# Patent

## Title
Light-emitting device with light guide for two way illumination

## 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.

## Background
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 n0; the first optical element includes a first material having a first refractive index n1, where n0<n1; the second optical element includes a second material having a refractive index n2, where n0<n2; 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 n0; the first optical element includes a first material having a first refractive index n1, where n0<n1; the second optical element includes a second material having a refractive index n2, where n0<n2; 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 RO) 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 R1 that is concentric with the optical interface 125, such that the extractor element 130 satisfies the Brewster configuration R1≧R1B. The Brewster radius is given by R1B=RO(1+n12)+1/2, where RO 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<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.

## Claims

1. A light-emitting device, comprising:
a base substrate having a base surface;
one or more light-emitting elements (LEEs) configured to emit light, the LEEs being 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, the first optical element comprising scattering centers arranged to scatter light from the LEEs;
a second optical element having an exit surface, the second optical element being 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, the optical interface being opposite the first surface of the first optical element, the second optical element being arranged to receive light from the first optical element through the optical interface; wherein:
a medium adjacent to the first surface of the first optical element has a refractive index n0;
the first optical element comprises a first material having a first refractive index n1, where n0<n1;
the second optical element comprises a second material having a refractive index n2, where n0<n2;
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, the reflector element having first and second surfaces extending away from the exit surface, the reflector element being arranged to reflect a first portion of light from the second optical element.

2. The light-emitting device of claim 1, wherein the first surface is reflective and facing the LEEs, the first surface being arranged to reflect the first portion of light.

3. The light-emitting device of claim 2, wherein the second surface is reflective and opposite the first surface, the second surface being arranged to reflect a second portion of light from the second optical element.

4. The light-emitting device of claim 2, wherein the second surface is opposite the first surface and configured to absorb a second portion of light from the second optical element.

5. The light-emitting device of claim 1, further comprising a heat sink coupled to the base substrate, the heat sink being configured to remove heat from the light-emitting element.

6. The light-emitting device of claim 1, wherein the first and second surfaces of the reflector element are arranged to reflect light received from the exit surface of the second optical element.

7. The light-emitting device of claim 1, wherein the first optical element has a dome shape.

8. The light-emitting device of claim 1, wherein the first optical element and the base surface form an enclosure surrounding the one or more LEEs.

9. A light-emitting device, comprising:
a base substrate having a base surface;
one or more light-emitting elements (LEEs) configured to emit light, the LEEs being 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, the first optical element comprising scattering centers arranged to scatter light from the LEEs;
a second optical element having an exit surface, the second optical element being 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, the optical interface being opposite the first surface of the first optical element, the second optical element being arranged to receive light from the first optical element through the optical interface; wherein:
a medium adjacent to the first surface of the first optical element has a refractive index n0;
the first optical element comprises a first material having a first refractive index n1, where n0<n1;
the second optical element comprises a second material having a refractive index n2, where n0<n2;
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, the light guide having 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.

10. The light-emitting device of claim 9, wherein a second surface of the one side of the light guide is configured to reflect a second portion of light from the second optical element, the second surface opposing the first surface.

11. The light-emitting device of claim 9, wherein the first optical element has a dome shape.

12. The light-emitting device of claim 9, wherein the first optical element and the base surface form an enclosure surrounding the one or more LEEs.