Abstract:
A lighting assembly includes an LED light source assembly and a unitary light-transmissive solid reflector optical element. The reflector optical element has a light output surface and n light-transmissive solid optical sub-elements having n-fold rotationally symmetrical about a central axis. Boundaries between adjacent optical sub-elements extend radially outward from the central axis. Each optical sub-element has a reflective surface positioned opposite the light output surface on the optical sub-element and shaped to create an internal reflection effect. The LED light source assembly has an LED light source for each optical sub-element. The LED light sources are positioned along an outline near the light output surface to direct light from each LED light source towards the reflective surface of the respective optical sub-element such that the light is reflected by the reflective surface to form an output light that exits the reflector optical element through the light output surface.

Description:
RELATED APPLICATION DATA 
     This application claims the benefit of U.S. Provisional Patent Application No. 61/894,701, filed Oct. 23, 2013, the disclosure of which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     Energy efficiency has become an area of interest for energy consuming devices. One class of energy consuming devices is lighting assemblies. Light emitting diodes (LEDs) show promise as energy efficient light sources for lighting assemblies. But light output distribution is an issue for lighting assemblies that use LEDs or similar light sources. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic perspective view of an exemplary lighting assembly. 
         FIGS. 2 and 3  are schematic perspective views of the reflector optical element in the lighting assembly of  FIG. 1 . 
         FIGS. 4 and 5  schematic perspective views of the light source assembly in the lighting assembly of  FIG. 1 . 
         FIG. 6  is a schematic plan view of the reflector optical element of in the lighting assembly of  FIG. 1 . 
         FIG. 7  is a cross-sectional view across a portion of the lighting assembly of  FIG. 1 . 
         FIGS. 8-10  are cross-sectional views across a portion of other configurations of the lighting assembly of  FIG. 1 . 
         FIG. 11  is a schematic perspective view of another exemplary lighting assembly, in a first rotational position. 
         FIG. 12  is a schematic perspective view of the lighting assembly of  FIG. 11 , in a second rotational position. 
         FIGS. 13 and 14  are schematic perspective views of the reflector optical element in the lighting assembly of  FIG. 11 . 
     
    
    
     DESCRIPTION 
     Embodiments will now be described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout. The figures are not necessarily to scale. Features that are described and/or illustrated with respect to one embodiment may be used in the same way or in a similar way in one or more other embodiments and/or in combination with or instead of the features of the other embodiments. In this disclosure, angles of incidence, reflection, and refraction and output angles are measured relative to the normal to the surface. 
     An exemplary lighting assembly  100  will now be described with reference to  FIGS. 1-7 .  FIG. 1  is a schematic perspective view of lighting assembly  100 . Lighting assembly  100  has a reflector optical element  150  and a light source assembly  128 . Reflector optical element  150  consists of three optical sub-elements  150 A,  150 B, and  150 C although reflector optical element  150  has been fabricated as a unitary solid component. Reflector optical elements can be made where the number of optical sub-elements is different from three.  FIGS. 2 and 3  are schematic perspective views of the reflector optical element  150  from two differing perspectives. Reflector optical element  150  includes a major surface (light output surface)  156  at its proximal end  151 . In this example, the major surface  156  is substantially planar. Each of the optical sub-elements  150 A,  150 B,  150 C, has a respective sidewall  159 A,  159 B,  159 C extending from the proximal end  151  to the respective distal ends  152 A,  152 B,  152 C. We define a central axis or axis of symmetry  170  ( FIG. 6 ). The three sub-elements  150 A,  150 B,  150 C are  3 -fold symmetrical around the central axis  170 . A direction parallel to the central axis  170  is called a longitudinal direction  30 . The sidewalls  159 A,  159 B,  159 C generally extend along the longitudinal direction  30 . In this example, the light output surface  156  is perpendicular to the longitudinal direction  30 . There is a converging reflective surface  154 A,  154 B,  154 C located at the respective distal ends  152 A,  152 B,  152 C. The sidewall  159 A,  159 B,  159 C is collectively referred to as sidewall  159 . Note that sidewall  159  includes a sidewall portion  157  at the proximal end  151  which also extends along the longitudinal direction  30  but has a slightly greater radial dimensions than the rest of the sidewall  159 . 
     Lighting assembly  100  includes a light source assembly  128 . The light source assembly  128  is shown from two differing perspectives in  FIGS. 4 and 5 . Solid-state light emitters  130 A,  130 B, and  130 C are mounted to tilted circuit board elements  134 A,  134 B, and  134 C, respectively. The tilted circuit board elements  134 A,  134 B, and  134 C are connected to a circuit board  136 . The circuit board  136  has a top major surface  133 , a bottom major surface  135 , an outer edge  139 , and an inner edge  137  that faces toward and generally follows the contour of the sidewalls  159 A,  159 B, and  159 C of the reflector optical element  150 . The tilted circuit board elements  134 A,  134 B, and  134 C are tilted with respect to the top major surface  133  or the bottom major surface  135  or both the top and bottom major surfaces  133 ,  135  of the circuit board  136 . In the example shown, the circuit board  136  is configured as a metal core printed circuit board (MCPCB) and its major surfaces  133 ,  135  are parallel to the light output surface  156  and hence perpendicular to the longitudinal direction  30 . 
     Light output from solid-state light emitter  130 A,  130 B, and  130 C is input to optical sub-element  150 A,  150 B, and  150 C, respectively. In the example shown, the solid-state light emitters  130 A,  130 B, and  130 C are nominally identical to each other in output characteristics, including output spectrum, output angular distribution, and output luminance. In this example, each solid-state light emitter  130 A,  130 B,  130 C is configured as a white LED and includes a light emitting diode (LED) die and a phosphor. A mixture of the phosphor and an encapsulant is positioned in a reflective cup to cover the LED die located at the bottom of the reflective cup. The LED die emits blue light and excites the photoluminescence of the phosphor. The combined output light of the solid-state light emitter is white light. 
     The solid-state light emitter  130 A,  130 B,  130 C is positioned at the light input surface  153 A,  153 B,  153 C, respectively. In an example, the solid-state light-emitter  130 A,  130 B,  130 C is affixed to the light input surface  153 A,  153 B,  153 C, using, for example, a suitable optical adhesive having a refractive index chosen to reduce Fresnel reflection losses as the light exits the solid state light emitter and enters the light input surface. 
       FIG. 6  is a schematic plan view of the reflector optical element  150 , as viewed from the side of the light output surface  156 . For ease of viewing, the light source assembly  128  has been removed. There is a boundary surface  155 AB between adjacent optical sub-elements  150 A and  150 B, a boundary surface  155 BC between adjacent optical sub-elements  150 B and  150 C, and boundary surface  155 CA between adjacent optical sub-elements  150 C and  150 A. The boundary surfaces  155 AB,  155 BC,  155 CA extend along the longitudinal direction  30  between the proximal end  151  and the distal ends  152 A,  152 B,  152 C. The boundary surfaces  155 AB,  155 BC, and  155 CA extend radially outward from a central axis (axis of symmetry)  170 . The central axis  170  extends along the longitudinal direction  30 . The three optical sub-elements are nominally identical to each other optical characteristics, and in combination with nominally identical solid-state light emitters  130 A,  130 B, and  130 C, the lighting assembly  100  is three-fold symmetric around the axis of symmetry  170 . 
     In order to explain the propagation of light in the reflector optical element  150 , we take a cross section across one of the optical sub-elements. The location of the cross section is shown as  7  in  FIG. 6  and cuts across optical sub-element  150 A and light input surface  153 A. Additionally, while not shown in  FIG. 6 , the cross section is taken across solid-state light emitter  130 A and respective portions of the light source assembly  128 . A schematic cross-sectional view is shown in  FIG. 7 . Light from solid-state light emitter  130 A enters the optical sub-element  150 A through the light input surface  153 A. Light input surface  153 A is a substantially planar surface located at an intersection of the light output surface  156  and the sidewall  159  of reflector optical element  150 . It is inclined (tilted) at an oblique angle to the light output surface  156 . The light rays propagate in the optical sub-element within a cone angle ranging from approximately +42 degrees to approximately −42 degrees relative to the normal to the light input surface  153 A. The actual range of angles depends on the refractive indices of the optical sub-element  150 A and the material in optical contact with the light input surface  153 A. In some cases, there is an air gap between the light input surface  153 A and the solid-state light emitter  130 A, so the material in optical contact with the light input surface  153 A is air. In some other cases, there is an optical adhesive between the light input surface  153 A and the solid-state light emitter  130 A. 
     After entering the optical sub-element  150 A through the light input surface  153 A, the light propagates towards the reflective surface  154 A located at the distal end  152 A. In  FIG. 7 , three exemplary rays are shown:  160 ,  162 , and  164 . Light ray  164  is referred to as an on-axis ray that is relatively closer to the normal to the light input surface  153 A than are off-axis rays  160  and  162 . We refer to angles between the light output surface  156  and the normal to the light input surface as positive angles. Light ray  160  is an example of a positive angle light ray and light ray  162  is an example of a negative angle light ray. To produce the collimated output light beam, reflective surface  154 A is parabolic in shape, or has a nearly parabolic shape designed by ray tracing. In other applications, reflective surface  154 A can have other shapes, such as ellipsoidal and aspheric. 
     Since the light is incident on reflective surface  154 A at relatively small angles of incidence, surface  154 A is made reflective by a reflective coating applied to the surface. The reflective coating may be a silver coating, an aluminum coating, or a multilayer thin film dielectric coating. The selection of the appropriate coatings depends on the performance requirements of the application and cost considerations. 
     The light input surface  153 A is angled non-parallel to light output surface  156  such that a normal to light input surface  153 A at the location at which solid-state light emitter  130 A is mounted intersects reflective surface  154 A near the center of the reflective surface  154 A. Furthermore, the reflective surface  154 A is angled away from the longitudinal direction  30  and toward the light input surface  153 A to increase the light incident on the reflective surface  154 A. 
     Reflective surface  154 A is tilted relative to the longitudinal direction  30  (or the normal to the light output surface of reflector optical element  150 ). In an example, the tilt of the reflective surface  154 A is such that the angle between longitudinal direction  30  and the normal to the center of the reflective surface  154 A is approximately one-half of the angle between the longitudinal direction  30  and the normal to light input surface  153 A. 
     In a conventional design that lacks solid reflector optical element  150  of a high refractive index material, the light exiting solid-state light emitter  130 A has a cone angle ranging from +90° to −90°. To reflect light with such a large cone angle would require a reflective surface substantially larger than reflective surface  154 A within reflector optical element  150 . This would make such conventional collimated light source impractically large for use in an application such as lighting assembly  100 . 
     In the lighting assembly  100  of  FIGS. 1-7 , light output from each sub-element  150 A,  150 B,  150 C is collimated along the longitudinal direction  30 . The light exiting reflector optical element  150  through output surface  156  is minimally refracted as it exits reflective optic  150  through planar output surface  156 . Furthermore, the total light output from the lighting assembly  100  is approximately three times the light output from each sub-element  150 A,  150 B,  150 C. In some applications of lighting assembly  100 , output surface  156  can be other than planar. Moreover, additional optics can be located downstream of output surface  156 . 
     We discuss some variations in optical configuration with reference to  FIGS. 8-10 . In these figures the light source assembly  128  has been abbreviated with the exception of the solid-state light source  130 A for ease of viewing. In  FIG. 8 , the solid-state light source  130 A is positioned on light input surface  153 A such that the light output from the sub-element is substantially parallel to longitudinal direction  30 . Three exemplary light rays are shown: positive light ray  160 , negative light ray  162 , and light ray  164  that enters through the light input surface  153 A normal thereto. All three light rays  160 ,  162 ,  164  are output through light output surface  156  parallel to longitudinal direction  30 . Note that since the light entering the sub-element is confined to a range of approximately ±42 degrees, the sub-element can be configured such that the most of the light is not incident on the outer surface  159 A and the boundary surfaces  150 AB,  150 CA. 
     In  FIG. 9 , the position of the solid-state light emitter  130 A on the light input surface  153 A has been moved away from the position in  FIG. 8  towards the light output surface  156 . This is along a direction  40 , which is also shown in plan view in  FIG. 6 . As a result, the light rays  160 ,  162 ,  164  are tilted away from the longitudinal direction  30  toward the solid-state light emitter  130 A (toward the light input surface  153 A). 
     In  FIG. 10 , the position of the solid-state light emitter  130 A on the light input surface  153 A has been moved away from the position in  FIG. 8  and away from the light output surface  156 , along the direction  40 . As a result, the light rays  160 ,  162 ,  164  are tilted away from the longitudinal direction  30  and away from the solid-state light emitter  130 A (away from the light input surface  153 A). The examples of  FIGS. 9 and 10  show the cases of displacement of solid-state light emitter  130 A on the light input surface  153 A along the direction  40 . Note from the plan view of  FIG. 6  that displacement along other directions is also possible, for example a direction  50  on the light input surface  153 A perpendicular to direction  40 . Another possible direction is a direction radially outward from the central axis  170 . 
     The three optical sub-elements  150 A,  150 B,  150 C are three-fold symmetrical around the central axis  170 . If a displacement of the solid-state light emitter  130 A on the sub-element  150 A (as illustrated for example in  FIG. 9 or 10 ) were replicated for the solid-state light emitters  130 B,  130 C on respective sub-elements  150 B,  150 C, the resulting perturbations on the combined light output would also be three-fold symmetrical around the central axis. In this example, an output light beam that deviates from collimated output where the deviation is three-fold symmetrical about the central axis, can be obtained. 
     In the example of  FIGS. 1-7 , the solid-state light emitter  130  is optically coupled directly to the light input surface  153 . This configuration presumes that the heat sink  134  is sufficiently small such that the light output is not obstructed. In other cases it may be necessary to displace the solid-state light emitter radially outwards from the light input surface  153  and provide a light pipe between the light input surface and the solid-state light emitter. An example of a lighting assembly that uses light pipes is explained below. 
     An adjustable lighting assembly  200  is explained with reference to  FIGS. 11-14 . The adjustability is achieved by rotation of an adjustable element  250  around the central axis  270 . The two states corresponding to the rotation of the adjustable element  250  to its two positions is shown in  FIGS. 11 and 12 . Similar to lighting assembly  100 , there is a reflector optical element  150 . As can be seen in  FIG. 14 , in this example the reflector optical element  150  consists of 5 sub-elements  150 A,  150 B,  150 C,  150 D, and  150 E, adjacent ones of the optical sub-elements being delineated by boundary surfaces  150 AB,  150 BC,  150 CD,  150 DE, and  150 EA. Therefore, this lighting assembly  200  is 5-fold symmetrical around the central axis  270 . Additionally, in this example the reflector optical element includes a central portion  174  not included in any of the sub-elements. There is a hole  172  in the middle of the reflector optical element (and hence in the middle of the central portion  174 ) through which a rod is positioned when the lighting assembly  200  is assembled. The hole  172  is located at the central axis  270 . 
     The lighting assembly  200  additionally includes an adjustable element  250 . The adjustable element  250  includes a disc-shaped element  280  that has two major surfaces  251 ,  252  parallel to each other and perpendicular to the longitudinal direction  30 . In the center of the disc-shaped element  280  is a hole  272  located at the central axis  270 . When the lighting assembly is fully assembled, the adjustable element  250  can be rotated around a rod that goes through the hole  272 . Top major surface  251  functions as light output surface  256  of the adjustable element. The other major surface  252  is juxtaposed with the major surface  156  (light output surface) of the reflector optical element  150  through which light is output therefrom. Around the perimeter of the disc-shaped element  280  is an outer sidewall  259 , extending substantially parallel to the longitudinal direction  30 , and an angled wall  257  located between the outer sidewall  259  and the light output surface  256  (angled relative to the sidewall  259  and the major surfaces  251 ,  252 ). 
     The adjustable element  250  also has 5 pairs of light pipes  240 ,  260 , where each pair of light pipes couples light to each of the sub-elements of the reflector optical element  150 . Each light pipe  240 ,  260  has a light input end  241 ,  261  through which light from a solid-state light emitter enters the light pipe, and a light output end  242 ,  262  through which light is output from the light pipe. The light output ends  242 ,  262  are coupled to the disc-shaped element at the angled wall  257 . The angled wall  257  is analogous to the light input surface  153 A,  153 B,  153 C in the lighting assembly  100 . The light exiting the light pipe propagates through disc-shaped element to the respective sub-element of the reflector optical element. The operation of the reflector optical element is as previously described with respect to lighting assembly  100 . 
     In the example shown, the light pipes  240  and  260  differ in cross-sectional dimension. The light pipes  240  increase in cross-sectional dimension from the light input end  241  to the light output end  242 . On the other hand the light pipes  260  stay substantially constant in cross-sectional dimension between the light input end  261  and the light output end  262 . The light input end  261  of light pipe  260  and the light input end  241  of light pipe  240  are approximately equal in cross-sectional dimension. The light output end  262  of light pipe  260  is smaller in cross-sectional dimension than the light output end  242  of light pipe  240 . 
     In the example shown in  FIGS. 11 and 12 , the light source assembly  228  includes a circuit board  236 . The circuit board  236  has a top major surface  233 , a bottom major surface  235  (facing toward the adjustable element), an outer edge  239 , and an inner edge  237 . The solid-state light emitters  130  are mounted onto the circuit board on the bottom major surface  235 . In the example shown, the circuit board  236  is configured as a metal core printed circuit board (MCPCB) and its major surfaces  233 ,  235  are parallel to the light output surface  256  and hence perpendicular to the longitudinal direction  30 . 
     The lighting assembly  200  can be operated in two rotational positions as shown in  FIGS. 11 and 12 . The adjustable member is rotated relative to the light source assembly  228  and the reflector optical element  150 . The light source assembly  228  and reflector optical element  150  are fixed relative to each other. In a first rotational position ( FIG. 11 ), the light output from the solid-state light emitters  130  enter the light pipes  260  and in a second rotational position ( FIG. 12 ), the light output from the solid-state light emitters  130  enter the light pipes  240 . The light entering the disc-shaped member has a greater cone angle in the first rotational position ( FIG. 11 ) than in the second rotational position ( FIG. 12 ) because the light enters the disc-shaped member from a light pipe of smaller cross-sectional dimension in first rotational position. Therefore, in this way the degree of collimation of the light output from the light output surface can be modified based on rotational position. 
     In some embodiments, the lighting assembly  100 ,  200  is a part of a lighting fixture, a sign, a light bulb (e.g., A-series LED lamp or PAR-type LED lamp), a portable lighting fixture (e.g., a flashlight) or an under-cabinet lighting fixture (e.g., lighting fixture for use under kitchen cabinets). For example, a flashlight with adjustable collimation can be made using lighting assembly  200 . 
     In this disclosure, the phrase “one of” followed by a list is intended to mean the elements of the list in the alterative. For example, “one of A, B and C” means A or B or C. The phrase “at least one of” followed by a list is intended to mean one or more of the elements of the list in the alterative. For example, “at least one of A, B and C” means A or B or C or (A and B) or (A and C) or (B and C) or (A and B and C).