U.S. patent application number 16/746737 was filed with the patent office on 2020-12-17 for lighting device having a 3d scattering element and optical extractor with convex output surface.
The applicant listed for this patent is Quarkstar LLC. Invention is credited to Roland H. Haitz, Ferdinand Schinagl.
Application Number | 20200393109 16/746737 |
Document ID | / |
Family ID | 1000005059287 |
Filed Date | 2020-12-17 |
United States Patent
Application |
20200393109 |
Kind Code |
A1 |
Haitz; Roland H. ; et
al. |
December 17, 2020 |
Lighting Device Having a 3D Scattering Element and Optical
Extractor With Convex Output Surface
Abstract
A lighting device includes (1) one or more solid-state lighting
(SSL) devices, (2) a thick, for example prism- or cylinder- or
spherical- or dome-shaped scattering element, and (3) an optical
extractor with a convex output surface.
Inventors: |
Haitz; Roland H.; (Portola
Valley, CA) ; Schinagl; Ferdinand; (North Vancouver,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Quarkstar LLC |
Las Vegas |
NV |
US |
|
|
Family ID: |
1000005059287 |
Appl. No.: |
16/746737 |
Filed: |
January 17, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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15529458 |
May 24, 2017 |
10546983 |
|
|
PCT/US2015/062749 |
Nov 25, 2015 |
|
|
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16746737 |
|
|
|
|
62084358 |
Nov 25, 2014 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F21Y 2115/10 20160801;
H01L 2933/0091 20130101; F21V 13/04 20130101; H01L 33/58 20130101;
H01L 33/50 20130101; G02B 19/0028 20130101; G02B 19/0066 20130101;
F21V 7/0066 20130101; G02B 5/0294 20130101; G02B 5/0278 20130101;
F21V 13/08 20130101; G02B 5/0236 20130101; H01L 33/505 20130101;
F21K 9/64 20160801; H01L 33/56 20130101; H01L 33/507 20130101 |
International
Class: |
F21V 13/04 20060101
F21V013/04; H01L 33/58 20060101 H01L033/58; G02B 5/02 20060101
G02B005/02; F21V 13/08 20060101 F21V013/08; G02B 19/00 20060101
G02B019/00; H01L 33/50 20060101 H01L033/50; H01L 33/56 20060101
H01L033/56 |
Claims
1-24. (canceled)
25. A lighting device comprising: a light-emitting element (LEE)
configured to provide light; a conversion element forming an input
interface at points of contact with the LEE, the input interface
having a first dimension, the scattering element having a second
dimension being orthogonal to the first dimension, the second
dimension being 1-10 times the size of the first dimension, the
conversion element comprising a phosphor and a transparent
material, the phosphor configured to convert received light into
converted light, the conversion element having an outer surface
configured to output at least a portion of light received from the
conversion element.
26. The lighting device of claim 25 further comprising a
transparent extractor in contact with the outer surface of the
conversion element.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation application of U.S.
application Ser. No. 15/529,458, filed on May 24, 2017, which is a
U.S. National Phase application of International Application No.
PCT/US2015/062749, filed on Nov. 25, 2015, which claims benefit
under 35 U.S.C. .sctn. 119(e)(1) of U.S. Provisional Application
No. 62/084,358, filed on Nov. 25, 2014, which are incorporated by
reference herein.
TECHNICAL FIELD
[0002] The present technology pertains in general to lighting
devices including solid-state lighting (SSL) devices and in
particular to lighting devices including thick, for example prism-
or cylinder- or spherical- or dome-shaped scattering elements and
an optical extractor with a convex output surface.
BACKGROUND
[0003] The development of lighting devices has focused in many ways
on how to extract as much light as possible into the ambient and
while doing so provide at least some directionality of propagation
to the light to make it useful for application in space
illumination, indication, display and/or other lighting
applications. Such aspects apply to all types of SSL and non-SSL
lighting devices and generally manifest themselves in the design of
the optical subsystem. These requirements are particularly relevant
when light is generated within optically dense material. Efficient
utilization of high brightness light that originates from
quasi-point sources and controlling respective glare provides a
number of challenges for optical subsystem design. These and other
aspects have become increasingly important in the configuration of
light-emitting diodes (LEDs), LED-based lighting devices and other
SSL devices.
[0004] SSL devices in particular are finding rapid adoption in
large portions of illumination applications due to their low power
consumption, high luminous efficacy and longevity in comparison to
incandescent and fluorescent light sources. SSL devices have been
developed that can generate quality white light via down-conversion
of short wavelength pump light, including ultraviolet, blue or
other light provided by corresponding LEDs, via a suitable
luminescent material (also referred to as a phosphor). Such devices
may be referred to as phosphor-based LEDs (PLEDs). Although subject
to losses in efficacy due to light-conversion, various aspects of
PLEDs promise reduced complexity, better cost efficiency and
durability of PLED-based luminaires in comparison to luminaires
that generate white light from light emitted by various
combinations of LEDs that directly generate red, green, blue, amber
and/or other colors of light, for example.
[0005] While new types of phosphors are being actively investigated
and developed, configuration of PLED-based lighting devices and/or
luminaires, however, provides further challenges due to the
properties of available luminescent materials. Challenges include
light-energy losses from photon conversion, generally referred to
as Stokes loss or Stokes shift, 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 lighting devices, for
example.
[0006] Therefore there is a need for a lighting device that
overcomes at least one of the deficiencies of the state-of-the
art.
SUMMARY
[0007] In general, innovative aspects of the technologies described
herein can be implemented in a lighting device that includes one or
more of the following aspects:
[0008] In a first aspect, a lighting device includes one or more
light-emitting elements (LEE) configured to provide pump light, and
a scattering element including a matrix of phosphor embedded in
dielectric material. The phosphor is configured to absorb at least
a portion of the pump light and to emit converted light with
converted light wavelengths longer than pump light wavelengths. The
dielectric material is transparent to the pump light and the
converted light. The scattering element forms an input interface
with the LEEs, such that the pump light emitted by the LEEs is
input into the scattering element through the input interface. The
input interface has a first dimension. The scattering element has a
second dimension orthogonal to and 1-10 times larger than the first
dimension. Additionally, the lighting device includes an optical
extractor forming an extraction interface with the scattering
element, such that mixed light from the scattering element is input
into the optical extractor through the extraction interface. An
output surface of the optical extractor is arranged and shaped
relative to the extraction interface such that the mixed light
received by the optical extractor through the extraction interface
impinges on the output surface at incident angles smaller than or
equal to the critical angle .theta..sub.C=arcsin(n.sub.E/n.sub.O),
where n.sub.E is a refractive index of the optical extractor, and
n.sub.O is a refraction index of an environment surrounding the
optical extractor.
[0009] The foregoing and other embodiments can each optionally
include one or more of the following features, alone or in
combination. In some implementations, the extraction interface has
a third dimension being along, and 3-30 times larger than, the
first dimension. In some implementations, the extraction interface
is shaped as a portion of a sphere, and the second dimension of the
scattering element corresponds to a radius of the sphere.
[0010] In some implementations, the phosphor can be uniformly
distributed within the dielectric material. In some
implementations, the dielectric material of the matrix can be
plastic or glass. In some implementations, the one or more LEEs can
include one or more LED dies. In some implementations, the one or
more LEEs can include one or more LED packages. In some
implementations, the mixed light can include a portion of the
converted light and a portion of the pump light that is unconverted
by the phosphor. In any of the foregoing implementations, the
lighting device further can include a reflector extending from the
input interface to a boundary of the extraction interface.
[0011] In some implementations, the optical extractor can be
arranged and shaped relative to the extraction interface such that
the incident angles at which the mixed light impinges on the
extraction interface are larger than or equal to the Brewster angle
.theta..sub.B=arctan(n.sub.E/n.sub.O). In some implementations, the
optical extractor can be arranged and shaped relative to the
extraction interface such that the incident angles at which the
mixed light impinges on the extraction interface are smaller than
the Brewster angle .theta..sub.B=arctan(n.sub.E/n.sub.O).
[0012] In a second aspect, a lighting device includes one or more
light-emitting diodes (LEDs) configured to provide pump light, and
a scattering element including a matrix of phosphor embedded in
dielectric material. The phosphor is configured to absorb at least
a portion of the pump light and to emit converted light with
converted light wavelengths longer than pump light wavelengths. The
dielectric material is transparent to the pump light and the
converted light. The scattering element forms an input interface
with the LEDs, such that the pump light emitted by the LEDs is
input into the scattering element through the input interface. The
input interface has a first dimension. The scattering element has a
second dimension orthogonal to and 1-10 times larger than the first
dimension. Additionally, the lighting device includes an optical
extractor forming an extraction interface with the scattering
element, such that mixed light from the scattering element is input
into the optical extractor through the extraction interface. An
output surface of the optical extractor has a radius R.sub.O that
satisfies the condition
R.sub.O.gtoreq.R.sub.E(n.sub.E/n.sub.O),
where R.sub.E is a radius of a notional sphere that inscribes the
extraction interface, and wherein n.sub.E is a refractive index of
the optical extractor and n.sub.O is a refraction index of an
environment surrounding the optical extractor.
[0013] The foregoing and other embodiments can each optionally
include one or more of the following features, alone or in
combination. In some implementations, the scattering element can be
shaped as a spherical dome of the notional sphere with the radius
R.sub.E, such that the second dimension of the scattering element
corresponds to the radius R.sub.E, and the optical extractor can be
shaped as a spherical shell having an inner radius that corresponds
to the radius R.sub.E. In some implementations, the scattering
element can be shaped as a cylinder having a height equal to the
second dimension, and a base diameter 2R.sub.E that is along, and
3-30 times larger than, the first dimension; and the optical
extractor can be shaped as a spherical dome with the radius
R.sub.O.
[0014] In some implementations, the radius R.sub.O can satisfy the
condition
R.sub.O=R.sub.E(n.sub.E/n.sub.O).
[0015] In some implementations, the radius R.sub.O can satisfy the
condition
R.sub.E(n.sub.E/n.sub.O)<R.sub.O<R.sub.E
[1+(n.sub.E/n.sub.O).sup.2].
[0016] In some cases of the latter implementations, the radius
R.sub.O can satisfy the condition
R.sub.O=R.sub.E [1+(n.sub.E/n.sub.O).sup.2].
[0017] In other cases of the latter implementations, the radius
R.sub.O can satisfy the condition
R.sub.O>R.sub.E [1+(n.sub.E/n.sub.O).sup.2].
[0018] In any of the above implementations, the lighting device
further can include a reflector extending from the input interface
to a boundary of the extraction interface.
[0019] In some implementations, the phosphor can be uniformly
distributed within the dielectric material. In some
implementations, the dielectric material of the matrix can be
plastic or glass. In some implementations, the one or more LEDs can
include one or more LED dies. In some implementations, the one or
more LEDs can include one or more LED packages. In some
implementations, the mixed light can include a portion of the
converted light and a portion of the pump light that is unconverted
by the phosphor.
[0020] The details of one or more implementations of the
technologies described herein are set forth in the accompanying
drawings and the description below. Other features, aspects, and
advantages of the disclosed technologies will become apparent from
the description, the drawings, and the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1A shows a schematic diagram of a lighting device
having a layer-shaped or 3D scattering element and an optical
extractor with a convex output surface.
[0022] FIG. 1B shows an example of a spectrum of mixed light output
by a lighting device like the one illustrated in FIG. 1A.
[0023] FIG. 2A shows a schematic cross section of an example of a
lighting device having a spherical shell-shaped scattering element
and a spherical shell-shaped optical extractor that have a common
extraction interface.
[0024] FIG. 2B shows a schematic cross section of an example of a
lighting device having a plate-shaped scattering element and a
spherical dome-shaped optical extractor that have a common
extraction interface.
[0025] FIG. 3 shows a schematic cross section of an example of a
lighting device having a cylinder-shaped scattering element and a
spherical dome-shaped optical extractor that have a common
extraction interface.
[0026] FIG. 4 shows a schematic cross section of an example of a
lighting device having a spherical dome-shaped scattering element
and a spherical shell-shaped optical extractor that have a common
extraction interface.
[0027] Reference numbers and designations in the various drawings
indicate exemplary aspects, implementations of particular features
of the present disclosure.
DETAILED DESCRIPTION
[0028] The present technology pertains to lighting devices
including SSL devices, layer-shaped or three-dimensional (3D)
scattering elements, and optical extractors with convex output
surfaces. The disclosed lighting devices can be used in
applications such as general illumination, and/or display
illumination, e.g., projection displays, backlit LCDs, signage,
etc.
[0029] FIG. 1A shows a schematic diagram of a lighting device 100
having a layer-shaped or 3D scattering element 120 and an optical
extractor 130 with a convex output surface 135. The lighting device
100 further includes one or more light emitting elements (LEEs) 110
and a conversion/recovery enclosure 140. The lighting device 100
efficiently provides broadband, homogenized light to an ambient
environment across a broad range of angles.
[0030] The LEEs are configured to produce and emit light during
operation. A spectral power distribution of light emitted by the
LEEs 110 (also referred to as pump light) can be concentrated in a
blue wavelength range, for instance. Depending on the context,
color of light may refer to its chromaticity. In general, the LEEs
110 are devices that emit radiation in a region or combination of
regions of the electromagnetic spectrum for example, the visible
region, infrared and/or ultraviolet region, when activated by
applying a potential difference across it or passing a current
through it, for example. The LEEs 110 can have monochromatic,
quasi-monochromatic, polychromatic or broadband spectral emission
characteristics. Examples of LEEs that are monochromatic or
quasi-monochromatic include semiconductor, organic,
polymer/polymeric light-emitting diodes (LEDs). In some
implementations, the one or more LEEs 110 can be a single specific
device that emits the radiation, for example an LED die, or/and can
be a combination of multiple instances of the specific device that
emit the radiation together. Such LEE(s) 110 can include a housing
or package within which the specific device or devices are placed.
As another example, the one or more LEEs 110 can be a single device
that includes one or more lasers and more specifically
semiconductor lasers, such as vertical cavity surface emitting
lasers (VCSELs) and edge emitting lasers. In embodiments utilizing
semiconductor lasers, the layer-shaped or 3D scattering element 120
functions to reduce (e.g., eliminate) spatial and temporal
coherence of the laser light, which may be advantageous where the
lighting device 100 may be viewed directly by a person. Further
examples of LEEs 110 include superluminescent diodes and other
superluminescent devices.
[0031] The layer-shaped or 3D scattering element 120 has an input
surface 115 positioned to receive the light from the LEEs 110. In
some cases, the input surface 115 is spaced apart from the one or
more LEEs 110. In other cases, the input surface 115 is an optical
interface of the 3D scattering element 120 with the one or more
LEEs 110. In the latter cases, the input surface 115 will be
referred to as the input interface 115. The layer-shaped or 3D
scattering element 120 includes scattering centers arranged to
scatter the light from the LEEs 110 and to provide mixed light.
Such scattering may be configured to be substantially isotropical.
The mixed light can include elastically scattered pump light
(represented as dashed-lines) and inelastically scattered pump
light (represented as dotted-lines). Depending on its nature,
scattering can be the result of combined absorption/emission and/or
refractive interaction with scattering centers. Elastically
scattered pump light, if any, includes photons that have undergone
elastic scattering at the scattering centers. Inelastically
scattered pump light includes photons that have undergone inelastic
scattering at the scattering centers. For example, the spectral
distribution of photons remains substantially unchanged due to
elastic scattering or, on the other hand, changes in effect of
inelastic scattering. Typical elastic scattering entails refraction
of light at a scattering center, for example. Typical inelastic
scattering entails emission of light from a scattering center in
effect of light that was previously absorbed by the scattering
center.
[0032] With respect to the technology described in this
specification, inelastic scattering typically is associated with
one visible or ultraviolet (UV) incoming photon and one visible
outgoing photon. Scattering of light by a scattering center can
result from effects such as light conversion, refraction, and/or
other effect and/or combination thereof. The distribution of a
plurality of outgoing photons that result from inelastic scattering
at one scattering center can be isotropic as is typically the case,
for example, in effect of light conversion. The distribution of a
plurality of outgoing photons that result from elastic scattering
at multiple scattering centers can be isotropic depending on, for
example, shapes, arrangements and/or compositions of the scattering
centers. A scattering center can include one or more portions that
each scatter light in one or more ways, for example, by light
conversion, refraction or other effect. Example scattering centers
include discontinuities in the composition or structure of matter.
In order to achieve a predetermined degree of randomness in its
propagation, light has to undergo multiple elastic scattering
events. As such multiple scattering events are required to exceed a
predetermined randomness, for example, when the light is scattered
by interaction with scattering centers that scatter light merely by
refraction. Scattering centers can include light-converting
material (LCM) and/or non-light converting material, for example.
Light conversion via LCM is a form of inelastic scattering.
[0033] LCM is a material which absorbs photons according to a first
spectral distribution and emits photons according to a second
spectral distribution, as described below in connection with FIG.
1B. The terms light conversion, wavelength conversion and/or color
conversion are used interchangeably. LCM is also referred to as
photoluminescent or color-converting material, for example. LCM can
include photoluminescent substances, fluorescent substances,
phosphors, quantum dots, semiconductor-based optical converters, or
the like. LCM also can include rare earth elements.
[0034] FIG. 1B shows an example of a spectrum 115 of mixed light
that is output by the lighting device 100. A blue LED used as LEE
110 in the lighting device 100 can have an emission spectrum 111.
In addition, FIG. 1B shows an absorption spectrum 112 and an
emission spectrum 113 of the scattering centers, along with the
spectrum of mixed light 115 (the latter is represented with a
dotted-line.) Spectral power distribution of the elastically
scattered light is the same as the spectral power distribution of
the pump light (corresponding to the spectrum 111.) Moreover, the
absorption spectrum of the scattering centers 112 overlaps the
spectrum of the light emitted by the light-emitting element 111.
Spectral power distribution of the inelastically scattered light is
different from the pump light. For instance, inelastically
scattered light will have a spectrum 113 that is shifted (e.g.,
Stokes shifted) to longer wavelengths than the pump light spectrum
111. For example, blue pump light, when inelastically scattered,
can yield light with an overall yellow/amber color, e.g.,
corresponding to the spectrum 113. Moreover, the spectrum of mixed
light 115 is a combination of the spectrum 111 of the elastically
scattered light and spectrum 113 of the inelastically scattered
light.
[0035] Referring again to FIG. 1A, the layer-shaped or 3D
scattering element 120 can be configured to substantially randomize
the direction of propagation of light received from LEEs 110 by
scattering substantially all light entering the layer-shaped or 3D
scattering element, while allowing substantial portions of light to
pass through the layer-shaped or 3D scattering element.
[0036] The optical extractor 130 is formed from a transparent
material, such as a transparent glass or a transparent organic
polymer, and has a convex output surface 135. The output surface
135 is generally a transparent surface. In other words, changes in
the mixed light passing through the output surface 135 can
generally be described by Snell's law of refraction, as opposed to,
for example, an opaque or diffuse surface where further scattering
of transmitted light occurs. The optical extractor 130 is in
contact with the layer-shaped or 3D scattering element 120, such
that there is an optical interface 125 between the layer-shaped or
3D scattering element and the optical extractor at the place of
contact, and the optical interface is opposite the input
surface/interface 115 of the layer-shaped or 3D scattering element.
The optical interface 125 is referred to as the extraction
interface 125. The layer-shaped or 3D extractor element 130 is
arranged so that mixed light transmitted through the extraction
interface 125 enters the optical extractor 130. Light from the
layer-shaped or 3D scattering element 120 that directly reaches the
output surface 135 of the optical extractor 130 is referred to as
forward light.
[0037] In some implementations, the lighting device 100 includes a
medium, such as a gas (e.g., air), between the LEEs 110 and the
input surface 115 of the layer-shaped or 3D scattering element 120
having a refractive index n.sub.0, and the layer-shaped or 3D
scattering element includes a material having a first refractive
index n.sub.S, where n.sub.0<n.sub.S. Light from the
layer-shaped or 3D scattering element 120 that reaches the input
surface 115 is referred to as backward light. Because
n.sub.0<n.sub.S, the input surface 115 allows only a fraction of
the backward light to escape into the low-index medium. Here, the
transparent material of the optical extractor 130 has a refractive
index n.sub.E, where n.sub.0.ltoreq.n.sub.E and is
immersion-coupled with the extraction interface 125. As such, the
lighting device 100 asymmetrically propagates mixed light because
the amount of transmitted forward light is greater than the amount
of backward light transmitted into the low index medium. In such a
case, depending on the degree of asymmetry between n.sub.0 and
n.sub.E, the extraction interface 125 between the layer-shaped or
3D scattering element 120 and the optical extractor 130 permits
varying ratios of forward to backward light transmission. A high
asymmetry in this ratio is reached if n.sub.E and n.sub.S are about
equal. Light emitting devices that feature asymmetric optical
interfaces (i.e., different refractive index mismatches) on
opposing sides of the layer-shaped or 3D scattering element 120 are
referred to as asymmetric scattering light valves (ASLV), or ASLV
lighting devices.
[0038] The output surface 135 of the optical extractor 130 is a
transparent surface that is shaped such that the mixed light that
directly impinges on the output surface satisfies specified
reflection conditions to ensure that the mixed light that directly
impinges on the output surface experiences little or no total
internal reflection (TIR). In this manner, the output surface 135
transmits a large portion of light impinging thereon that directly
propagates thereto from the layer-shaped or 3D scattering element
120 and propagates in at least certain planes and outputs it into
the ambient of the optical extractor 130 on first pass. The mixed
light output through the output surface 135 can be used for
illumination or indication functions provided by the lighting
device 100 or for further manipulation by another optical system
that works in conjunction with the lighting device.
[0039] Some of the specified reflection conditions satisfied by the
shape of the output surface 135 of the optical extractor 130 are
described below. In some embodiments, the output surface 135 of the
optical extractor 130 is shaped as a spherical or a cylindrical
dome or shell with a radius R.sub.O, such that the extraction
interface 125 is disposed within an area of the optical extractor
defined by a respective notional sphere or cylinder that is
concentric with the output surface and has a radius
R.sub.W=R.sub.O/n.sub.E, wherein n.sub.E is the refractive index of
the optical extractor. Such a configuration is referred to as
Weierstrass geometry or Weierstrass configuration. It is noted that
a spherical Weierstrass geometry can avoid TIR for rays passing
through the area circumscribed by a corresponding notional
R.sub.O/n.sub.E sphere irrespective of the plane of propagation. A
cylindrical Weierstrass geometry can exhibit TIR for light that
propagates in planes that intersect the respective cylinder axis at
shallow angles even if the light passes through an area
circumscribed by a corresponding notional R.sub.W=R.sub.O/n.sub.E
cylinder.
[0040] It is noted that other lighting devices can have an
extractor element 130 with non-spherical or non-cylindrical output
surface 135 the can be employed to refract light and aid in shaping
an output intensity distribution in ways different from those
provided by a spherical or cylindrical exit surface. The definition
of the Weierstrass geometry can be extended to include an output
surface 135 with non-circular sections by requiring that the
extraction interface 125 falls within cones, also referred to as
acceptance cones, subtended from points P of the output surface
whose axes correspond to respective surface normals at the points P
and which have an apex of 2*Arcsin(k*n.sub.O/n.sub.E), wherein
n.sub.O is the refractive index of the medium on the outside of the
output surface and k is a positive number smaller than n.sub.E. It
is noted that the output surface 135 needs to be configured such
that the plurality of all noted cones circumscribe a space with a
non-zero volume. It is further noted that k is assumed to refer to
a parameter that determines the amount of TIR at an uncoated output
surface 135 that separates an optically dense medium, having
n.sub.E>1, on one side of the output surface making up the
optical extractor 130 from a typical gas such as air with
n.sub.O.about.1.00 at standard temperature and pressure conditions,
on the outside of the output surface. Depending on the embodiment,
k can be slightly larger than 1 but is preferably less than 1. If
k>1, some TIR may occur at the output surface 135 inside the
optical extractor 130. In some embodiments, this results in the
extraction interface 125 being at least R(P)*(1-k/n.sub.E) away
from the output surface 135 in a direction normal to the output
surface at a point P thereof. Here, R(P) is the local radius of
curvature of the output surface 135 at the point P, and n.sub.E is
the refractive index of the optical extractor 130. For a spherical
or cylindrical output surface 135 with k=1, the boundaries
circumscribed by the noted cones correspond to a spherical or
cylindrical Weierstrass geometry, respectively. In this case, the
mixed light received by the optical extractor 130 through the
extraction interface 125 impinges on the output surface 135 at
incident angles smaller than the critical angle
.theta..sub.C=arcsin(n.sub.E). Some embodiments are configured to
allow for some TIR by choosing k>1. In such cases, k/n is
limited to k/n<0.8, for example. In summary, a lighting device
100 is said to satisfy the Weierstrass configuration if a radius
R.sub.O of the output surface 135 of the optical extractor 130,
which has an index of refraction n.sub.E, is equal to or larger
than R.sub.O.gtoreq.R.sub.W=n.sub.ER.sub.E, where R.sub.E is a
radius of the extraction interface 125 of the lighting device.
[0041] In some embodiments, the parameter k is not just smaller
than 1 to avoid TIR at the output surface 135 of the optical
extractor 130 for light propagating in at least one plane, but k is
made so small that certain Fresnel reflections are additionally
avoided. In such cases, the mixed light received by the optical
extractor 130 through the extraction interface 125 impinges on the
output surface 135 at incident angles equal to or smaller than the
Brewster angle .theta..sub.B=arctan(n.sub.E) against an air
interface. More generally, p-polarized light that impinges at a
point P of the output surface 135 from within directions bound by a
cone subtended from the point P with apex 2*Arctan(1/n.sub.E) whose
axis corresponds to the surface normal at the point P will not be
reflected at the exit surface. Such a configuration is referred to
as Brewster geometry (or Brewster configuration), and the output
surface 135 forms a Brewster sphere or a Brewster cylinder. In
summary, a lighting device 100 is said to satisfy the Brewster
configuration if a radius R.sub.O of the output surface 135 of the
optical extractor 130 is equal to or larger than
R.sub.O.gtoreq.R.sub.B=R.sub.E(1+n.sub.E.sup.2).sup.+1/2, where
R.sub.E is the radius of the extraction interface 125 of the
lighting device. Note that for a given radius R.sub.E of the
extraction interface 125 of the lighting device 100, an optical
extractor 130 that satisfies the Brewster condition has an output
surface 135 with minimum radius R.sub.O(Brewster;min)=R.sub.B that
is larger than a minimum radius R.sub.O (Weierstrass;min)=R.sub.W
of the output surface of an optical extractor that satisfies the
Weierstrass condition.
[0042] In a first implementation of the optical extractor 130, the
radius R.sub.O of its output surface 135 is larger than or equal to
the Brewster radius: R.sub.O.gtoreq.R.sub.B=R.sub.E
(1+n.sub.E.sup.2).sup.+1/2, for a given radius R.sub.E of the
extraction interface 125. A volume V.sub.E of the optical extractor
130 in the first implementations can vary from a minimum volume
equal to a Brewster volume, V.sub.E=V.sub.B for R.sub.O=R.sub.B, to
infinity, V.sub.E.fwdarw..infin. for R.sub.O.fwdarw..infin.. The
losses suffered by the mixed light due to Fresnel reflections at
the output surface 135 (of an optical extractor 130 having a
refraction index n.sub.E=1.5) increase by only about 20% when the
volume V.sub.E of the optical extractor 130 decreases from .infin.
to the Brewster volume V.sub.B.
[0043] In some other implementations of the optical extractor 130,
the radius R.sub.O of its output surface 135 is between the
Weierstrass radius R.sub.W=n.sub.ER.sub.E, for a given radius
R.sub.E of the extraction interface 125, and the Brewster radius:
R.sub.W.ltoreq.R.sub.O<R.sub.B. The volume V.sub.E of the
optical extractor 130 in the second implementations can vary from a
minimum volume equal to a Weierstrass volume, V.sub.E=V.sub.W for
R.sub.O=R.sub.W, to a maximum volume equal to the Brewster volume,
V.sub.E=V.sub.B for R.sub.O=R.sub.B. The losses suffered by the
mixed light due to Fresnel reflections at the output surface 135
(of an optical extractor 130 having a refraction index n.sub.E=1.5)
increase by 50% while the volume of the optical extractor 130
decreases by only 20% from the Brewster volume V.sub.B to the
Weierstrass volume V.sub.W. In view of the foregoing volume to loss
penalty considerations for the first and second implementations,
some embodiments of the optical extractor 130 will have a radius of
its output surface 135 that satisfies the condition
R.sub.O.apprxeq.1.5R.sub.B, 1.2R.sub.B, 1.1R.sub.B, R.sub.B,
0.9R.sub.B, 0.8R.sub.B, or 0.5R.sub.B, for instance. The above
estimates of the loss penalty for the optical extractor 130 as a
function of its volume are described in detail in the Annex of
provisional application 62/084,358 (which is incorporated by
reference herein), in connection with FIG. 2B.
[0044] Further in the example shown in FIG. 1A, the
conversion/recovery enclosure 140 is defined to enclose the
layer-shaped or 3D scattering element 120. The conversion/recovery
enclosure 140 is arranged and configured to recover a portion of
the mixed light that propagates in the backward direction by
causing at least some of this mixed light to exit the layer-shaped
or 3D scattering element 120 through the extraction interface 125
into the optical extractor 130, and reducing the amount of mixed
light that returns to the LEEs 110 (where it can be absorbed). If a
3D scattering element 120 fully fills the conversion/recovery
enclosure 140 as shown in FIGS. 3 and 4, then the
conversion/recovery enclosure represents simply a conversion
enclosure that is "bound" by the input interface 115, the
extraction interface 125 of the 3D scattering element and one or
more additional optical components that redirect back-scattered
light away from the input interface. If a layer-shaped scattering
element 120 does not fully fill the conversion/recovery enclosure
140 as shown in FIGS. 2A and 2B, then the conversion/recovery
enclosure also encloses a medium adjacent the input surface 115 of
the layer-shaped scattering element. In one such example
illustrated in FIG. 2A, the conversion/recovery enclosure 240a is
bound by the extraction interface 225a and a reflector 245a. In
another such example illustrated in FIG. 2B, the
conversion/recovery enclosure 240b is bound by the extraction
interface 225b and side surfaces 245b of an optical coupler 245b.
Referring again to FIG. 1A, note that the backscattered light
recovered from the conversion/recovery enclosure 140 further
increases asymmetry in the propagation of light through the
lighting device 100.
[0045] Moreover, the lighting device 100 can be fabricated using
conventional extrusion and molding techniques and conventional or
other assembly techniques--some examples are described herein.
Components of the lighting device 100 can include one or more
organic or inorganic materials, for example acrylic, silicone,
polypropylene (PP), polyethylene terephthalate (PET),
polycarbonate, polyvinylidene fluoride such as Kynar.TM., lacquer,
acrylic, rubber, polyphenylene sulfide (PPS) such as Ryton.TM.,
polysulfone, polyetherimide (PEI), polyetheretherketone (PEEK),
polyphenylene oxide (PPO) such as Noryl.TM., glass, quartz,
silicate, adhesive, other polymers organic or inorganic glasses
and/or other materials.
[0046] In some embodiments, the optical extractor 130 and the
layer-shaped or 3D scattering element 120 are integrally formed. In
an example of such an integral formation, the extraction interface
125 is a notional interface drawn between regions of a
corresponding integrally formed object, such that the extraction
interface substantially includes interfaces formed by the
scattering centers. This may be the case, when the layer-shaped or
3D scattering element 120 includes scattering centers inside a
material that is the same as the material used to form the optical
extractor 130, for example. In this manner, the layer-shaped or 3D
scattering element 120 can be shaped as a tile, disc, spherical or
aspherical shell or dome, tubular, prismatic or other elongate
shell, or other structure to provide a predetermined spatial
profile of conversion properties to achieve a predetermined
light-output profile including color and/or brightness homogeneity
from the layer-shaped or 3D scattering element.
[0047] The layer-shaped or 3D scattering element 120 can be
adjacent to, or partially or fully surrounded by, the optical
extractor 130. Various shapes of the layer-shaped or 3D scattering
element 120 and of the optical extractor 130, and their
combinations, are described in detail below in connection with
FIGS. 2A, 2B, 3 and 4.
[0048] FIG. 2A shows a schematic cross section in the x-z plane of
a lighting device 200a having a spherical shell-shaped scattering
element 220a and a spherical shell-shaped optical extractor 230a
that have a common extraction interface 225a. In some
implementations, the lighting device 200a has rotational symmetry
around the z-axis. In other implementations, the lighting device
200a is elongated along the y-axis (i.e., along a direction
perpendicular to the page). The lighting device 200a further
includes one or more LEEs 210 (e.g., a blue pump), and a flat
reflector 245a (e.g., a mirror represented by a double line.) The
scattering element 220a has an input surface 215a spaced apart from
the LEEs 210 and positioned to receive the light from the LEEs. In
this example, an LEE 210 is inserted into an opening (e.g., having
a half-width R.sub.d) of the flat reflector 245a. A dimension
2R.sub.d in the x-y plane of the LEE 210 can be of order 1 mm, for
instance. In some implementations, the reflector 245a extends to at
least the input surface 215a of the scattering element 220a. In
other implementations, the reflector 245a extends to at least an
output surface 235 of the optical extractor 230a. In this example,
the spherical shell-shaped scattering element 220a is located on
the inside of the optical extractor 230a and has substantially
uniform thickness, such that a distance between the extraction
interface 225a and the input surface 215a of the scattering element
is constant for any point of the optical extraction. The thickness
of the spherical shell-shaped scattering element 220a is less than
1 mm, e.g., 0.5, 0.2, 0.1 mm, or other thicknesses. Note that, in
this example, the thickness of the spherical shell-shaped
scattering element 220a is about 3.times.-10.times. smaller than
the dimension 2R.sub.d of the LEE 210. As such, the spherical
shell-shaped scattering element 220a is first embodiment of the
layer-shaped scattering element 120 described above in connection
with FIG. 1A.
[0049] Moreover, the input surface 215a of the spherical
shell-shaped scattering element 220a is adjacent an air filled
semispherical enclosure 240a of the optical extractor 230a. The
enclosure 240a encompasses the LEE 210 and its surrounding
reflector 245a. Here, a radius R.sub.E of the extraction interface
225a can be of order 3-5 mm. In some implementations, the output
surface 235 of the extractor element 230a is concentric with the
extraction interface 225a and has a radius R.sub.O that satisfies
one of the following reflection conditions. Reflection condition 1:
R.sub.O>R.sub.B, where the Brewster radius R.sub.B is related to
the radius R.sub.E of the extraction interface 225a through
R.sub.B=R.sub.E(1+n.sub.E.sup.2).sup.+1/2; Reflection condition 2:
R.sub.O=R.sub.B; Reflection condition 3:
R.sub.W<R.sub.O<R.sub.B, where the Weierstrass radius R.sub.W
is related to the radius R.sub.E of the extraction interface
through R.sub.W=n.sub.ER.sub.E; Reflection condition 4:
R.sub.O=R.sub.W. In this manner, mixed light that directly impinges
on the output surface 235 experiences little or no total internal
reflection thereon.
[0050] Further in this example, light propagation asymmetry in
large part arises from the refraction indices of materials on the
inside (index n.sub.0) and outside (index n.sub.E) of the spherical
shell-shaped scattering element 220a (with index n.sub.S) being
unequal. For instance, if 1.3<n.sub.S<1.6 and n.sub.0=1.0,
that is n.sub.0<n.sub.S, a large fraction (.about.75%) of the
isotropically distributed mixed light impinging on the input
surface 215a will be reflected by TIR back into the spherical
shell-shaped scattering element 220a and only a smaller fraction
(.about.25%) will be transmitted backwards into the air medium of
the recovery enclosure 240a from where some may reach the LEE 210.
In some implementations, at the extraction interface 225a, the
condition n.sub.S.ltoreq.n.sub.E will guarantee that substantially
all the mixed light reaching the extraction interface will
transition into the extractor element 230a, and either of the
above-noted reflection conditions 1, 2, 3 or 4 will further
guarantee that practically all the mixed light will transmit into
air without TIR through the output surface 235. Only a small
fraction (down to about .about.4% depending on incidence angle)
will be returned by Fresnel reflection at the output surface
235.
[0051] FIG. 2B shows a schematic cross section of an example of a
lighting device 200b having a plate-shaped scattering element 220b
and a spherical dome-shaped optical extractor 230b that have a
common extraction interface 225b. In some implementations, the
lighting device 200b has rotational symmetry around the z-axis. In
other implementations, the lighting device 200b is elongated along
the y-axis (i.e., along a direction perpendicular to the page). The
lighting device 200b further includes one or more LEEs 210 (e.g., a
blue pump), and an optical coupler 245b (e.g., configured as a
compound parabolic collector (CPC), a conical or other hollow
optical coupler having reflective side surfaces represented by
double lines.) Note that an air filled enclosure 240b of the
optical coupler 245b encompasses an LEE 210 and the plate-shaped
scattering element 220b. Here, the LEE 210 is positioned at an
input aperture of the optical coupler 245b. A dimension 2R.sub.d in
the x-y plane of the LEE 210 can be of order 1 mm, for instance.
The plate-shaped scattering element 220b is positioned at an output
aperture of the optical coupler 245b and has an input surface 215b
through which it receives the pump light from the LEE 210. In this
example, the plate-shaped scattering element 220b has substantially
uniform thickness, such that a distance between the extraction
interface 225b and the input surface 215b of the plate-shaped
scattering element is constant for any point of the optical
extraction. The thickness of the plate-shaped scattering element
220b is less than 1 mm, e.g., 0.5, 0.2, 0.1 mm, or other
thicknesses. Note that, in this example, the thickness of the
plate-shaped scattering element 220b is about 3.times.-10.times.
smaller than the dimension 2R.sub.d of the LEE 210. Additionally, a
dimension 2R.sub.E in the x-y plane of the scattering element 220b
can be of order 3-5 mm. As such, the plate-shaped scattering
element 220b is a second embodiment of the layer-shaped scattering
element 120 described above in connection with FIG. 1A.
[0052] Note that the extraction interface 225b is inscribed in
(i.e., forms a chord of) a nominal sphere (represented in
dashed-line) that is concentric with the output surface 235 of the
optical extractor 230b. The largest such nominal sphere has a
diameter equal to the dimension 2R.sub.E in the plane x-y of the
extraction interface 225b. In the current disclosure, a radius
R.sub.O of the output surface 235 satisfies one of the following
reflection conditions. Reflection condition 1: R.sub.O>R.sub.B,
where the Brewster radius R.sub.B is related to the dimension
2R.sub.E of the extraction interface 225b through
R.sub.B=R.sub.E(1+n.sub.E.sup.2).sup.+1/2; Reflection condition 2:
R.sub.O=R.sub.B; Reflection condition 3:
R.sub.W<R.sub.O<R.sub.B, where the Weierstrass radius R.sub.W
is related to the dimension 2R.sub.E of the extraction interface
through R.sub.W=n.sub.ER.sub.E; Reflection condition 4:
R.sub.O=R.sub.W. In this manner, mixed light that directly impinges
on the output surface 235 experiences little or no total internal
reflection thereon.
[0053] Further in this example, light propagation asymmetry arises
mostly from the refraction indices of materials on the inside
(index n.sub.0) and outside (index n.sub.E) of the plate-shaped
scattering element 220b (with index n.sub.S) being unequal. For
instance, if 1.3<n.sub.S<1.6 and n.sub.0=1.0, that is
n.sub.0<n.sub.S, a large fraction (.about.75%) of the
isotropically distributed mixed light impinging on the input
surface 215b will be reflected by TIR back into the plate-shaped
scattering element 220b and only a smaller fraction (.about.25%)
will be transmitted backwards into the air medium of the recovery
enclosure 240b from where some may reach the LEE 210. In some
implementations, at the extraction interface 225b, the condition
n.sub.S.ltoreq.n.sub.E will guarantee that substantially all the
mixed light reaching the extraction interface will transition into
the optical extractor 230b, and either of the above-noted
reflection conditions 1, 2, 3 or 4 will further guarantee that
practically all the mixed light will transmit into air without TIR
through the output surface 235. Only a small fraction (down to
about .about.4% depending on incidence angle) will be returned by
Fresnel reflection at the output surface 235.
[0054] As noted above, the lighting device 200a has a spherical
shell-shaped scattering element 220a and the lighting device 200b
has a plate-shaped scattering element 220b, each of these
layer-shaped scattering elements can have a thickness comparable to
a characteristic dimension of the LEEs 210. The lighting devices
described below have 3D scattering elements with a thickness that
can be a few to many times a characteristic dimension of the
LEEs.
[0055] For example, FIG. 3 shows a schematic cross section of a
lighting device 300 having a thick, for example cylinder-shaped,
scattering element 320 and a spherical dome-shaped optical
extractor 230b that have a common extraction interface 225b. The
cylinder-shaped scattering element 320 is an example embodiment of
the 3D scattering element 120 described above in connection with
FIG. 1A. As another example, FIG. 4 shows a schematic cross section
of an example of a lighting device 400 having a spherical
dome-shaped scattering element 420 and a spherical shell-shaped
optical extractor 230a that have a common extraction interface
225a. The spherical dome-shaped scattering element 420 is another
embodiment of the 3D scattering element 120 described above in
connection with FIG. 1A. In some implementations, the lighting
device 300/400 has rotational symmetry around the z-axis. In other
implementations, the lighting device 300/400 is elongated along the
y-axis (i.e., along a direction perpendicular to the page).
[0056] The lighting device 300/400 further includes one or more
LEEs 210. As described above in connection with FIG. 1A, the LEE(s)
210 can include light emitting diodes (LEDs). For example, the LEDs
can emit pump light, as described above in connection with FIG. 1B.
In some cases, the LEDs can be bare LED dies. In some other cases,
the LEDs can be packaged LED dies. In the latter cases, the
packaged LED dies can include a lens or other light shaping optical
element.
[0057] The 3D scattering element 320/420 can include a matrix of
phosphor particles embedded in dielectric material. The phosphor
can absorb a portion of the pump light and emit converted light
with converted light wavelengths longer than pump light
wavelengths, as illustrated in FIG. 1B, for instance. Here, the
dielectric material is transparent to the pump light and the
converted light. In this manner, the 3D scattering element 320/420
provides mixed light which includes a portion of the converted
light and a portion of the pump light that is not absorbed by the
phosphor, as illustrated in FIG. 1B, for instance. In some
implementations, the dielectric material of the matrix is plastic.
In other implementations, the dielectric material of the matrix is
glass. Moreover, the phosphor particles can be uniformly
distributed in the dielectric material. In this manner, an
effective refracting index of the 3D scattering element 320/420 is
n.sub.S>1, e.g., 1.3<n.sub.S<1.6.
[0058] The optical extractor 230b/230a can include a material that
is transparent to the mixed light and has a refractive index
n.sub.E that is larger than a refraction index n.sub.O of an
environment surrounding the optical extractor. The material of the
optical extractor 230b/230a can be plastic or glass. A value of the
refractive index n.sub.E of the optical extractor material is in
the range of 1.3<n.sub.E<1.9, for instance. In some
implementations, n.sub.E can be smaller than n.sub.S. In other
implementations, n.sub.E can be equal to or larger than
n.sub.S.
[0059] Further, the 3D scattering element 320/420 can form an
immersion-coupled input interface 315 with the LEE(s) 210, such
that the pump light emitted by the LEE(s) is input into the 3D
scattering element through the input interface. Furthermore, the
optical extractor 230b/230a forms an immersion-coupled extraction
interface 225b/225a with the 3D scattering element 320/420, such
that the mixed light is input into the optical extractor from the
3D scattering element through the extraction interface. Moreover,
an output surface 235 of the optical extractor 230b/230a is
arranged and shaped relative to the extraction interface 225b/225a
such that the mixed light received by the optical extractor through
the extraction interface impinges on the output surface at incident
angles smaller than a predetermined angle. Examples of
predetermined angles corresponding to particular reflection
conditions are provided below in this specification.
[0060] The lighting device 300/400 further includes a reflector
345/245a (represented in FIGS. 3 and 4 by double lines) extending
from the input interface 315 to a boundary of the extraction
interface 225b/225a. In this manner, a cylinder-shaped conversion
chamber (corresponding to the conversion enclosure 140 of the
lighting device 100 shown in FIG. 1A) of the lighting device 300
shown in FIG. 3 is bounded by the reflector 345 and the extraction
interface 225b and encloses the cylinder-shaped scattering element
320. Further, a spherical dome-shaped conversion chamber (taking
the position of the conversion enclosure 140 of the lighting device
100 shown in FIG. 1A) of the lighting device 400 shown in FIG. 4 is
bounded by the reflector 245a and the extraction interface 225a and
encloses the spherical dome-shaped scattering element 420. In some
implementations, the reflector 245a can extend along the x-axis
beyond the boundary of the extraction interface 225a at least to
the boundary of the output surface 235. The reflector 345/245a can
be configured to reflect the mixed light via specular reflection or
diffuse reflection. A reflectivity of the reflector 345/245a is
larger than 90%, e.g., 95%, 99%, etc. In some implementations the
reflectors 345/245a provide a white diffuse reflective surface,
which, when immersion coupled with the scattering element 320/420,
can provide very high reflectivity.
[0061] Moreover, the input interface 315 has a first dimension,
2R.sub.d. In the examples illustrated in FIGS. 3 and 4, the first
dimension 2R.sub.d is in the x-y plane and can represent a length
of the LED die or LED package that forms the LEE 210. The first
dimension 2R.sub.d is of order 1 mm, for instance.
[0062] Referring now to FIG. 3, the cylinder-shaped scattering
element 320 has a second dimension, T, which is orthogonal to and
1-10 times larger than the first dimension 2R.sub.d of the input
interface 315. Here, the second dimension T represents a thickness
along the z-axis of the cylinder-shaped scattering element 320.
Additionally, the cylinder-shaped scattering element 320 has a
third dimension, 2R.sub.E, which is along and 3-30 times larger
than the first dimension 2R.sub.d of the input interface 315. Here,
the third dimension 2R.sub.E represents a length in the x-y plane
of the cylinder-shaped scattering element 320. In this example, the
extraction interface 225b also has the third dimension 2R.sub.E in
the x-y plane.
[0063] In this example, the extraction interface 225b is inscribed
in (i.e., forms a chord of) a nominal sphere (represented in
dashed-line) that is concentric with the output surface 235 of the
spherical dome-shaped optical extractor 230b. The largest such
nominal sphere has a diameter equal to the third dimension 2R.sub.E
in the plane x-y of the extraction interface 225b. In the current
disclosure, a radius R.sub.O of the output surface 235 satisfies
one of the following reflection conditions. Reflection condition 1:
R.sub.O>R.sub.B, where the Brewster radius R.sub.B is related to
the third dimension 2R.sub.E of the extraction interface 225b
through R.sub.B=R.sub.E(1+n.sub.E.sup.2).sup.+1/2; Reflection
condition 2: R.sub.O=R.sub.B; Reflection condition 3:
R.sub.W<R.sub.O<R.sub.B, where the Weierstrass radius R.sub.W
is related to the third dimension 2R.sub.E of the extraction
interface through R.sub.W=n.sub.ER.sub.E; Reflection condition 4:
R.sub.O=R.sub.W. In this manner, mixed light that directly impinges
on the output surface 235 of the spherical dome-shaped optical
extractor 230b experiences little or no total internal reflection
thereon for the following reasons. For all reflection conditions
1-4, the mixed light directly impinges on the output surface 235 at
incidence angles smaller than or equal to the critical angle
.theta..sub.C=arcsin(n.sub.E/n.sub.O). Moreover, for conditions
1-2, the mixed light directly impinges on the output surface 235 at
incidence angles smaller than or equal to the Brewster angle
.theta..sub.B=arctan(n.sub.E/n.sub.O).
[0064] Referring now to FIG. 4, the scattering element 420 can be a
dome-shaped hemi-sphere. Here, the dome-shaped scattering element
420 has a second dimension, R.sub.E, which is radial with respect
to the input interface 315 and 1-10 times larger than the first
dimension 2R.sub.d of the input interface. Here, the second
dimension R.sub.E represents a radius of the extraction interface
225a. Additionally, the spherical dome-shaped scattering element
420 has a third dimension which coincides with a length of the
extraction interface 225a. Here, the length of the extraction
interface 225a is .about..pi.R.sub.E, e.g., 3-30 times larger than
the first dimension 2R.sub.d of the input interface 315.
[0065] In some implementations, the output surface 235 of the
spherical shell-shaped optical extractor 230a is concentric with
the extraction interface 225a and has a radius R.sub.O that
satisfies one of the following reflection conditions. Reflection
condition 1: R.sub.O>R.sub.B, where the Brewster radius R.sub.B
is related to the radius R.sub.E of the extraction interface 225a
through R.sub.B=R.sub.E(1+n.sub.E.sup.2).sup.+1/2; Reflection
condition 2: R.sub.O=R.sub.B; Reflection condition 3:
R.sub.W<R.sub.O<R.sub.B, where the Weierstrass radius R.sub.W
is related to the radius R.sub.E of the extraction interface
through R.sub.W=n.sub.ER.sub.E; Reflection condition 4:
R.sub.O=R.sub.W. In this manner, mixed light that directly impinges
on the output surface 235 of the spherical shell-shaped optical
extractor 230a experiences little or no total internal reflection
thereon for the following reasons. For all reflection conditions
1-4, the mixed light directly impinges on the output surface 235 at
incidence angles smaller than or equal to the critical angle
.theta..sub.C=arcsin(n.sub.E/n.sub.O). Moreover, for conditions
1-2, the mixed light directly impinges on the output surface 235 at
incidence angles smaller than or equal to the Brewster angle
.theta..sub.B=arctan(n.sub.E/n.sub.O).
[0066] Note that, in contrast with the lighting device 300 having a
cylinder-shaped scattering element 320 with a thickness T
(orthogonal to the input interface 315) that is larger than the
dimension 2R.sub.d of its LEE 210, e.g., T=1-10.times.2R.sub.d, the
corresponding lighting device 200b has a plate-shaped scattering
element 220b with a thickness that represents a fraction of the
dimension R.sub.d of its LEE 210, e.g.,
.about.0.5-0.1.times.2R.sub.d. Similarly, in contrast with the
lighting device 400 having a spherical dome-shaped scattering
element 420 with a radius R.sub.E that is larger than the dimension
2R.sub.d of its LEE 210, e.g., R.sub.E=1-10.times.2R.sub.d, the
corresponding lighting device 200a has a spherical shell-shaped
scattering element 220a with a thickness that represents a fraction
of the dimension R.sub.d of its LEE 210, e.g.,
.about.0.5-0.1.times.2R.sub.d. While the 3D scattering element
320/420 of the lighting device 300/400 and the layer-shaped
scattering element 220b/220a of the corresponding lighting device
200b/200a may contain similar quantities of phosphor, a volume of
the former can be much larger than a volume of the latter. Hence,
the phosphor in the 3D scattering element 320/420 of the lighting
device 300/400 can be more dilute than the phosphor in the
layer-shaped scattering element 220b/220a of the corresponding
lighting device 200b/200a. Likewise, the mean free path lengths can
be longer. In this manner, a likelihood for the converted light to
backscatter towards the input interface 315 for the lighting device
300/400 is beneficially smaller than a likelihood for the converted
light to backscatter towards the input interface 215b/215a for the
corresponding lighting device 200b/200a. As such, in the case of
the lighting device 300/400, a remaining portion of the
backscattered light is reflected off the reflector 345/245a (which
has a higher reflectance than a surface of an LEE 210--that is the
input interface 315 as viewed from the 3D scattering element
320/420.) Additionally, a likelihood for the converted light--that
scatters laterally (e.g., in the x-y plane) relative to a forward
direction (e.g., along the z-axis) between the input interface 315
and the extraction interface 225b/225a--to be absorbed for the
lighting device 300/400 is beneficially smaller than a likelihood
for the converted light--that scatters laterally (e.g., in the
tangential direction/x-y plane) relative to a forward direction
(e.g., along the radial direction/z-axis) between the input
interface 215b/215a and the extraction interface 225b/225a--to be
absorbed for the corresponding lighting device 200b/200a. In this
manner, in the case of the lighting device 300/400, a remaining
portion of the laterally scattered converted light is reflected off
the reflector 345/245a. Additionally, larger mean free path lengths
in the 3D scattering element 320/420 than in the corresponding
layer-shaped scattering element 220b/220a allow for better
spreading of light across the extraction interface 225b/225a. This
can provide greater uniformity in brightness and/or color, for
example.
[0067] As such, contributions to increasing the efficiency of the
lighting device 300/400 over the corresponding lighting device
200b/200a come from an effective conversion cavity enclosing the 3D
scattering element 320/420. Depending on the embodiment, the
thickness of the scattering element may be half to twice the mean
free path length and about one to ten times the first dimension of
the input interface. The foregoing embodiments of the technology
can be varied in many ways. Such present or future variations are
not to be regarded as a departure from the spirit and scope of the
technology, and all such modifications as would be obvious to one
skilled in the art are intended to be included within the scope of
the following claims.
[0068] The preceding figures and accompanying description
illustrate example methods, systems and devices for illumination.
It will be understood that these methods, systems, and devices are
for illustration purposes only and that the described or similar
techniques may be performed at any appropriate time, including
concurrently, individually, or in combination. In addition, many of
the steps in these processes may take place simultaneously,
concurrently, and/or in different orders than as shown. Moreover,
the described methods/devices may use additional steps/parts, fewer
steps/parts, and/or different steps/parts, as long as the
methods/devices remain appropriate.
[0069] In other words, although this disclosure has been described
in terms of certain aspects or implementations and generally
associated methods, alterations and permutations of these aspects
or implementations will be apparent to those skilled in the art.
Accordingly, the above description of example implementations does
not define or constrain this disclosure. Further implementations
are described in the following claims.
* * * * *