Abstract:
A lighting fixture is disclosed which provides a substantially uniform elongated light output, yet is powered by only a minimum number of inexpensive light emitting diodes. The lighting fixture has a curved back surface and a selected focal area to provide a substantially uniform output. Multiple LEDs may be controlled by a controller to provide special lighting effects. Each of the side surfaces and the back surface may include a reflector. The lighting fixtures preferably have flat end surfaces so they may be placed end-to-end to create an elongated light bar of any desired length.

Description:
This patent application claims priority from the U.S. Provisional Patent Application No. 60/332,702 filed Nov. 16, 2001, which is incorporated herein by reference. 

   BACKGROUND OF THE INVENTION 
   This invention relates to lighting fixtures. More particularly, this invention relates to lighting fixtures using light emitting diodes. 
   It is known to use fluorescent and neon tubes to provide accent or strip lighting wherein a substantially uniform elongated light output or bar of light is desired. However, fluorescent and neon tubes are relatively expensive to manufacture, and require special power supplies for their operation. 
   It is also known to use fluorescent and neon tubes, or liquid crystal displays as segments in a seven or fourteen segment alphanumerical character for scoreboards, signs and the like. Again, such displays are relatively expensive and complex. 
   SUMMARY OF THE INVENTION 
   A primary feature and advantage of the present invention is to provide a light fixture having reduced cost that provides a highly uniform, elongated light output or bar of light. The present invention uses a minimum number of light emitting diodes to achieve such an elongated output or light bar. The use of low cost light emitting diodes, translucent light guides, and novel reflective surfaces enables a uniform, elongated light output to be achieved at a relatively low cost. 
   The present invention comprises a lighting fixture having a translucent member or light guide that has an output surface, a curved back surface having a first reflector thereon, first and second side surfaces, an end surface, and at least one light emitting diode (“LED”) interconnected with the first end surface. In one embodiment, the first and second side surfaces are substantially planar and parallel to each other, although in another embodiment they are non-parallel and generally diverging so that the output surface is substantially wider than the back surface. 
   In one embodiment, the lighting fixture is modular in nature, so that lighting fixtures may be placed end to end to create an elongated light bar of any desired length. The modular unit preferably includes a first end surface having a first section and a recessed second section, with at least one light emitting diode being interconnected with the second section. The first section may be placed adjacent to a second end surface from another module so that the modules are placed end to end and thus form an elongated light bar. 
   A modular unit may also include several sections, each with one or more light emitting diodes and a curved back surface. Each light emitting section has a focal area toward which all light rays reflected off of the respective curve surface are directed before they proceed out of the output surface. Each light emitting section or module preferably has a blocking surface adjacent to a light emitting diode to prevent light emitted from the side of the LED from directly reaching the output surface without being reflected. This arrangement avoids non-uniform output or “hot spots”, which are areas of excessive brightness visible to the observer. 
   In another configuration, the invention includes two or even three adjacent LEDs on the first end surface, which are controlled by a preprogrammed controller. This enables the LEDs to be sequenced, flashed, faded or mixed to achieve a wide variety of colors and lighting effects. 
   In other embodiments, the light guide is formed with an air gap therein. In yet another embodiment, light diffusing particles are dispersed throughout the light guide. 
   It is a feature and advantage of the present invention to evenly distribute a point source of light on a predetermined output surface using a minimum number of LEDs. 
   Other features and advantages will be apparent to those skilled in the art from the detailed description of the invention and the drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of a single lighting fixture module according to a first embodiment of the present invention. 
       FIG. 2  is a perspective view of a series of modular lighting fixtures placed end to end. 
       FIG. 3  is a second modular unit including two LEDs and two respective curved back surfaces. 
       FIG. 4  is a lighting fixture similar to the lighting fixture  FIG. 3  except that two adjacent LEDs are used in each section. 
       FIG. 5  depicts another embodiment of the invention having multiple LED sections. 
       FIG. 6  depicts an embodiment having three LEDs in each section. 
       FIG. 7  depicts an alternate embodiment of a lighting fixture having a single light emitting diode. 
       FIG. 8  is a perspective view of another embodiment having an air gap in the light guide. 
       FIG. 9  is a cross section end view, taken along line  9 — 9  of FIG.  8 . 
       FIG. 10  is a perspective view of another embodiment having light diffusing particles. 
   

   DETAILED DESCRIPTION 
     FIG. 1  depicts a first embodiment of a lighting fixture  10  according to the present invention. Fixture  10  is preferably, though not necessarily, a modular unit that may be placed adjacent to other similar lighting fixtures. 
   In  FIG. 1 , fixture  10  includes an output surface  12 , a first end surface  14 , a curved back surface  16 , and a second end surface  18  that is opposite to first end surface  14 . Output surface  12  is either clear or has a diffusive reflector or diffuser formed integral therewith. 
   Fixture  10  is primarily comprised of a translucent wave guide  20  made from acrylic, glass, a gel, a liquid, air, or other translucent material. It has a high total internal reflection such that there is a large difference of the index of refraction between light guide&#39;s boundaries and the surrounding medium (which is typically air). Wave guide  20  is preferably transparent at the wavelength of the output of the light emitting diode  22 . Therefore, if LED  22  is a red LED, the light guide could be transparent or it could be made from a translucent red material. 
   Back surface  16  and second end surface  18  have respective reflectors  24  and  26  thereon. It is preferred that reflective surfaces  24  and  26  comprise specular reflectors, which act like mirrors to reflect incident light. The use of specular reflectors is preferred since scattering is reduced and thus more of the incident light will be reflected out of output surface  12  instead of out of parallel side surfaces  28  and  30 . To prevent such light loss out of surfaces  28  and  30 , surfaces  28  and  30  could also be formed with respective reflectors thereon. 
   First end surface  14  is preferably comprised of a first section  14   a  and a recessed second section  14   b , with an intermediate section  14   c  therebetween. LED  22  is interconnected with recessed section  14   b , preferably using an epoxy whose index of refraction is matched to the index of the light guide material to minimize refractive losses. An epoxy with a refractive index of 1.5 is preferred for use with an acrylic light guide. The purpose of recessing section  14   b  is to provide space for LED lead wires  22   a  and  22   b  so that lighting fixture  10  may be placed adjacent to a similar lighting fixture. 
   Opposite to first end surface  14  is a second end surface  18  having a corresponding shape. Again, this enables second end surface  18  to be placed adjacent to a first end surface of an adjacent lighting fixture, to create an elongated light bar having a relatively uniform light output. 
   The embodiment depicted in  FIG. 1  has a length (defined as the distance between end surfaces  14  and  18 ) of any length up to about 16 inches, with 8 inches being preferred. As the length becomes significantly longer than 8 inches, the light output becomes dimmer. 
   Also, lighting fixture  10  is designed such that approximately one-half of the total height of the lighting fixture is comprised of second end surface  18 , with the remainder of the height being due to the curvature of curved surface  16 . The height of fixture  10  is defined as the shortest distance between output surface  12  and the intersection  15  of first end surface  14  with curved surface  16 . The LED is positioned and the curved surface  16  is designed so that light incident on the curved surface  16  has a long focal length. 
   Curved surface  16  could be parabolic in shape, or as shown in  FIG. 1 , it may be curved in the length direction (i.e., the direction between end surfaces  14  and  18 ), but substantially flat in the width direction, that is the direction between side surfaces  28  and  30 . The curvature of end surface  16  is selected so that light output from LED  22  incident on reflective surface  24  is directed in an area  31  around a focal point  32  (hereinafter such area being called the “focal area”). Lighting fixture  10  and particularly back surface  16  are also selected such that approximately 70 percent of all the light output from LED  22  passes through the focal area  31 , and 30 percent of the output light from the LED does not pass through the focal area  31 . This configuration tends to minimize unusually bright or “hot” spots visible by an observer of the output surface  12 . The focal area is preferably located at about one-half of the height of lighting fixture  10 . 
   A power supply  33  converts line power to the low voltage DC power needed to operate controller  35 . LEDs typically require 1.5 to 4.5 VDC, 20 to 25 mA current, although some LEDs require up to 350 mA current. Controller  35  in turn provides power to LED  22 . Controller  35  may also be programmed to flash, fade or pulse the LED. One suitable controller is a model no. 600/8010 made by Everbrite, Inc. of Greenfield, Wis. 
     FIG. 2  depicts a plurality of lighting fixtures  10  disposed adjacent to each other to create an elongated light output or light bar. As readily apparent from  FIG. 2 , the corresponding shapes and configurations of first section  14   a  and second end surface  18  enable the modules  10  to be placed directly adjacent to each other to create a continuous bar of light. Also, the placement of LED  22  on recessed sections  14   b , together with the space  23  created by the curvature of back surface  16 , create sufficient clearance for the leads  22   a  and  22   b  of the respective LEDs  22 . This configuration depicted in  FIG. 2  is particularly suitable for decorative or accent lighting such as that used to mark the outlines of steps or floors, or as edge lighting for a backlit sign such as a restaurant drive-thru menu board. 
   Each lighting segment fixture  10  has a LED with an output of up typically three lumens, which results in an output on surfaces  12  of up to approximately 100 candelas per square meter. 
     FIGS. 3 and 4  relate to another embodiment of the invention in which a lighting fixture  50  has two light emitting sections  50   a  and  50   b , each section having at least one LED and a respective curved back surface  54 ,  56 . However, lighting fixture  50  has a single output surface  57 . 
   Lighting fixture  50  also has a first end surface  58  and an opposite corresponding end surface  60 . First end surface  58  has a first section  58   a , a recessed second section  58   b  to which is interconnected a LED  52 , and an intermediate section  58   c . Similarly, end surface  60  has a first section  60   a  whose shape and configuration corresponds to that of section  58   a , a recessed section  60   b  to which is interconnected a LED  52 , and an intermediate section  60   c . The uses of surfaces  58   a  and  60   a  that have corresponding shapes and configurations enables a plurality of modules  50  to be placed end to end to achieve an elongated light bar having a substantially uniform output. 
   As shown in  FIG. 3 , curved surfaces  54  and  56  meet in a raised section  62 , which may need to have a diffusive reflector to prevent a hot spot from forming at the raised section. Back surfaces  54  and  56  are preferably covered with respective specular reflectors, although diffusive reflectors could be used if side surfaces  64  and  66  are covered with respective reflectors. 
   Each of light emitting sections  50   a  and  50   b  has a respective focal point  68 ,  70 . As with the embodiment depicted in  FIG. 1 , approximately 70 percent of the light emitted by LEDs  52  is directed toward the focal areas  69 ,  71  around respective focii  68  and  70 , and the focii are positioned approximately one-half the distance between the output surface and the end surface. 
   The embodiment depicted in  FIG. 4  is similar to the embodiment depicted in  FIG. 3 ; respective components having similar configurations have been given the same part designations. 
     FIG. 4  differs from  FIG. 3  in two primary respects: first, respective blocking surfaces  72  and  74  are positioned adjacent respective LEDs  76  and  78  to prevent light emitted from the upper sides of LEDs  76  and  78  from being directly incident upon output surface  57  without being first reflected. This arrangement avoids hot spots which could otherwise occur. 
   Second, the embodiment in  FIG. 4  differs from the embodiment in  FIG. 1  in that two LEDs are used in each light emitting section of the lighting fixture  80 . That is, there are two LEDs  76  and  82  interconnected with end surface  84 , and there are two LEDs  78  and  86  that are interconnected with end surface  88 . The use of two LEDs in each light emitting section  80   a ,  80   b  enables certain effects to be achieved, such as fading from one color to another. Otherwise, the same considerations apply with respect to the embodiment in  FIG. 4  as in the embodiment in  FIGS. 1 and 3 , namely that each light emitting section has a focal area  69 ,  71  around a respective focal point  68 ,  70 , in which a significant part (about 70 percent) but not all of the light output passes. 
     FIG. 5  depicts an embodiment of the invention that is somewhat different from the other embodiments. In  FIG. 5 , lighting fixture  90  is comprised of light emitting sections  90   a ,  90   b ,  90   c ,  90   d , and  90   e . Each of sections  90   a  through  90   e  has a respective LED  92  and respective back curved surfaces  94   a  through  94   e . LEDs  92  are interconnected with respective intermediate surfaces  93 . Each of the curved back surfaces is coated with a reflector, which is preferably a specular reflector, but may also be a diffuse reflector. As clearly shown in  FIG. 5 , each of sections  90   a  through  90   e  also has a respective focal point  96   a  through  96   e . Each of the focal points defines a respective focal area  97   a  through  97   e  through which a majority, preferably about 70 percent, of light emitted from the respective LEDs passes. The remaining light may proceed directly from the LED to the output surface  100 . 
   Blocking surfaces  102  are also provided to prevent light emitted from the upper sides of LEDs  92  from directly being output through output surface  100 , thereby avoiding visible bright or hot spots. Output surface  100  could be clear, but it preferably has a diffuser layer or diffuser formed integral therewith to achieve a more uniform output. 
   Lighting fixture  90  also includes a first end surface  104  and a second, opposite end surface  106  having a corresponding shape and configuration. As discussed above in connection with  FIG. 1 , the corresponding shape and configuration of the end surfaces enable the lighting fixture  90  to be used as a module, by placing it adjacent to other similar lighting fixtures. 
     FIG. 6  is a variation of the lighting fixture  90  of  FIG. 5  wherein three LEDs  108 ,  110  and  112  are used in each section of the module. It is preferred that each of LEDs  108 ,  110  and  112  is of a different color, such as red, blue and yellow. The use of different colored LEDs, when properly controlled by a programmed control module  113 , enables any color or combination of colors to be output through the output surface  114 , including white. Of course, other lighting effects may be achieved, such as fading, sequencing and color changing. In other respects, the module  113  of  FIG. 6  is similar to the module depicted in FIG.  5 . Control module  113  is connected to LEDs  108 ,  110  and  112  by wires  115 . 
     FIG. 7  depicts another embodiment of the light fixture. In  FIG. 7 , light fixture  116  has a first end surface  118 , and a second surface  120  that functions both as a curved back surface and as the second end surface. Surface  120  is curved in section  120   a , but could be substantially flat in section  120   b . If section  120   b  is substantially flat, section  120   b  may act as the second end surface of the other embodiments. 
   The lighting fixture depicted in  FIG. 7  also has two side surfaces  122  and  124 , and an output surface  126 . Of course, the lighting module includes one or more LEDs  128 . 
   A key feature of the lighting fixture  116  in  FIG. 7  is that the output surface  126  is substantially wider than surface  120 . That is, side surfaces  122  and  124  are not substantially parallel as in the other embodiments, but together form an acute angle A which is preferably between 1 to 60 degrees. This configuration of the lighting fixture  116  makes it particularly suitable for use as a segment in either a 7 or 14 segment display, such as those used to display alphanumerical characters in scoreboards and the like. The lighting fixture  116  is particularly suitable for these applications because the output surface is wider and thus easier to see. Also, the lighting fixture  116 , due to its shape, is particularly suitable for injection molding or casting. Of course, each of the end, back and side surfaces may be covered with a reflector to further intensify the light output surface  126 . 
     FIGS. 8 and 9  relate to another embodiment of the present invention. In  FIGS. 8 and 9 , light guide  130  is comprised of two parallel side walls  132  and  134  with an air gap  136  therebetween. The light guide also includes an output surface  138  which is similar to the output surface  12  in FIG.  1 . The light guide includes a curved back surface  140  which is similar to the back surface  16  discussed above. The light guide includes a first end surface  142  which is similar to the first end surface  14  in  FIG. 1 , and a second end surface  144  that is similar to the second end surface  18  of FIG.  1 . 
   Unlike the embodiment depicted in  FIG. 1 , the embodiments of  FIGS. 8 and 9  includes an air cavity  136  between side surface  132  and  134  that transmits light from LED  22 . Focus point  146  is preferably disposed within the air cavity. The use of the air cavity reduces the overall weight of the light guide, and may also reduce its cost. Any of the embodiments shown in the figures or described herein could have an air gap in the light guide. 
     FIG. 10  depicts yet another embodiment of the invention which is similar to the embodiment of  FIG. 1  except that the light guide includes light reflective particles  148  dispersed therethrough. The remaining components in  FIG. 10  generally correspond to the components in  FIG. 1  having had been given the same part designations. Any of the embodiments depicted or described herein could alternatively use a light guide with light reflective particles. 
   The advantage of using an acrylic light guide material with light diffusive, or otherwise reflective particles is that superior light diffusion is achieved in a smaller light guide. As a result, the overall size of the light guide may be reduced, thereby reducing its cost. 
   One suitable material for the light guide of  FIG. 9  is sold under the trademark ELIT, manufactured by Atoglas Division, ELF Altochem North America, Inc. Philadelphia, Pa. 
   While several embodiments of the present invention have been shown and described, other embodiments will be apparent to those skilled in the art and are within the intended scope of the claims.