Abstract:
A light emitting diode (LED) lighting fixture having an elongated casing, an array of LEDs mounted on a printed circuit board and a holographic film element providing a near lossless optical element for redistributing the light emission patterns from adjacent ones of the LEDs into an array light emission pattern wherein the emitted light in a region of the array light emission pattern is comprised of a sum of overlapping light emission patterns of a plurality of the LEDs. The casing is divided into a lighting element compartment containing the LED printed circuit board and holographic film element and a power supply compartment containing at least one power supply, each being thermally isolated from the other.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is the National Phase application of PCT/IB2011/000358 filed Feb. 22, 2011, which claims benefit from U.S. Provisional Patent Application Ser. No. 61/362,862 filed Jul. 9, 2010 and claims benefit from U.S. Provisional Patent Application Ser. No. 61/309,049 filed Mar. 1, 2010 and claims benefit from U.S. Provisional Patent Application Ser. No. 61/306,655 filed Feb. 22, 2010. 
     FIELD OF THE INVENTION 
     The present invention relates to a light emitting diode (LED) lighting fixture and, more particularly, to a linear LED lighting fixture eliminating scalloping effects and overcoming the effects of Kelvin variations in LEDs. 
     BACKGROUND OF THE INVENTION 
     Current lighting technology includes a number of different types of light sources, such as incandescent bulbs and various versions thereof, such a halogen and xenon bulbs, and flourescent tubes and bulbs, including compart fluorescent lamps (CFLs). One of the more recent light sources is light emitting diodes (LEDs) which have been, for a number of years, used for a variety of purposes. In particular, LEDs have been developed and used for lighting purposes of all types including general area and spot lighting and special purpose lighting applications, such as architectural lighting. 
     Such LED lighting fixtures typically include an LED or an array of white and/or red, green and blue LEDs wherein, the type and number of LEDs depend upon the desired output light spectrum and illumination output power of the fixture. The array or LEDs will often be linear but may be circular or of any other desired orientation or shape chosen to provide the desired light emission pattern. The LEDs are typically mounted onto a printed circuit board, together with a power supply unit and, in some fixtures, control circuitry that controls the illumination and the power output levels of the individual LEDs are included. The circuit board provides mechanical support for and interconnections between the LEDs, the power supply unit and the control circuitry, typically by soldered or bonded connections, and the assembly of the LED array, the power supply and the control circuitry is mounted into a casing that includes an optical enclosure. 
     LED lighting fixtures, however, typically have a number of associated problems which tend to limit generally their use in lighting fixtures. For example, the range of variation in the output power levels and even the output spectrums of the LEDs of a given type are often significantly greater than the variations found, for example, in conventional light sources, such as incandescent bulbs. Due to the tolerances of the LEDs with regard to degree Kelvin temperature, the LEDs on a printed circuit board strip typically do not have precisely or exactly the same brightness and/or color over the entire length of the strip. This problem, which is a function of the Kelvin temperature tolerances of the individual LEDs and which is often referred to as the “Kelvin variation”, increases with the power output level of the LEDs and is particularly noticeable with high-power LEDs, which are otherwise particularly advantageous for use in general lighting fixtures because of their significantly higher per unit illumination power output. As a result of the variations in light output power and spectrum, that is, brightness and light color, the light output from an LED fixture is often of noticeable lower quality than the light output of a more conventional fixture, such as a fixture using incandescent or fluorescent elements. While these problems may be addressed, for example, by pretesting, sorting and/or selecting the LEDs to obtain sets of LEDs having more uniform characteristics, such methods significantly increase the associated time and costs in fabricating LED lighting fixtures which, in turn, leads to increased production costs. 
     Further, a commonly occurring problem for LED lighting fixtures arise from the light emission patterns of the LEDs. That is, light is emitted from the LEDs in a “spot-light beam” pattern, that is, in a conical or beam-like pattern having a relatively narrow emission angle, resulting in a light emission pattern having a relatively narrow central zone with high light level surrounded by a circular zone wherein the light level tapers rapidly off to zero. By comparison, a more conventional light source, such as an incandescent or fluorescent light source, more generally approximates a point or a linear light source and thus provides a generally uniform level of light emission over a generally spherical or cylindrical pattern. 
     The overlapping or adjoining light emission patterns of adjacent individual LEDs of an array of LEDs in a LED fixture thereby typically result in a light emission pattern for the fixture having a “scalloping effect.” A “scalloping effect” is most commonly described as, an overall light emission pattern comprising, at least in part, a repeating pattern of adjacent lighter and darker illumination regions wherein each region is circular or forms a part of a circle. 
     The LED lighting fixtures of the prior art have attempted to eliminate the scalloping effect by various techniques and methods, but such methods significantly increase the cost and complexity of the LED fixtures. In addition, while such methods of the prior art can, for example, widen the beam emitted by an LED element or array to a certain limited degree, such methods still cannot achieve a generally uniform wide area light emission pattern of a more conventional point or linear light source, such as an incandescent or a fluorescent element, and, such methods typically reduce the emitted light level of the LED element or array by absorbing at least a part of the light emitted from the LEDs. 
     A still further problem of LED light fixtures is that, as described above, such fixtures comprise a relatively large number of components, such as an array of LEDs, a power supply unit, control circuitry, a printed circuit board providing mechanical support for and interconnections between the LEDs, a power supply unit and control circuits, and a casing that includes an optical enclosure and/or beam shaping elements. The assembly of these components into a lighting fixture of a reasonable or acceptable size often proves to be somewhat difficult as dimensions and shape factors imposes a number of design restrictions, such as mounting the components to the printed circuit board and making circuit connections typically by soldered or bonded connections. Other restrictions imposes by size and the form factor constraints may include, for example, close and interlocking packing of the components that, in turn, require that the components be assembled or disassembled in a fixed order rather than being individually accessible. 
     Such component assembly restrictions, in turn, result in still further problems, such as local heat build-up with a consequential increase in the component failure rate due to the lack of adequate cooling. Such restrictions also significantly increase the difficulty, time and costs required to remove and replace failed component(s) due to the need to remove one or more components to access the failed component(s) and the need to unsolder and/or unbond connections in order to remove the failed component(s), and the reversal of the steps following replacement of the failed component(s). 
     The present invention provides a solution to these and other related problems associated with the prior art. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a light emitting diode (LED) lighting fixture having an elongated casing, an array of LEDs mounted on a printed circuit board mounted into the casing wherein each LED of the LED array has a light emission pattern having a generally narrow conical emitted light distribution or illumination pattern, and a holographic film element mounted into the casing. The holographic film element is a near lossless optical element for redistributing the light emission patterns, from adjacent ones of the LEDs, into an array light emission pattern wherein the emitted light, in a region of the array light emission pattern, comprises a sum of overlapping light emission patterns of a plurality of the LEDs. 
     In a further aspect of the LED lighting fixture, according to the present invention, the elongated casing includes two parallel casing walls which are connected to one another by a partition wall which divides the casing into a lighting element compartment and a power supply compartment, wherein the lighting element compartment and the power supply compartment are mutually thermally isolated from one another by the casing partition wall. The printed circuit board and the holographic film element are mounted within the lighting element compartment of the casing and at least one power supply is mounted on a power supply support which is mounted within the power supply compartment of the casing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be described, by way of example, with reference to the accompanying drawings in which: 
         FIG. 1A  is an exploded diagrammatic isometric representation of a linear LED light fixture; 
         FIG. 1B  is a diagrammatic cross section view of a first embodiment of a linear LED light fixture; 
         FIG. 1C  is a diagrammatic cross section view of a second embodiment of a linear LED light fixture; 
         FIG. 2A  is a diagrammatic side elevational view a linear LED light fixture; 
         FIG. 2B  is a diagrammatic top plan view the linear LED light fixture of  FIG. 2A ; 
         FIG. 2C  is a diagrammatic bottom plan view a linear LED light fixture of  FIG. 2A ; 
         FIGS. 3A ,  3 B,  3 C and  3 D are diagrammatic embodiments of exemplary LED lighting circuits according to the present invention; 
         FIGS. 4A and 4B  are diagrammatic embodiments of exemplary illustrations of the light emission patterns of a LED array and of an LED array with a holographic optical film element; 
         FIGS. 5A and 5B  are diagrammatic isometric representations of a linear LED light fixture with pivoting mounting brackets; 
         FIG. 6  is an exploded diagrammatic isometric representation of a power supply assembly of a linear LED light fixture; and 
         FIG. 7  is an exploded diagrammatic isometric representation of a mounting bracket for the linear LED light fixture. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring first to  FIGS. 1A ,  1 B and  1 C and  2 A,  2 B and  2 C, the linear LED light fixture  10  of the present invention includes an elongated casing  12  comprising two spaced apart parallel casing walls  12 A and  12 B intereconnected with one another by a partition wall  12 C that divides casing  12  into a first lighting element compartment  14 A and a second power supply compartment  14 B. As shown, the overall length or “height” of the casing walls  12 A and  12 B are typically greater than the overall length or “width” of the partition wall  12 C and the height of the power supply compartment  14 B will typically be greater than the height of the lighting element compartment  14 A. In this regard, and as will be seen from the following description of the fixture  10 , the use of the terms “height” and “width” is not intended to and should not be taken as referring to a particular vertical or horizontal orientation of the fixture  10 , particularly as the fixture  10  may be oriented along any axis with respect to the vertical and/or the horizontal directions. In a like manner, the relative dimensions and proportions of the casing  12 , the casing walls  12 A and  12 B, the partition wall  12 C and the first lighting element compartment  14 A and the second power supply compartment  14 B will be determined by the dimensions of the components to be contained therein and may vary accordingly from implementation to implementation of any desired fixture  10 . 
     According to the present invention, the lighting components  16  located or accommodated within lighting element compartment  14 A, include a plurality of LEDs  16 A arranged in an array  16 B on a printed circuit board  16 C that provides a mechanical support for LEDs  16 A and for circuit interconnections between LEDs  16 A and potentially, for example, the LED power supply or LED power supplies, which are described below in further detail. The LEDs  16 A may be arranged in an LED array  16 B in a number of configurations, such as a single line of adjacent LEDs  16 A, as multiple parallel lines of LEDs  16 A, as one or more staggered rows of adjacent LEDs  16 A, as a linear arrangement of groups of LEDs  16 A, as a circular groups of LEDs  16 A, etc., depending upon the particular application, and a few exemplary LED circuits are diagrammatically illustrated in  FIGS. 3A ,  3 B,  3 C and  3 D, for example. It will also be recognized that the dimensions of the LED array  16 B, such as the array length, may vary substantially between one fixture  10  and another fixture  10 , as may the dimensions of the LEDs  16 A and the spacing between adjacent LEDs  16 A and spacing between groups of LEDs  16 A within the array  16 B. 
     As shown in  FIG. 1B , and for example, the printed circuit board  16 C and the LEDs  16 A mounted thereon in the LED array  16 A are supported and retained in the lighting element compartment  14 A by between two pairs of adjacent printed circuit board rails  16 E respectively formed in or on or mounted to the interior sides of the casing walls  12 A and  12 B. The LED array  16 B is slid longitudinally into engagement with and between each pair of the printed circuit board rails  16 E from a first end or from the opposite end  12 E of the casing  12 . 
     The lighting components  16 , located in lighting element compartment  14 A, further include a holographic film element  16 D which is also supported and retained, within the lighting element compartment  14 A, by two pairs of adjacent film rails  16 F, which are also respectively formed in or on or mounted to the interior sides of the casing walls  12 A and  12 B. The holographic film element  16 D is slid longitudinally into engagement with and between the two pairs of the holographic film rails  16 F from the first end or the opposite end  12 E of the casing  12 . It will be appreciated that the arrangement of printed circuit board rails  16 E and the film rails  16 F, for respectively mounting printed circuit board  16 C and the holographic film element  16 D shown in  FIG. 1B , are exemplary and that other functionally equivalent arrangements and structures will be readily apparent to those of ordinary skill in the relevant art. 
     Turning now to  FIG. 1C , an alternative arrangement for the lighting fixture is shown. According to this embodiment, the holographic film element  16 D is supported on one side by a pair of spaced apart rails  16 F, and is supported on the opposing side by a pair of spaced apart spacers  16 H. The lighting element compartment  14 A, of the lighting fixture  10 , is then sealingly close to the elements by a covering element  16 G. The pair of spacers  16 H may ideally be attached to the covering element  16 G so that when the covering element  16 G is removed, the holographic film element  16 D may easily removed, replaced, repaired, etc., and provide access to the LEDs  16 A without having to slide the LED array  16 B out of the casing  12 A. Conversely, when the covering element  16 G is attached, the pair of spacers  16 H apply a frictional force to and against the holographic film element  16 D thereby retaining and securing holographic film element  16 D in its desired location between the pair of rails  16 F and the pair of spacers  16 H. 
     The covering element  16 G generally functions to close and seal the fixture  10  from the elements while still allowing the light, emitted from the LED array  16 B, to readily pass through, substantially unaffected, and exit the fixture  10  through the transparent covering element  16 G. At least one portion of the covering element  16 G will be made from at least a partially transparent material, such as glass and/or plastic, and that partially transparent material may have a desired magnification value of less than 1 or greater than 1, or no magnification value, i.e., a magnification value of 1. 
     Now considering the holographic film element  16 D in further detail, and referring to  FIG. 4A , the scalloping effect briefly described above is diagrammatically shown. The LEDs of a conventional LED array, diagrammatically shown in  FIG. 4A , emits light at a relatively narrow conical emission angle thereby resulting in a relatively narrow circular light emission pattern having high intensity light level central zones surrounded by relatively narrow lower intensity light level zones. Thus, the light emission pattern  18  of the conventional LED arrays typically demonstrates a “scalloping effect”, that is, a repeating pattern of adjacent circular or partially circular regions having higher intensity, i.e., lighter regions, and lower intensity, i.e., darker regions. As described, the LED lighting fixtures of the prior art have attempted to eliminate such “scalloping effect” by various methods and techniques. While such methods and techniques can, for example, widen the beam emitted by an LED element or array to a limited extent, such elements still do not achieve the wide area light emission patterns of more conventional point or linear light sources, such as incandescent or fluorescent elements. In addition, such methods typically reduce the emitted light level of the LED element or array by absorbing at least a part of the light emitted from the LEDs. 
     The present invention, however, as shown in exemplary illustration in  FIG. 4B , thus includes a holographic film element  16 D which functions as a near lossless optical element that redistributes the light patterns, emitted from adjacent individual LEDs  16 A or groups of LEDs  16 A of the LED array  16 B, into a desired light emission pattern  20 . The emitted light falling within any region  20 R of the fixture light emission pattern  20  comprises the sum of overlapping light emission patterns of a plurality of LEDs  16 A, including adjacent LEDs  16 A and typically including non-adjacent LEDs  16 A. Therefore, the light emission pattern  20 A, of each region  20 R of the light emission pattern  20  of the fixture  10  having the holographic film element  16 D, essentially comprises averaged emissions of a plurality of LEDs  16 A. As a result, the emission pattern  20  according to the present invention is significantly more uniform over a relatively wide area, by significantly reducing or effectively eliminating the scalloping effect normally present in conventional LED lighting fixtures, and approximates the light emission pattern of more conventional light sources, such as incandescent and fluorescent elements. 
     According to a further aspect of the present invention, the holographic film  16 D also provides a solution to the problems resulting from Kelvin variations between the LEDs  16 A of the LED array  16 B. That is, and as described above, the emitted light falling in any region  20 R of the fixture light emission pattern  20 , comprises an overlapping, averaged sum of the light emission patterns of a plurality of LEDs  16 A. As a consequence of this, the Kelvin variations between adjacent LEDs  16 A or groups of LEDs  16 A contributing to the light emission pattern  20 A, in any region  20 R of the fixture light emission pattern  20 , are averaged over that region  20 R. Such averaging significantly reduces the apparent Kelvin variations between the LEDs  16 A contributing to the light emission falling within any region  20 R. The light emission patterns  20 A of adjacent and overlapping regions  20 R of the light fixture emission pattern  20  likewise comprise contributions from adjacent LEDs  16 A and groups of LEDs  16 A so that the Kelvin variations, between adjacent or overlapping regions  20 R of the fixture light emission pattern  20 , are likewise averaged across each corresponding group of LEDs  16 A, thereby significantly reducing or effectively eliminating the effects of the individual LED  16 A Kelvin variations of the LEDs  16 A of the LED array  16 B. As a result, the present invention thereby provides a more uniform illumination pattern for the fixture  10 . 
     It will be appreciated that the specific holographic pattern and the dimensions of holographic film element  16 D are dependent, at least in part, upon the dimensions of the emission light patterns of the LEDs  16 A, the locations and spacing of the adjacent LEDs  16 A or groups of LEDs  16 A in the LED array  16 B, and the relative spatial geometry between the LED array  16 B, the LEDs  16 A of LED array  16 B, the holographic film element  16 D and the covering element  16 G. 
     The methods for designing holographic film elements  16 D, and the holographic patterns thereof for different LED arrays  16 B and LEDs  16 A, to achieve the desired results, will be well understood by those of ordinary skill in the relevant art. As such, a further detailed description concerning same is not provided herein. 
     Next considering further aspects of the present invention, it has been described above that the printed circuit board  16 C and the LEDs  16 A, of the LED array  16 B, are mounted within the lighting element compartment  14 A of the casing  12 . In a like manner, one or more power supplies  18  are mounted on a slidable elongated power supply support  18 A that is, in turn, supported and retained within the power supply compartment  14 B by a pair of spaced apart power rails  18 B formed in or on, or mounted to an interior surface of one of both of the casing walls  12 A and/or  12 B. As a result, the power supply support  18 A can be readily slid longitudinally into engagement with power supply rails  18 B from either the first end or the opposite end  12 E of the casing  12 , to facilitate either removal or insertion thereof. It is noted that  FIG. 1B  discloses an embodiment where the elongated power supply support  18 A engages a set of rails which are supported by only one of the casing walls  12 A or  12 B, e.g., the casing wall  12 B, while  FIG. 1C  discloses an embodiment where the elongated power supply support  18 A engages with and is located between two sets of spaced apart rails, with one set of rails  18 B being supported by the first casing wall  12 A and the other set of rails  18 B being supported by the second casing wall  12 B. 
     As illustrated in  FIGS. 1B and 1C , a bottom portion or lower area of the power supply compartment  14 B is typically closed by an elongated power supply cover  12 P, that slidably engages with corresponding cover rails  12 R that, like power supply rails  18 B, may be generally similar in structure to the printed circuit board rails  16 E and/or the holographic film rails  16 F. Similar to the covering element  16 G, the elongated power supply cover  12 P provides a barrier which closes and seals a bottom portion of the power supply compartment  14 B and protects that compartment from the elements. 
     It is to be appreciated that the number of power supplies  18 , mounted in power supply compartment  14 B, is determined by the number and power requirements of the LEDs  16 A of the LED array  16 B to be powered by the fixture. The power outputs of the power supplies  18  (not shown in detail) are connected to the printed circuit board  16 C of the LED array  16 B in a conventional manner by, for example, conventional leads, contacts and/or studs typically passing through the casing partition wall  12 C (not shown in detail). As diagrammatically illustrated in  FIGS. 1A ,  2 A,  2 B and  2 C, for example, the power inputs  22  are connected to the power supplies  18  through conventional connectors  22 C and cables  22 D, mounted on the end plates  18 C that are, in turn, mounted on the first end or the opposite end  12 E of the casing  12 , which retain the printed circuit board  16 C within the lighting element compartment  14 A and the power supply support  18 A within power supply compartment  14 B. As can be seen from  FIGS. 1A ,  2 A,  2 B and  2 C for example, the connectors  22 C and the cables  22 D may be used to connect the power supplies  18  to a conventional power source, such as a 117 volt AC line or to fixture power and control cabling, and may be used to sequentially connect the power supplies  18  of two or more fixtures  18  with one another into a single circuit that is ultimately connected to the 117 volt AC line or to the fixture power and the control cabling to facilitate control thereof. 
     According to the present invention, the lighting components  16  and the power supplies  18  are mounted in thermally separated compartments of the fixture  10 . That is, the lighting components  16  are mounted and accommodated within the lighting element compartment  14 A while the power supplies  18  are mounted and accommodated within the power supply compartment  14 B. Such separate mounting of the lighting components  16  from the power supplies  18  thereby thermally isolates the lighting components  16  and the power supplies  18  from one another. As a result of this, the heat load imposed on the lighting components  16  and/or the power supplies  18 , due to heat generated and dissipated by the other of the power supplies  18  and/or the lighting components  16 , is thereby significantly reduced which, in turn, significantly reduces the heat load effects on the lighting components  16  and/or the power supplies  18 . Due to such thermal isolation of these components, this in turn reduces the failure rate of the lighting components  16  as well as the failure rate of the power supplies  18  and thereby improves the overall reliability of the lighting fixture according to the present invention. 
     With reference now to  FIGS. 5A and 5B , a pair of opposed swivel brackets  24  are diagrammatically shown for mounting the fixture  10  to a desired surface.  FIGS. 5A and 5B  are diagrammatic isometric illustrations of the fixtures  10  in which the pair of swivel brackets  24  allow a range of movement of the light fixture  10 , e.g., a range of movement of approximately 300° about a longitudinal a longitudinal axis of the fixture  10 . It is to be appreciated that the mounting of the fixture  10 , via the swivel brackets  24 , is especially advantageous for grazing applications, e.g., façade illumination, which permits desired alignment of the illumination emitted from the fixture  10  as required or necessary to achieve the particular lighting effect. As shown in  FIGS. 5A ,  5 B, and  7 , the swivel bracket  24  connects the fixture  10  to a desired supporting element, such as a wall (not shown), via a plate  30 , a first hinge part  28 , a second hinge part  26 , and an exterior mount  32 . Once the fixture  10  is positioned in a desired orientation with respect to the swivel bracket  24 , the various components are sufficiently tightened to retain the fixture  10  in that adjusted orientation. As a result of such arrangement, the fixture  10  can be readily mounted to any desired surface, such as a ceiling, an exterior wall, an interior wall, a floor, a ledge, a façade, etc., and then positioned in any desired orientation so as to provide the desired illumination effect for the particular lighting application. 
     As can be seen in  FIGS. 1A and 6 , the present invention facilitates ease of repair and/or replacement of one or more of the power supplies  18  and/or any other component(s) which are mounted or accommodated within the power supply compartment  14 B or possibly the lighting element compartment  14 A. That is, when any servicing, repair and/or replacement of any component(s) contained within the power supply compartment  14 B or possibly the lighting element compartment  14 A is desired or necessary, the service personnel will first remove the bearing  24  and then the end cover  18 C so as to provide access to one end of the power supply compartment  14 B or possibly the lighting element compartment  14 A. The service personnel can then easily grasp the adjacent end of the elongated power supply support  18 A and either partially or completely withdraw or remove the same, from the power supply compartment  14 B, by sliding the elongated power supply support  18 A relative to the two sets of spaced apart rails  18 B, e.g., sufficiently sliding the elongated power supply support  18 A until the elongated power supply support  18 A is adequately withdrawn or retracted from the power supply compartment  14 B so as to provide access to the component(s) to be serviced, repaired or replaced. 
     Once the component is adequately serviced, repaired and/or replaced, the service personnel then reverses the process by sliding the elongated power supply support  18 A, relative to the two sets of spaced apart rails  18 B, back into the power supply compartment  14 B until the elongated power supply support  18 A is completely accommodated within the power supply compartment  14 B. Next, the service personnel will then first reattach the end cover  18 C and the bearing  24  to the fixture  10  and then readjust the fixture  10  so it is again located in its previous orientation, to provide the desired illumination effect. 
     Since certain changes may be made in the above described improved LED lighting fixture, without departing from the spirit and scope of the invention herein involved, it is intended that all of the subject matter of the above description or shown in the accompanying drawings shall be interpreted merely as examples illustrating the inventive concept herein and shall not be construed as limiting the invention.