Abstract:
A variety of light-emitting devices are disclosed that are configured to manipulate light provided by one or more light-emitting elements (LEEs). In general, a light-emitting device includes one or more light-emitting elements (LEEs) disposed on a base surface that are configured to emit light, a first optical element having a first surface spaced apart from the LEEs and positioned to receive light from the LEEs, a transparent second optical coupled to the first optical element, and a reflector element adjacent the second optical element arranged to reflect a portion of light output from the second optical element.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit under 35 U.S.C. §119(e)(1) of U.S. Provisional Application No. 61/774,391, filed on Mar. 7, 2013, which is incorporated by reference herein. 
    
    
     TECHNICAL FIELD 
     The described technology relates to light-emitting devices including a light guide configured to produce two way illumination profiles. 
     BACKGROUND 
     The present technology relates generally to light-emitting devices and, in particular, to light-emitting devices that feature a solid state light-emitting element and a scattering element and an extractor element remote from a light-emitting element. 
     Light-emitting elements are ubiquitous in the modern world, being used in applications ranging from general illumination (e.g., light bulbs) to lighting electronic information displays (e.g., backlights and front-lights for LCDs) to medical devices and therapeutics. Solid state light emitting devices, which include light emitting diodes (LEDs), are increasingly being adopted in a variety of fields, promising low power consumption, high luminous efficacy and longevity, particularly in comparison to incandescent and other conventional light sources. 
     One example of a SSL device increasingly being used for in luminaires is a so-called “white LED.” Conventional white LEDs typically include an LED that emits blue or ultraviolet light and a phosphor or other luminescent material. The device generates white light via down-conversion of blue or UV light from the LED (referred to as “pump light”) by the phosphor. Such devices are also referred to as phosphor-based LEDs (PLEDs). Although subject to losses due to light-conversion, various aspects of PLEDs promise reduced complexity, better cost efficiency and durability of PLED-based luminaires in comparison to other types of luminaires. 
     While new types of phosphors are being actively investigated and developed, configuration of PLED-based light-emitting devices, however, provides further challenges due to the properties of available luminescent materials. Challenges include light-energy losses from photon conversion, phosphor self-heating from Stokes loss, dependence of photon conversion properties on operating temperature, degradation due to permanent changes of the chemical and physical composition of phosphors in effect of overheating or other damage, dependence of the conversion properties on intensity of light, propagation of light in undesired directions in effect of the random emission of converted light that is emitted from the phosphor, undesired chemical properties of phosphors, and controlled deposition of phosphors in light-emitting devices, for example. 
     SUMMARY 
     The present technology relates generally to light-emitting devices and, in particular, to light-emitting devices that feature a solid state light-emitting element and a scattering element and an extractor element remote from a light-emitting element. The light-emitting devices can be configured to provide two-way illumination. 
     In one aspect, a light-emitting device includes a base substrate having a base surface; one or more light-emitting elements (LEEs) configured to emit light, where the LEEs are disposed on the base surface; a first optical element having a first surface spaced apart from the LEEs and positioned to receive light from the LEEs, where the first optical element includes scattering centers arranged to scatter light from the LEEs; a second optical element having an exit surface, where the second optical element is transparent and in contact with the first optical element, there being an optical interface between the first and second optical elements at the place of contact, where the optical interface is opposite the first surface of the first optical element, and the second optical element is arranged to receive light from the first optical element through the optical interface; where a medium adjacent to the first surface of the first optical element has a refractive index n 0 ; the first optical element includes a first material having a first refractive index n 1 , where n 0 &lt;n 1 ; the second optical element includes a second material having a refractive index n 2 , where n 0 &lt;n 2 ; the exit surface is shaped such that an angle of incidence on the exit surface of the light provided by the first optical element that directly impinges on the exit surface is less than a critical angle for total internal reflection; and a reflector element adjacent the second optical element, where the reflector element has first and second surfaces extending away from the exit surface, and the reflector element is arranged to reflect a first portion of light from the second optical element. 
     The foregoing and other embodiments can each optionally include one or more of the following features, alone or in combination. In some embodiments the first surface can be reflective and face the LEEs, where the first surface can be arranged to reflect the first portion of light. In some embodiments, the second surface can be reflective and opposite the first surface, where the second surface can be arranged to reflect a second portion of light from the second optical element. In some embodiments, the second surface can be opposite the first surface and configured to absorb a second portion of light from the second optical element. In some embodiments, the light-emitting device can further include a heat sink coupled to the base substrate, where the heat sink can be configured to remove heat from the light-emitting element. 
     In another aspect, a light-emitting device includes a base substrate having a base surface; one or more light-emitting elements (LEEs) configured to emit light, where the LEEs are disposed on the base surface; a first optical element having a first surface spaced apart from the LEEs and positioned to receive light from the LEEs, where the first optical element includes scattering centers arranged to scatter light from the LEEs; a second optical element having an exit surface, where the second optical element is transparent and in contact with the first optical element, there being an optical interface between the first and second optical elements at the place of contact, where the optical interface is opposite the first surface of the first optical element, and the second optical element is arranged to receive light from the first optical element through the optical interface; where a medium adjacent to the first surface of the first optical element has a refractive index n 0 ; the first optical element includes a first material having a first refractive index n 1 , where n 0 &lt;n 1 ; the second optical element includes a second material having a refractive index n 2 , where n 0 &lt;n 2 ; the exit surface is shaped such that an angle of incidence on the exit surface of the light provided by the first optical element that directly impinges on the exit surface is less than a critical angle for total internal reflection; and a light guide adjacent to the second optical element, where the light guide has a reflective first surface on one side of the light guide facing the LEEs and arranged to reflect a first portion of light from the second optical element. 
     The foregoing and other embodiments can each optionally include one or more of the following features, alone or in combination. In some embodiments a second surface of the one side of the light guide can be configured to reflect a second portion of light from the second optical element, where the second surface can be opposing the first surface. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a cross-sectional side view of an example of a light-emitting device with a reflector element. 
         FIG. 2  shows examples of rays of light output by a light-emitting device. 
         FIG. 3A  shows an example distribution of radiant light intensity of a light-emitting device in an upward direction. 
         FIG. 3B  shows an example distribution of radiant light intensity of a light-emitting device in a downward direction. 
         FIG. 4  shows an example of a light-emitting device with a heat sink. 
         FIG. 5  shows an example of a light-emitting device with a radial light guide. 
         FIG. 6  shows an example of rays of light output by a light-emitting device. 
         FIG. 7A  shows an example distribution of radiant light-intensity of a light emitting device in an upward direction. 
         FIG. 7B  shows an example distribution of radiant light-intensity of a light-emitting device in a downward direction. 
         FIG. 8  shows an example of a polar plot of a radiation pattern for a light-emitting device. 
     
    
    
     DETAILED DESCRIPTION 
     When using light-emitting devices, it may be desired to provide two-way illumination, for example, it may be desired that a light-emitting device hanging from a ceiling illuminates an area below the light-emitting device and also illuminates the ceiling. Such two-way illumination can be provided, for example, by adding a reflector element (e.g., conical mirror) or a light guide extension to a light-emitting device. 
       FIG. 1  shows a cross-sectional side view of an example of a light-emitting device  100  with a reflector element  160 . The light-emitting device  100  can include a base substrate  150 , one or more light-emitting elements, such as light-emitting element  110  (e.g., a blue pump LED), a scattering element  120 , and an extractor element  130 . The base substrate  150  has a surface  155 , which can be diffuse and/or specular reflective (e.g., a mirror). The scattering element  120  has a first surface  115  spaced apart from the light-emitting element  110  and positioned to receive the light from the light-emitting element  110 . The light-emitting element  110  can be disposed on the surface  155  of the base substrate  150 , in an opening that is, at least in part, defined by the first surface  115 . The scattering element  120  includes scattering centers configured to elastically and/or inelastically scatter light. As such the scattering element may or may not alter the spectral composition of light passing through it. 
     In some implementations, the surface  155  extends to at least the first surface  115  of the scattering element  120 . In some implementations, the surface  155  extends to at least an exit surface  135  of the extractor element  130 . The scattering element  120  can be located on the inside of the extractor element  130  adjacent an enclosure  140  (e.g., a semispherical enclosure of radius R O ) of the extractor element  130  to form an optical interface  125 . The enclosure  140  can be filled with a medium (e.g., gas or air) and encloses the light-emitting element  110 , and at least a portion of the surface  155 . 
     In some implementations, the exit surface  135  of the extractor element  130  can have a radius R 1  that is concentric with the optical interface  125 , such that the extractor element  130  satisfies the Brewster configuration R 1 ≧R 1B . The Brewster radius is given by R 1B =R O (1+n1 2 ) +1/2 , where R O  is the radius of the optical interface  125  of the light-emitting device  100 , and n1 denotes the index of refraction of the material of the extractor element  130 . As the extractor element  130  satisfies the Brewster configuration, an angle of incidence on the exit surface  135  of the scattered light that directly impinges on the exit surface  135  is less than the Brewster angle, and as such, the scattered light that directly impinges on the exit surface  135  experiences little or no total internal reflection thereon. 
     In this example, light propagation asymmetry arises from the materials on the inside (index n0) and outside (index n1) of the scattering element  120  with index np being unequal. For instance, if np=1.5 and n0=1.0, that is n0&lt;np, a large fraction (˜75%) of the isotropically distributed photons impinging on the first surface  115  will be reflected by total internal reflection (TIR) back into the scattering element  120  and only a smaller fraction (˜25%) will be transmitted backwards into the recovery enclosure  140  from where some may reach the light-emitting element  110 . At the optical interface  125 , the condition np≦n1 will guarantee that substantially all photons reaching the optical interface  125  will transition into the extractor element  130 , and the Brewster condition will further guarantee that practically all these photons will transmit into air without TIR through the exit surface  135 . Only a small fraction (down to about ˜4% depending on incidence angle) will be returned by Fresnel reflection at the exit surface  135 . 
     In some implementations, the reflector element  160  can be coupled with the extractor element and configured (e.g., as a conical mirror) to redirect some of the light output through the exit surface  135  of the extractor element  130 . The reflector element  160  has a reflective surface  162  (e.g., diffuse and/or specular reflective) that faces the light-emitting element  110  and is arranged to redirect a portion of the light output through the exit surface  135 . A surface  164  of the reflector element  160  is opposite the reflective surface  162 . In some implementations, the surface  164  can be reflective (e.g., a layer of aluminum, silver, or a coat of white paint) to redirect a portion of the light that is output through the exit surface  135 . In other implementations, the surface  164  can be absorbent (e.g., a black layer or coat of black paint) to absorb a portion of the light that is output through the exit surface  135 . 
       FIG. 2  shows example rays  210 ,  220 ,  230 ,  240 , and  250  of light output by the light-emitting device  100 . At least some of the light output from the exit surface of the extractor element can be reflected by the reflector element  160 . For example, ray  210  shows light emitted by the light-emitting element  110  that passes through the scattering element and the extractor element, and is reflected by reflector element  160  in an upward direction (having a component parallel to the z-axis). Ray  220  shows light emitted by the light-emitting element  110  that passes through the scattering element and the extractor element, and is output through the exit surface of the extractor element in an upward direction (having a component parallel to the z-axis) without reflection off the reflector element  160 . Rays  230  and  240  show light emitted by the light-emitting element  110  that passes through the scattering element and the extractor element below the reflector element  160  (having a component antiparallel to the z-axis). Ray  250  shows light emitted by the light-emitting element  110  that passes through the scattering element, is reflected by the surface of the base substrate within the extractor element, output through the exit surface of the extractor element towards the reflector element  160 , and reflected by the reflector element  160  in an upward direction (having a component parallel to the z-axis). 
       FIG. 3A  shows radiant light intensity of the light-emitting device  100  in an upward direction (e.g., in the +z direction of  FIGS. 1-2 ).  FIG. 3B  shows radiant light intensity of the light-emitting device  100  in a downward direction (e.g., in the −z direction of  FIGS. 1-2 ). The areas  310 ,  320 ,  325 ,  330 ,  350 ,  360 , and  370  shown in  FIGS. 3A and 3B  indicate different levels of radiant intensity of the light-emitting device  100  in a horizontal plane above the light-emitting device  100  ( FIG. 3A ) and below the light-emitting device  100  ( FIG. 3B ). For example, in the upward direction, the radiant light intensity is lowest in the area  310  and gradually increases through area  320  to the highest upward radiant light intensity in area  330 . In the downward direction, the radiant light intensity is lowest in area  350  and gradually increases through area  360  to the highest downward radiant light intensity in area  370 . Dependent on the configuration of the light-emitting device  100 , the radiant light intensity can decrease above the optical center of the light-emitting device as shown in area  325  of  FIG. 3A . This decrease in radiant light intensity can be caused, for example by the shape (e.g., doughnut shape) and relative narrowness of the reflector element  160  of the light-emitting device  100 . The upward light radiation pattern can be modified by adjusting the angle and position of the reflector element  160 . 
     In some implementations, a heat sink can be added to the light-emitting element  100 .  FIG. 4  shows an example of a light-emitting device  400  with a heat sink  410 . Light-emitting elements, such as light-emitting element  110 , can produce heat and it may be desired to remove the heat from the light-emitting elements, for example to increase the lifecycle of the light-emitting elements. The heat sink  410  can be directly or indirectly coupled to the light-emitting elements. For example, to remove excess heat from the light-emitting element  110 , a heat sink  410  can be coupled to the base substrate  150  of the light-emitting device  400 . In some implementations, the base substrate  150  can be thermally conductive and transfer heat from the light-emitting element  110  to the heat sink  410 . In some implementations, the heat sink can cover the entire base substrate or a portion thereof. 
       FIG. 5  shows a light-emitting device  500  with a radial light guide  510  to redirect light. The light emitting device  500  can include a base substrate  150 , one or more light-emitting elements, such as light-emitting element  110  (e.g., a blue pump LED), a scattering element, and an extractor element. The base substrate  150  can have a surface  155 . In some implementations, the surface  155  can be reflective (e.g., a mirror). The radial light guide  510  can be coupled to the extractor element of the light-emitting device  500 . In some implementations, the radial light guide  510  can include a reflective surface  515  (e.g., a total internal reflection (TIR) mirror or a reflective coat) to redirect a portion of the light output through the exit surface  135  of the extractor element  130 , for example, in an upward direction (e.g., in the +z direction). The radial light guide  510  can also include an exit surface  520  through which the light that is received by the radial light guide  510  (e.g., through the extractor element) is output. 
     In some implementations, a layer  517  (e.g., coating) can be coupled with the reflective surface  515 . In some implementations, the layer  517  can be reflective (e.g., aluminum, silver, or a coat of white paint) to redirect (e.g., in the −z direction) a portion of the light that is output through the exit surface  135 . In other implementations, the layer  517  can be absorbent (e.g., a coat of black paint) to absorb a portion of the light that is output through the exit surface  135 . In other implementations (not shown), for example when the light guide is a solid material (e.g., glass), a reflective layer (e.g., aluminum, silver, or white coating) can be coupled with the surface  515  and an absorbent layer (e.g., black coating) can be coupled with the reflective layer. 
       FIG. 6  shows example rays  610 ,  620 ,  630 ,  640 , and  650  of light output by the light-emitting device  500 . At least some of the light emitted by the light-emitting element  110  can be reflected by the reflective surface  515  of the radial light guide  510 . For example, ray  610  shows light emitted by the light-emitting element  110  that passes through the scattering element and extractor of the light-emitting device  500 , and is reflected by the reflective surface  515  of the radial light guide  510  and output in an upward direction (e.g., in the +z direction) through the exit surface  520 . Dependent on the embodiment, the substrate  150  may extend only across around the vicinity of the light-emitting element  110  without protruding beyond (not illustrated in  FIG. 6 ) the optical interface  125 . Ray  620  shows light emitted by the light-emitting element  110  that passes through the scattering element and extractor of the light-emitting device  500 , and is output in an upward direction (e.g., in the +z direction) through the exit surface  520  of the radial light guide  510  without reflection off the reflective surface  515 . Rays  630  and  640  show light that passes, through the scattering element and extractor of the light-emitting device  500 , below the radial light guide  510 . Ray  650  shows light that passes through the scattering element, is reflected by the surface  155  of the base substrate  150  within the extractor element towards the reflective surface  515  of the radial light guide  510 , reflected by the reflective surface  515 , and output through the exit surface  520  in an upward direction (e.g., in the +z direction). 
       FIG. 7A  shows radiant light intensity of the light emitting device  500  in an upward direction (e.g., in the +z direction of  FIGS. 5-6 ).  FIG. 3B  shows radiant light-intensity of the light-emitting device  500  in a downward direction (e.g., in the −z direction of  FIGS. 5-6 ). The areas  710 ,  720 ,  730 ,  735 ,  740 ,  760 ,  770 , and  780  shown in  FIGS. 7A and 7B  indicate different levels of radiant intensity of the light-emitting device  500  in a horizontal plane above the light-emitting device  500  ( FIG. 7A ) and below the light-emitting device ( FIG. 7B ). For example, in the upward direction, the radiant light intensity is lowest in the area  710  and gradually increases through areas  720  and  730  to the highest upward radiant light intensity in area  740 . In the downward direction, the radiant light intensity is lowest in area  760  and gradually increases through area  770  to the highest downward radiant light intensity in area  780 . 
     Dependent on the configuration of the light-emitting device  500 , the radiant light intensity can decrease above the optical center of the light-emitting device as shown in area  735  of  FIG. 7A . The decrease in radiant light intensity can be caused, for example, by the shape of the radial light guide. The upward light radiation pattern can be modified by adjusting the angle and position of reflective surface and exit surface of the radial light guide. 
       FIG. 8  shows a polar plot of the radiation pattern for the light-emitting device  500 . Lobes  810  of the radiation pattern correspond to the upward light radiation and lobe  820  of the radiation pattern corresponds to the downward light radiation of the light-emitting device  500 . The radiation pattern in the upward and/or downward direction can be modified by adjusting the radial light guide  510 . For example, the angle and position of the reflective and exit surface of the radial light guide  510  can impact the radiation pattern of the light-emitting device  500 . Also, the material properties (e.g., refractive index, composition, etc.) of the radial light guide  510  can affect the radiation pattern of the light-emitting device  500 .