Abstract:
A low-profile strip illumination device comprises a substrate supporting an elongate heat conductor and positively and negatively energized elongate rails. A plurality of spaced apart light emitting diodes (LEDs) are mounted so as to be powered by the elongate rails. The LEDs are arranged generally adjacent the elongate heat conductor so that a heat flow path is defined from each LED to the elongate heat conductor and to the environment.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 60/901,138, which was filed on Feb. 14, 2007, the entirety of which is hereby incorporated by reference. 
     
    
     BACKGROUND 
       [0002]    1. Field of the Invention 
         [0003]    The present invention is in the field of illumination devices and, more specifically, light emitting diode (LED)-based illumination devices. 
         [0004]    2. Description of the Related Art 
         [0005]    Strip-type illumination devices are particularly useful for lighting applications such as under-cabinet lighting and cove lighting. Such strip illumination devices are typically made up of a plurality of light sources spaced apart from one another along a length of an elongate substrate. Generally, it is desirable to hide such strip illumination devices from direct view. Thus, manufacturers try to design strip devices having a comparably low profile as compared to other luminaires. Also, due the their typical positioning, for example as under-cabinet lighting or cove lighting, strip luminaires may be difficult to install and service. 
         [0006]    Strip illumination devices employing light emitting diodes (LEDs) have been developed in an effort to take advantage of the long life and small packaging of LEDs. However, such LED-based devices often are not conducive to customized installations, in which the length of a prefabricated strip may need to be adjusted during installation. Also, LEDs tend to decrease both in brightness and in expected lifetime if they operate in configurations in which the heat generated by the LED is not efficiently evacuated. 
       SUMMARY 
       [0007]    Accordingly, there is a need in the art for a low-profile, LED-based strip illumination device that is easy to adapt to customized installations. There is also a need for an LED-based strip illumination device that efficiently directs heat away from the LED. 
         [0008]    In accordance with one embodiment, the present invention provides an illumination apparatus, comprising an elongate substrate, first and second electrically conductive rails, and a plurality of LED modules. The first and second rails are supported by the substrate so that the first and second rails are spaced apart and electrically insulated from one another. Each LED module comprises a module body, an LED, and an electrical current path. The current path is configured so that electrical current flows from a first electrical contact to a second electrical contact. The LED is interposed in the current path between the first and second contacts so that electrical current flows along the path and through the LED. A plurality of fasteners are provided and are adapted to connect the plurality of LED modules to the elongate substrate so that the first and second contacts of each LED module are electrically connected to the first and second rails, respectively. 
         [0009]    In accordance with one embodiment, a pair of fasteners are used to connect each LED module to the elongate substrate. In one such embodiment, a first one of each pair of fasteners is adapted to engage the first rail and the first contact so as to conduct current between the first rail and the first contact. In another embodiment, a second one of each pair of fasteners is adapted to engage the second rail and the second contact so as to conduct current between the second rail and the second contact. 
         [0010]    In yet another such embodiment, the first fastener comprises a threaded fastener, the first rail comprises a threaded portion, and the first fastener threadingly engages the first rail threaded portion. In one such embodiment, the LED module comprises a dielectric layer having a dielectric thickness, the dielectric layer disposed on a first side of the LED module body, the first and second contacts disposed on the dielectric layer and having a contact thickness. A first aperture is formed through the body, dielectric layer and first contact, and the first aperture is configured to accommodate a shank portion of the first fastener extending therethrough. The first fastener has a head portion adapted to engage the first contact, and a ratio of a diameter of the head portion to the combined dielectric thickness and contact thickness is between about 80:1-125:1. 
         [0011]    In another embodiment, the first and second rails are substantially embedded in the elongate substrate. 
         [0012]    In yet another embodiment, a heat conductive insert is supported by the elongate substrate so that the LED module body generally directly contacts the insert. In one such embodiment, the heat conductive insert has an insert thickness, and the elongate substrate comprises a substrate cavity configured to generally accommodate the heat conductive insert, the substrate cavity having a cavity depth. The cavity depth is less than the insert thickness. 
         [0013]    In still another embodiment, an elongate cavity is formed in the substrate, and the heat conductive insert is elongate and sits at least partially in the elongate cavity. In one such embodiment, each LED module body has opposing first and second sides, and the LED is disposed adjacent a mounting point on the first side of the body. The body is connected to the heat conductive insert so that the insert directly contacts the second side of the body directly opposite the mounting point. 
         [0014]    In accordance with another embodiment, an illumination apparatus is provided. The apparatus comprises an elongate substrate, first and second electrically conductive rails, a heat sink supported by the substrate, and a plurality of pre-packaged LEDs. The first and second rails are supported by the substrate so that the first and second rails are spaced apart and electrically insulated from one another. The LEDs are electrically connected to the first and second rails so that an electric current path is established between the rails and across at least one of the LEDs, and the LEDs are mounted so that the associated LED package is substantially directly aligned with the heat sink. 
         [0015]    In another embodiment, the LED package is vertically aligned with the heat sink. In one such embodiment, the heat sink is horizontally spaced from the rails. In another embodiment, the heat sink is vertically spaced from the rails. 
         [0016]    In yet another embodiment, the LED package comprises a package heat sink, and the package heat sink is in substantially direct contact with the heat sink. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  is a perspective view of an embodiment. 
           [0018]      FIG. 2  is a cross-sectional view of the embodiment of  FIG. 1  taken along line  2 - 2 . 
           [0019]      FIG. 3  is a perspective view of a substrate portion of the embodiment of  FIG. 1 . 
           [0020]      FIG. 4  is an exploded view of the cross-section of  FIG. 2 , showing additional detail. 
           [0021]      FIG. 5  is a plan view of one embodiment of an LED module. 
           [0022]      FIG. 6  is a back-side view of an embodiment in which two illumination strips are fit together end-to-end. 
           [0023]      FIG. 7  is a perspective view of another embodiment for electrically joining strips together. 
           [0024]      FIG. 8  is a cross-sectional view of an embodiment of an illumination strip having a housing fit thereon, but not showing any LED modules that may be mounted thereon. 
           [0025]      FIG. 9  is a sectional view of another embodiment of an illumination strip. 
           [0026]      FIG. 10  is a sectional view of yet another embodiment of an illumination strip. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0027]    With initial reference to  FIGS. 1-6 , an embodiment of a strip illumination device  30  is presented. Such a device comprises a light strip section  32  that can be used alone, trimmed to a desired size, and/or combined with other sections to create an illumination system. 
         [0028]    In the illustrated embodiment the strip section  32  comprises an elongate substrate  34  upon which a plurality of light emitting diode (LED) modules  40  are mounted spaced apart from each other. Each LED module  40  comprises one or more LEDs  42  that provide light when energized. The illustrated embodiment includes modules  40  having two LEDs  42 . Preferably, the LED modules  40  have an easily-mounted and thermally managed structure such as is disclosed in assignee&#39;s U.S. Pat. No. 7,114,831, the entirety of which is hereby incorporated by reference. For example, the LED module  40  preferably has a heat conductive body  44 , such as an aluminum body, upon which an electric circuit  46  is disposed. Preferably, the circuit is electrically insulated from the body  44 . LEDs  42  are arranged on the circuit  46 . The circuit terminates at positive and negative contacts  48 A,  48 B at which positive and negative fasteners  50 A,  50 B (bolts in the illustrated embodiments) are attached to the module  40 . 
         [0029]    As best shown in  FIGS. 2-4 , the illustrated substrate  34  comprises a module mounting cavity  52  having a module mount surface  54  upon which the modules  40  are placed. An elongate positive rail  60 A and an elongate negative rail  60 B are also supported by the substrate  34 . The positive and negative rails  60 A,  60 B are spaced apart from each other and from the module mount surface  54 . Preferably, the rails  60  are elongate and electrically conductive. In the illustrated embodiment, each module  40  is arranged on the module mount surface  54  and the positive and negative module bolts  50  are advanced through the substrate  34  into contact with the corresponding rail  56 . Thus, the bolts  50  secure the LED modules  40  in place on the substrate  34 , connect electrically to the rails  60 , and connect electrically to the positive and negative contacts  48 A,  48 B. Preferably, the rails  60  are energized so that electric current will flow from one rail  60  through a bolt  50  to the module  40 , through the circuit  46  on the module to the opposing bolt  50 , and further to the opposing rail  60 . In this manner, multiple LED modules  40  are attached to the substrate  34  and rails  60  in an electrically parallel fashion. 
         [0030]    In the present specification the term “rail” is a broad term used in accordance with its ordinary meaning, and also including an elongate member of any cross-sectional shape to which other devices or members may be connected, be it by a bolt  50  as in the embodiment discussed above or by clip, solder, or some other type of structure or method. Additionally, a rail may in some embodiments or may not in others be configured to provide structural support, such as to support a threaded fastener. 
         [0031]    Continuing with specific reference to  FIGS. 1 ,  2  and  4 , an elongate heat spreader strip  62  preferably is supported by the substrate  34  and is arranged so that the body  44  of each LED module  40  directly contacts the heat spreader  62 . Heat generated by the LEDs  42  is communicated to the body  44  of the module  40 . From the body  44  the heat is communicated at least to the heat spreading strip  62 , which acts as a heat sink, and which also helps communicate heat to the environment. Thus, heat generated by the LEDs  42  is drawn away from the LEDs in order to keep the LEDs from becoming excessively hot during extended use. 
         [0032]    With particular reference to  FIGS. 1-4 , the illustrated substrate  34  has a front side  64  and a back side  66 . Preferably, the module mounting cavity  52  is formed in the front side  64 . The module mounting cavity  52  preferably is defined by a cavity wall  68  and the module mount surface  54 . The cavity wall  68  intersects with the front side  64  at a front edge  70  of the cavity wall  68 . Preferably, LED modules  40  are mounted within the cavity  52  so that the modules, including the LED light sources  42 , do not extend outwardly beyond the front edges  20  of the opposing cavity walls  68 . As such, the substrate  34  blocks bright point light sources, as well as other components within the cavity  52 , from view when the illumination strip  32  is viewed from a side direction. 
         [0033]    Preferably, the substrate  34  is electrically non-conductive. In a preferred embodiment, the substrate is made of a plastic such as Delrin™ or the like. Preferably, the substrate is a dielectric rated for use up to about 90° C. 
         [0034]    A heat-spreader cavity  72  is formed in the cavity mounting surface  54 . The heat spreader cavity  72  is defined by a cavity wall  74  that extends into the substrate  34  and terminates in a base surface  75 . The elongate heat spreader  62  is adapted to fit within the heat spreader cavity  72 . As shown, the heat spreader  62  has a generally rectangular cross-section that generally corresponds to the cross-sectional shape of the heat spreader cavity  72 . In one embodiment, the depth D 1  of the heat spreader cavity  72  is less than a thickness D 2  of the heat spreader member  62 . As such, even though the heat spreader  62  generally fits within the cavity  72 , since D 1 &lt;D 2  the heat spreader  62  protrudes from the module mount surface  74  a short distance such as, for example, about 10/1000 inch. With such a configuration, when an LED module  40  is mounted on the mounting surface  54 , direct and secure contact is established between the heat spreader  62  and the body  44  of the module  40  despite minor variations that may be expected in the substrate  34 . Such direct contact facilitates heat transfer from the LED module  40  to the heat spreader  62 . Preferably, the heat spreader  62  comprises an elongate metal strip, such as aluminum, having advantageous heat transfer properties. Of course, other materials having advantageous heat transfer properties can be used. Also, in other embodiments portions of the heat spreader may be ribbed or otherwise shaped and/or treated to enhance heat transfer to the environment. 
         [0035]    As mentioned above and with additional reference to  FIG. 5 , the LED module  40  preferably comprises the body  44  that is made of a heat conductive material such as aluminum. The electric circuit  46  is supported by the body  44 , and preferably is electrically insulated relative to the body by a dielectric layer  76 . The electric circuit  46  preferably comprises contacts  78 , such as copper contacts. The dielectric and contact layers  76 ,  78  are specifically illustrated in  FIG. 4 , but it is to be understood that they are not necessarily shown to scale, and the dielectric and contact layers  76 ,  78  preferably are very thin, such as on the order of 1 to 2 mils in thickness each. The one or more LEDs  42  are attached to the circuit  46 , which is supported by the body  44 . In a preferred embodiment the LEDs  42  are provided in a prepackaged form that facilitates easy assembly of the module  40 . 
         [0036]    Preferably, LED modules  40  are arranged on the substrate  34  at predetermined, spread-apart intervals. In one embodiment, LED modules are arranged on six inch centers. In another embodiment, LED modules are arranged on three inch centers. Preferably, holes  80  are provided through the substrate  34  to accommodate mount bolts  50  at the appropriate mounting locations. Preferably, the bolts  50  have an elongate shank  82  and a head portion  84 . The head portions  84 , when tightened, engage the associated positive or negative contact  48  of the circuit  46  on the LED module  40 . As such, the bolts  50 A,  50 B are electrically polarized, and current flows through the bolts  50 A,  50 B to the LEDs  42  on the modules  40 . 
         [0037]    As best shown in  FIGS. 3 and 4 , a raised portion  86  of the illustrated substrate  34  surrounds each module bolt hole  80  at the module mount surface  54 . Preferably, the raised portions  86  are positioned on the substrate  34  so as to generally correspond to apertures  88  formed through the LED module body  44  and through which the bolts  50  extend. In the illustrated embodiment, the raised portions  86  extend upwardly from the mount surface  54  a distance up to or less than the thickness of the module body  44 ; however, preferably the raised portions  86  extend upwardly enough to act as a guide and insulator for the bolts  50  relative to the module body  44 . Accordingly, there is no metal-to-metal contact of the bolts  50  with the module body  44 , and thus short-circuits are avoided. In other embodiments, a plastic washer, spacer, or the like can be employed instead of the raised portion being formed integrally with or bonded to the substrate. 
         [0038]    During manufacture, the substrate  34  preferably is extruded, and then portions are machined, if desired, to provide the shapes illustrated. It is to be understood that other manufacturing processes, such as injection molding, may also be used. 
         [0039]    With continued specific reference to  FIGS. 1-4 , preferably the substrate  34  has a pair of elongate rail cavities  90  provided therein in which the electrically conductive elongate rails  60  are disposed. The rails  60  preferably are metal rails adapted to conduct electricity. As indicated above, during use the rails  60 A,  60 B are energized so that there is a voltage difference between them. As shown, preferably the LED module mount bolts  50 A,  50 B engage the rails through corresponding bolt mount holes  80 . As such, electric current from one rail  60 A flows through the bolts  50 A,  50 B to the LEDs  42  on the module  40  and to the opposing rail  60 B. The rails  60  thus supply electric current across LED modules  40 , and a plurality of such LED modules  40  may be arranged electrically in parallel when the bolts  50  are connected the rails  60 . 
         [0040]    In the illustrated embodiment, the elongate rails  60  are formed of an electrically conductive material that is also heat conductive. The illustrated rails comprise aluminum. Additionally, in the illustrated embodiment, the rails  60  have a substantially rectangular cross-sectional profile. This profile is advantageous for multiple reasons. For example, the profile makes it simple to create bolt holes  92  that threadingly engage the LED mounting bolts  50 . Additionally, the rails  60  preferably have sufficient thickness to provide a secure mounting connection via the bolt holes  92 . The mass of the rails  60  is also advantageously chosen to assist in evacuating heat from attached LED modules  40 . More specifically, a portion of the heat generated by the LEDs  42  is communicated through the bolts  50  to the rails  60 . The rails function as a heat sink, dispersing the heat through the mass of the rails and also diffusing heat to the environment. 
         [0041]    With continued reference to  FIGS. 1-4 , the rails  60  sit within the rail cavities  90  formed in the substrate  34 . However, access cavities  96  are also aligned with the rail cavities  92  so that a portion of each rail  60  is exposed through the back  66  of the substrate  34 . This assists in heat transfer, but also assists in joining multiple strip sections  32  to form an illumination system comprising multiple strip sections. 
         [0042]    With reference next to  FIG. 6 , a back side view of two abutting strip sections  32  is shown. As illustrated, the ends of the strip sections  32  are aligned with and adjacent one another. The rails  60  are visible and accessible through the rail access cavities  96 . As shown, module bolt mount holes  92  extend through the rails  60 . These module bolt holes  92  are already being used by LED module mount bolts  50 . However, additional holes  98  are formed through the rails  60  adjacent the end of each lighting strip  32 . Conductive jumpers  100  are provided for attaching to the rails  60  of adjacent strip sections  32  at these holes  98 . Each jumper  100  preferably comprises an electrically conductive material, such as aluminum, having a width sized to fit within the access cavity  96  of the adjacent substrates  34  so as to engage the rails  60 . A plurality of spaced-apart mount holes  102  are provided on each jumper  100  to provide some versatility in aligning with jumper mount holes  98  formed in the rails  60 . As illustrated, to connect strip sections  32  end-to-end an elongate jumper  100  is aligned with desired jumper mount holes  98  of adjacent strip sections  32 , and jumper bolts  102  are extended through the holes  102  to threadingly engage the jumper mount hole  98  of the corresponding rail  60  in order to secure the jumper  100  in place. Preferably, the access cavity  96  is of sufficient depth so that the jumper  100  and jumper bolts  104  do not extend outwardly beyond the back surface  66  of the substrate  34 . Thus, even with the jumpers  100  bolted in place, the adjoined strip sections  32  will fit flush against an installation surface such as the undersurface of a cabinet. 
         [0043]    With the jumpers  100  in place, the adjacent strip sections  32  are joined end-to-end both mechanically and electrically. As such, if the rails  60  of one of the strip sections  32  are energized, such electrical energy is communicated to both strip sections. Further, such an electrical and mechanical connection can be used to connect several strip sections  32 . Still further, although the illustrated embodiment illustrates strip sections joined end-to-end, it is to be understood that strip sections can be joined at various angles, such as 90°, 45°, or the like, by using jumpers having curving or bending shapes and dimensions to accommodate such varying angular relationships between adjacent strip sections. Also, the strip sections can be cut as desired to fit a given situation or installation configuration. 
         [0044]    It is to be understood that other structures and methods can be employed for joining adjacent strip sections  32  electrically to one another. For example,  FIG. 7  illustrates an embodiment in which a wire connector  105 , such as the two-position poke-in connector available from Tyco (part number 1954097-1), is connected to a circuit board  106  having a positive contact  108 A and a negative contact  108 A. The circuit board  106  is mounted on the mount surface  54  and, in a preferred embodiment, positive and negative bolts  50 A,  50 B extend through corresponding holes in the circuit board  106  to engage and electrically connect the rails  60 A,  60 B to the positive and negative contacts  108 ,  108   b  of the circuit board  106 . Wires  109  extend from the wire connector  105  to a wire connector mounted on an adjacent strip section. As such, adjacent strip sections  32  are electrically connected to one another, but are not rigidly mechanically connected to one another, thus providing further versatility in installation. Additionally, a wire connector  105  as in this embodiment can advantageously attach to a power source to supply power to a strip illumination device  30  comprising one or more electrically-connected strip sections  32 . 
         [0045]    Mounting a single or a plurality of the strip sections  100  to an installation surface, such as the undersurface of kitchen cabinets, can be achieved in any of several ways. For example, in one embodiment, holes are provided through the center of the substrate, and even through the heat spreader. A screw, bolt, or the like can be extended through such holes and into the installation surface to hold the strip section in place. A plurality of such connections may advantageously be provided. In another embodiment, an adhesive may be applied to the back surface of the substrate in order to install the strip sections. In still another embodiment, screws or the like may be advanced through the substrate. Other methods and apparatus, such as clips, can also be employed for installing the strip sections. 
         [0046]    As discussed above, the heat spreading metal strip  62  advantageously helps to evacuate heat generated by the LEDs  42 . As such, in the illustrated embodiment, the heat spreader  62  is arranged so as to contact the LED module body  44  at a location directly beneath the LED  42 . This places the heat spreader  62  in an ideal position to evacuate heat generated by the LED  42 . Such heat generated by the LED  42  flows first to the portion of the body  44  directly below the LED and is then radiated through the body  44  and to the heat spreader  62 . In its position directly below the LEDs, the heat spreader is in an ideal position to receive such heat without necessitating such heat being communicated further along the body. Thus, more efficient and direct heat transfer is provided between the LEDs and the heat spreader. 
         [0047]    With reference next to  FIG. 8 , another embodiment is provided in which a housing/shroud  110  is arranged over the substrate  32 .  FIG. 8  shows a cross-sectional view taken through an embodiment of the strip section at a location of the strip section between LED modules. Thus, LED modules are not shown in the drawing. In the illustrated embodiment, an elongate heat conductive shroud  110  is disposed over the substrate  32 . Preferably, the shroud  110  fits generally complimentarily over the front face  64  of the substrate  34 , including the cavity wall  68  and module mount surface  54 . In one embodiment, apertures (not shown) are formed through a base portion  112  of the shroud  110  in order to accommodate and avoid interference with LED modules. 
         [0048]    Preferably, the shroud  110  is attached, such as with a bolt  114 , to at least the heat spreader member  62  so as to encourage metal-to-metal contact between the shroud  110  and the heat spreader  62 , thus maximizing the transfer of heat from the heat spreader  62  to the shroud  110  so that such heat can be communicated to the environment. Preferably, the shroud  110  includes cover mounts  116  to which a cover  120  can be releasably mounted, preferably extending across the module mounting cavity  52 . The cover  120  preferably comprises a plastic and/or glass member adapted to communicate light from the LEDs  42  therethrough. The cover  120  also may include optical elements and/or may function as a light diffuser. Further, the cover can function to protect the LED modules within the cavity of the substrate. 
         [0049]    In the illustrated embodiment, the LED modules  40  each comprise two LEDs,  42  which have a combined voltage requirement of about 7.4 volts. Correspondingly, a power supply is provided that is adapted to output a power of 7.4 volts. As such, the power supply is well matched to the LED module power requirements. Thus, there is little or no requirement for resistors or other electrical componentry to further modify the power provided to each module. Accordingly, efficiency of the LED modules is increased as losses to other componentry is avoided. Although the illustrated embodiment employs a power supply adapted to provide 7.4 volts, it is to be understood that, in other embodiments, different arrangements of LEDs of various sizes and colors can necessitate differing power requirements. For such embodiments, the power supply preferably is matched to the voltage requirement of the illumination device. It is also to be understood that other embodiments may employ power conditioning componentry on the module circuit so as to modify and maximize the efficiency of power delivery to the LEDs. 
         [0050]    With reference again to  FIGS. 6 and 7 , strip sections  32  can be joined end-to-end by, for example, jumpers  100  or a wire connector  105 /circuit board  106 , attached to jumper mount bolt holes  98  provided in the rails  60  adjacent ends of the strip section  32 . In another embodiment, jumper mount bolt holes  98  are provided at a plurality of spaced-apart locations along the length of the strip section  32  and not just adjacent the ends. The substrate and/or rails preferably are marked adjacent such jumper mount holes. The markings correspond to suggested cut points at which an installer may advantageously cut the strip section in order to custom-fit the illumination device for a particular installation. The extra jumper mount holes  98  ease the installer&#39;s job by providing cut points for several standardized lengths of the strip section, even though strip sections may be supplied only in a limited number of specified lengths. Such marked strip sections with pre-made jumper mark and holes are easily customized in the field using a simple hack saw or the like. 
         [0051]    As discussed above, in embodiments employing LED modules having an aluminum body, since the bolts  50  are electrically charged and extend through an aperture through the aluminum module body, it is important that the bolts do not engage the body  44 , which would short out the circuit  46 . Additionally, Applicants have noted that in this type of embodiment, if a bolt using a standard 3/16″ bolt head is tightened excessively, damage may be caused to the module contacts, deforming the contacts  48  and possibly the dielectric  76 , thus possibly creating a short circuit in which the bolt  50  and/or copper from the contacts makes contact with the aluminum body. 
         [0052]    In the illustrated embodiment, the LED modules are secured in place using number 440×⅜ inch long bolts. Such bolts have a head diameter of about 0.250 inches, which is far greater than typically used in such applications. Applicants have discovered that when employing a bolt having such a broad head, forces exerted on the contact and dielectric layers  78 ,  76  from tightening the bolt are distributed so that the thin contact and dielectric layers  78 ,  76  are substantially undamaged upon tightening of the bolt  50 . This configuration has been determined to work effectively when the combined thickness of the dielectric and copper trace layers  78 ,  76  is between about 2-3 mils (0.002-0.003 inch). Since a preferred bolt head  84  size is about 0.250 inches, in order to have sufficient distribution for bolt tightening forces with such thin layers of dielectric and traces, it is anticipated that an advantageous ratio of the bolt head width, or the bolt head diameter, to the overall thickness of the dielectric and copper trace layers is between about 80-125 to 1 (80:1-125:1). Applicants have demonstrated that using bolts within such parameters provides acceptable electrical and structural connection without causing damage to the thin dielectric and/or copper contact layers when tightened in the range of about 25-35 in-lb. 
         [0053]    Since LEDs operate on a direct current, the direction of the current is important for proper operation of the LEDs. For example, if the LEDs are arranged in the circuit with the current flowing in the incorrect direction, the LEDs will not light. Thus, it is important that the LED modules are connected in the correct alignment. In accordance with another embodiment, a mechanical structure is provided for insuring correct polarity, or correct directional installation, of each LED module. In one embodiment, a third aperture is formed through the module. Correspondingly, a third raised portion of the substrate is provided extending upwardly from the mount surface in the cavity of the substrate. When LED modules are placed in the correct polarity position to align the mount holes, the third hole will engage and align with the raised portion of the substrate. However, if the modules are arranged in an incorrect polarity, even though the bolt apertures may align, the raised portion of the substrate will engage the bottom surface of the LED module, preventing mounting of the module. 
         [0054]    It is to be understood that other structures may be employed to ensure that the LED module is not mounted in a reverse-polarity direction. For example, in another embodiment, an LED module is configured so that the holes  88  are not placed symmetrically in the body  44 . As such, when the holes  88  are aligned with the corresponding holes  80  in the substrate, it can be visually determined that the LED module is incorrectly mounted and/or a portion of the body  44  will interfere with a portion of the substrate to prevent reverse-polarity mounting of the module. 
         [0055]    With reference next to  FIG. 9 , another embodiment of a lighting strip section  132  is depicted in cross-section. This embodiment has an elongate substrate  34  having front  164  and back  166  sides. A light source mounting cavity  152  is formed in the front side, and includes a mount surface  154 . The plurality of LEDs  142  preferably are mounted spaced apart upon the mount surface  154 . Preferably, an elongate heat spreader  162  is disposed within a heat spreader cavity  172  as formed into the mount surface  154 . As illustrated, preferably the LEDs  142  rest upon the heat spreader  162  so that heat generated by the LED is communicated easily to the heat spreader  162 . 
         [0056]    Elongate rail cavities  190  are formed in the mount surface  154  of the substrate  134  on either side of the heat spreader cavity  172 . Preferably, positive and negative rails  160 A,  160 B are fit into the rail cavities  190 . As with the rails  60  discussed above, the rails  160 A,  160 B preferably are oppositely energized. However, as illustrated, the rails  160 A,  160 B in the preferred embodiment are accessible at the mount surface  154 . 
         [0057]    In the embodiment illustrated in  FIG. 9 , the LED  142  comprises a pre-packaged LED having positive and negative leads  165 A,  165 B. Preferably, the positive lead  165 A is attached to the positive rail  160 A and the negative lead  165 B is attached to the negative rail  160 B. As such, the LED  142  is energized. Further, preferably the LED package  142  includes a heat sink, and the heat sink of the package is in close contact with the heat spreader  162  so as to even further facilitate evacuation of heat from the diode of the LED package to the heat spreader  162  and to the environment. In another embodiment, the heat sink of the package is in substantially direct contact with the heat spreader. In the illustrated construction, the embodiment of  FIG. 9  enables direct mounting of a LED package onto a light strip section. 
         [0058]    With reference next to  FIG. 10 , another embodiment is illustrated comprising an elongate substrate  134  having front and back sides  164 ,  166  and a mounting cavity  152  formed through the front side  164 . A mount surface  154  is disposed in the mount cavity  152 . A pair of elongate heat spreader cavities  172  are formed in the mount surface  154  and three elongate rail cavities  190  are formed in the mount surface  154 . In the illustrated configuration, positive rails  160 A are disposed outwardly of the heat spreaders  162 , and a negative rail  160 B is disposed between the heat spreaders  162 . Preferably, elongate heat spreaders  162  are disposed in the heat spreader cavities  174  and elongate rails  160 A,  160 B are disposed in the elongate rail cavities  190 . 
         [0059]    Continuing with reference to  FIG. 10 , a plurality of pre-packaged LEDs  142  are provided, each having positive and negative leads  165 A,  165 B. As illustrated, positive leads  165 A of the LEDs  142  are mounted onto one or the other of the two positive rails  160 A. However, the negative leads  165 B are all electrically attached to the same negative rail  160 B. Although the LEDs  142  are shown in  FIG. 10  as being immediately adjacent one another, it is to be understood that LEDs can be mounted so as to be linearly staggered relative to one another. 
         [0060]    In a preferred embodiment, both positive rails  160 A are simultaneously energized. However, in another embodiment, the positive rails can be energized independently, thus selectively lighting the LEDs attached thereto. Further, in other embodiments, multiple colors of LEDs can be employed, and selective actuation of the positive rails can alter both the brightness and color hue of the illumination device. Still further, one or more dimming circuits can be employed to even further control brightness and color hue. 
         [0061]    The embodiments discussed above have illustrated certain inventive principles by showing specific embodiments. As noted, other structures may apply such principles in other ways. For example, in another embodiment, rails may be exposed so that an LED module can connect to the rails by clip fasteners rather than bolts, and the clips may communicate electricity to the circuit on the module. In another embodiment, the module may clip onto a substrate that supports the rails, and a contact portion of the LED module may engage so as to energize the LEDs. Accordingly, it is envisioned that fasteners, substrates, rails, LED modules, and parts incident thereto may have configurations and properties that differ substantially from this disclosure. 
         [0062]    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.