U.S. patent application number 11/831306 was filed with the patent office on 2009-02-05 for illumination assembly including wavelength converting material having spatially varying density.
This patent application is currently assigned to Luminus Devices, Inc.. Invention is credited to David Doyle, Alexei A. Erchak, Michael Lim, Nikolay I. Nemchuk, Alexander L. Pokrovskiy, Gianni Taraschi.
Application Number | 20090034230 11/831306 |
Document ID | / |
Family ID | 40337912 |
Filed Date | 2009-02-05 |
United States Patent
Application |
20090034230 |
Kind Code |
A1 |
Lim; Michael ; et
al. |
February 5, 2009 |
ILLUMINATION ASSEMBLY INCLUDING WAVELENGTH CONVERTING MATERIAL
HAVING SPATIALLY VARYING DENSITY
Abstract
Illumination assemblies, components, and related methods are
described. An illumination assembly can include at least one solid
state light-emitting device, an emission surface through which
light is emitted, and a wavelength converting material that
wavelength converts at least some light emitted by the solid state
light-emitting device. The wavelength converting material can have
a first density per unit area of the emission surface at a first
location and a second density per unit area of the emission surface
at a second location, wherein the second density is substantially
different from the first density, and wherein the density per unit
area is defined with a 1.times.1 cm.sup.2 averaging area. Another
illumination assembly can include a light guide configured to
receive light emitted by a solid state light-emitting device. The
light guide can have a length along which received light propagates
and an emission surface substantially parallel to the length of the
light guide and through which light is emitted. A wavelength
converting material can have a density per unit area of the
emission surface that substantially increases along the length of
the light guide.
Inventors: |
Lim; Michael; (Cambridge,
MA) ; Doyle; David; (Somerville, MA) ;
Pokrovskiy; Alexander L.; (Burlington, MA) ; Erchak;
Alexei A.; (Cambridge, MA) ; Taraschi; Gianni;
(Somerville, MA) ; Nemchuk; Nikolay I.; (North
Andover, MA) |
Correspondence
Address: |
LUMINUS DEVICES , INC.;C/O WOLF, GREENFIELD & SACKS , P.C.
600 ATLANTIC AVENUE
BOSTON
MA
02210-2206
US
|
Assignee: |
Luminus Devices, Inc.
Billerica
MA
|
Family ID: |
40337912 |
Appl. No.: |
11/831306 |
Filed: |
July 31, 2007 |
Current U.S.
Class: |
362/84 |
Current CPC
Class: |
G02B 6/0061 20130101;
G02B 6/0036 20130101; G02B 6/0068 20130101; G02B 6/0028
20130101 |
Class at
Publication: |
362/84 |
International
Class: |
F21V 9/16 20060101
F21V009/16 |
Claims
1. An illumination assembly comprising: at least one solid state
light-emitting device; an emission surface through which light is
emitted; and a wavelength converting material that wavelength
converts at least some light emitted by the solid state
light-emitting device, the wavelength converting material having a
first density per unit area of the emission surface at a first
location and a second density per unit area of the emission surface
at a second location, wherein the second density is substantially
different from the first density, and wherein the density per unit
area is defined with a 1.times.1 cm.sup.2 averaging area.
2. The illumination assembly of claim 1, wherein the second density
is substantially different from the first density at least
partially due to a differing microscopic density of wavelength
converting material at the first location and the second
location.
3. The illumination assembly of claim 1, wherein the second density
is substantially different from the first density at least
partially due to a differing thickness of the wavelength converting
material at the first location and the second location.
4. The illumination assembly of claim 1, further comprising a
plurality of wavelength converting material regions that include
the wavelength converting material, and wherein the second density
is substantially different from the first density at least
partially due to a differing spatial arrangement of the plurality
of wavelength converting material regions at the first location and
the second location.
5. The illumination assembly of claim 4, wherein the plurality of
wavelength converting material regions have substantially similar
shapes.
6. The illumination assembly of claim 1, further comprising a
plurality of wavelength converting material regions that include
the wavelength converting material, and wherein the second density
is substantially different from the first density at least
partially due to a differing size of the plurality of wavelength
converting material regions at the first location and the second
location.
7. The illumination assembly of claim 1, wherein the second
location is further away from the solid state light-emitting device
than the first location and the second density is substantially
greater than the first density.
8. The illumination assembly of claim 1, wherein the first and
second densities are such that wavelength converted light intensity
from the first location is at least 90% the wavelength converted
light intensity from the second location and no greater than 110%
the wavelength converted light intensity from the second
location.
9. The illumination assembly of claim 1, wherein the second density
is greater than or equal to 2 times the first density.
10. The illumination assembly of claim 1, wherein the wavelength
converting material comprises a phosphor.
11. The illumination assembly of claim 1, wherein the wavelength
converting material has a density that increases further away from
the solid state light-emitting device.
12. The illumination assembly of claim 1, wherein the illumination
assembly further comprises: a light guide configured to receive
light emitted by the solid state light-emitting device, the light
guide having a length along which received light propagates, and
wherein the wavelength converting material has a varying density
per unit area of the emission surface along the length of the light
guide.
13. The illumination assembly of claim 12, wherein the density of
the wavelength converting material per unit area of the emission
surface along the length of the light guide varies monotonically
with distance along the length of the light guide.
14. The illumination assembly of claim 12, wherein the light guide
includes an edge configured to receive the light emitted by the
solid state light-emitting device
15. The illumination assembly of claim 12, wherein the wavelength
converting material is at least partially disposed within the light
guide.
16. The illumination assembly of claim 12, wherein the wavelength
converting material is at least partially disposed over a light
emission surface of the light guide.
17. The illumination assembly of claim 12, wherein the wavelength
converting material is at least partially disposed in contact with
the light emission surface of the light guide.
18. The illumination assembly of claim 12, wherein the light guide
includes a backside surface opposing a light emission surface of
the light guide, and wherein the wavelength converting material is
at least partially disposed under the backside surface.
19. The illumination assembly of claim 18, wherein the wavelength
converting material is at least partially disposed in contact with
the backside surface of the light guide.
20. The illumination assembly of claim 12, wherein the wavelength
converting material has a lower density in locations illuminated
with a higher intensity of light from the solid state
light-emitting device than in locations illuminated with a lower
intensity of light from the solid state light-emitting device.
21. The illumination assembly of claim 1, wherein the wavelength
converting material comprises a phosphor.
22. The illumination assembly of claim 1, wherein the solid state
light-emitting device includes a light emission surface, and
wherein the wavelength converting material is disposed over the
light emission surface of the solid state light-emitting
device.
23. The illumination assembly of claim 22, wherein the at least one
solid state light-emitting device includes a plurality of solid
state light-emitting devices located on a first plane, and wherein
the first and second locations are located at different locations
of a second plane parallel to the first plane.
24. The illumination assembly of claim 23, wherein the wavelength
converting material has a lower density in locations illuminated
with a higher intensity of light from the plurality of solid state
light-emitting devices than in locations illuminated with a lower
intensity of light from the plurality of solid state light-emitting
device.
25. An illumination assembly comprising: a solid state
light-emitting device; a light guide configured to receive light
emitted by the solid state light-emitting device, the light guide
having a length along which received light propagates and an
emission surface substantially parallel to the length of the light
guide and through which light is emitted; and a wavelength
converting material having a density per unit area of the emission
surface that substantially increases along the length of the light
guide.
26. A display comprising: at least one solid state light-emitting
device; an emission surface through which light is emitted; a
wavelength converting material that wavelength converts at least
some light emitted by the solid state light-emitting device, the
wavelength converting material having a first density per unit area
of the emission surface at a first location and a second density
per unit area of the emission surface at a second location, wherein
the second density is substantially different from the first
density, and wherein the density per unit area is defined with a
1.times.1 cm.sup.2 averaging area; and a liquid crystal layer
arranged to receive at least some wavelength converted light
emitted by the wavelength converting material.
27. A display comprising: at least one solid state light-emitting
device; a first wavelength converting material region that
wavelength converts at least some light emitted by the solid state
light-emitting device to a first wavelength spectrum; a second
wavelength converting material region that wavelength converts at
least some light emitted by the solid state light-emitting device
to a second wavelength spectrum different from the first wavelength
spectrum; and a liquid crystal layer comprising a first pixel light
valve arranged to receive at least some wavelength converted light
emitted by the first wavelength converting material, and a second
pixel light valve arranged to receive at least some wavelength
converted light emitted by the second wavelength converting
material.
28. A method of making an illumination assembly comprising:
providing at least one solid state light-emitting device; and
providing a wavelength converting material that wavelength converts
at least some light emitted by the solid state light-emitting
device, the wavelength converting material having a first density
per unit area of an emission surface at a first location and a
second density per unit area of the emission surface at a second
location, wherein the second density is substantially different
from the first density, and wherein the density per unit area is
defined with a 1.times.1 cm.sup.2 averaging area.
Description
FIELD
[0001] The present embodiments are drawn generally towards
illumination systems, and more specifically, illumination systems
including solid state light-emitting devices.
BACKGROUND
[0002] Illumination assemblies can provide light for a variety of
applications, including general lighting and electronic
applications. For example, a backlighting assembly can be used to
provide light for a display, such as a liquid crystal display
(LCD). Currently such backlighting assemblies mainly employ cold
cathode fluorescent tubes (CCFLs) light sources. Although these
fluorescent tubes can provide efficient distributed lighting,
serious disadvantages of fluorescent tubes include complicated
inverter electronics, slow switching speeds, and the presence of
hazardous materials, such as mercury, within the fluorescent
tubes.
SUMMARY
[0003] Illumination systems, components, and methods associated
therewith are provided.
[0004] In one aspect, an illumination assembly comprises at least
one solid state light-emitting device, an emission surface through
which light is emitted, and a wavelength converting material that
wavelength converts at least some light emitted by the solid state
light-emitting device, the wavelength converting material having a
first density per unit area of the emission surface at a first
location and a second density per unit area of the emission surface
at a second location, wherein the second density is substantially
different from the first density, and wherein the density per unit
area is defined with a 1.times.1 cm.sup.2 averaging area.
[0005] In another aspect, an illumination assembly comprises a
solid state light-emitting device, a light guide configured to
receive light emitted by the solid state light-emitting device, the
light guide having a length along which received light propagates
and an emission surface substantially parallel to the length of the
light guide and through which light is emitted, and a wavelength
converting material having a density per unit area of the emission
surface that substantially increases along the length of the light
guide.
[0006] In one aspect, a display comprises at least one solid state
light-emitting device, an emission surface through which light is
emitted, a wavelength converting material that wavelength converts
at least some light emitted by the solid state light-emitting
device, the wavelength converting material having a first density
per unit area of the emission surface at a first location and a
second density per unit area of the emission surface at a second
location, wherein the second density is substantially different
from the first density, and wherein the density per unit area is
defined with a 1.times.1 cm.sup.2 averaging area, and a liquid
crystal layer arranged to receive at least some wavelength
converted light emitted by the wavelength converting material.
[0007] In one aspect, a display comprises at least one solid state
light-emitting device, a first wavelength converting material
region that wavelength converts at least some light emitted by the
solid state light-emitting device to a first wavelength spectrum, a
second wavelength converting material region that wavelength
converts at least some light emitted by the solid state
light-emitting device to a second wavelength spectrum different
from the first wavelength spectrum, and a liquid crystal layer
comprising a first pixel light valve arranged to receive at least
some wavelength converted light emitted by the first wavelength
converting material, and a second pixel light valve arranged to
receive at least some wavelength converted light emitted by the
second wavelength converting material.
[0008] In one aspect, a method of making an illumination assembly
comprising providing at least one solid state light-emitting
device, and providing a wavelength converting material that
wavelength converts at least some light emitted by the solid state
light-emitting device, the wavelength converting material having a
first density per unit area of an emission surface at a first
location and a second density per unit area of the emission surface
at a second location, wherein the second density is substantially
different from the first density, and wherein the density per unit
area is defined with a 1.times.1 cm.sup.2 averaging area.
[0009] Other aspects, embodiments and features of the invention
will become apparent from the following detailed description of the
invention when considered in conjunction with the accompanying
figures. The accompanying figures are schematic and are not
intended to be drawn to scale. Each identical or substantially
similar component that is illustrated in various figures is
represented by a single numeral or notation.
[0010] For purposes of clarity, not every component is labeled in
every figure. Nor is every component of each embodiment of the
invention shown where illustration is not necessary to allow those
of ordinary skill in the art to understand the invention. All
patent applications and patents incorporated herein by reference
are incorporated by reference in their entirety. In case of
conflict, the present specification, including definitions, will
control.
BRIEF DESCRIPTION OF FIGURES
[0011] FIG. 1A is a perspective view of an illumination assembly
including a wavelength converting material, in accordance with one
embodiment;
[0012] FIG. 1B is a cross-section view of an illumination assembly
including a tapered extraction region, in accordance with one
embodiment;
[0013] FIG. 1C is a cross-section view of a display including an
illumination assembly as a backlight unit, in accordance with one
embodiment;
[0014] FIGS. 2A-B are flowcharts of methods for wavelength
converting and spatially homogenizing light, in accordance with one
embodiment;
[0015] FIG. 3A is a cross-section view of an illumination assembly
having a spatially varying density of a wavelength converting
material, in accordance with one embodiment;
[0016] FIG. 3B is a chart of a density of wavelength converting
material versus distance from a light source, in accordance with
one embodiment;
[0017] FIG. 4 is a cross-section view of an illumination assembly
having a spatially varying density of a wavelength converting
material due to a differing microscopic density of the wavelength
converting material, in accordance with one embodiment;
[0018] FIG. 5 is a cross-section view of an illumination assembly
having a spatially varying density of a wavelength converting
material due to a differing thickness of a wavelength converting
material layer, in accordance with one embodiment;
[0019] FIG. 6 is a top view of an illumination assembly having a
spatially varying density of a wavelength converting material due
to a differing spatial arrangement of a plurality of wavelength
converting material regions, in accordance with one embodiment;
[0020] FIG. 7 is a top view of an illumination assembly having
spatially varying density of a wavelength converting due to a
differing size of a plurality of wavelength converting material
regions, in accordance with one embodiment;
[0021] FIGS. 8A-B are cross-section and top views, respectively, of
an illumination assembly including wavelength converting material
over a light emission surface of a light guide, in accordance with
one embodiment;
[0022] FIG. 9 is a cross-section view of an illumination assembly
including wavelength converting material under a backside surface
of a light guide, in accordance with one embodiment;
[0023] FIG. 10 is a cross-section view of an illumination assembly
including wavelength converting material over a light emission
surface of a light guide, in accordance with one embodiment;
[0024] FIG. 11A is a top view of an illumination assembly including
a plurality of wavelength converting material regions, in
accordance with one embodiment;
[0025] FIG. 11B is a top view of an illumination assembly including
a plurality of wavelength converting material regions, in
accordance with one embodiment;
[0026] FIGS. 12A-B are cross-section and top views, respectively,
of an illumination assembly including a wavelength converting
material, in accordance with one embodiment;
[0027] FIG. 13 is a top view of an illumination assembly including
a wavelength converting material, in accordance with one
embodiment;
[0028] FIGS. 14A-B are cross-section and top views, respectively,
of an illumination assembly including a wavelength converting
material and one or more wavelength filters, in accordance with one
embodiment;
[0029] FIGS. 15A-B are cross-section and top views, respectively,
of an illumination assembly including a wavelength converting
material, in accordance with one embodiment; and
[0030] FIG. 16 is a perspective view of a solid state
light-emitting device, in accordance with one embodiment.
DETAILED DESCRIPTION
[0031] Illumination assemblies presented herein can include one or
more solid state light-emitting devices, such as light-emitting
diodes and/or laser diodes. These solid state light-emitting
devices can serve as high brightness compact light sources for a
variety of applications. Since solid state light-emitting devices
are typically compact light sources, for applications where
distributed lighting is desired, light emitted by the solid state
light-emitting devices can be incorporated into an illumination
assembly that can redirect and emit light via an extended light
emission surface having a surface area substantially greater than
the emission surface of the light-emitting devices (e.g., greater
than about 100 times, greater than about 500 times, greater than
about 1000 times, greater than about 2000 times). Some embodiments
presented herein can accomplish such redirection and emission of
light from one or more solid state light-emitting devices and can
provide for distributed illumination via an extended light emission
surface. In some embodiments, during the process of light
redirection and/or emission, some or all of the light from the
light-emitting devices may be wavelength converted. Wavelength
conversion of some or all of the light can facilitate redirection
and/or emission of the light from the illumination assembly.
[0032] Some embodiments presented herein include illumination
assemblies with one or more solid state light-emitting devices that
can emit primary light having a first wavelength spectrum and a
wavelength converting material (e.g., phosphors and/or quantum
dots) that can covert the primary light to secondary light having a
different wavelength spectrum (e.g., down-convert the primary light
to a lower energy). As used herein, a wavelength converting
material refers to a material that can absorb some or substantially
all of the primary light having a first wavelength spectrum (e.g.,
blue light, UV light) and emit secondary light having a second
different wavelength spectrum (e.g., white light, yellow light, red
light, green light, and/or blue light). The wavelength converting
material can down-convert light from shorter wavelengths (higher
energies) to longer wavelengths (shorter energies). Phosphors are
examples of typical wavelength converting materials, which can take
the form of phosphor particles. Quantum dots can also serve as
wavelength converting materials.
[0033] In some embodiments presented herein, the wavelength
converting material can have a density that differs in different
locations. The density of wavelength converting material per unit
area is the amount of wavelength converting material per averaging
area disposed above and underneath an averaging area of 1.times.1
cm.sup.2. For example, in some embodiments, the averaging area can
be located on the emission surface of an illumination assembly, and
in such cases, the density is referred to as the density of
wavelength converting material per unit area of the emission
surface. Such an averaging area excludes variations of wavelength
converting material density at the package level of a solid state
light-emitting device, for example, variations of wavelength
converting material density within an encapsulant layer of a
light-emitting device.
[0034] FIG. 1A illustrates an illumination assembly including one
or more solid state light-emitting devices, in accordance with one
embodiment. Illumination assembly 100a can include a solid state
light-emitting device 150 which may include one or more
light-emitting diodes and/or laser diodes. Although the
illumination assembly illustrated in FIG. 1A is edge-lit by one or
more solid state light-emitting devices, alternatively or
additionally, an illumination assembly can be back-lit by one or
more solid sate light-emitting devices. In some embodiments, a
plurality of illumination assemblies, similar to illumination
assembly 100a, can be arranged adjacent each other (e.g., tiled
along either one or two dimensions) to form a combined illumination
assembly having a combined light emission surface (e.g., adjacent
light emission surfaces that can tile a surface, such as a plane).
The light emission surface area of an illumination assembly (or
combined assembly) may be greater than about 0.01 m.sup.2 (e.g.,
greater than or equal to about 0.05 m.sup.2, greater than or equal
to about 0.1 m.sup.2, greater than or equal to about 0.16 m.sup.2,
greater than or equal to about 0.5 m.sup.2, greater than or equal
to about 1 m.sup.2). In some embodiments, the light emission
surface area of an illumination assembly ranges between about 0.01
m.sup.2 and about 0.05 m.sup.2, between about 0.05 m.sup.2 and
about 0.1 m.sup.2, between about 0.1 m.sup.2 and about 0.5 m.sup.2,
or between about 0.5 m.sup.2 and about 1 m.sup.2.
[0035] Light 152 (referred to as primary light) emitted by the
light-emitting device 150 may be coupled into a light
homogenization region 112 that can spatially distribute the light
such that light emitted via a light output boundary 113 (e.g.,
light output surface) has a substantially uniform intensity on
different locations of the light output boundary 113. Light
homogenization region 112 may be a region where light is not
substantially extracted along the length of the homogenization
region 112.
[0036] Light homogenization region 112 may comprise a light guide
having a higher index than a surrounding medium. The light guide
can include an edge configured to receive the light emitted by the
solid state light-emitting device 150. For example, light
homogenization region 112 may include part or all of a light guide
formed of an optically transparent material such as transparent
plastic (e.g., PMMA, acrylic) and/or glass. The light guide can
have any suitable shape. In some embodiments, the light guide has a
slab shape (e.g., rectangular slab, square slab, trapezoidal slab),
a cylindrical shape (e.g., rod with a circular or elliptical
cross-section), and/or other suitable light guiding shapes. The
shape of the light output boundary of the homogenization region may
be related to the shape of the light guide, for example, a
rectangular light guide including a homogenization region may be
such that the light output boundary is a rectangular cross-section
of the rectangular guide, as illustrated in FIG. 1A.
[0037] Light 153 outputted by the light homogenization region 112
may be coupled to a light extraction region 114 where light is
substantially extracted along the light extraction region 114.
Light extraction region 114 can include a light emission surface
120 through which light 102 can be emitted. The emission surface of
the light extraction region may be substantially perpendicular to
the general direction of the light 153 inputted into the light
extraction region 114. Light extraction region 114 can include
light scattering features that can scatter light out via the light
emission surface 120. In some embodiments, light extraction region
114 can be configured and arranged such that light emission form
emission surface 120 has a substantially uniform (e.g., less than
about 20% variation, less than about 15% variation, less than about
10% variation) light intensity across the emission surface 120.
[0038] Light extraction region 114 may comprise a light guide.
Light scattering features may be located in the light guide volume
and/or on the top and/or bottom surfaces of the light guide. The
number of scattering features may vary along the length of the
light guide so as to ensure that light emission via the light
emission surface is substantially uniform along the length of the
light guide. As illustrated in FIG. 1A, the light emission surface
120 can be substantially parallel to the length of the light guide.
In some embodiments, the intensity variation of light emitted along
the length of the light guide is less than about 20% (e.g., less
than about 15%, less than about 10%, less than about 5%). In some
embodiments, light extraction region 114 may include part or all of
a light guide formed of an optically transparent material such as
glass or a plastic material (e.g., acrylic, PMMA).
[0039] In some embodiments, a gap 104 may be present between the
light output boundary 113 of homogenization region 112 and the
light extraction region 114. the gap 104 can ensure that any light
that is coupled into the light extraction region 114 remains
confined in the light extraction region due to total internal
reflection (e.g., in the absence of scattering features and/or a
light guide tapering). Alternatively, homogenization region 112 and
extraction region 114 may be in contact with each other. For
example, homogenization region 112 and extraction region 114 may
both be part of a single light guide.
[0040] Illumination assembly 100a can include wavelength converting
material in one or more locations, such as one or more phosphors
and/or one or more types of quantum dots. The wavelength converting
material can absorb and convert primary light having a first
wavelength spectrum to secondary light having a second wavelength
spectrum different from the first wavelength spectrum. In some
embodiments, the wavelength converting material can down-convert
light having higher energy (e.g., shorter wavelengths) to light
having lower energy (e.g., longer wavelengths). For example, the
wavelength converting material can down-convert blue and/or
ultraviolet light to longer wavelength light, such as red, green,
yellow, or blue light, or combinations thereof. White light can be
created with a combination of multiple colors, for example, blue
and yellow, or blue, green, and red. Thus, one method of forming
white light using a wavelength converting material can include
down-converting some blue primary light to yellow and forming white
light with a combination of secondary yellow light and unconverted
primary blue light. Another method of forming white light includes
down-converting some primary blue light to red and green light, for
example using two or more different wavelength converting materials
(e.g., a red-emitting and a green-emitting wavelength converting
material). Another method of forming white light includes
down-converting ultraviolet light to red, green, and blue light,
for example using two or more different wavelength converting
materials (e.g., a red-emitting, a green-emitting, and a
blue-emitting wavelength converting material).
[0041] In some embodiments, wavelength converting material is
disposed within homogenization region 112. Alternatively, or
additionally, wavelength converting material may be disposed within
extraction region 114. The presence of wavelength converting
material in the illumination assembly can facilitate the process of
spatial homogenization and/or extraction of light from the
illumination assembly (e.g., via the light emission surface
120).
[0042] The wavelength converting material may be located within
part or all of the homogenization region 112 such that some or all
of the primary light from light-emitting device 150 may be
wavelength converted within the homogenization region 112. The
process of wavelength conversion can facilitate light
homogenization since primary light 152 traveling in a given
direction based on the arrangement of the light-emitting device 150
can be absorbed by the wavelength converting material and secondary
light can be re-emitted in any other direction with equal
probability. This can also allow for a decrease in the length of
the homogenization region used to provide for a substantially
uniform light intensity at light output boundary 113. The placement
of the wavelength converting material in the homogenization region
112 can provide for the output of secondary light from the
homogenization region 112, or a combination of secondary and
primary light.
[0043] In some embodiments, the wavelength converting material may
be uniformly distributed throughout the light homogenization region
112. In other embodiments, the wavelength converting material may
have a varying density for at least two locations in the
homogenization region 112. For example, the density of wavelength
converting material can be highest at the light output boundary
113. Alternatively, the density of wavelength converting material
can be lowest at the light output boundary 113. The wavelength
converting material density may be graded and may vary (e.g.,
decrease or increase) as a function of distance from the light
output boundary (or equivalently, as a function of distance from
the light source).
[0044] One or more different wavelength converting materials can be
included in the illumination assembly. In some embodiments, the
wavelength converting material includes a first wavelength
converting material that can emit secondary light having a first
dominant wavelength and a second wavelength converting material
that can emit secondary light having a second dominant wavelength
different from the first dominant wavelength. The first wavelength
converting material can be disposed in the optical path between the
solid state light-emitting device and the second wavelength
converting material. The first dominant wavelength can be larger
than the second dominant wavelength. In other embodiments, the
first dominant wavelength can be smaller than the second dominant
wavelength. A wavelength filter can be disposed in the optical path
between the first and the second wavelength converting materials,
and configured to reflect light emitted by the second wavelength
converting material and transmit light emitted by the first
wavelength material and the solid state light-emitting device.
[0045] Alternatively, or additionally, wavelength converting
material may be located within part or throughout all of the light
extraction region 114. Primary light traveling within light
extraction region 114 can thus be wavelength converted and
secondary light can be generated and extracted via emission surface
120. Primary light traveling through the light extraction region
114 can also be scattered by wavelength converting material within
the light extraction region 114 and some of the primary light can
thus be extracted via emission surface 120 by such a mechanism.
Light outputted by the illumination assembly can include both some
primary light and secondary light. Alternatively, the light
outputted by the illumination assembly may include secondary light
with no primary light. In some embodiments, the light outputted by
the illumination assembly is white light, which may be formed by
the combination of primary light (e.g., blue light) and secondary
light (e.g., yellow light). Alternatively, the light outputted by
the illumination assembly is white light including the secondary
light and not including any substantial amount of primary light
(e.g., UV light).
[0046] FIG. 1B is a cross-section view of an illumination assembly
100b including a tapered extraction region 114, in accordance with
one embodiment. The taper can be provided by a wedge-shaped light
guide. The light guide can include an edge configured to receive
the light emitted by the solid state light-emitting device. A
tapered extraction region 114 can facilitate light extraction via
the frustration of total internal reflection in the light guide.
Such a mechanism can be used alone, or in combination with light
scattering features (e.g., surface features such as prisms and/or
lens, volume features such as regions with different refractive
indices than the surrounding light guide material), to provide for
light extraction via light emission surface 120.
[0047] It should be appreciated that illumination assemblies can
include one or more reflectors. A backside reflector can be
disposed under the backside surface (e.g., opposite the light
emission surface 120) of the light extraction region and can
reflect back any light that is scattered downwards (e.g., by light
extraction features). That reflected light can then be extracted
via light emission surface 120.
[0048] In some embodiments, an illumination assembly can serve as a
backlight unit for a display, such as a LCD. Such an embodiment is
illustrated in the cross-section schematic of FIG. 1C. One or more
layers 190 of the display 100c may be illuminated by the
illumination assembly. Layer(s) 190 may include a liquid crystal
light valve layer (corresponding to the liquid crystal light-valve
pixels of the display) located over light emission surface 120. The
illumination assembly can thus serve as a backlighting assembly for
the liquid crystal display layer and light 102 from the
illumination assembly can impinge on the liquid crystal display
layer.
[0049] Other layers often used in LCDs, such as diffuser layers,
brightness enhancement films (BEFs), and/or color filters may be
located over the light emission surface of the illumination
assembly. In addition to display backlighting, the illumination
assembly can be used for illumination purposes, including but not
limited to, signage backlighting, outdoor lighting, indoor
lighting, automotive lighting, and other lighting applications. For
a general lighting assembly, the illumination assembly can be used
as is or may have other layers disposed over the emission surface
of the assembly, for example one or more layers may be located over
the assembly so as to alter the lightening character. For example,
a textured or patterned layer or optic (e.g., a polymer and/or
glass component) may be placed over the assembly.
[0050] In some embodiments, a liquid crystal display system can
include a small number of high light output power light-emitting
devices that provide illumination for a large display area. Such a
liquid crystal display can include a liquid crystal display panel
having an illumination area, and at least one sold state
light-emitting device associated with the liquid crystal display
panel such that light emitted from the solid state light-emitting
device illuminates the liquid crystal display panel. The display
can include a wavelength converting material located remotely
(e.g., in a light homogenization region 112 and/or a light
extraction region 114) from solid state light-emitting device. In
some embodiments, the number of solid state light-emitting device
per m.sup.2 of the illumination area is less than 100, as discussed
further below.
[0051] In some embodiments, a small number of high light output
power light-emitting devices can be used to illuminate a large
emission area of an illumination assembly (e.g., an LCD
backlighting assembly). In some embodiments, the number of
light-emitting devices per unit area of the emission surface of an
illumination assembly is less than or equal to about 300 per
m.sup.2 (e.g., less than or equal to about 200 per m.sup.2, less
than or equal to about 100 per m.sup.2, less than or equal to about
50 per m.sup.2, less than or equal to about 25 per m.sup.2, less
than or equal to about 12 per m.sup.2). For example, the number of
light-emitting devices per m.sup.2 of the emission surface of an
illumination assembly may be between 5 to 100, between 25 to 100,
or between 50 to 100. A small number of light-emitting devices per
unit area can be enabled by the use of high-power light-emitting
devices which can be designed to emit a substantial amount of their
generated light via a large die surface area (e.g., greater than
about 4 mm.sup.2, greater than about 10 mm.sup.2, greater than
about 30 mm.sup.2, greater than about 100 mm.sup.2), as discussed
further below.
[0052] The number of light-emitting devices per illumination
assembly may be less than or equal to 12 (e.g., less than or equal
to about 8, less than or equal to about 6, less than or equal to
about 4, less than or equal to about 2). In some embodiments, a
single light-emitting device may illuminate an entire illumination
assembly.
[0053] The total number of light-emitting devices for certain
illumination assemblies has been provided above. For numbering
purposes, each of the following may count as one light-emitting
device: a light-emitting die, two or more associated light-emitting
dies, a partially packaged light-emitting die or dies, or a fully
packaged light-emitting die or dies. For example, one
light-emitting device may include a red light-emitting die
associated with a green light-emitting die and associated with a
blue light-emitting die.
[0054] In some embodiments, a light-emitting device is a
light-emitting device that emits light of a single color. For
example, the light-emitting device may be a red, green, blue,
yellow, and/or cyan light-emitting device. In other embodiments,
the light-emitting device is a multi-colored light-emitting device
that emits light having a spectrum of wavelengths. For example, the
light-emitting device may be a red-green-blue light-emitting
device. In other embodiments, the light-emitting device may be a
red-green-blue-yellow light-emitting device. In yet other
embodiments, the light-emitting device may be a red-green-blue-cyan
light-emitting device. In yet other embodiments, the light-emitting
device is a red-green-blue-cyan-yellow light-emitting device.
Illumination assemblies can also include combinations of
light-emitting device types such as the ones described above. Of
course, light-emitting devices of different colors can also be used
in embodiments.
[0055] Illumination assemblies such as those illustrated herein can
be used to perform light homogenization and/or light extraction.
FIG. 2A illustrates a flowchart 200a of a method for homogenizing
and wavelength converting light simultaneously, in accordance with
one embodiment. The method can be performed by an illumination
assembly that can include a wavelength converting material in a
light homogenization region, such as the illumination assemblies
illustrated in FIGS. 1A-C. The method can begin with the production
of primary light (act 202a). The primary light may be generated by
a solid state light-emitting device, such as one or more
light-emitting diodes and/or laser diodes.
[0056] The primary light may then be spatially homogenized and some
or substantially all of the primary light may be wavelength
converted to secondary light (act 204a). The wavelength conversion
may be performed by wavelength converting material, such as one or
more phosphors and/or one or more types of quantum dots. Since the
process of wavelength conversion can involve the absorption of
primary light by the wavelength converting material and the
emission of secondary light (e.g., down-converted to lower
energies) with any direction of emission having an equal
probability, spatial homogenization can be accomplished using
shorter homogenization lengths that without the use of a wavelength
converting material. The method can proceed with the extraction of
the secondary light and optionally also some or all of any
unconverted primary light (act 206a). Light extraction may occur
via a light emission surface of a light extraction region of an
illumination assembly. The light emission surface may be a surface
of a light guide, such as a top face of a slab light guide, as
previously described. In some embodiments, wavelength conversion
occurs only within the homogenization region and not within the
light extraction region.
[0057] FIG. 2B illustrates a flowchart 200b of a method for
wavelength converting and extracting light simultaneously, in
accordance with one embodiment. The method can be performed by an
illumination assembly that can include a wavelength converting
material in an extraction region, such as the illumination
assemblies illustrated in FIGS. 1A-C. The method can begin with the
production of primary light (act 202b). The primary light may be
generated by a solid state light-emitting device, such as one or
more light-emitting diodes and/or laser diodes. The primary light
may then be spatially homogenized (act 204b).
[0058] The method can proceed with the simultaneous wavelength
conversion of at least some of the primary light to secondary light
and extraction of the secondary light and optionally also some or
all of any unconverted primary light. The wavelength conversion may
be performed by wavelength converting material, such as one or more
phosphors and/or one or more types of quantum dots. In some
embodiments, the wavelength converting material (e.g., phosphor
particles and/or quantum dots) can absorb some primary light
impinging thereon and/or scatter some light (e.g., primary or
secondary light) impinging thereon. The process of wavelength
conversion can involve the absorption of primary light by the
wavelength converting material and the emission of secondary light
(e.g., down-converted to lower energies) with any direction of
emission having an equal probability. Also, some primary light that
impinges on wavelength converting material within the light
extraction region may be scattered and thereby extracted.
Therefore, the wavelength converting material can perform both
wavelength conversion and light scattering. The method can proceed
with the extraction of some or all of the secondary light and
optionally some or all of any unconverted primary light (act 206a).
Light extraction may occur via a light emission surface of a light
extraction region of an illumination assembly. The light emission
surface may be a surface of a light guide, such as a top face of a
slab light guide. In some embodiments, wavelength conversion occurs
only within the light extraction region and not within the light
homogenization region.
[0059] FIG. 3A is a cross-section view of an illumination assembly
300 having a different density of a wavelength converting material
for at least two locations, in accordance with one embodiment. By
arranging the wavelength converting material with a density that
differs in different locations, the percentage of primary light
that is wavelength converted to secondary light at various
locations can be different. Spatial variation in the percentage of
primary light that is wavelength converted at different locations
can be used to output light with a desired intensity at different
locations of a light emission surface 120. For example, the
wavelength converting material density can be higher in locations
where the primary light intensity is lower (as compared to
locations with a higher primary light intensity). Such a
configuration may be used to compensate for the spatial variation
of primary light intensity along the light extraction region 114
such that the amount of secondary light generated and outputted at
different locations along the light emission surface 120 is
substantially uniform. Furthermore, the wavelength converting
material can serve as light scattering features that can scatter
primary light out via the emission surface 120, therefore the
spatial variation of the wavelength converting material density may
also allow for the primary light outputted from the light emission
surface 120 to be substantially uniform over the entire
surface.
[0060] The density of wavelength converting material per unit area
of the light emission surface 120 may vary substantially (e.g., at
least 30% variation, at least 60% variation, at least 100%
variation) at different locations. For example, the density of the
wavelength converting material per unit area of the light emission
surface may vary as a function of distance from the solid state
light-emitting device 150. The density of the wavelength converting
material can vary at different locations of the light extraction
region 114. Alternatively, or additionally, the density of the
wavelength converting material can vary at different locations of
the light homogenization region 112. For example, locations 172 and
174 of FIG. 3A represent two opposing ends of the light extraction
region 114 at which the wavelength converting material density per
unit emission area can differ.
[0061] In some embodiments, the density of the wavelength
converting material can substantially increase (e.g.,
monotonically) further away from the solid state light source, such
as the solid state light-emitting device 150. In some embodiments,
the density of the wavelength converting material is such that at
locations further away from the solid state light-emitting device
150, the density is substantially greater (e.g., greater than about
30%, greater than about 60%, greater than about 100%) than that at
locations closer to the solid state light-emitting device 150.
[0062] FIG. 3B is a plot of the density of wavelength converting
material versus distance from a light source, in accordance with
one embodiment. Curve 101 represents the wavelength converting
material density (e.g., per unit volume, area, or length) as a
function of distance from the light source, where in the
illustrated plot the wavelength converting material density
increases with distance from the solid state light-emitting device
150.
[0063] For the illustrated example, the variation of the wavelength
converting material density can be expressed in terms of the
distance along the light extraction region 114. For example, the
left-most portion of curve 101 may be associated with the density
at location 172 of the light extraction region 114 and the
right-most portion of the curve 101 may be associated with the
density at location 174 of the light extraction region 114. In some
embodiments, the wavelength converting material density can be
lower in locations illuminated with a higher intensity of light
(e.g., primary light) from the solid state light-emitting device
150 than in locations illuminated with a lower intensity of light
(e.g., primary light) from the solid state light-emitting device
150. For illumination assemblies having a plurality of solid state
light-emitting devices, the wavelength converting material can have
a lower density in locations illuminated with a higher intensity of
light (e.g., primary light) from the plurality of solid state
light-emitting devices than in locations illuminated with a lower
intensity of light (e.g., primary light) from the plurality of
solid state light-emitting devices.
[0064] In some embodiments, a spatial variation of the density of
wavelength converting material can be used to facilitate spatially
uniform light emission across the light emission surface 120 of the
light extraction region 114. The intensity of the secondary light
and/or primary light emitted and/or scattered by the wavelength
converting material can vary by less than about 20% (e.g., less
than about 15%, less than about 10%, less than 5%) across the light
extraction region 114. For example, in the case of a variation of
light intensity of less than about 10% across the light extraction
region, a first density at a first location and a second density at
a second location of the light extraction region 114 can be such
that the wavelength converted light intensity (e.g., secondary
light intensity) from the first location is at least about 90% the
wavelength converted light intensity (e.g., secondary light
intensity) from the second location and no greater than about 110%
the wavelength converted light intensity from the second location.
In some embodiments, the density can vary inversely with the
primary light intensity at different locations along the light
extraction region 114. For example, the second density can be
greater than or equal to about 2 times (e.g., greater than or equal
to about 3 times, greater than or equal to about 4 times) the first
density, which can compensate for approximately a 50% reduction in
primary light intensity so as to produce substantially the same
intensity of secondary light at the first and second locations
along the light extraction region 114. As should be appreciated,
the first and second locations can be opposing ends of a light
extraction region 114 (e.g., locations 172 and 174), however the
embodiments are not limited in this respect.
[0065] FIG. 4 is a cross-section view of an illumination assembly
400 having a different density of a wavelength converting material
(e.g., per unit area over an averaging area of 1.times.1 cm.sup.2
on the emission surface 120) for at least two locations due to a
differing microscopic density of the wavelength converting
material, in accordance with one embodiment. A first location 172
can have a first density of wavelength converting material 117 and
a second location 174 can have a second density of wavelength
converting material 117. The second density can be substantially
different from the first density at least partially due to a
differing microscopic density of wavelength converting material at
the first and second locations. As described herein, the wavelength
converting material can include one or more phosphors and/or
quantum dots, and the microscopic density can be the number of
phosphor molecules and/or quantum dots per unit volume over a
length-scale much smaller than the averaging length-scale used to
calculate the density (e.g., much smaller than an averaging area of
1.times.1 cm.sup.2). As illustrated in FIG. 4, wavelength
converting material 117 can be dispersed throughout the light
extraction region 114 or on portions of the light extraction region
114. In some embodiments, the wavelength converting material 117
microscopic density can vary (e.g., increase monotonically,
decreases monotonically) along the length of the light extraction
region 114.
[0066] FIG. 5 is a cross-section view of an illumination assembly
500 having a different density of a wavelength converting material
(e.g., per unit area over an averaging area of 1.times.1 cm.sup.2
on the emission surface 120) for at least two locations due to a
differing thickness of a wavelength converting material region, in
accordance with one embodiment. The wavelength converting material
region 116 can include a wavelength converting material layer that
can comprise wavelength converting material (e.g., phosphor and/or
quantum dot particles) in a host material (e.g., polymer, glass).
The density of wavelength converting material per unit area of the
light emission surface 120 at a first location 172 may be
substantially different from the density at a second location 174
at least partially due to a differing thickness of the wavelength
converting material region 116 at the first location 172 and second
location 174. In some embodiments, the wavelength converting
material region 116 (e.g., layer) can be part of the light
extraction region 114. When a light extraction region 114 includes
a light guide 110, the wavelength converting material region 116
(e.g., layer) may be disposed over the light guide 110 (e.g., on
light emission surface 121 of the light guide 110), disposed under
the light guide 110 (e.g., on a backside opposing the light
emission surface 121 of the light guide), and/or embedded in the
light guide 110.
[0067] Other ways of varying the density of wavelength converting
material (e.g., per unit area over an averaging area of 1.times.1
cm.sup.2 on the emission surface 120) are possible. For example, in
some embodiments, the wavelength converting material can be part of
a plurality of wavelength converting material regions (e.g., each
region having a size of less than about 50 microns, less than about
100 microns, or less than about 500 microns) and the density of the
wavelength converting material (e.g., per unit area over an
averaging area of 1.times.1 cm.sup.2 on the emission surface 120)
can vary from one location to another at least partially due to a
differing spatial arrangement and/or size of the plurality of
wavelength converting material regions. In some embodiments, the
wavelength converting material regions include dots, squares,
rectangles, triangles, hexagons, stripes, and/or any other shapes
that can include wavelength converting material (e.g., dispersed in
and/or on a host material).
[0068] FIG. 6 is a top view of an illumination assembly 600 having
a different density (e.g., per unit area over an averaging area of
1.times.1 cm.sup.2 on the emission surface 120) of a wavelength
converting material for at least two locations due to a differing
spatial arrangement of a plurality of wavelength converting
material regions 116, in accordance with one embodiment. The
wavelength converting material regions 116 can comprise wavelength
converting material (e.g., phosphor and/or quantum dot particles)
in a host material (e.g., polymer, glass).
[0069] In the illustrated illumination assembly 600, the wavelength
converting material regions 116 can be dots, squares, stripes,
and/or any other suitable shapes. The plurality of wavelength
converting material regions 116 can have substantially similar
shapes. The wavelength converting material regions 116 can be
arranged spatially so as to have different nearest neighbor
distances as a function of location along the light extraction
region 114. In some embodiments, the wavelength converting material
regions 116 can be arranged in a periodic or non-periodic pattern.
Examples of such patterns are described in further detail
below.
[0070] FIG. 7 is a top view of an illumination assembly 700 having
a different density of a wavelength converting material for at
least two locations due to a differing size of a plurality of
wavelength converting material regions 116, in accordance with one
embodiment. As illustrated, the size of the wavelength converting
material regions 116 can vary with location along the light
extraction region 114 (e.g., as a function of distance from the
light-emitting device 150), and the spatial arrangement (of the
centers) of the wavelength converting material regions 116 can be
the same for all locations. It should be appreciated that the
density of wavelength converting material (e.g., per unit area over
an averaging area of 1.times.1 cm.sup.2 on the emission surface
120) can be different in different locations due to one or more of
the aforementioned reasons and/or other reasons.
[0071] FIGS. 8A-B are cross-section and top views, respectively, of
an illumination assembly 800 including wavelength converting
material disposed over a light emission surface 121 of a light
guide 110, in accordance with one embodiment. The light guide 110
can be configured to receive light 152 emitted by the solid state
light-emitting device 150. Light guide 110 can include an edge 122
configured to receive light 152 emitted by the solid state
light-emitting device 150. The light guide 110 can include a length
along which received light propagates. As previously described,
light from the light-emitting device 150 may be spatially
homogenized in light homogenization region 112. Homogenized light
may be coupled into the light extraction region 114.
[0072] Light guide 110 can include a light emission surface 121. In
some embodiments, wavelength converting material regions 116 may be
disposed over the light emission surface 121 of the light guide
110. It should be appreciated that since the wavelength converting
material regions 116 can emit secondary light (e.g., wavelength
converted light) and potentially scatter primary light that
impinges on the wavelength converting material features 116, both
the wavelength converting material regions 116 and the light guide
110 can be considered to be part of the light extraction region 114
of the illumination assembly 800. Therefore the light emission
surface of the illumination assembly 800 can comprise the exposed
surfaces of the wavelength converting material features 116 and the
exposed surface of the light guide 110.
[0073] Light coupled into the extraction region 114 may travel and
remain confined within light guide 110 in part or completely due to
total internal reflection off of the surfaces of the light guide
110. Alternatively, or additionally, light confinement within the
light guide 110 may be due to reflective regions disposed in
contact with at least a portion of the light guide 110 surfaces.
For example, reflective layer 126 may be located over the edge of
the light guide 110 opposing the light input edge 122. A reflector
124 may be disposed under the backside surface of the light guide
110. Reflective layers may be directly in contact with the light
guide or may be separated from the light guide by a gap. Reflective
layers may be formed of any suitable material, including but not
limited to a reflective metal (e.g., aluminum, silver, and/or
combinations thereof), and may be specular and/or diffuse
reflectors.
[0074] Light traveling within the extraction region 114 may be
emitted due to a frustration of total internal reflection which may
be due to light scattering due to light scattering features 118
(e.g., convex lens, concave lens, convex prisms, concave prisms,
refractive index variations), a tapering of the light guide
thickness along the length of the guide (not shown), scattering of
primary or secondary light due to interaction with wavelength
converting material in regions 116, and/or emission of wavelength
converted light (e.g., secondary light) by wavelength converting
material in regions 116. In some embodiments, the scattering of
primary light can be solely due to interaction with the wavelength
converting material and no light scattering features 118 need be
present. In some embodiments, scattering features 118 may be
present on the backside surface and/or emission surface 121 of the
light guide.
[0075] In some embodiments, the wavelength converting material may
have a varying density per unit area of the emission surface along
the length of the light guide. In some embodiments, the wavelength
converting material has a density per unit area of the emission
surface that substantially increases along the length of the light
guide. Density can thus generally increase along the length of the
light guide, however there may exist minor variations about the
generally increasing density trend.
[0076] Wavelength converting material features 116 may have any
desired shapes (e.g., stripes, dots, squares) and may be arranged
in with varying nearest neighbor distances along the length of the
light guide 110. In the illustrated illumination assembly shown in
FIGS. 8A-B, the wavelength converting region(s) 116 take the form
of stripes and can be spaced closer to each other further away from
the light-emitting device 150. The wavelength converting material
regions 116 may include a layer at least partially or completely
disposed over the emission surface of the light guide 110. The
wavelength converting material regions 116 may be partially (or
completely) disposed in contact with the light emission surface 121
of the light guide 110. Alternatively, or additionally, wavelength
converting material may be disposed within and/or under the light
guide.
[0077] The density of the wavelength converting material per unit
area of the emission surface can vary monotonically with distance
along the length of the light guide (e.g., related to distance from
the light-emitting device). The density of wavelength converting
material per unit area of the emission surface can vary at least
partially due to a varying density of wavelength converting
material, a varying thickness, a varying spatial arrangement and/or
size of a plurality of wavelength converting material regions 116,
as previously described. In the illustrated assembly of FIGS. 8A-B,
the density varies along the length of the light guide due to a
varying distance between wavelength converting material regions 116
(e.g., distance between strips that include wavelength converting
material).
[0078] Illumination assembly 800 may include one or more wavelength
filters. The wavelength filters may be reflective filters that can
reflect light in some range of wavelengths and transmit light with
wavelengths outside the range, and/or the wavelength filter may be
absorptive filters that can absorb light in some range of
wavelengths and transmit light with wavelengths outside the range.
The wavelength filters may include short-pass, long-pass filters,
or combinations thereof.
[0079] In some embodiments, a wavelength filter may be disposed in
the optical path between the solid sate light-emitting device and
the wavelength converting material. This filter may prevent any
wavelength converted light from entering the light-emitting device
or escaping via the exposed region of the light input edge. For
example, illumination assembly 800 may include a wavelength filter
129 arranged over the input edge 122 of the light guide 110.
Wavelength filter 129 may be configured to allow primary light
(e.g., blue and/or UV light) emitted by the light emitted device
150 to be transmitted, and to reflect secondary light (e.g.,
down-converted light) emitted by the wavelength converting material
in regions 116. Thus, wavelength filter 129 may prevent secondary
light from escaping the light guide 110 via edge 122.
[0080] In some embodiments, a wavelength filter may be disposed in
the optical path between the wavelength converting material and the
before the output of the illumination assembly. This filter may
prevent any primary light from escaping the illumination assembly
and may be particularly useful when the primary light is UV light.
Illumination assembly 800 may include such a wavelength filter 128
which may be disposed over the emission surface of the light
extraction region 114.
[0081] In some embodiments, light 102 emitted by the illumination
assembly 800 can include a mixture of secondary and primary light.
In other embodiments, light 102 emitted by the illumination
assembly 800 can include substantially only secondary light. For
example, if wavelength filter 128 is absent, light 102 emitted by
the illumination assembly may include a combination of primary and
secondary light (e.g., white light formed from a combination of
various wavelengths, such as blue and yellow light, or blue, green
and red light).
[0082] FIG. 9 is a cross-section view of an illumination assembly
900 including wavelength converting material disposed under a
backside surface of a light guide 110, in accordance with one
embodiment. In the illustrated illumination assembly 900, light
extraction features may be absent. The light guide 110 can include
a backside surface opposing the light emission surface 121 of the
light guide 110, and wavelength converting material regions 116 may
be partially (or completely) disposed under the backside surface.
The wavelength converting material regions 116 can be partially (or
completely) disposed in contact with the backside surface of the
light guide 110. Alternatively, or additionally, the wavelength
converting material may be disposed within the light guide 110. The
wavelength converting material regions 116 may be disposed in
contact with backside reflector 124, which can aid in the
extraction of any heat generated by the wavelength converting
material. Backside reflector 124 may be thermally coupled to a heat
sink to provide for heat dissipation.
[0083] FIG. 10 is a cross-section view of an illumination assembly
1000 including wavelength converting material disposed over a light
emission surface 121 of a light guide 110, in accordance with one
embodiment. A wavelength filter 132 may be disposed between the
light emission surface 121 of the light guide 110 and wavelength
converting material regions 116. Wavelength filter 132 may be
configured to transmit primary light and reflect secondary light
emitted by the wavelength converting material. Thus, wavelength
filter 132 may reflect secondary light that is emitted by the
wavelength converting material in regions 116 so as to prevent the
secondary light from entering the light guide 110.
[0084] FIG. 11A is a top view of an illumination assembly 1100a
including a plurality of wavelength converting material regions
116, in accordance with one embodiment. The wavelength converting
material regions 116 may be arranged with a varying nearest
neighbor distance at different locations along a light guide 110,
thereby providing for a varying density of wavelength converting
material along the light extraction region 114. The wavelength
converting material regions 116 may have any shape, for example,
the regions may comprise dots, as illustrated in FIG. 11A.
Additionally or alternatively, the thickness and/or size of the
wavelength converting material regions 116 may vary in different
locations of the light extraction region 114. For example, the
regions 116 may be thicker closer to the light-emitting device
150.
[0085] FIG. 11B is a top view of an illumination assembly 100b
including a wavelength converting material, in accordance with one
embodiment. Illumination assembly 1100b can include a plurality of
wavelength converting material regions (e.g., dots 116a-c) that can
be arranged so as to aligned with and disposed over a plurality of
display pixel light valves (of a liquid crystal layer) so as to
individually illuminate the pixel light valves. For example, the
display pixel light valves may be part of a liquid crystal layer
(not shown for clarity) placed over the emission surface 121 of the
illumination assembly 110b, as previously illustrated and described
in FIG. 1C. The size of each wavelength converting material region
(e.g., dots 116a-c) can be about the size of the display pixel
light-valves.
[0086] Different wavelength converting materials (e.g.,
red-emitting phosphor, green-emitting phosphor, blue-emitting
phosphor) can be located in different wavelength converting
material regions (e.g., dots 116a-c) such that different pixel
light valves can be illuminated with a different color of light.
Such assemblies can allow for the elimination of color filters in
LCDs and can thus improve the LCD system efficiency. In some such
assemblies, the light-emitting devices can emit UV primary light
which can be converted by different wavelength converting materials
in different regions (e.g., dots). In some such assemblies, the
light-emitting devices can emit blue primary light. When blue
primary light is used, red-emitting and green-emitting wavelength
converting materials can be used to illuminate red and green pixel
light valves, respectively, whereas blue pixel light valves can be
illuminated by the primary light (e.g., which can be extracted
locally using light scattering features of the light guide 110
aligned with the blue pixel light valves).
[0087] FIGS. 12A-B are cross-section and top views, respectively,
of an illumination assembly 1200 including wavelength converting
material having a spatially varying density (e.g., per unit area
over an averaging area of 1.times.1 cm.sup.2 on the emission
surface of the assembly), in accordance with one embodiment. A
plurality of light-emitting devices 150 can be arranged to emit
light into one or more edges of the light guide 110. The wavelength
converting material density (e.g., per unit area over an averaging
area of 1.times.1 cm.sup.2 on the emission surface of the assembly)
can vary in one or two dimensions. FIG. 12B illustrates an
embodiment where the spatial variation of the wavelength converting
material density per unit area can vary in two dimensions that
define the emission surface 121.
[0088] The density of the wavelength converting material per unit
area can be configured so as be higher in portions of the light
guide 110 where the primary light intensity is lower. For example,
when the primary light intensity is lower in the center portion 181
and the corner portions 182 of the light guide 110, the wavelength
converting material may have a higher density (as illustrated by
the darker shaded portions of the top view in FIG. 12B) in those
portions of the light guide 110. Such an inverse relationship can
allow for compensation of decreased primary light intensity along
the light guide 110 such that light 102 emitted by the illumination
assembly can be substantially spatially uniform across the entire
emission surface 121.
[0089] FIG. 13 is a top view of an illumination assembly 1300
including a wavelength converting material having a spatially
varying density (e.g., per unit area over an averaging area of
1.times.1 cm.sup.2 on the emission surface), in accordance with one
embodiment. Illumination assembly 1300 is similar to illumination
assembly 1200, except that the plurality of light-emitting devices
150 can emit light into the corner portions of light guide. Such an
arrangement can allow for a more spatially uniform primary light
intensity within the light guide 110, as compared to the assembly
1200 of FIG. 12. In turn, for circumstances where a spatially
uniform light emission is desired from the illumination assembly,
the wavelength converting material density per unit area need only
have a higher value in the center portion 181 of the light guide.
In some embodiments, a portion or all of the edges of the light
guide (not coupling light from light-emitting devices 150) may be
coated with a reflective material (e.g., a metal such as aluminum
and/or silver) so as to prevent any light (e.g., primary and/or
secondary light) from escaping the light guide.
[0090] FIGS. 14A-B are cross-section and top views, respectively,
of an illumination assembly 1400 including a wavelength converting
material and one or more wavelength filters, in accordance with one
embodiment.
[0091] Illumination assembly 1400 can include one or more solid
state light-emitting devices 150. A light guide 110 can be
configured to receive primary light 152 emitted by the solid state
light-emitting device 150, where the light guide 110 can have a
length along which light propagates and an emission surface 121
through which light is emitted. A wavelength converting material
that can generate secondary light 153 can be disposed in the
optical path between the solid state light-emitting device 150 and
the emission surface 121 of the light guide.
[0092] One or more wavelength filter(s) (e.g., filter 129) can be
disposed in the optical path between the solid sate light-emitting
device 150 and the wavelength converting material. The wavelength
filter 129 can be configured to transmit primary light emitted by
the light-emitting device 150 and reflect secondary light (e.g.,
wavelength converted light). Thus, wavelength filter 129 can
comprise a short pass wavelength filter disposed over (e.g.,
directly on) the light input side 122 of the light homogenization
region, wherein the short pass wavelength filter is configured to
transmit light from the solid state light-emitting device 150 and
reflect wavelength converted light from the wavelength converting
material. Wavelength filter 129 can thus prevent wavelength
converted light that is back-emitted or back-scattered from
escaping the homogenization region 112.
[0093] Illumination assembly 1400 can include light homogenization
region 112 disposed in the optical path between the solid state
light-emitting device 150 and the emission surface 121 of the light
guide 110. The wavelength converting material may be disposed
within the light homogenization region 112. As used herein, the
term "disposed within" means located inside the homogenization
region and not located at the input or output edges of the
homogenization region.
[0094] The wavelength converting material can be disposed within at
least a portion of the homogenization region 112 or throughout the
entire homogenization region 112. Alternatively, or additionally,
the wavelength converting material can be located at one or more
edges of the light homogenization region, for example on the light
input edge 122 and/or the light output edge 113 of the
homogenization region. In some embodiments, the density of the
wavelength converting material can vary at different locations in
the homogenization region 112. For example, the density of the
wavelength converting material may be higher further away from the
light input edge 122.
[0095] In some embodiments, illumination assembly 1400 can include
wavelength filter 128 (e.g., a long pass wavelength filter) on a
light output side of the light homogenization region 112.
Wavelength filter 128 can be configured to transmit the wavelength
converted light (e.g., secondary light) from the wavelength
converting material and reflect primary light emitted by the solid
state light-emitting device 150.
[0096] Multiple wavelength filters can be arranged in a cascading
configuration, where the light output of one wavelength filter can
serve as the light input of another wavelength filter. Wavelength
converting material can be disposed in the optical path between the
light output side of one wavelength filter and the light input side
of another wavelength filter. The wavelength converting material
can be different (e.g., wavelength convert different wavelength
ranges and/or generate different wavelengths of secondary light) in
different regions. For example, different wavelength converting
materials can be cascaded in the optical path. In some embodiments,
lower energy (e.g., longer wavelength) light can be generated by a
wavelength converting material closer to the light-emitting device
150 and successfully higher energy light (e.g., shorter wavelength)
can be generated by one or more different wavelength converting
materials arranged in succession thereafter. In other embodiments,
high energy (e.g., shorter wavelength) light can be generated by a
wavelength converting material closer to the light-emitting device
150 and successfully lower energy light (e.g., longer wavelength)
can be generated by one or more different wavelength converting
materials arranged in succession thereafter.
[0097] Different wavelength converting materials can be isolated
from another by one or more wavelength filters. The wavelength
filter(s) can be configured to prevent secondary light from a given
wavelength converting material from entering a different wavelength
converting material located closer to the light-emitting device
150. For example, the illumination assembly 1400 can comprise a
second short pass wavelength filter (in addition to wavelength
filter 129) and a second wavelength converting material different
from the first wavelength converting material. The second short
pass filter can be disposed in the optical path between the
wavelength converting material and the second wavelength converting
material, and the second short pass wavelength filter can be
configured to transmit light from the solid state light-emitting
device, transmit wavelength converted light from the wavelength
converting material, and reflect wavelength converted light from
the second wavelength converting material.
[0098] In some embodiments, illumination assembly 1400 can include
one or more reflective surfaces 125 on one or more surfaces and/or
edges of the light homogenization region 114. The reflective
surfaces 125 can prevent light (e.g., primary and/or secondary
light) from escaping via edges and/or surfaces of the
homogenization region 112. Thus, in such an embodiment, light can
essentially be outputted only from the light output edge 113 of the
light homogenization region and not via other edges or surfaces of
the light homogenization region 112.
[0099] FIGS. 15A-B are cross-section and top views, respectively,
of an illumination assembly 1500 including a backlight wavelength
converting region 116, in accordance with one embodiment.
Illumination assembly 1500 can include one or more light-emitting
devices 150 including light emission surfaces 38. The wavelength
converting material 116 can be disposed over the light emission
surfaces 38 of the solid state light-emitting devices 150. Thus, in
such an arrangement, the light-emitting devices 150 can directly
backlight the wavelength converting material 116 with primary light
152 emitted by the light-emitting devices 150.
[0100] The one or more solid state light-emitting devices 150 can
be located on a first plane. In one embodiment, the solid state
light-emitting devices 150 are supported by a thermal management
system, which can include a heat conductive plane 159 (e.g., a
metal planar layer). The wavelength converting material 116 can be
disposed over the emission surfaces of the light-emitting devices
150 and, in some instances, may be arranged on a second plane
substantially parallel to the first plane on which the
light-emitting devices 150 can be arranged.
[0101] In one embodiment, the wavelength converting material 116
can have a density per unit area that is different at different
locations (e.g., at different locations of the second plane). For
example, first and second locations of the wavelength converting
material 116 may be located at different locations of the second
plane parallel to the first plane one which the light-emitting
devices 150 can be located. The first locations may be disposed
over the light emission surfaces 38 of the light-emitting devices
150 and second locations may be disposed over regions in-between
the light emission surfaces 38 of the light-emitting devices 150.
The density of wavelength converting material in the first regions
may be lower than the density of wavelength converting material in
the second regions. Such an arrangement can compensate for a lower
primary light intensity at regions in-between the light-emitting
devices 150 (e.g., not directly above a light-emitting device 150
emission area 38) so as to provide for substantially similar
secondary light intensity across the entire emission surface of the
illumination assembly (e.g., the second plane). Generally, in some
embodiments, the wavelength converting material 116 can have a
lower density per unit area in locations illuminated with a higher
intensity of primary light than in locations illuminated with a
lower intensity of primary.
[0102] In some embodiments, the illumination assembly 1500 can
include one or more wavelength filters. Wavelength filter 129 may
be disposed between the light-emitting devices 150 and the
wavelength converting material 116. Wavelength filter 129 may
include a short pass filter configured to transmit primary light
from the light-emitting devices and reflect secondary light
generated by the wavelength converting material in region 116. In
some embodiments, wavelength filter 128 may be disposed over the
emission surface of the wavelength converting material 116.
Wavelength filter 128 may include a long pass filter configured to
transmit secondary light generated by the wavelength converting
material in region 116 and reflect primary light emitted by the
light-emitting devices 150. Such an arrangement can be beneficial
when the primary light is ultra-violet light and the secondary
light is visible light. In these arrangement, it may be desirable
to only output secondary visible light (e.g., light 102) and
reflect back ultra-violet primary light (e.g., using filter 128) so
as not to expose a viewer of the illumination assembly to
ultra-violet light. Alternatively, light 102 may include a mixture
of primary and secondary light, for example a mixture of blue
primary light and secondary light, such as yellow, red, and/or
green light. Such arrangements can be used to generate white
light.
[0103] Various methods can be employed to make the illumination
assemblies described herein. With regards to forming the wavelength
converting material regions, methods such as printing, molding
(e.g., injection molding), coating, spraying, and/or embossing may
be employed. For example, a printing process (e.g., a jet printing
process) may be used to create wavelength converting material
having a spatially varying density (e.g., per unit area of the
emission surface of the illumination assembly). The printer
cartridge may include a solution comprising the wavelength
converting material (e.g., phosphor and/or quantum dots). Varying
thickness of a wavelength converting material region can then be
created by performing a longer printing step at different
locations. Alternatively, or additionally, small features (e.g.,
dots, stripes) with small sizes (e.g., less than 500 microns, less
than 200 microns, less than 100 microns) can be printed with a
spatially varying nearest neighbor distance. In other embodiments,
wavelength converting material may be included in a molding
material (e.g., a polymer such as PMMA or acrylic) so as to have a
varying density at different locations of the molded component,
such as a molded light guide.
[0104] In some embodiments, an illumination assembly may include a
thermal management system that can dissipate heat produced by the
light-emitting devices. In some embodiments, the thermal management
system may be located on the backside of the illumination assembly
(e.g., the side opposite the light emission surface). Such a
feature may be desirable when the light-emitting devices are
high-power light-emitting devices that generate significant amounts
of heat, as may be the case when few light-emitting devices are
used to illuminate each tile. Examples of thermal management
systems for display and illumination systems are provided in U.S.
patent application Ser. No. 11/413,968, entitled "LCD Thermal
Management Methods and Systems," filed on Apr. 28, 2006, which is
herein incorporated by reference in its entirety. Generally, a
thermal management system may include a suitable system that can
conduct and dissipate heat which may be generated by devices and
components of the illumination assembly. In some embodiments, a
thermal management system may be characterized by, or may include
one or more components that are characterized by, a thermal
conductivity greater than 5,000 W/mK, greater than 10,000 W/mK,
and/or greater than 20,000 W/mK. In some embodiments, the thermal
conductivity lies in a range between 10,000 W/mK and 50,000 W/mK
(e.g., between 10,000 W/mK and 20,000 W/mK, between 20,000 W/mK and
30,000 W/mK, between 30,000 W/mK and 40,000 W/mK, between 40,000
W/mK and 50,000 W/mK).
[0105] In some embodiments, a thermal management system can include
passive and/or active heat exchanging mechanisms. Passive thermal
management systems can include structures formed of one or more
materials that rapidly conduct heat as a result of temperature
differences in the structure. Thermal management systems may also
include one or more protrusions which can increase the surface
contact area with the surrounding ambient and therefore facilitate
heat exchange with the ambient. In some embodiments, a protrusion
may include a fin structure that may have a large surface area. In
a further embodiment, a thermal management system can include
channels in which fluid (e.g., liquid and/or gas) may flow so as to
aid in heat extraction and transmission. For example, the thermal
management system may comprise one or more heat pipes to facilitate
heat removal. Various heat pipes are well known to those in the
art, and it should be understood that the embodiments presented
herein are not limited to merely to such examples of heat pipes.
Heat pipes can be designed to have any suitable shape, and are not
necessarily limited to only cylindrical shapes. Other heat pipe
shapes may include rectangular shapes which may have any desired
dimensions. In some embodiments, one or more heat pipes may be
arranged such that a first end of the heat pipes is located in
regions of the illumination assembly that are exposed to high
temperatures, such as in proximity to one or more light-emitting
devices. A second end of the heat pipes (i.e., a cooling end) may
be exposed to the ambient. The heat pipes may be in thermal contact
with protrusions to aid in heat exchange with the ambient by
providing increased surface area. Since heat pipes may have a
thermal conductivity that is many times greater (e.g., 5 times
greater, 10 times greater) than the thermal conductivity of many
metals (e.g., copper), the conduction of heat may be improved via
the incorporation of the heat pipes into illumination systems.
[0106] Active thermal management systems may include one or more
suitable means that can further aid in the extraction and
transmission of heat. Such active thermal management systems can
include mechanical, electrical, chemical and/or any other suitable
means to facilitate the exchange of heat. In one embodiment, an
active thermal management system may include a fan used to
circulate air and therefore provide cooling. In another embodiment,
a pump may be used to circulate a fluid (e.g., liquid, gas) within
channels in the thermal management system. In further embodiments,
the thermal management system may include a thermal electric cooler
that may further facilitate heat extraction.
[0107] In some embodiments, the solid state light-emitting devices
in the illumination assemblies presented herein can include a
light-emitting diode. FIG. 16 illustrates a light-emitting diode
(LED) which may be one example of a light-emitting device, in
accordance with one embodiment. It should be understood that
various embodiments presented herein can also be applied to other
light-emitting devices, such as laser diodes, and LEDs having
different structures (such as organic LEDs, also referred to as
OLEDs). LED 1600 shown in FIG. 16 comprises a multi-layer stack 31
that may be disposed on a support structure (not shown). The
multi-layer stack 31 can include an active region 34 which is
formed between n-doped layer(s) 35 and p-doped layer(s) 33. The
stack can also include an electrically conductive layer 32 which
may serve as a p-side contact, which can also serve as an optically
reflective layer. An n-side contact pad 36 may be disposed on layer
35. Electrically conductive fingers (not shown) may extend from the
contact pad 36 and along the surface 38, thereby allowing for
uniform current injection into the LED structure.
[0108] It should be appreciated that the LED is not limited to the
configuration shown in FIG. 16, for example, the n-doped and
p-doped sides may be interchanged so as to form a LED having a
p-doped region in contact with the contact pad 36 and an n-doped
region in contact with layer 32. As described further below,
electrical potential may be applied to the contact pads which can
result in light generation within active region 34 and emission
(represented by arrows 152) of at least some of the light generated
through an emission surface 38. As described further below, holes
39 may be defined in an emission surface to form a pattern that can
influence light emission characteristics, such as light extraction
and/or light collimation. It should be understood that other
modifications can be made to the representative LED structure
presented, and that embodiments are not limited in this
respect.
[0109] The active region of an LED can include one or more quantum
wells surrounded by barrier layers. The quantum well structure may
be defined by a semiconductor material layer (e.g., in a single
quantum well), or more than one semiconductor material layers
(e.g., in multiple quantum wells), with a smaller electronic band
gap as compared to the barrier layers. Suitable semiconductor
material layers for the quantum well structures can include InGaN,
AlGaN, GaN and combinations of these layers (e.g., alternating
InGaN/GaN layers, where a GaN layer serves as a barrier layer). In
general, LEDs can include an active region comprising one or more
semiconductors materials, including III-V semiconductors (e.g.,
GaAs, AlGaAs, AlGaP, GaP, GaAsP, InGaAs, InAs, InP, GaN, InGaN,
InGaAlP, AlGaN, as well as combinations and alloys thereof), II-VI
semiconductors (e.g., ZnSe, CdSe, ZnCdSe, ZnTe, ZnTeSe, ZnS, ZnSSe,
as well as combinations and alloys thereof), and/or other
semiconductors. Other light-emitting materials are possible such as
quantum dots or organic light-emission layers.
[0110] The n-doped layer(s) 35 can include a silicon-doped GaN
layer (e.g., having a thickness of about 4000 nm thick) and/or the
p-doped layer(s) 33 include a magnesium-doped GaN layer (e.g.,
having a thickness of about 40 nm thick). The electrically
conductive layer 32 may be a silver layer (e.g., having a thickness
of about 100 nm), which may also serve as a reflective layer (e.g.,
that reflects upwards any downward propagating light generated by
the active region 34). Furthermore, although not shown, other
layers may also be included in the LED; for example, an AlGaN layer
may be disposed between the active region 34 and the p-doped
layer(s) 33. It should be understood that compositions other than
those described herein may also be suitable for the layers of the
LED.
[0111] As a result of holes 39, the LED can have a dielectric
function that varies spatially according to a pattern. Typical hole
sizes can be less than about one micron (e.g., less than about 750
nm, less than about 500 nm, less than about 250 nm) and typical
nearest neighbor distances between holes can be less than about one
micron (e.g., less than about 750 nm, less than about 500 nm, less
than about 250 nm). Furthermore, as illustrated in the figure, the
holes 39 can be non-concentric.
[0112] The dielectric function that varies spatially according to a
pattern can influence the extraction efficiency and/or collimation
of light emitted by the LED. In some embodiments, a layer of the
LED may have a dielectric function that varies spatially according
to a pattern. In the illustrative LED 1600, the pattern is formed
of holes, but it should be appreciated that the variation of the
dielectric function at an interface need not necessarily result
from holes. Any suitable way of producing a variation in dielectric
function according to a pattern may be used. For example, the
pattern may be formed by varying the composition of layer 35 and/or
emission surface 38. The pattern may be periodic (e.g., having a
simple repeat cell, or having a complex repeat super-cell), or
non-periodic. As referred to herein, a complex periodic pattern is
a pattern that has more than one feature in each unit cell that
repeats in a periodic fashion. Examples of complex periodic
patterns include honeycomb patterns, honeycomb base patterns,
(2.times.2) base patterns, ring patterns, and Archimedean patterns.
In some embodiments, a complex periodic pattern can have certain
holes with one diameter and other holes with a smaller diameter. As
referred to herein, a non-periodic pattern is a pattern that has no
translational symmetry over a unit cell that has a length that is
at least 50 times the peak wavelength of light generated by one or
more light-generating portions. As used herein, peak wavelength
refers to the wavelength having a maximum light intensity, for
example, as measured using a spectroradiometer. Examples of
non-periodic patterns include aperiodic patterns, quasi-crystalline
patterns (e.g., quasi-crystal patterns having 8-fold symmetry),
Robinson patterns, and Amman patterns. A non-periodic pattern can
also include a detuned pattern (as described in U.S. Pat. No.
6,831,302 by Erchak, et al., which is incorporated herein by
reference in its entirety). In some embodiments, a device may
include a roughened surface. The surface roughness may have, for
example, a root-mean-square (rms) roughness about equal to an
average feature size which may be related to the wavelength of the
emitted light.
[0113] In certain embodiments, an interface of a light-emitting
device is patterned with holes which can form a photonic lattice.
Suitable LEDs having a dielectric function that varies spatially
(e.g., a photonic lattice) have been described in, for example,
U.S. Pat. No. 6,831,302 B2, entitled "Light emitting devices with
improved extraction efficiency," filed on Nov. 26, 2003, which is
herein incorporated by reference in its entirety. A high extraction
efficiency for an LED implies a high power of the emitted light and
hence high brightness which may be desirable in various optical
systems.
[0114] It should also be understood that other patterns are also
possible, including a pattern that conforms to a transformation of
a precursor pattern according to a mathematical function,
including, but not limited to an angular displacement
transformation. The pattern may also include a portion of a
transformed pattern, including, but not limited to, a pattern that
conforms to an angular displacement transformation. The pattern can
also include regions having patterns that are related to each other
by a rotation. A variety of such patterns are described in U.S.
Patent Publication No. 20070085098, entitled "Patterned devices and
related methods," filed on Mar. 7, 2006, which is herein
incorporated by reference in its entirety.
[0115] Light may be generated by the LED as follows. The p-side
contact layer can be held at a positive potential relative to the
n-side contact pad, which causes electrical current to be injected
into the LED. As the electrical current passes through the active
region, electrons from n-doped layer(s) can combine in the active
region with holes from p-doped layer(s), which can cause the active
region to generate light. The active region can contain a multitude
of point dipole radiation sources that generate light with a
spectrum of wavelengths characteristic of the material from which
the active region is formed. For InGaN/GaN quantum wells, the
spectrum of wavelengths of light generated by the light-generating
region can have a peak wavelength of about 445 nanometers (nm) and
a full width at half maximum (FWHM) of about 30 nm, which is
perceived by human eyes as blue light. The light emitted by the LED
may be influenced by any patterned surface through which light
passes, whereby the pattern can be arranged so as to influence
light extraction and/or collimation.
[0116] In other embodiments, the active region can generate light
having a peak wavelength corresponding to ultraviolet light (e.g.,
having a peak wavelength of about 370-390 nm), violet light (e.g.,
having a peak wavelength of about 390-430 nm), blue light (e.g.,
having a peak wavelength of about 430-480 nm), cyan light (e.g.,
having a peak wavelength of about 480-500 nm), green light (e.g.,
having a peak wavelength of about 500 to 550 nm), yellow-green
(e.g., having a peak wavelength of about 550-575 nm), yellow light
(e.g., having a peak wavelength of about 575-595 nm), amber light
(e.g., having a peak wavelength of about 595-605 nm), orange light
(e.g., having a peak wavelength of about 605-620 nm), red light
(e.g., having a peak wavelength of about 620-700 nm), and/or
infrared light (e.g., having a peak wavelength of about 700-1200
nm).
[0117] In certain embodiments, the LED may emit light having a high
light output power. As previously described, the high power of
emitted light may be a result of a pattern that influences the
light extraction efficiency of the LED. For example, the light
emitted by the LED may have a total power greater than 0.5 Watts
(e.g., greater than 1 Watt, greater than 5 Watts, or greater than
10 Watts). In some embodiments, the light generated has a total
power of less than 100 Watts, though this should not be construed
as a limitation of all embodiments. The total power of the light
emitted from an LED can be measured by using an integrating sphere
equipped with spectrometer, for example a SLM12 from Sphere Optics
Lab Systems. The desired power depends, in part, on the optical
system that the LED is being utilized within. For example, a
display system (e.g., a LCD system) may benefit from the
incorporation of high brightness LEDs which can reduce the total
number of LEDs that are used to illuminate the display system.
[0118] The light generated by the LED may also have a high total
power flux. As used herein, the term "total power flux" refers to
the total optical power divided by the emission area. In some
embodiments, the total power flux is greater than 0.03
Watts/mm.sup.2, greater than 0.05 Watts/mm.sup.2, greater than 0.1
Watts/mm.sup.2, or greater than 0.2 Watts/mm.sup.2. However, it
should be understood that the LEDs used in systems and methods
presented herein are not limited to the above-described power and
power flux values.
[0119] In some embodiments, the LED may be associated with one or
more wavelength converting regions. The wavelength converting
region(s) may include one or more phosphors and/or quantum dots.
The wavelength converting region(s) can absorb light emitted by the
light-generating region of the LED and emit light having a
different wavelength than that absorbed. In this manner, LEDs can
emit light of wavelength(s) (and, thus, color) that may not be
readily obtainable from LEDs that do not include wavelength
converting regions. In some embodiments, one or more wavelength
converting regions may be disposed over (e.g., directly on) the
emission surface (e.g., surface 38) of the light-emitting
device.
[0120] As used herein, an LED may be an LED die, a partially
packaged LED die, or a fully packaged LED die. It should be
understood that an LED may include two or more LED dies associated
with one another, for example a red light-emitting LED die, a green
light-emitting LED die, a blue light-emitting LED die, a cyan
light-emitting LED die, or a yellow light-emitting LED die. For
example, the two or more associated LED dies may be mounted on a
common package. The two or more LED dies may be associated such
that their respective light emissions may be combined to produce a
desired spectral emission. The two or more LED dies may also be
electrically associated with one another (e.g., connected to a
common ground).
[0121] As used herein, when a structure (e.g., layer, region) is
referred to as being "on", "over" "overlying" or "supported by"
another structure, it can be directly on the structure, or an
intervening structure (e.g., layer, region) also may be present. A
structure that is "directly on" or "in contact with" another
structure means that no intervening structure is present.
[0122] Having thus described several aspects of at least one
embodiment of this invention, it is to be appreciated various
alterations, modifications, and improvements will readily occur to
those skilled in the art. Such alterations, modifications, and
improvements are intended to be part of this disclosure, and are
intended to be within the spirit and scope of the invention.
Accordingly, the foregoing description and drawings are by way of
example only.
* * * * *