Abstract:
A light emitting diode (LED) luminaire that produces a uniform light pattern at close distances is provided. The LED luminaire includes a housing, a printed circuit board assembly thermally coupled to the housing, a plurality of high brightness (HB) LED emitters, thermally coupled to the printed circuit board assembly to form a linear array, and a linear reflector assembly, attached to the housing, to concentrate the light generated by the LED emitters over a beam angle formed by the upper surface of the housing and the linear reflector assembly.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation of International Patent Application No. PCT/US2010/044452, filed on Aug. 4, 2010, which claims priority to U.S. Provisional Patent Application 61/231,096, filed on Aug. 4, 2009, the disclosures of which are incorporated herein by reference in their entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to a light emitting diode (LED) luminaire that produces a uniform light pattern at close distances. More specifically, the present invention relates to an LED luminaire that includes a linear array of High Brightness (HB) emitters. 
     BACKGROUND OF THE INVENTION 
     Conventional linear shaped LED luminaires used for lighting applications typically make use of a tightly spaced array of low to medium power LED emitters. The use of a tightly spaced LED array makes the luminaire capable of casting a uniform light pattern at short distances. 
     Due to the somewhat inefficient power conversion characteristics of LED emitters however, a tightly spaced LED array with a large number of LED emitters also results in increased power dissipation for the luminaire in relation to light output. Thus, as the number of LED emitters is increased, more of the available energy is dissipated in the form of heat as opposed to generating usable light output. In addition, the low to medium power LED emitters employed in tightly spaced LED arrays tend to have poor thermal transfer characteristics. These two factors combine to either limit the maximum power dissipation for the luminaire or to increase the size and weight of the heat sink surface required to prevent irreparable LED junction damage. 
     Conventional LED luminaires used for lighting applications typically make use of a diffused lens or some other form of secondary optics in order to blend the produced light pattern into a uniform presentation at close distances. Any such diffusion or optics however, results in a substantial reduction in light output due to transmission losses in the diffuser or optics material. As a result, the LED array must be driven at a higher level in order to offset these light losses, resulting in higher luminaire power consumption. 
     Another disadvantage of conventional LED luminaire designs relates to when they are employed in wall and/or ceiling applications where the luminaire is visible to the observer, such as, for example, within an aircraft. In such an application, the LED presentation must be heavily diffused otherwise the observer will be able to view the LED point sources in the luminaire directly. Direct viewing of the LED point sources is not only unsightly, but in addition, it is very unpleasant for the observer. 
     SUMMARY OF THE INVENTION 
     Embodiments of the present invention advantageously provide a light emitting diode (LED) luminaire that produces a uniform light pattern at close distances. More specifically, one embodiment provides an LED luminaire that includes a housing, a printed circuit board assembly thermally coupled to the housing, a plurality of high brightness (HB) LED emitters, thermally coupled to the printed circuit board assembly to form a linear array, and a linear reflector assembly, attached to the housing, to concentrate the light generated by the LED emitters over a beam angle formed by the upper surface of the housing and the linear reflector assembly. 
     In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of embodiments in addition to those described and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein, as well as the abstract, are for the purpose of description and should not be regarded as limiting. 
     As such, those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts a perspective view of a sidewall luminaire, in accordance with an embodiment of the present invention. 
         FIG. 2  depicts a partial perspective view of the sidewall luminaire depicted in  FIG. 1 . 
         FIG. 3  depicts a top view of the sidewall luminaire depicted in  FIG. 1 . 
         FIG. 4  depicts a front view of the sidewall luminaire depicted in  FIG. 1 . 
         FIG. 5  depicts a sectional view of the sidewall luminaire depicted in  FIG. 4 . 
         FIG. 6  depicts a sidewall installation geometry, in accordance with an embodiment of the present invention. 
         FIG. 7  depicts a perspective view of a ceiling luminaire, in accordance with another embodiment of the present invention. 
         FIG. 8  depicts a partial perspective view of the ceiling luminaire depicted in  FIG. 7 . 
         FIG. 9  depicts a top view of the ceiling luminaire depicted in  FIG. 7 . 
         FIG. 10  depicts a front view of the ceiling luminaire depicted in  FIG. 7 . 
         FIG. 11  depicts a sectional view of the ceiling luminaire depicted in  FIG. 10 . 
         FIG. 12  depicts a ceiling installation geometry, in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     The invention will now be described with reference to the drawing figures, in which like reference numerals refer to like parts throughout. 
     Embodiments of the present invention advantageously provide a widely spaced linear array of High Brightness (HB) emitters, used in conjunction with a linear reflector assembly, that prevents loss of LED luminaire output in unused directions while, at the same time, providing uniform light pattern blending at close distance for the spaced LED emitters. 
     In these embodiments, a widely spaced array of HB LED emitters is thermally bonded to a linear shaped luminaire by means of a thermal-clad or other high thermal efficiency PCB design. The HB emitters have a much higher thermal efficiency than low or medium power LED emitters which translates directly to higher power conversion efficiency and higher allowable operating temperatures. These factors in turn, translate to reduced heat sink surface area and weight for a given light output level. 
     The HB LED array is used in conjunction with a linear reflector assembly which maximizes LED light recovery and increases light projection in the direction of interest. The linear reflector also provides low loss blending of the light emissions from the individual LED point sources resulting in a completely uniform lighting presentation within one inch of the luminaire. The use of the reflector assembly makes possible various LED spacing intervals, such as, less than an inch (e.g., 0.5 inches) up to several inches (e.g., 3 inches) between emitters. Fewer LED emitters in the luminaire translates to greater power conversion efficiency, lower luminaire weight, increased reliability, and lower cost. 
     Embodiments of the present invention may be used with equal utility in sidewall and ceiling applications simply by adjusting the angular relationship between the LED emitter and reflector. In general, a narrow beam width presentation is more desirable for sidewall applications and wider beam width lighting pattern is more useful for ceiling applications. 
     Embodiments of the present invention also do not require the use of a diffusing lens or secondary optics to achieve uniform light blending from the LED point sources at short working distances. Thus, light level depreciation due to transmission losses through the diffuser or secondary optics system are not a factor and the power dissipation of the luminaire does not have to be increased to offset these effects. 
     Although used primarily for white lighting applications, in some embodiments of the present invention, other colors of LED emitters may be utilized to create colored lighting effects. In some embodiments, a second array of LED emitters with a different overall color, or color temperature, can be interspersed between the primary LED emitter array and can be used to generate different light output colors in different modes of luminaire operation. 
     The linear reflector additionally serves to shield the observer from direct observation of the LED emitters in the event that the luminaire is visible in the installation such as in sidewall applications. Out of necessity, the LED emitters must be placed as close as is practical to the conjunction of the linear reflector and the luminaire body to maximize LED light recovery. This serves to shield the LED emitters from direct observation. 
     Generally, the linear reflector concentrates all available light projection from the HB emitters, more than doubling the light output in the direction of interest and preventing wasted light and power, and blends light output from adjacent LED light sources such that a uniform light pattern is projected at distances of less than 1 inch, for example, from the luminaire housing. Accordingly, LED emitters spaced at intervals of 1.5 inches, for example, do not compromise the blending of the projected light pattern. 
     Sidewall Luminaire Embodiment 
     In the sidewall luminaire embodiment depicted in  FIGS. 1-6 , sidewall luminaire  100  employs a linear array of HB LED emitters  102  which are directly bonded to a thermally conductive printed circuit board assembly  104 , which is mounted on a surface of housing  106 . The LED emitters  102  may be arranged with a center-to-center spacing between about 0.5 inches and 3 inches, or, preferably, between 1 and 2 inches. In one embodiment, the center-to-center spacing is 1.5 inches. An LED driver assembly is disposed within the housing  106  and provides power to the LED emitters. The HB LED emitters  102  employed can be discriminated from low or medium power LED emitters because they have drive current capability in excess of 300 ma. Very low profile LED emitters may be used which advantageously have a Lambertian projection pattern. These LED emitters are placed as close as is practical to the conjunction of the luminaire housing  106  and the reflector  108  to maximize light recovery from the surface of the LED closest to the reflector. This arrangement more than doubles the projected light output in the forward direction. 
     The beam pattern projected from the light is dictated by the angular relationship between housing  106  and the reflector  108 . In the sidewall embodiment, the beam angle of the projected light pattern is typically less than 90 degrees. The surface of the reflector  108  is angled to roughly parallel the surface of the sidewall panel  110 . From the observers position, the LED emitters  102  will not be visible, only the projected light pattern. This relationship is illustrated, for example, in  FIG. 6 . 
     In addition to maximizing light recovery from the LED emitters  102  and controlling the beam pattern of the projected light, the linear reflector  108  also serves to homogenize the light from the LED point sources so that a completely blended light pattern is projected onto the sidewall panel  110  at distances of less than 1 inch from the luminaire. This eliminates the “hot spotting” that would typically be experienced with linear LED luminaires employing widely spaced LED emitters. 
     Thermal efficiency is maximized by employing HB LED emitters which have a minimal junction to ambient thermal resistance. These LED emitters are either soldered or bonded to a PCB assembly  104  which is designed for efficient thermal transfer between the LED bonding surface and the back of the PC board. The PCB assembly is in turn, bonded to housing  106  of the luminaire  100 . By employing HB LED emitters  102  in conjunction with suitable inter-LED spacing and a highly efficient heat transfer method, it is possible to limit the heat sink surface area requirement to the thermal PCB assembly  104  and the housing  106  of the luminaire  100  with no additional heat sink surface. This advantageously results in a light weight luminaire which still has high light output capacity. 
     Plug  114  and receptacle  116  may be used to join multiple luminaire  100  together, and provide power and/or control signals thereto. 
     Ceiling Luminaire Embodiment 
     In the embodiment depicted in  FIGS. 7-12 , ceiling luminaire  200  is similar in many respects to sidewall luminaire  100 , with one exception being the angular relationship between the luminaire housing  206  and the reflector  208 —this angle has been changed to create a wider projected beam angle. Ceiling luminaire  200  employs a linear array of HB LED emitters  202  which are directly bonded to a thermally conductive printed circuit board assembly  204 , which is mounted on a surface of housing  206 . The LED emitters  202  may be arranged with a center-to-center spacing between about 0.5 inches and 3 inches, or, preferably, between 1 and 2 inches. In one embodiment, the center-to-center spacing is 1.5 inches. An LED driver assembly is disposed within the housing  206 , and provides power to the LED emitters. 
     Additionally, a protective lens cap  212  may be placed over each LED emitter  202  to protect the emitter from impact, since it is more exposed in this application. The protective lens cap  212  may be completely clear in order to minimize transmission losses. The lens cap  212  may be seamless and placed very close to the HB LED emitter lens  202 . By moving the focal point of the protective lens  212  very close to the emitter, the focal plane of the projected image will be extremely far from the luminaire  200 . This results in no unsightly aberrations being projected onto the ceiling panel  210 . 
     Once again, the reflector  208  is angled so that is approximately parallel to the plane of the panel  210 . In the ceiling embodiment, the beam angle of the projected light pattern is typically greater than 90 degrees. Despite the fact that the angular relationship between the luminaire housing  206  and the reflector  208  has been increased however, the HB LED emitters  202  cannot be directly viewed by an observer because the observer&#39;s position is below the lip of the angled reflector  208  and in addition, the LED lens is kept close to the reflector  208 . This relationship is illustrated in  FIG. 12 . 
     In the wide beam angle configuration employed for the ceiling luminaire  200 , light power output is not equal in all directions from the luminaire. However, the angular relationship between the reflector  208  and the housing  206  has been tuned to maximize light projection in a direction which is roughly centered between the reflector  208  and housing  206 . This is the direction where the projected light has the greatest distance to travel to the panel  210  and where the greatest light output level is therefore beneficial. 
     The many features and advantages of the invention are apparent from the detailed specification, and, thus, it is intended by the appended claims to cover all such features and advantages of the invention which fall within the true spirit and scope of the invention. Further, since numerous modifications and variations will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation illustrated and described, and, accordingly, all suitable modifications and equivalents may be resorted to that fall within the scope of the invention.