Abstract:
An LED apparatus including (a) a mounting board, (b) a plurality of LED packages thereon, (c) a lens member over each LED package, and (d) a safety barrier positioned over the mounting board, the barrier having sufficient thickness for enclosure of electrical elements on the mounting board and including a plurality of openings each sized to permit light from an LED package to pass therethrough and through a light-transmission portion of the lens member over such LED package to prevent finger-contact of electrical elements on the mounting board when the light-transmission portion is not present.

Description:
RELATED APPLICATION 
       [0001]    This is a continuation-in-part of patent application Ser. No. 11/744,807, filed on May 4, 2007 and entitled “Sealing and Thermal Accommodation Arrangement in LED Package/Secondary Lens Structure.” 
       FIELD OF THE INVENTION 
       [0002]    The invention relates generally to the field of LED lighting systems and, more particularly, relates to configurations for LED modules in lighting fixtures. 
       BACKGROUND OF THE INVENTION 
       [0003]    In the field of lighting, many different types of light sources have been developed. Recently, LED light sources involving multi-LED arrays, each with a large number of LED packages, have been developed as a means of bringing the many advantages of LED lighting—LED efficiency and long life—into the general illumination field. In particular, such LED light fixtures have been developed for use in outdoor settings, including by way of example lighting for parking lots, roadways, display areas and other large areas. 
         [0004]    LED fixtures in the prior art have certain shortcomings and disadvantages. Among these, there is a need for an improved arrangement for operation of LEDs having one lens positioned over another. Significant heat levels in such products can pose particular problems for lens-over-lens mounting and stability. One potential problem is that temperature changes may cause thermal expansion and related alignment problems. 
         [0005]    Protection against various environmental factors is also rendered difficult for LED general illumination products which necessarily utilize a large number of LEDs—sometimes plural LED modules with each module having many LED packages thereon. 
         [0006]    The product safety of lighting fixtures creates an additional area of difficulty, and such fixtures are most often required to comply within standards put forward by organizations such as Underwriters Laboratories Inc. (UL) in order to gain acceptance in the marketplace. One such set of standards deals with the accessibility of the electrically-active parts of a fixture during operation, and, more importantly, during periods of stress on the fixture such as in a fire situation during which some elements of the lighting fixture are compromised. The UL “finger test” mandates that a human finger of certain “standard” dimensions (defined in NMX-J-324-ANCE, UL1598, Dec. 30, 2004, FIG. 19.22.1, page 231) should not be able come in contact with any electrically-live parts of the fixture under such circumstances. The standards also establish certain material limitations on the enclosures of such products, all of which are dependent on the voltages and power levels within the fixtures. 
         [0007]    Increased product safety can be costly to achieve, both in terms of the economic cost associated with providing safety as well as with the loss of lighting performance such as reduced optical efficiency. For example, placing a fixture behind a sheet of glass to provide increased safety can result in an optical efficiency loss of up to 10%. 
         [0008]    For LED-based lighting fixtures, the cost of the power supply is an important part of the overall fixture cost. When a large number of LEDs are used to provide the necessary level of illumination, it is advantageous to use a single power supply providing higher voltages and higher power levels, which, in turn, requires more stringent safety standards. In particular, power supplies with a Class 2 power supply rating are limited to 100 watts at a maximum of 60 volts (30 volts if under wet conditions). LED-based lighting fixtures with a large number of LEDs can benefit (both by cost and efficiency) by using a Class 1 power supply, in which both the power and voltage limitations of a Class 2 power supply are exceeded. If power requirements for a lighting fixture are higher than the Class 2 limits, then multiple Class 2 power supplies are required (which can be costly) unless the more stringent safety standards which using a Class 1 supply brings about can be achieved. 
         [0009]    As mentioned above, such more stringent requirements include satisfying the “finger test” under certain fire conditions during which it is possible that lighting module elements such as lenses made of polymeric materials may be removed. For example, in an LED package with a primary lens made of glass and a secondary lens made of polymeric material, ti is necessary to provide enclosure barriers over the entire electrical portion of the module (on which the LED packages are mounted) except over the primary lenses. It is assumed that under these circumstances, the polymeric secondary lenses will be destroyed in the fire, leaving the primary lenses exposed. Also for example, if a single polymeric lens is used in place of both the primary and secondary lenses, then the enclosure barriers must prevent “standard finger” access to the electrical elements under the assumption the single lens has been removed. 
         [0010]    Thus there is a need for improved LED lighting fixtures which can better serve the requirements of general-illumination lighting fixtures and which can provide both the safety and cost-effectiveness which the marketplace requires and/or prefers. 
       OBJECTS OF THE INVENTION 
       [0011]    It is an object of this invention to provide LED modules which overcome certain problems and shortcomings of the prior art including those referred to above. 
         [0012]    An object of the invention is to provide an improved LED module which achieves the electrical product safety demanded by the marketplace. 
         [0013]    Another object of the invention is to provide an improved LED module which achieves such safety in a cost-effective manner. 
         [0014]    Still another object of the invention is to provide an improved LED module which achieves such electrical product safety under conditions during which no lens remains place over each LED package. 
         [0015]    These and other objects of the invention will be apparent from the following descriptions and the drawings. 
       SUMMARY OF THE INVENTION 
       [0016]    The invention is LED apparatus which provides electrical safety by satisfying a set of stringent safety standards for the enclosures in which such LED apparatus are encased, and doing so in a cost-effective manner. The LED apparatus of this invention includes a mounting board having a plurality of LED packages thereon with a lens member over each LED package and a safety barrier positioned over the mounting board. The barrier has sufficient thickness for enclosure of electrical elements on the mounting board and includes a plurality of openings each sized to permit light from an LED package to pass therethrough and through a light-transmission portion of the lens member over such LED package to prevent finger-contact of electrical elements on the mounting board when the light-transmission portion is not present. 
         [0017]    In some embodiments of the LED apparatus, the barrier includes a metal layer, which in more preferred embodiments, the barrier also includes an insulating layer positioned between the mounting board and the metal layer. In some of these embodiments, the metal layer and the insulating layer form a laminate. 
         [0018]    In other embodiments of the inventive apparatus, the safety barrier has a layer portion spaced from the mounting board, and in some of these embodiments, the safety barrier has at least one spacing structure supporting the layer portion on the mounting board. 
         [0019]    In preferred embodiments of the invention, the LED apparatus further includes a resilient gasket member having apertures for each of the lens members, and the gasket member yieldingly constrains movement caused by thermal expansion during operation. 
         [0020]    In more preferred embodiments of the inventive LED apparatus, the lens members each include a light-transmission portion and a flange thereabout. The gasket member is positioned against the flanges and includes an inner surface which faces and yieldingly abuts the flanges. 
         [0021]    In highly-preferred embodiments of the invention, the LED apparatus further includes a cover which has openings aligned with the lens members and secures them over the LED packages, pressing the gasket member toward the safety barrier. 
         [0022]    In other highly-preferred embodiments of the inventive LED apparatus, each of the lens members is a secondary lens and each LED package includes a primary lens in alignment with the secondary lens over such LED package. In some of these embodiments, the safety barrier is positioned between the flanges of the secondary lenses and the mounting board. 
         [0023]    Further, this invention includes an LED light fixture which has a plurality of such inventive LED modules. 
         [0024]    The term “LED package” as used herein means an assembly including (a) a base, (b) at least one LED (sometimes referred to as “die”) on the base, and (c), optionally, a primary lens over the die(s). One or more, typically several, LED packages are arranged on a mounting board in forming what is referred to as an “LED module.” One or more LED modules are used as the light source for various innovative lighting fixtures. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]      FIG. 1  is an exploded perspective view of one embodiment of the LED lighting apparatus of this invention. 
           [0026]      FIG. 2  is an perspective view of the inventive LED lighting apparatus of  FIG. 1 . 
           [0027]      FIG. 3  is a cross-sectional view of the lighting apparatus of  FIG. 1 , taken along line  3 - 3  of  FIG. 2 . 
           [0028]      FIGS. 4A and 4B  are schematic drawings illustrating a safety barrier embodied in a laminate structure. 
           [0029]      FIG. 5  is a simplified view of the inventive apparatus, illustrating the cross-sectional plane CS at which the cross-sectional views of  FIGS. 6-10  are taken. 
           [0030]      FIG. 6  is an enlarged detailed cross-sectional view of another embodiment of the LED lighting apparatus of this invention, the apparatus having a safety barrier with a metal layer and an insulating layer. 
           [0031]      FIG. 7  is an enlarged detailed cross-sectional view of yet another embodiment of the LED lighting apparatus of this invention, the apparatus having a safety barrier comprising a single layer. 
           [0032]      FIG. 8  is an enlarged detailed cross-sectional view of yet another embodiment of the LED lighting apparatus of this invention, the apparatus having additional space between the mounting board and the safety barrier. 
           [0033]      FIG. 9  is an enlarged detailed cross-section view of yet another embodiment of the LED lighting apparatus of this invention, the apparatus having a single lens member over each LED package and no optional primary lens in each LED package. 
           [0034]      FIG. 10  is an enlarged detailed cross-sectional view of yet another embodiment of the LED lighting apparatus of this invention, the apparatus having the safety barrier positioned above the flange of each secondary lens member. 
           [0035]      FIG. 11  is an enlarged detailed cross-sectional view of yet another embodiment of the LED lighting apparatus of this invention, the apparatus having the safety barrier positioned above the flange of each lens member, with the LED packages not including the optional primary lens. 
           [0036]      FIG. 12A  is a perspective view of a lighting fixture of this invention incorporating a plurality of LED modules. 
           [0037]      FIG. 12B  is a bottom view of the lighting fixture of  FIG. 12A . 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0038]      FIGS. 1-3  illustrate an LED apparatus  10  which includes a mounting board  12  with a plurality of LED packages  14  thereon. The LED packages include primary lenses  16 . Secondary lens  20  are positioned over primary lenses  16 , establishing light paths  32  therebetween. Mounting board  12  is connected to a heat sink  18  as shown in  FIG. 1 . Apparatus  10 , having such plural LED packages mounted thereon, is also referred to as an LED module  42  as indicate din  FIG. 1 . One or more LED modules  42  are used as the light source for various inventive lighting fixtures. One example of such an inventive LED lighting  100  is shown in  FIGS. 12A and 12B . LED apparatus  10  includes a resilient member  22  against secondary lenses  20  in positions other than in light path  32 . Resilient member  22  is yieldingly constrains secondary lenses  20  and accommodates the movement of secondary lenses  20  caused by thermal expansion during operation, primarily by that of primary lenses  16  in the embodiment shown in  FIG. 1 . 
         [0039]    As shown in  FIG. 1 , resilient member  22 , in the form of a gasket layer, is positioned over mounting board  12  and LED packages  14 . Gasket  22  has a plurality of gasket apertures  34 . Resilient member  22  is preferably made from closed-cell silicone which is soft, solid silicone material which is not porous. Resilient member  22  may also be made from any non-porous material which may be tailored for gasket use. 
         [0040]    Secondary lens  20  includes a lens portion (or “light-transmission portion”)  36  which is substantially transparent and a flange  38  portion thereabout. Lens portions  36  are adjacent to flange portions  38  as illustrated in  FIG. 1 . Flange portion  38  is planar and has outer and inner surfaces. Resilient member  22  includes an inner surface  44  which faces and yieldingly abuts flange  38 . 
         [0041]    Secondary lenses  20 , as illustrated in  FIGS. 1 and 2 , are in close proximity to primary lenses  16  and at least partially abut primary lenses  16 . Preferably separate and discrete secondary lenses  20  are each provided over each LED package  14  and primary lens  16  as seen in  FIG. 2 . However, persons skilled in the art will appreciate that plural secondary lenses  20  can be formed together as a single part. 
         [0042]      FIGS. 1 and 2  illustrate that cover  26  secures resilient member  22  with respect to secondary lens  20 , primary lens  16  and LED package  14 . Cover  26  has openings  28  aligned with the light paths  32  as shown in  FIGS. 1-3 . Resilient member  22  is sandwiched between cover  26  and flanges  38  of secondary lenses  20 , causing outer surface of the flange portion  38  to abut the facing resilient member  22  inner surface  44 . This action forms a sandwich-like structure in which cover  26  urges resilient member  22  against flange portions  38  as illustrated in  FIG. 2 . 
         [0043]    Thermal expansion of primary lenses  16  results in abutment of lenses and displacement of secondary lenses  20 . Resilient member  22  permits the displacement while holding secondary lenses  20  in place over primary lenses  16 . 
         [0044]    In certain embodiments a shield member  24 , in the form of a layer, is positioned over the resilient member layer  22  as illustrated in  FIG. 1 . 
         [0045]    LED apparatus  10  includes a metal layer  30 , preferably of aluminum. Layer  30  is positioned preferably immediately over the LED packages and includes a plurality of openings each sized to receive primary lens  16 . Layer  30  is sandwiched between mounting board  12  and secondary lens  20  as seen in  FIG. 1 . Metal layer  30  is herein referred to as safety barrier  30 , the details of which are described further below. 
         [0046]    LED apparatus  10  can include only one LED package  14  on a mounting board  12  with primary lens  16 , a corresponding secondary lens  20  and a resilient member layer  22  against the secondary lens  20 . 
         [0047]      FIGS. 4A and 4B  illustrate a layered structure of safety barrier  30 ; barrier  30  includes a metal layer 30 m  and an insulating layer  30   i.  Layers  30   m  and  30   i  may be laminated together, forming laminate  46  as indicated. Layers  30   m  and  30   i  may also be separate layers. Under certain UL standards, metal layer  30   m  is a made of a flat, unreinforced aluminum sheet having a thickness of at least 0.016 inches. The minimum thickness requirements of layer  30  depends on the structure and composition of metal layer  30  as set forth in the specific UL the standards referred to above. If safety barrier  30  is a laminate  46 , the different layers of laminate  46  may or may not have the same width and length dimensions.  FIGS. 4A and 4B  illustrate laminate  46  with layers  30   m  and  30   i  having such different width and length. 
         [0048]    Insulating layer  30   i  serves to electrically isolate layer  30   m  from the electrical elements on mounting board  12 . In some embodiments, these electrical elements may be isolated from layer  30   m  by a conformal coating on mounting board  12 . Such conformal coating may be any of a number of available coatings, such as acrylic coating 1B73 manufactured by the HumiSeal Division of Chase Specialty Coatings of Pittsburgh, Pa. 
         [0049]    Safety barrier  30  may also be made of a single layer of polymeric material having minimum thickness as set forth by the UL standards. Acceptable polymeric materials include BASF 130FR (polyethylene terephthalate with glass fiver reinforcement) supplied by the Engineering Plastics Division of BASF Corporation in Wyandotte, Mich. The layer has a minimum thickness of 0.028 inches. Other acceptable polymeric materials must satisfy certain detailed specifications related to material behavior such as hot-wire ignition, horizontal burning, and high-current arcing resistance, all of which are set forth in the UL standards referred to above. 
         [0050]    LED module  46  may include safety barrier  30  which is positioned in several ways relative to mounting board  12  and secondary lenses  20 . When LED packages  14  do not include optional primary lens  16 , secondary lenses  20  are herein referred to as “lens members  50 .” 
         [0051]      FIGS. 6-11  illustrate several such configurations of safety barrier  30  in LED module  46 .  FIG. 5  illustrates cross-sectional plane CS-CS which applies to each of  FIGS. 6-11 . 
         [0052]      FIG. 6  is an enlarged detailed cross-sectional view of one embodiment of LED module  46  with safety barrier  30  comprising metal layer  30   m  and insulating layer  30   i.    
         [0053]      FIG. 7  is an enlarged detailed cross-sectional view of another embodiment of LED module  46  with safety barrier  30  comprising metal layer  30   m.    
         [0054]      FIG. 8  is an enlarged detailed cross-sectional view of another embodiment of LED module  46  in which there is additional space  52  provided between mounting board  12  and safety barrier  30 . Spacing structures  54  are provided as part of the bases of LED packages  14  but may also be configured as separate elements.  FIG. 9  illustrates a similar embodiment in which LED packages  14  do not include optional primary lenses  16 . LED module  46  includes lens members  50  each having light-transmission portions  50   p  and flanges  50   f.    
         [0055]      FIGS. 6-9 , LED module  46  has safety barrier  30  positioned below secondary lenses  20  or lens members  50 .  FIGS. 10 and 11  illustrate enlarged detailed cross-sectional view of additional embodiments of LED module  46  in which safety barrier  30  is positioned above flanges  38  of each secondary lens  20  ( FIG. 10 ) and above flanges  50   f  of lens members  50  ( FIG. 11 ). In both such embodiments, additional space  52  from mounting board  12  is provided. 
         [0056]      FIG. 11  is an enlarged detailed cross-sectional view of yet another embodiment of the LED lighting apparatus of this invention, the apparatus having the safety barrier positioned above the flange of each lens member, with the LED packages not including the optional primary lens. 
         [0057]    In some forms of such highly preferred embodiments with the plurality of LED packages on the mounting board, it is preferred to use a Flame Resistant 4 (“FR4”) board formed by a conductor layer and an insulator layers. The conductor layer may be made of any suitable conductive material, preferably copper or aluminum. It is most highly preferred that such mounting board include, for each LED package thereon, a plurality of channels (“thermal vias”) extending through the mounting board at positions beneath the package, such channels having therein conductive material and/or an opening to facilitate transfer of heat through the board. The thermal vias provide an isolated thermal path for each LED package. 
         [0058]    In the forms of the present invention using the FR4 mounting board with thermal vias, it is most highly preferred that each LED package  14  is constructed to have its cathode terminal electrically neutral from the thermal path, thus avoiding shortage of other LED packages  14  on the board. 
         [0059]    A wide variety of materials are available for the various parts discussed and illustrated herein. While the principles of this apparatus have been described in connection with specific embodiments, it should b understood clearly that these descriptions are made only by way of example and are not intended to limit the scope of the invention.