Patent Publication Number: US-2022229221-A1

Title: Edge-lit light panel

Description:
CROSS REFERENCE TO RELATED APPLICATION(S) 
     This application claims the benefit of U.S. Provisional Application No. 62/846,221, filed May 10, 2019, and U.S. Provisional Application No. 63/021,716, filed May 8, 2020, which are incorporated by reference as if disclosed herein in their entireties. 
    
    
     FIELD 
     The present disclosure relates to a light panel, in particular to, an edge-lit light panel. 
     BACKGROUND 
     Back-lit light panels work by placing light sources (e.g., light emitting diodes (LEDs)) at the back of the panel. The light panel is configured to project light forward across the full expanse of the light panel from the front. The thickness of back-lit light panels includes the light sources, the panel and a distance between the light sources and the panel. The distance between the light sources and the panel is configured to enable an overall uniform and bright illumination of the entire lamp. In order to achieve an even light distribution, the back-lit panel light may typically have a thickness of about 30 mm in a direction perpendicular to the light panel. 
     For edge-lit light panels, the light sources are positioned at the side (i.e., edge) of the panel with light beaming into a light transmitting/guiding medium that re-directs the light to the viewing/extraction surface. Edge-lit LED panel lights are generally thinner than the back-lit lights because the LEDs used in them are placed at the edge of the panel and rather than at the back. However, edge-lit light panels may use relatively more energy compared to back-lit light panels for a same light intensity output. Such relative energy inefficiency may occur when transmitted light is lost between a light source and the panel (light coupling loss) or lost within the panel itself (light extraction loss). 
     SUMMARY 
     In some embodiments, there is provided a light guide for an edge-lit light panel. The light guide includes a first light coupling surface; a second light coupling surface opposing the first light coupling surface; a first light output surface; and a second light output surface opposing the first light output surface. The first light output surface and the second light output surface are coupled between the first light coupling surface and the second light coupling surface. Each light coupling surface is configured to receive incident light from a respective light source and to produce at least a portion of a batwing light beam inside the light guide. The at least a portion of the batwing light beam is concentrated adjacent the first light output surface. The first light output surface corresponds to a first light extraction surface. 
     In some embodiments of the light guide, each light coupling surface includes at least one leg of a V groove. 
     In some embodiments of the light guide, the first light extraction surface includes a light extraction feature selected from the group comprising prismatic, spherical, cylindrical, conical and asymmetric. 
     In some embodiments of the light guide, the first light extraction surface comprises a plurality of prismatic features having a separation, S, pitch, P and angle, μ. 
     In some embodiments of the light guide, each light coupling surface corresponds to a V groove and each V groove has an angle ω with a maximum value of arctan (L/H), where L corresponds to a length of the light guide and H corresponds to a height of the light guide. 
     In some embodiments of the light guide, the second light output surface corresponds to a second light extraction surface and each coupling surface is configured to produce a batwing light beam inside the light guide. In some embodiments of the light guide, the second light output surface corresponds to a reflective surface. 
     In some embodiments, there is provided an edge-lit light panel. The edge-lit light panel includes a plurality of light guides; and a plurality of light sources. Each light guide includes a first light coupling surface positioned relative to a first edge of the edge-lit light panel, a second light coupling surface opposing the first light coupling surface and positioned relative to a second edge of the edge-lit light panel. The second edge opposes the first edge. Each light guide further includes a first light output surface, and a second light output surface opposing the first light output surface. The first light output surface and the second light output surface are coupled between the first light coupling surface and the second light coupling surface. Each light coupling surface is configured to receive incident light from a respective light source and to produce at least a portion of a batwing light beam inside the light guide. The at least a portion of the batwing light beam is concentrated adjacent the first light output surface. The first light output surface corresponds to a first light extraction surface. 
     In some embodiments, the edge-lit light panel further includes a plurality of light source reflectors. Each light source reflector is positioned relative to a respective light source and is configured to reflect the emitted light from the light source onto the corresponding coupling surface of the light guide. 
     In some embodiments, the edge-lit light panel further includes a diffuse reflector positioned relative to the first light output surface or the second light output surface. 
     In some embodiments of the edge-lit light panel, each light coupling surface includes at least one leg of a V groove. 
     In some embodiments of the edge-lit light panel, the first light extraction surface includes a light extraction feature selected from the group comprising prismatic, spherical, cylindrical, conical and asymmetric. 
     In some embodiments of the edge-lit light panel, the first light extraction surface comprises a plurality of prismatic features having a separation, S, pitch, P and angle, μ. 
     In some embodiments of the edge-lit light panel, the second light output surface corresponds to a second light extraction surface and each coupling surface is configured to produce a batwing light beam inside the light guide. 
     In some embodiments of the edge-lit light panel, each of the plurality of light sources is a light emitting diode (LED). 
     In some embodiments, there is provided a lighting system. The lighting system includes a light source controller; an edge-lit light panel; and a plurality of light source drivers. The edge-lit light panel includes a plurality of light guides, and a plurality of light sources. Each light source driver is configured to drive a respective light source based, at least in part, on a signal from the light source controller. Each light guide includes a first light coupling surface positioned relative to a first edge of the edge-lit light panel, and a second light coupling surface opposing the first light coupling surface and positioned relative to a second edge of the edge-lit light panel. The second edge opposes the first edge. Each light guide further includes a first light output surface, and a second light output surface opposing the first light output surface. The first light output surface and the second light output surface are coupled between the first light coupling surface and the second light coupling surface. Each light coupling surface is configured to receive incident light from a respective light source and to produce at least a portion of a batwing light beam inside the light guide. The at least a portion of the batwing light beam concentrated adjacent the first light output surface, the first light output surface corresponding to a first light extraction surface. 
     In some embodiments of the lighting system, the edge-lit light panel further includes a diffuse reflector positioned relative to the first light output surface or the second light output surface. 
     In some embodiments of the lighting system, each light coupling surface includes at least one leg of a V groove. 
     In some embodiments of the lighting system, the first light extraction surface includes a light extraction feature selected from the group comprising prismatic, spherical, cylindrical, conical and asymmetric. 
     In some embodiments of the lighting system, each of the plurality of light sources is a light emitting diode (LED). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings show embodiments of the disclosed subject matter for the purpose of illustrating features and advantages of the disclosed subject matter. However, it should be understood that the present application is not limited to the precise arrangements and instrumentalities shown in the drawings, wherein: 
         FIG. 1A  is a functional block diagram of a lighting system including an edge-lit light panel, consistent with several embodiments of the present disclosure; 
         FIG. 1B  is a sketch of an edge-lit light panel, consistent with several embodiments of the present disclosure; 
         FIG. 1C  is a sketch illustrating a batwing shaped light beam in a light guide, consistent with several embodiments of the present disclosure; 
         FIG. 1D  is a sketch illustrating a wedge shaped coupling surface and a corresponding portion of a batwing light beam in a light guide, consistent with several embodiments of the present disclosure; 
         FIGS. 2A through 2D  are sketches of cross sections of various example edge-lit light panels corresponding to  FIGS. 1A and 1B ; and 
         FIGS. 3A through 3J  are sketches of cross sections of various example first light output surfaces, illustrating various light extraction feature geometries. 
     
    
    
     DETAILED DESCRIPTION 
     Generally, this disclosure relates to an edge-lit light panel. The edge-lit light panel is configured to provide relatively efficient light coupling between a light source and a corresponding light guide and relatively efficient light extraction between the light guide and a light output. In one example, the edge-lit light panel may be used in a display (e.g., backlit). In another example, the edge-lit light panel may correspond to or be utilized in a lighting luminaire. The light source and light guide are configured to produce at least a portion of a batwing shaped light beam within the light guide with the light intensity concentrated at or near at least one light output surface. In other words, a light source and a light guide consistent with the present disclosure may be configured to provide relatively higher flux density and illuminance uniformity at a light output surface (i.e., a light extraction surface) and may thus provide improved extraction efficiency and panel luminance uniformity. A light extraction surface may include at least one light extraction feature configured to facilitate light extraction efficiency and/or creation of an output beam shape. 
     The edge-lit light panel includes a plurality of light guides and a plurality of light sources positioned along an edge of the edge-lit light panel. Each light guide has a first end and an opposing second end with each end corresponding to a respective light coupling surface. Each light guide may have a generally rectangular (e.g., square) cross section oriented generally perpendicular to a line drawn between the first and second ends. Thus, each light guide may have four generally perpendicular sides coupled between the first end and the second end. A first side and an opposing second side correspond to respective light output surfaces. At least one light output surface corresponds to a light extraction surface configured to emit light. A third side and an opposing fourth side may be configured to couple (e.g., touch) to adjacent light guides or a side of the edge-lit light panel. 
     In an embodiment, there is provided a light guide for an edge-lit light panel. The light guide includes a first light coupling surface; a second light coupling surface; a first light output surface; and a second light output surface. The second light coupling surface opposes the first light coupling surface. The second light output surface opposes the first light output surface. The first light output surface and the second light output surface are coupled between the first light coupling surface and the second light coupling surface. Each light coupling surface is configured to receive incident light from a respective light source. In one example, the light coupling surface may be configured receive a Lambertian light beam and to produce at least a portion of a batwing light beam inside the light guide. In another example, the light source may include or be coupled to secondary optics configured to produce at least a portion of a batwing light beam inside the light guide. The at least a portion of a batwing light beam is concentrated adjacent the first light output surface. The batwing light beam is configured to facilitate light extraction efficiency. 
     Luminaire (e.g., edge-lit light panel) efficiency (η luminaire ) corresponds to a ratio of light output (i.e., luminous flux, φ) from the light guide to light output from the source, i.e., η luminaire =φ out /φ src . Luminaire efficiency is related to light coupling efficiency (η LC ) and light extraction efficiency (η LE ). Light coupling efficiency corresponds to a ratio of luminous flux (φ in ) in the light guide to luminous flux (φ src ) emitted from the light source (η LC =φ in /φ src ). Light extraction efficiency, η LE , is a ratio of luminous flux (φ out ) output from the light guide to the luminous flux in the light guide (η LE =φ out /φ in ). Thus, luminaire efficiency corresponds to a product of the light coupling efficiency and light extraction efficiency. 
     It may be appreciated that a relatively higher flux density (i.e., concentration) relatively close to a light output surface may improve extraction efficiency. A batwing shaped input beam may have a relatively higher percentage of light concentrated at a light output surface compared to, for example, a Lambertian input beam. A batwing input beam may have a better illuminance uniformity along the light guide compared to the Lambertian input beam. In an embodiment, a V groove shaped coupling surface that receives an Lambertian source beam is configured to produce a batwing shaped light beam within the light guide. For a rectangular light guide having opposing extraction surfaces, the V groove may be defined by an angle, ω, between a leg of the V groove and a line perpendicular to the extraction surfaces. As the angle, ω, is increased towards its limit, ω max =arctan L/H, where L is a length and H is a height of the light guide, the total light redirected efficiency may increase. In another embodiment, a coupling surface corresponding to one leg of a V groove (i.e., a wedge-shaped coupling surface) may be configured to produce a portion of a batwing shaped light beam within a light guide adjacent an output surface. 
     Light extraction efficiency may be facilitated through a light extraction feature of at least one light output surface of a light guide. The light extraction feature may be further configured to provide a selected extracted beam pattern (e.g., batwing). In an embodiment, the light extraction feature may be geometric and may be configured to provide total internal reflection over a portion of the light extraction surface. 
       FIG. 1A  is a functional block diagram  100  of a lighting system including an edge-lit light panel  102 , consistent with several embodiments of the present disclosure. Lighting system  100  includes the edge-lit light panel  102 , a light source controller  104 , a power source  106 , and a plurality of light source drivers  108 - 1 , . . .  108 -Q. Edge-lit light panel  102  includes a plurality of light sources  110 - 1 , . . .  110 -N. Edge-lit light panel  102  further includes a plurality of light guides  112 - 1 , . . . ,  112 -M. In one nonlimiting example, a number of light sources  110 - 1 , . . .  110 -N may be twice a number of light guides  112 - 1 , . . . ,  112 -M. 
     Power source  106  is configured to provide power to the plurality of light source drivers  108 - 1 , . . . ,  108 -Q, under control of light source controller  104 . Light source controller  104  may be further configured to control the plurality of light source drivers  108 - 1 , . . . ,  108 -Q, and to thus control power to light sources  110 - 1 , . . . ,  110 -M. Power source  106  may include, but is not limited to, a power supply, a battery, a DC to DC converter, etc. Light source controller  104  may include, but is not limited to, a microcontroller, an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), a programmable logic device (PLD), etc. Light source drivers  108 - 1 , . . . ,  108 -Q may include, but are not limited to, switches, transistors, diodes, etc. Light sources  110 - 1 , . . . ,  110 -M may include, but are not limited to, light emitting diodes (LEDs), incandescent bulbs, fluorescent bulbs, etc. 
     Thus, edge-lit light panel  102  may be configured to receive power from the power source  106  via light source drivers  108 - 1 , . . . ,  108 -Q under the control of light source controller  104 . Edge-lit light panel  102  may then be configured to provide illumination. A light output of the edge-lit light panel  102  is related to features of light guides  112 - 1 , . . . ,  112 -M, as will be described in more detail below. 
       FIG. 1B  is a sketch of an edge-lit light panel  120 , consistent with several embodiments of the present disclosure. Edge-lit light panel  120  is one example of edge-lit light panel  102  of  FIG. 1A . Edge-lit light panel  120  includes a plurality of light guides  122 - 1 , . . . ,  122 -M and a plurality of light sources  125 - 1 , . . . ,  125 -M. The light guides are formed of a transparent material. In one nonlimiting example, the light guides may be formed of PMMA (poly(methyl methacrylate)). However, this disclosure is not limited in this regard. The plurality of light guides  122 - 1 , . . . ,  122 -M are positioned adjacent each other to form the edge-lit light panel  120 . Each light guide, e.g., light guide  122 - 1  has a height, H, a width, W, and a length, L. Thus, the edge-lit light panel  120  that may include a number, M, light guides, has an overall width of M*W, a height, H, and a length, L. The edge-lit light panel  120  may have a generally rectangular shape. 
     Each light guide  122 - 1 , . . . ,  122 -M has a respective first light output surface  132 - 1 , . . . ,  132 -M and an opposing respective second light output surface  134 - 1 , . . . ,  134 -M. The plurality of first light output surfaces  132 - 1 , . . . ,  132 -M together may form a first light output surface of the edge-lit light panel  120 . Each light output surface  132 - 1 , . . . ,  132 -M may then correspond to a light extraction surface. Each light guide  122 - 1 , . . . ,  122 -M has a respective first coupling surface  124 - 1 , . . . ,  124 -M. Each light source  125 - 1 , . . . ,  125 -M is positioned relative to a respective first coupling surface  124 - 1 , . . . ,  124 -M. Each coupling surface  124 - 1 , . . . ,  124 -M is configured to receive incident light from its respective light source  125 - 1 , . . . ,  125 -M, and is configured to produce at least a portion of a batwing light beam within the respective light guide  122 - 1 , . . . ,  122 -M. Each at least a portion of a batwing may be positioned adjacent each respective light output surface  132 - 1 , . . . ,  132 -M. 
       FIG. 1C  is a sketch  140  illustrating a batwing shaped light beam in a light guide, consistent with several embodiments of the present disclosure. Sketch  140  corresponds to cross section A-A′ of  FIG. 1B  and includes a light guide  142  and a light source  145 . Light guide  142  includes a first coupling surface  144  configured to receive incident light from the light source  145 . Light guide  142  further includes a first light output surface  152 - 1  and a second light output surface  152 - 2 , opposing the first light output surface  152 - 1 . Sketch  140  further includes a cross section of a batwing shaped light beam having a first portion  146 - 1  of the batwing and a second portion  146 - 2  of the batwing. The first batwing portion  146 - 1  of the light beam is positioned adjacent the first light output surface  152 - 1  and the second batwing portion  146 - 2  of the light beam is positioned adjacent the second light output surface  152 - 2 . Thus, the batwing light beam  146 - 1 ,  146 - 2  in the light guide  142  is concentrated generally near light output surfaces  152 - 1 ,  152 - 2 . The light output surfaces  152 - 1 ,  152 - 2  may thus correspond to light extraction surfaces. The batwing light beam  146 - 1 ,  146 - 2  may be formed by a feature of the first coupling surface  144  and/or of the light source  145 . The batwing light beam may facilitate luminaire efficiency and uniform illumination. 
       FIG. 1D  is a sketch  160  illustrating a wedge shaped coupling surface and a corresponding portion of a batwing light beam in a light guide, consistent with several embodiments of the present disclosure. The wedge shaped coupling surface may correspond to one leg of a V groove, as described herein. Sketch  160  corresponds to cross section A-A′ of  FIG. 1B  and includes a light guide  162  and a light source  165 . Light guide  162  includes a first coupling surface  164  configured to receive incident light from the light source  165 . Light guide  162  further includes a first light output surface  172 - 1  and a second light output surface  172 - 2  opposing the first light output surface  172 - 1 . The coupling surface  164  is at an angle, ω, with respect to a normal (i.e. perpendicular line) to the first output surface  172 - 1 . The coupling surface  164  may thus have a wedge shape and may correspond to one leg of a V groove, as described herein. Sketch  160  further includes a cross section of a portion  166 - 1  of a batwing shaped light beam. The batwing portion  166 - 1  of the light beam is positioned adjacent the first light output surface  172 - 1 . The batwing light beam portion  166 - 1  in the light guide  162  is concentrated generally near the first output surface  172 - 1 . Thus, first light output surface  172 - 1  corresponds to a light extraction surface and may be configured to emit light. The batwing light beam portion  166 - 1  may be formed by a feature of the first coupling surface  164  and/or of the light source  165 . The batwing light beam portion geometry and efficiency may facilitate luminaire efficiency and uniform illumination. 
       FIGS. 2A through 2D  are sketches  200 ,  220 ,  240 ,  260  of cross sections A-A′ of various example edge-lit light panels corresponding to the edge-lit light panels of  FIGS. 1A and 1B . In  FIGS. 2A through 2D , like elements have like reference designators. Turning first to  FIG. 2A , example edge-lit light panel  200  includes a light guide  202 , two light sources,  204 - 1 ,  204 - 2 , and two light source reflectors  206 - 1 ,  206 - 2 . In some embodiments, edge-lit light panel  200  may include a diffuse reflector  208 . Each light source  204 - 1 ,  204 - 2  has a corresponding emission surface  205 - 1 ,  205 - 2 . Each emission surface  205 - 1 ,  205 - 2  faces the respective light source reflector  206 - 1 ,  206 - 2 . In other words, each emission surface  205 - 1 ,  205 - 2  faces away from the light guide  202 . 
     Example light guide  202  includes a first light coupling surface  210 - 1  and a second light coupling surface  210 - 2  opposing the first light coupling surface  210 - 1 . Light guide  202  further includes a first light output surface  212 - 1  and a second light output surface  212 - 2  opposing the first light output surface  212 - 1 . The first light output surface  212 - 1  and the second light output surface  212 - 2  are coupled between the first light coupling surface  210 - 1  and the second light coupling surface  210 - 2 . Each light coupling surface  210 - 1 ,  210 - 2  is configured to receive incident light from a respective light source  204 - 1 ,  204 - 2 . Each light coupling surface  210 - 1 ,  210 - 2  is further configured to produce a batwing light beam inside the light guide  202 . The batwing light beam may be concentrated adjacent the first light output surface  212 - 1  and the second light output surface  212 - 2 . 
     In this example edge-lit light panel  200 , each light coupling surface  210 - 1 ,  210 - 2  has a generally V groove shape. For each light coupling surface  210 - 1 ,  210 - 2 , an angle of each leg of each V with a respective line  211 - 1 ,  211 - 2  drawn between ends of the V is ω. The lines  211 - 1 ,  211 - 2  may be generally perpendicular to the second output surface  212 - 2  and may be generally parallel to a surface of each respective light source  204 - 1 ,  204 - 2 . Each V groove  210 - 1 ,  210 - 2  is concave with respect to its respective light source  204 - 1 ,  204 - 2 . 
     The first light output surface  212 - 1  has a plurality of light extraction features, e.g., light extraction feature  203 . The first light output surface  212 - 1  may thus correspond to a light extraction surface configured to emit light. In this example, the light extraction features may be generally prismatic. The light extraction features may include, but are not limited to, prismatic, spherical, cylindrical, conical and asymmetric geometric shapes. The light extraction features may be configured to facilitate capture of photons within the light guide  202 , achieve a light extraction efficiency and generate an output beam with a particular shape. In one nonlimiting example, the shape of the output beam may correspond to a batwing. In another example, the plurality of light extraction features may be configured to facilitate total internal reflection over at least a portion of the first light output surface  212 - 1 . 
     Each light extraction feature  203  may have a spacing of dimension, S, and a pitch of dimension, P. Each portion of the first light output surface  212 - 1  corresponding to the spacing, S, may be generally parallel to the second light output surface  212 - 2 . Each portion of the first light output surface  212 - 1  corresponding to the pitch, P, may have a nonzero angle, μ, with respect to a line parallel to the second light output surface  212 - 2 . In an embodiment, the plurality of light extraction features may be configured to provide total internal reflection over at least a portion of the first light output surface  212 - 1 . 
     The first light output surface  212 - 1 , and thus the light guide  202 , may have two regions  213 - 1  and  213 - 2 . A first region  213 - 1  may extend from the first coupling surface  210 - 1  to approximately a centerline  201  of the light guide  202 . A second region  213 - 2  may extend from the centerline  201  to the second coupling surface  210 - 2 . In this example, the light extraction features included in the second region  213 - 2  may correspond to mirror images of the light extraction features, e.g., light extraction feature  203 , included in the first region  213 - 1 . In this example, each region  213 - 1 ,  213 - 2 , includes four light extraction features. However, this disclosure is not limited in this regard. 
     In this example  200 , each light source  204 - 1 ,  204 - 2  is configured to emit emitted light from the corresponding emission surface  205 - 1 ,  205 - 2  to respective light source reflectors  206 - 1 ,  206 - 2 . The light source reflectors  206 - 1 ,  206 - 2  are configured to reflect received emitted light onto respective coupling surfaces  210 - 1 ,  210 - 2  as incident light. The incident light may be refracted at the coupling surfaces  210 - 1 ,  210 - 2  producing a batwing light beam inside the light guide  202 . The batwing light beam may be concentrated adjacent the first light output surface  212 - 1  and the second light output surface  212 - 2 . 
     The first light output surface (i.e., light extraction surface)  212 - 1  is configured to facilitate capture of photons within the light guide  202 , achieve a light extraction efficiency and may be configured to generate an output beam with a particular shape. The second light output surface  212 - 2  may be configured to emit light reflected from the first light output surface  212 - 1 . In some embodiments, the diffuse reflector  208  is configured to scatter light from inside the light guide  202  such that light incident on the second light output surface  212 - 2  is scattered at a number of angles. 
     In an embodiment, at least a subset of the light extraction features may be configured for total internal reflection. The subset may include one or more light extraction features that are positioned relatively closer to the centerline  201 . In this embodiment, the light extraction features may be configured to facilitate producing a batwing shaped output beam from the light guide  202 . 
     Turning now to  FIG. 2B , edge-lit light panel  220  includes the light guide  202  and the plurality of light sources,  204 - 1 ,  204 - 2 , as described herein. Each light source  204 - 1 ,  204 - 2  has a corresponding emission surface  205 - 1 ,  205 - 2 . In this example  220 , each emission surface  205 - 1 ,  205 - 2  faces the light guide  202 . 
     In this example edge-lit light panel  220 , each light source  204 - 1 ,  204 - 2  is configured to emit emitted light from the corresponding emission surface  205 - 1 ,  205 - 2  onto respective coupling surfaces  210 - 1 ,  210 - 2  as incident light. The incident light may be refracted at the coupling surfaces  210 - 1 ,  210 - 2  producing a batwing light beam inside the light guide  202 . The batwing light beam and may be concentrated adjacent the first light output surface  212 - 1  and the second light output surface  212 - 2 , as described herein. 
     Turning now to  FIG. 2C , edge-lit light panel  240  includes a light guide  242 , a plurality of light sources,  204 - 1 ,  204 - 2 , and a plurality of light source reflectors  206 - 1 ,  206 - 2 . In some embodiments, edge-lit light panel  240  may include a diffuse reflector  208 . Each light source  204 - 1 ,  204 - 2  has a corresponding emission surface  205 - 1 ,  205 - 2 . Each emission surface  205 - 1 ,  205 - 2  faces the respective light source reflector  206 - 1 ,  206 - 2 . In other words, each emission surface  205 - 1 ,  205 - 2  faces away from the light guide  202 . 
     Light guide  242  includes a first light coupling surface  250 - 1  and a second light coupling surface  250 - 2  opposing the first light coupling surface  250 - 1 . Light guide  242  further includes a first light output surface  252 - 1  and a second light output surface  252 - 2  opposing the first light output surface  252 - 1 . The first light output surface  252 - 1  and the second light output surface  252 - 2  are coupled between the first light coupling surface  250 - 1  and the second light coupling surface  250 - 2 . Each light coupling surface  250 - 1 ,  250 - 2  is configured to receive incident light from a respective light source  204 - 1 ,  204 - 2 . Each light coupling surface  250 - 1 ,  250 - 2  is further configured to produce a batwing light beam inside the light guide  242 . The batwing light beam may be concentrated adjacent the first light output surface  252 - 1  and the second light output surface  252 - 2 , as described herein. 
     In this example, each light coupling surface  250 - 1 ,  250 - 2  has a generally V groove shape. An angle of each leg of the V with a vertical line drawn between ends of the V is ω. The vertical line may be generally perpendicular to the second output surface  252 - 2  and may be generally parallel to a surface of each light source  204 - 1 ,  204 - 2 . Each V groove  210 - 1 ,  210 - 2  is convex with respect to its respective light source  204 - 1 ,  204 - 2 . 
     In this example  200 , each light source  204 - 1 ,  204 - 2  is configured to emit emitted light from the corresponding emission surface  205 - 1 ,  205 - 2  to respective light source reflectors  206 - 1 ,  206 - 2 . The light source reflectors  206 - 1 ,  206 - 2  are configured to reflect received emitted light onto respective coupling surfaces  250 - 1 ,  250 - 2  as incident light. The incident light may be refracted at the coupling surfaces  250 - 1 ,  250 - 2  producing a batwing light beam inside the light guide  242 . The batwing light beam and may be concentrated adjacent the first light output surface  252 - 1  and the second light output surface  252 - 2 . 
     The first light output surface (i.e., light extraction surface)  252 - 1  is configured to facilitate capture of photons within the light guide  242 , achieve a light extraction efficiency and generate an output beam with a particular shape. The second light output surface  252 - 2  may be configured to emit light reflected from the first light output surface  252 - 1 . In some embodiments, the diffuse reflector  208  is configured to scatter light from inside the light guide  242  such that light incident on the second light output surface  252 - 2  is scattered at a number of angles. 
     Turning now to  FIG. 2D , edge-lit light panel  260  includes a light guide  262  and the plurality of light sources,  204 - 1 ,  204 - 2 , as described herein. In some embodiments, edge-lit light panel  260  may include a reflector  268 . Each light source  204 - 1 ,  204 - 2  has a corresponding emission surface  205 - 1 ,  205 - 2 . In this example  260 , each emission surface  205 - 1 ,  205 - 2  faces the light guide  262 . 
     Example light guide  262  includes a first light coupling surface  270  land a second light coupling surface  270 - 2  opposing the first light coupling surface  270 - 1 . Light guide  262  further includes a first light output surface  272 - 1  and a second light output surface  272 - 2  opposing the first light output surface  272 - 1 . The first light output surface  272 - 1  and the second light output surface  272 - 2  are coupled between the first light coupling surface  270 - 1  and the second light coupling surface  270 - 2 . Each light coupling surface  270 - 1 ,  270 - 2  is configured to receive incident light from a respective light source  204 - 1 ,  204 - 2 . Each light coupling surface  270 - 1 ,  270 - 2  is further configured to produce a portion of a batwing light beam inside the light guide  262 . The batwing light beam portion is configured to be concentrated adjacent the first light output surface  272 - 1 , in this example. 
     In this example edge-lit light panel  260 , each light coupling surface  270 - 1 ,  270 - 2  has a generally wedge shape. The wedge shape may correspond to one leg of a V groove, as described herein. For each light coupling surface  270 - 1 ,  270 - 2 , an angle of the wedge (and thus the leg of the V groove) between each light coupling surface  270 - 1 ,  270 - 2  and a respective line  271 - 1 ,  271 - 2  is ω, similar to the V groove, as described herein. The lines  271 - 1 ,  271 - 2  may be generally perpendicular to the second output surface  272 - 2  and may be generally parallel to a surface of each respective light source  204 - 1 ,  204 - 2 . 
     The light coupling surfaces  270 - 1 ,  270 - 2  of example edge-lit light panel  260  generally correspond to an upper leg of a V groove coupling surface, as described herein. In another example, the light coupling surfaces of an edge-lit light panel may correspond to a lower leg of a V groove, consistent with the present disclosure. 
     The first light output surface  272 - 1  has a plurality of light extraction features, as described herein. The first light output surface  272 - 1  may thus correspond to a light extraction surface configured to emit light. In this example, the light extraction features may be generally prismatic. The light extraction features may include, but are not limited to, prismatic, spherical, cylindrical, conical and asymmetric geometric shapes. The light extraction features may be configured to facilitate capture of photons within the light guide  262 , achieve a light extraction efficiency and generate an output beam with a particular shape. In one nonlimiting example, the shape of the output beam may correspond to a batwing. In another example, the plurality of light extraction features may be configured to facilitate total internal reflection over at least a portion of the first light output surface  272 - 1 . 
     In this example edge-lit light panel  260 , each light source  204 - 1 ,  204 - 2  is configured to emit emitted light from the corresponding emission surface  205 - 1 ,  205 - 2  onto respective coupling surface  270 - 1  as incident light. The incident light may be refracted at the coupling surfaces  270 - 1 ,  270 - 2  producing a portion of a batwing light beam inside the light guide  262 . The batwing light beam portion may be concentrated adjacent the first light output surface  272 - 1 . 
     Example edge-lit light panel  260  may further include a reflector  268 . Reflector  268  may be positioned at or near the second light output surface  272 - 2  and is configured to reflect light out towards the first light output surface  272 - 1 . Reflector  268  may thus be configured to facilitate and/or enhance emission of light from edge-lit light panel  260 . 
     Thus, an edge-lit light panel, consistent with the present disclosure, may include a plurality of light guides and corresponding light sources. Each light source and light guide are configured to produce at least a portion of a batwing shaped light beam within the light guide with the light intensity concentrated at or near at least one light output surface, i.e., at or near at least one light extraction surface. The light source and light guide may be configured to provide relatively higher flux density and illuminance uniformity at a light output surface and may thus provide improved extraction efficiency and panel luminance uniformity. A light extraction surface may include at least one light extraction feature configured to facilitate light extraction efficiency and/or creation of an output beam shape. 
       FIGS. 3A through 3J  are sketches of cross sections of various example first light output surfaces, illustrating various light extraction feature geometries. Each first light output surface corresponds to the first light output surface  132 -M and the cross sections correspond to cross section A-A′ of  FIG. 1B . 
       FIGS. 3A and 3B  are sketches  302 ,  312  of cross sections of example first light output surfaces including a plurality of generally semicircular extraction features. In these examples  302 ,  312 , the extraction features may be positioned internal to a light guide. Sketch  302  includes a plurality of generally semicircular concave extraction feature geometries, e.g., concave semicircular extraction feature  303 . Sketch  312  includes a plurality of generally semicircular convex extraction feature geometries, e.g., convex semicircular extraction feature  313 . 
       FIGS. 3C and 3D  are sketches  322 ,  332  of cross sections of example first light output surfaces including a plurality of generally triangular extraction features. Sketch  322  includes a plurality of generally triangular convex extraction feature geometries, e.g., triangular extraction feature  323 . Sketch  332  includes a plurality of generally triangular convex extraction feature geometries, e.g., triangular extraction feature  333 . 
       FIGS. 3E and 3F  are sketches  342 ,  352  of cross sections of example first light output surfaces including a plurality of generally triangular extraction features. Sketch  342  includes a plurality of generally triangular concave extraction feature geometries, e.g., triangular extraction feature  343 . Sketch  352  includes a plurality of generally triangular concave extraction feature geometries, e.g., triangular extraction feature  353 . 
       FIGS. 3G and 3H  are sketches  362 ,  372  of cross sections of example first light output surfaces including a plurality of generally semicircular extraction features. In these examples  302 ,  312 , the extraction features may be positioned on an external surface of a light guide. Sketch  362  includes a plurality of generally semicircular concave extraction feature geometries, e.g., concave semicircular extraction feature  363 . Sketch  372  includes a plurality of generally semicircular convex extraction feature geometries, e.g., convex semicircular extraction feature  373 . 
       FIGS. 3I and 3J  are sketches  382 ,  392  of cross sections of example first light output surfaces including a plurality of generally semicircular extraction features. In a first example  382 , the extraction features may be positioned on an external surface of a light guide. In a second example  392 , the extraction features may be positioned internal to a light guide. Sketch  382  includes a plurality of generally semicircular concave extraction feature geometries, e.g., concave semicircular extraction features  383 - 1 ,  383 - 2 ,  383 - 3 , having varying diameters. Sketch  392  includes a plurality of generally semicircular convex extraction feature geometries, e.g., convex semicircular extraction feature  393 - 1 ,  393 - 2 ,  393 - 3 , having varying diameters. 
     Thus, a light output surface, consistent with the present disclosure may include light extraction features having a variety of geometries. 
     Generally, this disclosure relates to an edge-lit light panel. The edge-lit light panel is configured to provide relatively efficient light coupling between a light source and a corresponding light guide and relatively efficient light extraction between the light guide and a light output. In one example, the edge-lit light panel may be used in a display (e.g., backlit). In another example, the edge-lit light panel may correspond to or be utilized in a lighting luminaire. The light source and light guide are configured to produce at least a portion of a batwing shaped light beam within the light guide with the light intensity concentrated at or near at least one light output surface. A light source and a light guide consistent with the present disclosure may be configured to provide relatively higher flux density and illuminance uniformity at a light output surface (i.e., a light extraction surface) and may thus provide improved extraction efficiency and panel luminance uniformity. A light output surface may include at least one light extraction feature configured to facilitate light extraction efficiency and/or creation of an output beam shape. In one nonlimiting example, an edge-lit light panel, consistent with the present disclosure, may be configured with a light output efficiency of more than 70%.