certain desired lighting effects.  
         [0044]     The illustrated circuit board  50  preferably is about 0.05 inches thick, 1 inch long and 0.5 inch wide. It includes three layers: a copper contact layer  52 , an epoxy dielectric layer  54  and an aluminum main body layer  56 . The copper contact layer  52  is made up of a series of six elongate and generally parallel flat copper plates  60  that are adapted to attach to the leads  40 ,  44  of the LEDs  32 . Each of the copper contacts  60  is electrically insulated from the other copper contacts  60  by the dielectric layer  54 . Preferably, the copper contacts  60  are substantially coplanar.  
         [0045]     The pre-packaged LEDs  32  are attached to one side of the circuit board  50 , with the body portion  36  of each LED generally abutting a side of the circuit board  50 . The LED lens portion  38  is thus pointed outwardly so as to direct light in a direction substantially coplanar with the circuit board  50 . The LED leads  40 ,  44  are soldered onto the contacts  60  in order to create a series array of LEDs. Excess material from the leads of the individual pre-packaged LED lamps may be removed, if desired. Each of the contacts  60 , except for the first and last contact  62 ,  64 , have both a negative lead  40  and a positive lead  44  attached thereto. One of the first and last contacts  62 ,  64  has only a negative lead  40  attached thereto; the other has only a positive lead  44  attached thereto.  
         [0046]     A bonding area of the contacts accommodates the leads  40 ,  44 , which are preferably bonded to the contact  60  with solder  68 ; however, each contact  60  preferably has a surface area much larger than is required for adequate bonding in the bonding area  66 . The enlarged contact surface area allows each contact  60  to operate as a heat sink, efficiently absorbing heat from the LED leads  40 ,  44 . To maximize this role, the contacts  60  are shaped to be as large as possible while still fitting upon the circuit board  50 .  
         [0047]     The dielectric layer  54  preferably has strong electrical insulation properties but also relatively high heat conductance properties. In the illustrated embodiment, the layer  54  is preferably as thin as practicable. For example in the illustrated embodiment, the dielectric layer  54  comprises a layer of Thermagon® epoxy about 0.002 inches thick.  
         [0048]     It is to be understood that various materials and thicknesses can be used for the dielectric layer  54 . Generally, the lower the thermal conductivity of the material used for the dielectric layer, the thinner that dielectric layer should be in order to maximize heat transfer properties of the module. For example, in the illustrated embodiment, the layer of epoxy is very thin. Certain ceramic materials, such as beryllium oxide and aluminum nitride, are electrically non-conductive but highly thermally conductive. When the dielectric layer is constructed of such materials, it is not as crucial for the dielectric layer to be so very thin, because of the high thermal conductivity of the material.  
         [0049]     In the illustrated embodiment, the main body  56  makes up the bulk of the thickness of the circuit board  50  and preferably comprises a flat aluminum plate. As with each of the individual contacts  60 , the main body  56  functions as a heat conduit, absorbing heat from the contacts  60  through the dielectric layer  54  to conduct heat away from the LEDs  32 . However, rather than just absorbing heat from a single LED  32 , the main body  56  acts as a common heat conduit, absorbing heat from all of the contacts  60 . As such, in the illustrated embodiment, the surface area of the main body  56  is about the same as the combined surface area of all of the individual contacts  60 . The main body  56  can be significantly larger than shown in the illustrated embodiment, but its relatively compact shape is preferable in order to increase versatility when mounting the light module  30 . Additionally, the main body  56  is relatively rigid and provides structural support for the lighting module  30 .  
         [0050]     In the illustrated embodiment, aluminum has been chosen for its high thermal conductance properties and ease of manufacture. It is to be understood, however, that any material having advantageous thermal conductance properties, such as having thermal conductivity greater than about 100 watts per meter per Kelvin (W/m-K), would be acceptable.  
         [0051]     A pair of holes  70  are preferably formed through the circuit board  50  and are adapted to accommodate a pair of aluminum pop rivets  72 . The pop rivets  72  hold the circuit board  50  securely onto a heat conductive mount member  76 . The mount member  76  functions as or communicates with a heat sink. Thus, heat from the LEDs  32  is conducted with relatively little resistance through the module  30  to the attached heat sink  76  so that the junction temperature of the diode chip  34  within the LED  32  does not exceed a maximum desired level.  
         [0052]     With reference again to  FIGS. 3 and 5 , a power supply wire  78  is attached across the first and last contacts  62 ,  64  of the circuit board  50  so that electrical current is provided to the series-connected LEDs  32 . The power supply is preferably a 12-volt system and may be AC, DC or any other suitable power supply. A 12-volt AC system may be fully rectified.  
         [0053]     The small size of the LED module  30  provides versatility so that modules can be mounted at various places and in various configurations. For instance, some applications will include only a single module for a particular lighting application, while other lighting applications will employ a plurality of modules electrically connected in parallel relative to each other.  
         [0054]     It is also to be understood that any number of LEDs can be included in one module. For example, some modules may use two LEDs, while other modules may use 10 or more LEDs. One manner of determining the number of LEDs to include in a single module is to first determine the desired operating voltage of a single LED of the module and also the voltage of the power supply. The number of LEDs desired for the module is then roughly equal to the voltage of the power supply divided by the operating voltage of each of the LEDs.  
         [0055]     The present invention rapidly conducts heat away from the diode chip  34  of each LED  32  so as to permit the LEDs  32  to be operated in regimes that exceed normal operating parameters of the pre-packaged LEDs  32 . In particular, the heat sinks allow the LED circuit to be driven in a continuous, non-pulsed manner at a higher long-term electrical current than is possible for typical LED mounting configurations. This operating current is substantially greater than manufacturer-recommended maximums. The optical emission of the LEDs at the higher current is also markedly greater than at manufacturer-suggested maximum currents.  
         [0056]     The heat transfer arrangement of the LED modules  30  is especially advantageous for pre-packaged LEDs  32  having relatively small packaging and for single-diode LED lamps. For instance, the HLMT-PL00 model LED lamps used in the illustrated embodiment employ only a single diode, but since heat can be drawn efficiently from that single diode through the leads and circuit board and into the heat sink, the diode can be run at a higher current than such LEDs are traditionally operated. At such a current, the single-diode LED shines brighter than LED lamps that employ two or more diodes and which are brighter than a single-diode lamp during traditional operation. Of course, pre-packaged LED lamps having multiple diodes can also be employed with the present invention. It is also to be understood that the relatively small packaging of the model HLMT-PL00 lamps aids in heat transfer by allowing the heat sink to be attached to the leads closer to the diode chip.  
         [0057]     With next reference to  FIG. 5 , a first reflective layer  80  is preferably attached immediately on top of the contacts  60  of the circuit board  50  and is held in position by the rivets  72 . The first reflector  80  preferably extends outwardly beyond the LEDs  32 . The reflective material preferably comprises an electrically non-conductive film such as visible mirror film available from 3M. A second reflective layer  82  is preferably attached to the mount member  76  at a point immediately adjacent the LED lamps  32 . The second strip  82  is preferably bonded to the mount surface  76  using adhesive in a manner known in the art.  
         [0058]     With reference also to  FIG. 6 , the first reflective strip  80  is preferably bent so as to form a convex reflective trough about the LEDs  32 . The convex trough is adapted to direct light rays emitted by the LEDs  32  outward with a minimum of reflections between the reflector strips  80 ,  82 . Additionally, light from the LEDs is limited to being directed in a specified general direction by the reflecting films  80 ,  82 . As also shown in  FIG. 6 , the circuit board  50  can be mounted directly to any mount surface  76 .  
         [0059]     In another embodiment, the aluminum main body portion  56  may be of reduced thickness or may be formed of a softer metal so that the module  30  can be partially deformed by a user. In this manner, the module  30  can be adjusted to fit onto various surfaces, whether they are flat or curved. By being able to adjust the fit of the module to the surface, the shared contact surface between the main body and the adjacent heat sink is maximized, improving heat transfer properties. Additional embodiments can use fasteners other than rivets to hold the module into place on the mount surface/heat sink material. These additional fasteners can include any known fastening means such as welding, heat conductive adhesives, and the like.  
         [0060]     As discussed above, a number of materials may be used for the circuit board portion of the LED module. With specific reference to  FIG. 7 , another embodiment of an LED module  86  comprises a series of elongate, flat contacts  88  similar to those described above with reference to  FIG. 3 . The contacts  88  are mounted directly onto the main body portion  89 . The main body  89  comprises a rigid, substantially flat ceramic plate. The ceramic plate makes up the bulk of the circuit board and provides structural support for the contacts  88 . Also, the ceramic plate has a surface area about the same as the combined surface area of the contacts. In this manner, the plate is large enough to provide structural support for the contacts  88  and conduct heat away from each of the contacts  88 , but is small enough to allow the module  86  to be relatively small and easy to work with. The ceramic plate  89  is preferably electrically non-conductive but has high heat conductivity. Thus, the contacts  88  are electrically insulated relative to each other, but heat from the contacts  88  is readily transferred to the ceramic plate  89  and into an adjoining heat sink.  
         [0061]     With next reference to  FIG. 8 , another embodiment of an LED lighting module  90  is shown. The LED module  90  comprises a circuit board  92  having features substantially similar to the circuit board  50  described above with reference to  FIG. 3 . The diode portion  94  of the LED  96  is mounted substantially directly onto the contacts  60  of the lighting module  90 . In this manner, any thermal resistance from leads of pre-packaged LEDs is eliminated by transferring heat directly from the diode  94  onto each heat sink contact  60 , from which the heat is conducted to the main body  56  and then out of the module  90 . In this configuration, heat transfer properties are yet further improved.  
         [0062]     As discussed above, an LED module having features as described above can be used in many applications such as, for example, indoor and outdoor decorative lighting, commercial lighting, spot lighting, and even room lighting. With next reference to  FIGS. 9-12 , a self-contained lighting apparatus  100  incorporates an LED module  30  and can be used in many such applications. In the illustrated embodiment, the lighting apparatus  100  is adapted to be installed on the side of a row of theater seats  102 , as shown in  FIG. 13 , and is adapted to illuminate an aisle  104  next to the theater seats  102 .  
         [0063]     The self-contained lighting apparatus  100  comprises a base plate  106 , a housing  108 , and an LED module  30  arranged within the housing  108 . As shown in  FIGS. 9, 10  and  13 , the base plate  106  is preferably substantially circular and has a diameter of about 5.75 inches. The base plate  106  is preferably formed of 1/16 th  inch thick aluminum sheet. As described in more detail below, the plate functions as a heat sink to absorb and dissipate heat from the LED module. As such, the base plate  106  is preferably formed as large as is practicable, given aesthetic and installation concerns.  
         [0064]     As discussed above, the lighting apparatus  100  is especially adapted to be mounted on an end panel  110  of a row of theater chairs  102  in order to illuminate an adjacent aisle  104 . As shown in  FIGS. 13 and 14 , the base plate  106  is preferably installed in a vertical orientation. Such vertical orientation aids conductive heat transfer from the base plate  106  to the environment.  
         [0065]     The base plate  106  includes three holes  112  adapted to facilitate mounting. A ratcheting barb  116  (see  FIG. 15 ) secures the plate  106  to the panel  110 . The barb  116  has an elongate main body  118  having a plurality of biased ribs  120  and terminating at a domed top  122 .  
         [0066]     To mount the apparatus on the end panel  110 , a hole is first formed in the end panel surface on which the apparatus is to be mounted. The base plate holes  112  are aligned with mount surface holes and the barbs  116  are inserted through the base plate  106  into the holes. The ribs  120  prevent the barbs  116  from being drawn out of the holes once inserted. Thus, the apparatus is securely held in place and cannot be easily removed. The barbs  116  are especially advantageous because they enable the device to be mounted on various surfaces. For example, the barbs will securely mount the illumination apparatus on wooden or fabric surfaces.  
         [0067]     With reference next to  FIGS. 16-19 , a mount tab  130  is provided as an integral part of the base plate  106 . The mounting tab  130  is adapted to receive an LED module  30  mounted thereon. The tab  30  is preferably plastically deformed along a hinge line  132  to an angle θ between about 20-45° relative to the main body  134  of the base plate  106 . More preferably, the mounting tab  130  is bent at an angle θ of about 33°. The inclusion of the tab  130  as an integral part of the base plate  106  facilitates heat transfer from the tab  130  to the main body  134  of the base plate. It is to be understood that the angle θ of the tab  130  relative to the base plate body  134  can be any desired angle as appropriate for the particular application of the lighting apparatus  100 .  
         [0068]     A cut out portion  136  of the base plate  106  is provided surrounding the mount tab  130 . The cut out portion  136  provides space for components of the mount tab  130  to fit onto the base plate  106 . Also, the cut out portion  136  helps define the shape of the mount tab  130 . As discussed above, the mount tab  130  is preferably plastically deformed along the hinge line  132 . The length of the hinge line  132  is determined by the shape of the cut out portion  136  in that area. Also, a hole  138  is preferably formed in the hinge line  132 . The hole  138  further facilitates plastic deformation along the hinge line  132 .  
         [0069]     Power for the light source assembly  100  is preferably provided through a power cord  78  that enters the apparatus  100  through a back side of the base plate  106 . The cord  78  preferably includes two 18 AWG conductors surrounded by an insulating sheet. Preferably, the power supply is in the low voltage range. For example, the power supply is preferably a 12-volt alternating current power source. As depicted in  FIG. 18 , power is preferably first provided through a full wave ridge rectifier  140  which rectifies the alternating current in a manner known in the art so that substantially all of the current range can be used by the LED module  40 . In the illustrated embodiment, the LEDs are preferably not electrically connected to a current-limiting resistor. Thus, maximum light output can be achieved. It is to be understood, however, that resistors may be desirable in some embodiments to regulate current. Supply wires  142  extend from the rectifier  140  and provide rectified power to the LED module  30  mounted on the mounting tab  130 .  
         [0070]     With reference again to  FIGS. 9-12 ,  16  and  17 , the housing  108  is positioned on the base plate  106  and preferably encloses the wiring connections in the light source assembly  100 . The housing  108  is preferably substantially semi-spherical in shape and has a notch  144  formed on the bottom side. A cavity  146  is formed through the notch  144  and allows visual access to the light source assembly  100 . A second cavity  148  is formed on the top side and preferably includes a plug  150  which may, if desired, include a marking such as a row number. In an additional embodiment, a portion of the light from the LED module  30 , or even from an alternative light source, may provide light to light up the aisle marker.  
         [0071]     The housing  108  is preferably secured to the base plate  106  by a pair of screws  152 . Preferably, the screws  152  extend through countersunk holes  154  in the base plate  106 . This enables the base plate  106  to be substantially flat on the back side, allowing the plate to be mounted flush with the mount surface. As shown in  FIG. 17 , threaded screw receiver posts  156  are formed within the housing  108  and are adapted to accommodate the screw threads.  
         [0072]     The LED module  30  is attached to the mount tab  130  by the pop rivets  72 . The module  30  and rivets  72  conduct heat from the LEDs  32  to the mount tab  130 . Since the tab  130  is integrally formed as a part of the base plate  106 , heat flows freely from the tab  130  to the main body  134  of the base plate. The base plate  106  has high heat conductance properties and a relatively large surface area, thus facilitating efficient heat transfer to the environment and allowing the base plate  106  to function as a heat sink.  
         [0073]     As discussed above, the first reflective strip  80  of the LED module  30  is preferably bent so as to form a convex trough about the LEDs. The second reflector strip  82  is attached to the base plate mount tab  130  at a point immediately adjacent the LED lamps  32 . Thus, light from the LEDs is collimated and directed out of the bottom cavity  146  of the housing  108 , while minimizing the number of reflections the light must make between the reflectors (see  FIG. 6 ). Such reflections may each reduce the intensity of light reflected.  
         [0074]     A lens or shield  160  is provided and is adapted to be positioned between the LEDs  32  and the environment outside of the housing cavity  108 . The shield  160  prevents direct access to the LEDs  32  and thus prevents harm that may occur from vandalism or the like, but also transmits light emitted by the light source  100 .  
         [0075]      FIG. 20  shows an embodiment of the shield  160  adapted for use in the present invention. As shown, the shield  160  is substantially lenticularly shaped and has a notch  162  formed on either end thereof. With reference back to  FIG. 18 , the mounting tab  130  of the base plate  106  also has a pair of notches  164  formed therein.  
         [0076]     As shown in  FIG. 16 , the lens/shield notches  162  are adapted to fit within the tab notches  164  so that the shield  160  is held in place in a substantially arcuate position. The shield thus, in effect, wraps around one side of the LEDs  32 . When the shield  160  is wrapped around the LEDs  32 , the shield  160  contacts the first reflector film  80 , deflecting the film  80  to further form the film in a convex arrangement. The shield  160  is preferably formed of a clear polycarbonate material, but it is to be understood that the shield  160  may be formed of any clear or colored transmissive material as desired by the user.  
         [0077]     The LED module  30  of the present invention can also be used in applications using a plurality of such modules  30  to appropriately light a lighting apparatus such as a channel illumination device. Channel illumination devices are frequently used for signage including borders and lettering. In these devices, a wall structure outlines a desired shape to be illuminated, with one or more channels defined between the walls. A light source is mounted within the channel and a translucent diffusing lens is usually arranged at the top edges of the walls so as to enclose the channel. In this manner, a desired shape can be illuminated in a desired color as defined by the color of the lens.  
         [0078]     Typically, a gas-containing light source such as a neon light is custom-shaped to fit within the channel. Although the diffusing lens is placed over the light source, the light apparatus may still produce “hot spots,” which are portions of the sign that are visibly brighter than other portions of the sign. Such hot spots result because the lighting apparatus shines directly at the lens, and the lens may have limited light-diffusing capability. Incandescent lamps may also be used to illuminate such a channel illumination apparatus; however, the hot spot problem typically is even more pronounced with incandescent lights.  
         [0079]     Both incandescent and gas-filled lights have relatively high manufacturing and operation costs. For instance, gas-filled lights typically require custom shaping and installation and therefore can be very expensive to manufacture. Additionally, both incandescent and gas-filled lights have high power requirements.  
         [0080]     With reference next to  FIG. 21 , an embodiment of a channel illumination apparatus  170  is disclosed comprising a casing  172  in the shape of a “P.” The casing  172  includes a plurality of walls  174  and a bottom  176 , which together define at least one channel. The surfaces of the walls  174  and bottom  176  are diffusely-reflective, preferably being coated with a flat white coating. The walls  174  are preferably formed of a durable sturdy metal having relatively high heat conductivity. A plurality of LED lighting modules  30  are mounted to the walls  174  of the casing  172  in a spaced-apart manner. A translucent light-diffusing lens (not shown) is preferably disposed on a top edge  178  of the walls  174  and encloses the channel.  
         [0081]     With next reference to  FIG. 22 , the pop rivets  72  hold the LED module  30  securely onto a heat conductive mount tab  180 . The mount tab  180 , in turn, may be connected, by rivets  182  or any other fastening means, to the walls  174  of the channel apparatus as shown in  FIG. 23 . Preferably, the connection of the mount tab  180  to the walls  174  facilitates heat transfer from the tab  180  to the wall  174 . The channel wall has a relatively large surface area, facilitating efficient heat transfer to the environment and enabling the channel wall  174  to function as a heat sink.  
         [0082]     In additional embodiments, the casing  172  may be constructed of materials, such as certain plastics, that may not be capable of functioning as heat sinks because of inferior heat conductance properties. In such embodiments, the LED module  30  can be connected to its own relatively large heat sink base plate, which is mounted to the wall of the casing. An example of such a heat sink plate in conjunction with an LED lighting module has been disclosed above with reference to the self-contained lighting apparatus  100 .  
         [0083]     With continued reference to  FIGS. 22 and 23 , the LED modules  30  are preferably electrically connected in parallel relative to other modules  30  in the illumination apparatus  170 . A power supply cord  184  preferably enters through a wall  174  or bottom surface  176  of the casing  172  and preferably comprises two 18 AWG main conductors  186 . Short wires  188  are attached to the first and last contacts  62 ,  64  of each module  30  and preferably connect with respective main conductors  186  using insulation displacement connectors (IDCs)  190  as shown in  FIG. 23 .  
         [0084]     Although the LEDs  32  in the modules  30  are operated at currents higher than typical LEDs, the power efficiency characteristic of LEDs is retained. For example, a typical channel light employing a neon-filled light could be expected to use about 60 watts of power during operation. A corresponding channel illumination apparatus  170  using a plurality of LED modules can be expected to use about 4.5 watts of power.  
         [0085]     With reference again to  FIG. 23 , the LED modules  30  are preferably positioned so that the LEDs  32  face generally downwardly, directing light away from the lens. The light is preferably directed to the diffusely-reflective wall and bottom surfaces  174 ,  176  of the casing  172 . The hot spots associated with more direct forms of lighting, such as typical incandescent and gas-filled bulb arrangements, are thus avoided.  
         [0086]     The reflectors  80 ,  82  of the LED modules  30  aid in directing light rays emanating from the LEDs toward the diffusely-reflective surfaces. It is to be understood, however, that an LED module  30  not employing reflectors can also be appropriately used.  
         [0087]     The relatively low profile of each LED module  30  facilitates the indirect method of lighting because substantially no shadow is created by the module when it is positioned on the wall  174 . A higher-profile light module would cast a shadow on the lens, producing an undesirable, visibly darkened area. To minimize the potential of shadowing, it is desired to space the modules  30  and accompanying power wires  186 ,  188  a distance of at least about ½ inch from the top edge  178  of the wall  174 . More preferably, the modules  30  are spaced more than one inch from the top  178  of the wall  174 .  
         [0088]     The small size and low profile of the LED modules  30  enables the modules to be mounted at various places along the channel wall  174 . For instance, with reference to  FIGS. 21 and 24 , light modules  30  must sometimes be mounted to curving portions  192  of walls  174 . The modules  30  are preferably about 1 inch to 1½ inch long, including the mounting tab  180 , and thus can be acceptably mounted to a curving wall  192 . As shown, the mounting tab  180  may be separated from the curving wall  192  along a portion of its length, but the module is small enough that it is suitable for riveting to the wall.  
         [0089]     In an additional embodiment shown in  FIG. 25 , the module  30  comprises the circuit board without the mount tab  180 . In such an embodiment, the circuit board  50  may be mounted directly to the wall, having an even better fit relative to the curved surface  192  than the embodiment using a mount tab. In still another embodiment, the LED module&#39;s main body  56  is formed of a bendable material, which allows the module to fit more closely and easily to the curved wall surface.  
         [0090]     Although the LED modules  30  disclosed above are mounted to the channel casing wall  174  with rivets  182 , it is to be understood that any method of mounting may be acceptably used. With reference next to FIGS.  26 A-C, an additional embodiment comprises an LED module  30  mounted to a mounting tab  200  which comprises an elongate body portion  202  and a clip portion  204 . The clip portion  204  is urged over the top edge  178  of the casing wall  172 , firmly holding the mounting tab  200  to the wall  174  as shown in  FIG. 26B . The lens  206  preferably has a channel portion  208  which is adapted to engage the top edge  178  of the casing wall  174  and can be fit over the clip portion  204  of the mount tab  200  as shown in  FIGS. 26B and 26C . This mounting arrangement is simple and provides ample surface area contact between the casing wall  174  and the mounting tab  200  so that heat transfer is facilitated.  
         [0091]     In the embodiment shown in  FIG. 21 , the casing walls  174  are about 3 to 4 inches deep and the width of the channel is about 3 to 4 inches between the walls. In an apparatus of this size, LED modules  30  positioned on one side of the channel can provide sufficient lighting. The modules are preferably spaced about 5-6 inches apart. As may be anticipated, larger channel apparatus will likely require somewhat different arrangements of LED modules, including employing more LED modules. For example, a channel illumination apparatus having a channel width of 1 to 2 feet may employ LED modules on both walls and may even use multiple rows of LED modules. Additionally, the orientation of each of the modules may be varied in such a large channel illumination apparatus. For instance, with reference to  FIG. 26D , some of the LED modules may desirably be angled so as to direct light at various angles relative to the diffusely reflective surfaces.  
         [0092]     In order to avoid creating hot spots, a direct light path from the LED  32  to the lens  206  is preferably avoided. However, it is to be understood that pre-packaged LED lamps  32  having diffusely-reflective lenses may advantageously be directed toward the channel letter lens  206 .  
         [0093]     Using LED modules  30  to illuminate a channel illumination apparatus  170  provides significant savings during manufacturing. For example, a number of LED modules, along with appropriate wiring and hardware, can be included in a kit which allows a technician to easily assemble a light by simply securing the modules in place along the wall of the casing and connecting the wiring appropriately using the IDCs. Although rivet holes may have to be drilled through the wall, there is no need for custom shaping, as is required with gas-filled bulbs. Accordingly, manufacturing effort and costs are significantly reduced.  
         [0094]     Individual LEDs emit generally monochromatic light. Thus, it is preferable that an LED type be chosen which corresponds to the desired illumination color. Additionally, the diffuser is preferably chosen to be substantially the same color as the LEDs. Such an arrangement facilitates desirable brightness and color results. It is also to be understood that the diffusely-reflective wall and bottom surfaces may advantageously be coated to match the desired illumination color.  
         [0095]     Although this invention has been disclosed in the context of certain preferred embodiments and examples, it will be understood by those skilled in the art that the present invention extends beyond the specifically-disclosed embodiments to other alternative embodiments and/or uses of the invention and obvious modifications and equivalents thereof. In addition, while a number of variations of the invention have been shown and described in detail, other modifications, which are within the scope of this invention, will be readily apparent to those of skill in the art based upon this disclosure. It is also contemplated that various combinations or subcombinations of the specific features and aspects of the embodiments may be made and still fall within the scope of the invention. Accordingly, it should be understood that various features and aspects of the disclosed embodiments can be combined with or substituted for one another in order to form varying modes of the disclosed invention. Thus, it is intended that the scope of the present invention herein disclosed should not be limited by the particular disclosed embodiments described above, but should be determined only by a fair reading of the claims that follow.