具体实施方式：
[0060]Some of the devices described herein utilize a “back-lit” approach in which one or more LED element(s) are located at least partially within one or more coupling cavities each in the form of a hole or depression in a waveguide body. In the embodiment shown in the figures, the coupling cavity extends fully through the waveguide body, although the coupling cavity may extend only partially through the waveguide body. A plug member disposed at least partially in the coupling cavity or formed integrally with the waveguide body to define the coupling cavity diverts light into the waveguide body. Light extraction features may be disposed in or on one or more surfaces of the waveguide body. A diffuser may be disposed adjacent the waveguide body proximate the plug member(s). In such an arrangement, light emitted by the LED element(s) is efficiently coupled into the waveguide body with a minimum number of bounces off of potentially absorbing surfaces, thus yielding high overall system efficiency. This arrangement also offers additional potential benefits in that multiple LED elements may be placed apart at greater distances, thereby reducing the need for costly and bulky heat sinking elements. Further, this approach is scalable in that the distance that light must travel through the waveguide body may be effectively constant as the luminaire size increases.
[0061]In the back-lit approach described in the immediately preceding paragraph, it is desirable that the proper amount of light is transmitted through each plug member such that the local region on the diffuser aligned with the plug member shows neither a bright nor a dark spot, nor a spot with a color that differs noticeably from the surrounding regions. Because the volume of the plug member is generally small, it is necessary to provide the plug member with a high degree of opacity, which can be achieved by incorporating highly scattering particles that are typically small in diameter in the material of the plug member. However, small particle diameter typically leads to preferential scattering of short wavelength (blue) light. As a result, the light transmitted through the plug member may have a noticeable yellowish tint, which is typically undesirable.
[0062]Further, there exist practical limits on the amount of scattering material that may be incorporated into the plug member. As a result, it may not be possible to achieve sufficient opacity without high absorption using scattering particles that are incorporated into the plug member material. Finally, in regions where the plug member is in contact with the sidewall of the coupling cavity, the index of refraction difference interface at the surface of the cavity may be interrupted, thereby allowing light to transmit from the plug member into the waveguide but not subject to refraction necessary to ensure total TIR within the waveguide.
[0063]Still further, a number of LEDs of the same color together comprising an LED element may be disposed in one or more of the coupling cavities. Alternatively, a number of LEDs not all of the same color and together comprising a multi-color LED element may be used in one or more of the coupling cavities of the luminaire in order to achieve a desired lighting effect, such as a particular color temperature. In the former case, a non-uniform intensity of light may be produced. In the latter case, a multi-color LED element may be subject to non-uniform color distribution at high angles, leading to non-uniformity in the color and intensity of output luminance. A non-uniform color distribution also may result from a multi-color LED element having different color LEDs with varying heights. For example, a multi-color LED element may include one or more red LEDs surrounded by a plurality of blue-shifted yellow LEDs. Each red LED has a height that is less than a height of the surrounding blue-shifted yellow LEDs. The light emitted from the red LED, therefore, is obstructed at least in part by the blue-shifted yellow LED, such that the light emanating from the LED element is not uniform. In addition to height differences, differences in the nature of the red and blue-shifted yellow LEDs affect the way the light is emitted from the respective LED.
[0064]According to an aspect of the present invention, the coupling cavities may have any of a number of geometries defined by surfaces that promote redirection of the light rays (e.g., through refraction) to better mix the light rays developed by the LEDs. Other design features are disclosed herein according to other aspects that promote light mixing and/or color and/or light intensity uniformity. Thus, for example, some embodiments comprehend the use of a thin reflective layer, such as a metal layer, on a portion of each plug member wherein the layer is of appropriate thickness to allow sufficient light to transmit without substantial shift in color.
[0065]Other embodiments relate to the fabrication and surface smoothness of the surface(s) defining the cavity or cavities, change in LED position and/or other modifications to the LED(s) or LED element(s), use of internal TIR features inside the waveguide body, and/or use of one or more masking elements to modify luminance over the surface of the luminaire module.
[0066]Specifically, FIGS. 1 and 2 illustrate a low profile luminaire 30 utilizing one or more back-lit waveguide luminaire portions 32a-32d to spread light uniformly. Each waveguide luminaire portion 32a-32d is joined or secured to other portions 32 by any suitable means, such as a frame 34 including outer frame members 36a-36d and inner frame members 36e-36g that are secured to one another in any suitable manner. One or more of the frame members may be coated with a reflective white or specular coating or other material, such as paper or a scattering film, on surfaces thereof that abut the portions 32. Alternatively, the luminaire portions 32 may abut one another directly, or may be separated from one another by an air gap, an optical index matching coupling gel, or the like. In these latter embodiments, the luminaire portions 32 may be secured together by any suitable apparatus that may extend around all of the portions 32 and/or some or all of the individual portions 32. In any event, the luminaire 30 may comprise a troffer sized to fit within a recess in a dropped ceiling, or may have a different size and may be suspended from a ceiling, either alone or in a fixture or other structure. The luminaire 30 is modular in the sense that any number of luminaire portions 32 may be joined to one another and used together. Also, the size of each luminaire portion 32 may be selected so that the luminaire portions may all be of a small size (e.g., about 6 in by 6 in or smaller), a medium size (e.g., about 1 ft by 1 ft), or a large size (e.g., about 2 ft by 2 ft or larger), or may be of different sizes, as desired. For example, as seen in FIG. 1A, an alternative luminaire 30-1 may have one large luminaire portion 32a-1 of a size of about 2 ft by 2 ft, a medium luminaire portion 32b-1 of a size of about 1 ft by 1 ft, and four small luminaire portions 32c-1 through 32c-4 each of a size of about 6 in by 6 in, wherein the luminaire portions 32 are maintained in assembled relation by a frame 34 comprising frame members 36a-1 through 36a-4 and 36b-1 through 36b-5. (The luminaire portion sizes noted above are approximate in the sense that the frame dimensions are not taken into account.) Any other overall luminaire size and/or shape and/or combinations of luminaire portion size(s), number(s), and relative placement are possible.
[0067]As seen in FIG. 2, each luminaire portion 32 includes a base element in the form of a substrate 52 having a base surface 56. If desired, the base surface 56 may be covered or coated by a reflective material, which may be a white material or a material that exhibits specular reflective characteristics. A light source 60 that may include one or more light emitting diodes (LEDs) is mounted on the base surface 56. The light source 60 may be one or more white or other color LEDs or may comprise multiple LEDs either mounted separately or together on a single substrate or package including a phosphor-coated LED either alone or in combination with at least one color LED, such as a green LED, a yellow or amber LED, a red LED, etc. In those cases where a soft white illumination is to be produced, the light source 60 typically includes one or more blue shifted yellow LEDs and one or more red LEDs. Different color temperatures and appearances could be produced using other LED combinations, as is known in the art. In one embodiment, the light source comprises any LED, for example, an MT-G LED element incorporating TrueWhite® LED technology or as disclosed in U.S. patent application Ser. No. 13/649,067, filed Oct. 10, 2012, entitled “LED Package with Multiple Element Light Source and Encapsulant Having Planar Surfaces” by Lowes et al., (Cree docket no. P1912US1-7), the disclosure of which is hereby incorporated by reference herein, both as developed by Cree, Inc., the assignee of the present application. In any of the embodiments disclosed herein the LED(s) have a particular emission distribution, as necessary or desirable. For example, a side emitting LED disclosed in U.S. Pat. No. 8,541,795, the disclosure of which is incorporated by reference herein, may be utilized inside the waveguide body. More generally, any lambertian, symmetric, wide angle, preferential-sided, or asymmetric beam pattern LED(s) may be used as the light source.
[0068]The light source 60 is operated by control circuitry (not shown) in the form of a driver circuit that receives AC or DC power. The control circuitry may be disposed on the substrate 52 or may be located remotely, or a portion of the control circuitry may be disposed on the substrate and the remainder of the control circuitry may be remotely located. In any event, the control circuitry is designed to operate the light source 60 with AC or DC power in a desired fashion to produce light of a desired intensity and appearance. If necessary or desirable, a heat exchanger (not shown) is arranged to dissipate heat and eliminate thermal crosstalk between the LEDs and the control circuitry. Preferably, the light source 60 develops light appropriate for general illumination purposes including light similar or identical to that provided by an incandescent, halogen, or other lamp that may be incorporated in a down light, a light that produces a wall washing effect, a task light, a troffer, or the like.
[0069]A waveguide 70 has a main body of material 71 (FIG. 2), which, in the illustrated embodiment, has a width and length substantially greater than an overall thickness d thereof and, in the illustrated embodiment, is substantially or completely rectangular or any other shape in a dimension transverse to the width and thickness (FIG. 1). Preferably, the thickness d may be at least about 500 microns, and more preferably is between about 500 microns and about 10 mm, and is most preferably between about 3 mm and about 5 mm. The waveguide body 71 may be made of any suitable optical grade material including one or more of acrylic, air, molded silicone, polycarbonate, glass, and/or cyclic olefin copolymers, and combinations thereof, particularly (although not necessarily) in a layered arrangement to achieve a desired effect and/or appearance.
[0070]In the illustrated embodiment, the waveguide body 71 has a constant thickness over the width and length thereof, although the body 71 may be tapered linearly or otherwise over the length and/or width such that the waveguide body 71 is thinner at one or more edges than at a central portion thereof. The waveguide body 71 further includes a first or outer side or surface 71a, a second opposite inner side or surface 71b, and an interior coupling cavity 76. The interior coupling cavity 76 is defined by a surface 77 that, in the illustrated embodiment, extends partially or fully through the waveguide 70 from the first side toward the second side. Also in some of the illustrated embodiments, the surface 77 defining the cavity 76 is preferably (although not necessarily) normal to the first and second sides 71a, 71b of the waveguide 70 and the cavity 76 is preferably, although not necessarily, centrally located with an outer surface of the main body of material 71. In some or all of the embodiments disclosed herein, the surface 77 (and, optionally, the surfaces defining alternate cavities described herein) is preferably polished and optically smooth. Also preferably, the light source 60 extends into the cavity 76 from the first side thereof. Still further in the illustrated embodiment, a light diverter of any suitable shape and design, such as a conical plug member 78, extends into the cavity 76 from the second side thereof. Referring to FIGS. 2-4, in a first embodiment, the surface 77 is circular cylindrical in shape and the conical plug member 78 includes a first portion 80 that conforms at least substantially, if not completely, to the surface 77 (i.e., the first portion 80 is also circular cylindrical in shape) and the first portion 80 is secured by any suitable means, such as, an interference or press fit or an adhesive, to the surface 77 such that a second or conical portion 82 of the plug member 78 extends into the cavity 76. Preferably, although not necessarily, the conformance of the outer surface of the first portion 80 to the surface 77 is such that no substantial gaps exist between the two surfaces where the surfaces are coextensive. Still further, if desired, the conical plug member 78 may be integral with the waveguide body 71 rather than being separate therefrom. Further, the light source 60 may be integral with or encased within the waveguide body 71, if desired. In the illustrated embodiment, the first portion 80 preferably has a diameter of at least 500 um, and more preferably between about 1 mm and about 20 mm, and most preferably about 3 mm. Further in the illustrated embodiment, the first portion 80 has a height normal to the diameter of at least about 100 um, and more preferably between about 500 um and about 5 mm, and most preferably about 1 mm. Still further in the illustrated embodiment, the second portion 82 forms an angle relative to the portion 80 of at least about 0 degrees, and more preferably between about 15 degrees and about 60 degrees, and most preferably about 20 degrees. The plug member 78 may be made of white polycarbonate or any other suitable transparent or translucent material, such as acrylic, molded silicone, polytetrafluoroethylene (PTFE), Delrin® acetyl resin, or any other suitable material. The material of the plug member 78 may be the same as or different than the material of the waveguide body 71.
[0071]In all of the embodiments disclosed herein, one or more pluralities of light extraction features or elements 88 may be associated with the waveguide body 71. For example one or more light extraction features 88 may be disposed in one or both sides or faces 71a, 71b of the waveguide body 71. Each light extraction feature 88 comprises a wedge-shaped facet or other planar or non-planar feature (e.g., a curved surface such as a hemisphere) that is formed by any suitable process, such as embossing, cold rolling, or the like, as disclosed in U.S. patent application Ser. No. 13/842,521. Preferably, in all of the embodiments disclosed herein the extraction features are disposed in an array such that the extraction features 88 are disposed at a first density proximate the cavity and gradually increase in density or size with distance from the light source 60, as seen in U.S. patent application Ser. No. 13/842,521. In any of the embodiments disclosed herein, as seen in FIGS. 3A and 3B, the extraction features may be similar or identical to one another in shape, size, and/or pitch (i.e., the spacing may be regular or irregular), or may be different from one another in any one or more of these parameters, as desired. The features may comprise indents, depressions, or holes extending into the waveguide, or bumps or facets or steps that rise above the surface of the waveguide, or a combination of both bumps and depressions. Features of the same size may be used, with the density of features increasing with distance from the source, or the density of features may be constant, with the size of the feature increasing with distance from the source and coupling cavity. For example, where the density of the extraction features is constant with the spacing between features of about 500 microns, and each extraction feature comprises a hemisphere, the diameter of the hemisphere may be no greater than about 1 mm, more preferably no greater than about 750 microns, and most preferably no greater than about 100 microns. Where each extraction feature comprises a shape other than a hemisphere, preferably the greatest dimension (i.e., the overall dimension) of each feature does not exceed about 1 mm, and more preferably does not exceed about 750 microns, and most preferably does not exceed about 100 microns. Also, the waveguide body 71 may have a uniform or non-uniform thickness. Irrespective of whether the thickness of the waveguide body 71 is uniform or non-uniform, a ratio of extraction feature depth to waveguide body thickness is preferably between about 1:10,000 and about 1:2, with ratios between about 1:10,000 and about 1:10 being more preferred, and ratios between about 1:1000 and about 1:5 being most preferred.
[0072]It should also be noted that the extraction features may be of differing size, shape, and/or spacing over the surface(s) of the waveguide body so that an asymmetric emitted light distribution is obtained. For example, FIG. 3C illustrates an arrangement wherein a relatively large number of extraction features 88a are disposed to the left of the coupling cavity 76 and a relatively small number of extraction features 88b are disposed to the right of the coupling cavity 76. As should be evident, more light is extracted from the left side of the waveguide body 71 and relatively less light is extracted from the right side of the waveguide body 71.
[0073]In all of the embodiments disclosed herein, the waveguide body may be curved, thereby obviating the need for some or all of the extraction features. Further, a diffuser 90 (FIG. 2) is preferably (although not necessarily) disposed adjacent the side 71a of the waveguide body 71 and is retained in position by any suitable means (not shown).
[0074]In the first embodiment, and, optionally, in other embodiments disclosed herein, the second portion 82 of the plug member 78 is coated with a reflecting material using any suitable application methodology, such as a vapor deposition process. Preferably, a thin reflective layer, such as a metal layer of particles, of appropriate layer thickness is uniformly disposed on the conical portion 82 to allow sufficient light to transmit through the plug member 78 so that development of a visually observable spot (either too bright or too dark or color shifted with respect to surrounding regions) is minimized at an outer surface of the diffuser 90 adjacent the plug member 78. In the preferred embodiment the metal layer comprises aluminum or silver. In the case of silver, the reflective layer preferably has a thickness of no greater than about 100 nm, and more preferably has a thickness between about 10 nm and about 70 nm, and most preferably has a thickness of about 50 nm. In the case of aluminum, the reflective layer preferably has a thickness of no greater than about 100 nm, and more preferably has a thickness between about 10 nm and about 50 nm, and most preferably has a thickness of about 30 nm.
[0075]In any of the embodiments disclosed herein the second portion 82 of the plug member 78 may be non-conical and may have a substantially flat shape, a segmented shape, a tapered shape, an inclined shape to direct light out a particular side of the waveguide body 71, etc.
[0076]In alternate embodiments, as seen in FIGS. 6-16, the plug member 78 has a first portion of any other suitable noncircular shape, including a symmetric or asymmetric shape, as desired, and a second portion preferably (although not necessarily) of conical shape as noted above. The coupling cavity may also (although it need not) have a noncircular shape or the shape may be circular where the first portion 80 is disposed and secured (in which case the first portion 80 is circular cylindrical) and the shape of the coupling cavity may be noncircular in other portions (i.e., at locations remote from the first portion 80).
[0077]Specifically referring to FIGS. 6 and 7, a first alternative cavity 100 is illustrated in a waveguide body 71 wherein the cavity 100 is defined by four surfaces 102a-102d. Preferably, the four surfaces 102 are normal to the upper and lower sides 71a, 71b and together define a quadrilateral shape, most preferably, a square shape in elevation as seen in FIG. 6. Each of the surfaces 102 preferably has a side-to-side extent (as seen in FIG. 6) of no less than about 500 um, and more preferably between about 1 mm and 20 mm, depending upon the size of the LED element. The LED light source 60 is disposed in the cavity 100, similar or identical to the embodiment of FIG. 3. A plug member 104 includes a first portion 106 that conforms at least substantially, if not fully, as described in connection with the embodiment of FIG. 3, to the preferably square shape defined by the surfaces 102. Each of the surfaces defining the first portion 106 has a height of no less than about 100 um, and more preferably between about 500 um and 5 mm, and most preferably about 1 mm. The plug member 104 further includes a conical second portion 108 similar or identical to the portion 82 of FIG. 3 both in shape and dimensions. The plug member 104 is otherwise identical to the plug member 78 and, in all of the embodiments disclosed in FIGS. 6-18, the second portion 108 may be coated with the metal layer as described in connection with the plug member 78. The first portion 106 is disposed and retained within the cavity 100 in any suitable manner or may be integral therewith such that the second portion 108 is disposed in the cavity 100 facing the light source 60, as in the embodiment of FIG. 3. Preferably, the surfaces 102 are disposed at 45 degree angles with respect to edges or sides 114a, 114b, 114c, and 114d, respectively, of an LED element 114 comprising the light source 60. Referring to FIG. 5, the illustrated LED element 114 comprises six blue-shifted yellow LEDs 118a-118f disposed in two rows of three LEDs located adjacent the edges or sides 114a, 114c. Three red LEDs 120a-120c are disposed in a single row between the two rows of blue-shifted LEDs 118. (The embodiments of FIGS. 6-18 are illustrated with the LED 114 element disposed in the same orientation as that illustrated in FIG. 6). The light from the LEDs 118 and 120 is mixed by the interaction of the light rays with the index of refraction interface at the surfaces 102 so that the ability to discern separate light sources is minimized.
[0078]FIGS. 8-10 illustrate embodiments wherein a star-shaped cavity 130 is formed in the waveguide body 71 and a star shaped plug member 132 is retained within the star shaped cavity. Thus, for example, FIG. 8 a star-shaped cavity 130-1 having eight equally spaced points 130a-130h is formed in the waveguide body 71 such that points 130a, 130c, 130e, and 130g are aligned with the sides 114a, 114b, 114c, and 114d, respectively, of the LED element 114. FIG. 10 illustrates a cavity 130-2 identical to the cavity 130-1 of FIG. 8 except that the cavity 130-2 is rotated 22.5 degrees counter-clockwise relative to the cavity 130-1. In both of the embodiments of FIGS. 8-10 the plug member 132 includes a first portion 134 that substantially or completely conforms to the walls defining the cavity 130. In this embodiment, the cavity 130 and plug member 132 have sharp points.
[0079]FIGS. 11-13 illustrate embodiments identical to FIGS. 8-10 with the exception that eight-pointed cavities 150-1 and 150-2 and plug member 152 have rounded or filleted points. Preferably, each fillet has a radius of curvature between about 0.1 mm and about 0.4 mm, and more preferably has a radius of curvature between about 0.2 mm and 0.3 mm, and most preferably has a radius of curvature of about 0.25 mm.
[0080]Of course, any of the embodiments disclosed herein may have a different number of points, whether sharp pointed or rounded, or a combination of the two. FIGS. 14-16 illustrate embodiments of cavities 170, 190 (and corresponding first portions of associated plug members) having relatively large numbers of points (16 points in FIG. 14, 32 points in FIGS. 15 and 16) of different shapes and sizes. In these alternative embodiments, the star shaped coupling cavity includes a first plurality of points 172 (FIG. 14) and a second plurality of points 174, and the first plurality of points 172 have a different shape than the second plurality of points 174. Thus, the coupling cavity is defined by a first set of surfaces 176a-176d (defining the first plurality of points 172) that direct a first distribution of light into the waveguide body and a second set of surfaces 178a-178d (defining the second plurality of points 174) that direct a second distribution of light different than the first distribution of light into the waveguide body. In these embodiments, the angles of the surfaces with respect to the central axis impact the luminance uniformity and color mixing of the light emitted from the light source. In particular, light uniformity and color mixing improve as the angled surface(s) of the coupling cavity become increasingly parallel with light rays (within Fresnel scattering angular limits, as should be evident to one of ordinary skill in the art), thus maximizing the angle of refraction, and hence light redirection, as the rays traverse the interface between the low index of refraction medium (air) and the higher index of refraction medium (the waveguide). While light uniformity and color mixing may be enhanced using complex shapes, such benefit must be weighed against the difficulty of producing such shapes.
[0081]In each of the embodiments of FIGS. 8, 10, 11 and 13-16, each cavity may have radially maximum size (i.e., the distance between a center or centroid (in the case of noncircular coupling cavity shapes) of the cavity and an outermost portion of the surface(s) defining the cavity) of at least about 100 um, and more preferably between about 1 mm and no more than about 50 mm, and most preferably between about 3 mm and about 20 mm. Further, each cavity may have radially minimum size (i.e., the distance between a center or centroid of the cavity and an innermost portion of the surface(s) defining the cavity) of at least about 100 um, and more preferably between about 1 mm and about 50 mm, and most preferably between about 3 mm and about 20 mm. (The term “centroid” as used herein is defined as the center of gravity of an imaginary mass of constant thickness and uniform density fully occupying the coupling cavity.)
[0082]The first and second portions of the plug members of FIGS. 9 and 12 (and plug members that may be used with FIGS. 14 and 15) may be identical to the plug members described previously, with the exception of the outside shape of the first portion, as should be evident.
[0083]Ray fan and full simulation analyses of the embodiments shown in FIGS. 6-16 were performed to compare color mixing, luminance, and efficiency of waveguides having various shapes of coupling cavities with the design shown in FIGS. 2-4. Ray fan simulations of LED elements within various-shaped coupling cavities demonstrated the color mixing of light rays emitted horizontally from the LED into the waveguide. Full simulations of LED elements within various shaped coupling cavities demonstrated the color mixing, luminance, and efficiency of light rays emitted from the LED into the waveguide having extraction features. LightTools 8.0 by Synopsys was utilized to perform the simulations, although other software known in the art, such as Optis by Optis or Radiant Zemax by Zemax, may be used.
[0084]It should be noted that the coupling cavity may have an asymmetric shape, if desired. FIG. 16A illustrates a triangular coupling cavity 179 defined by three coupling features 179a-179c that extend at least partially between upper and lower surfaces of a waveguide body 180. The cavity 179 has an asymmetric triangular shape with respect to a centroid 181. Although not shown, one or more LEDs and a light diverter extend into the coupling cavity 179 as in the other embodiments disclosed herein.
[0085]In embodiments disclosed herein, a coupling cavity is defined by one or more coupling features that extend between the first and second faces wherein at least one of the coupling features extends into the waveguide body to a lateral extent transverse to a depth dimension greater than a lateral extent to which another of the waveguide features extends into the waveguide body. Thus, for example, as seen in FIG. 16A, the coupling feature 179a includes at least one portion 179a-1 that is disposed to a greater extent farther into the waveguide body 180 than portions 179c-1 and 179c-2 of the feature 179c. The same is true of other embodiments. Further, where the coupling surfaces do not extend fully through the waveguide body, the resulting blind cavity may have one or more shaped cavity base surface(s) or a planar cavity base surface and the cavity base surface(s) may (but need not) be coated with a reflective and/or partially light transmissive material, if desired.
[0086]Referring next to FIGS. 17 and 18, the placement of LEDs on the substrate can be modified to enhance color mixing. FIG. 17 illustrates an embodiment in which the red LEDs 120 are reduced in number to two LEDs 120a, 120b. FIG. 18 illustrates an embodiment wherein the blue shifted yellow LEDs 118 comprise first and second single LEDs 118a, 118c disposed adjacent the edges or sides 114a, 114c and first and second pairs of LEDs 118b1, 118b2 and 118d1, 118d2, adjacent the sides 114b, 114d, respectively. Two red LEDs 120a, 120b are disposed between the LEDs 118 remote from the edges or sides 114. FIG. 18A illustrates an embodiment in which the LEDs 118, 120 are disposed in a checkerboard pattern with the red LEDs 120 being disposed between the blue-shifted LEDs 118.
[0087]In addition to the foregoing, the shape or other characteristic of any optics in the path of light may be varied. More particularly, a modified primary or secondary lens 192 (FIG. 32) may be used in conjunction with the LED light source 60 to further improve the luminance and/or color uniformity of the light emitted from the surface of the waveguide. In any embodiment, the primary LED light source lens may be varied and optimized to use refraction or scattering to direct light into preferred directions prior to entering the coupling cavity, thereby improving uniformity. The orientation and/or shape of the LED element relative to the surface(s) defining the coupling cavity may also be varied and optimized to improve light mixing. The lens 192 and/or any of the waveguides disclosed herein may be formed with one or more materials in accordance with the teachings of either U.S. patent application Ser. No. 13/843,928, filed Mar. 15, 2013, entitled “Multi-Layer Polymeric Lens and Unitary Optic Member for LED Light Fixtures and Method of Manufacture” by Craig Raleigh et al., (Cree docket no. P1988US1), or U.S. patent application Ser. No. 13/843,649, filed Mar. 15, 2013, entitled “One-Piece Multi-Lens Optical Member and Method of Manufacture” by Craig Raleigh et al., (Cree docket no. P2026US1), the disclosures of which are hereby incorporated by reference herein. If desired, a scatterer, which may be effectuated by scattering particles coated on or formed within the lens 192, may be provided to further mix the light developed by the LEDs.
[0088]Non-uniform illuminance by the luminaire 30 may be addressed by securing a masking element 210 to the diffuser 90 to obscure bright spots, as seen in FIGS. 19 and 20. The masking element 210 may have any desired shape, may comprise single or multiple sub-elements, and/or may be translucent or opaque. The masking element may be made of any desired material, and should minimize the absorption of light.
[0089]In the illustrated embodiment, the light emitted out the waveguide body is mixed such that point sources of l