U.S. patent application number 14/519445 was filed with the patent office on 2015-05-14 for high na optical system and device.
The applicant listed for this patent is Illumitex, Inc.. Invention is credited to Dung T. Duong, Randall E. Johnson, Robert McAlister.
Application Number | 20150131261 14/519445 |
Document ID | / |
Family ID | 45874184 |
Filed Date | 2015-05-14 |
United States Patent
Application |
20150131261 |
Kind Code |
A1 |
Duong; Dung T. ; et
al. |
May 14, 2015 |
HIGH NA OPTICAL SYSTEM AND DEVICE
Abstract
Embodiments described herein provide an optical system having a
light source (e.g., LED) and a high numerical aperture
multi-element optical stack. According to one embodiment, the
optical stack can reimage an entrance aperture. The multi-element
optical stack can include a number of optical elements forming a
series of lenses. The series of lenses comprises, a first lens
positioned to receive light emitted in a first beam angle and a
second lens more distal from the LED than the first lens, the
second lens defining a second lens exit aperture that has at least
a minimum area necessary to conserve radiance for the emission beam
angle in air. The lenses in said series of lenses are configured,
in combination, to successively reduce a beam angle of light from
the first beam angle to the emission beam angle.
Inventors: |
Duong; Dung T.; (Bee Cave,
TX) ; McAlister; Robert; (Georgetown, TX) ;
Johnson; Randall E.; (Austin, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Illumitex, Inc. |
Austin |
TX |
US |
|
|
Family ID: |
45874184 |
Appl. No.: |
14/519445 |
Filed: |
October 21, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13243052 |
Sep 23, 2011 |
8899792 |
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14519445 |
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61386050 |
Sep 24, 2010 |
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61406503 |
Oct 25, 2010 |
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61479661 |
Apr 27, 2011 |
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61487511 |
May 18, 2011 |
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Current U.S.
Class: |
362/84 ;
362/268 |
Current CPC
Class: |
F21K 9/62 20160801; F21V
5/10 20180201; G02B 19/0028 20130101; H01L 33/58 20130101; F21V
5/008 20130101; G02B 19/0061 20130101; F21V 13/08 20130101; F21K
9/60 20160801 |
Class at
Publication: |
362/84 ;
362/268 |
International
Class: |
F21V 5/00 20060101
F21V005/00; F21V 13/02 20060101 F21V013/02; F21K 99/00 20060101
F21K099/00 |
Claims
1. An optical system to emit light in an emission beam angle
comprising: an LED; a high numerical aperture multi-element imaging
optical stack, the multi-element optical stack comprising a series
of lenses, wherein the series of lenses comprise: a first lens
positioned to receive light emitted in a first beam angle; a second
lens more distal from the LED than the first lens, the second lens
defining a second lens exit aperture that has at least a minimum
area necessary to conserve radiance for the emission beam angle in
air; wherein lenses in said series of lenses are configured, in
combination, to successively reduce a beam angle of light from the
first beam angle to the emission beam angle.
2. The optical system of claim 1, wherein the lenses in said series
of lenses are configured, in combination, to emit in the emission
beam angle at least 80% of the light entering the multi-element
optical stack.
3. The optical system of claim 1, wherein the multi-element optical
stack has a numerical aperture of at least 0.85.
4. The optical system of claim 1, wherein the series of lenses
further comprises an intermediate lens between the first lens and
the second lens.
5. The optical system of claim 1, wherein the multi-element optical
stack comprises a first optical element and a second optical
element forming the first lens.
6. The optical system of claim 5, wherein the first optical element
reduces the beam angle of light from the first beam angle to a
second beam angle, the second optical element the beam angle of
light from the second beam angle to a third beam angle and the
second lens reduces the beam angle from the third beam angle to the
emission beam angle.
7. The optical system of claim 1, further comprising a homogenizer
having an entrance face positioned to receive light from the LED
and sidewalls extending from the entrance face of the homogenizer
to the first lens.
8. The optical system of claim 7, wherein the homogenizer is
untapered.
9. The optical system of claim 7, wherein the homogenizer is
tapered.
10. The optical system of claim 7, further comprising: a
homogenizer housing structure having a portion forming the
homogenizer and a portion forming a first optical element; a second
optical element coupled to the first optical element to form first
lens.
11. The optical system of claim 10, wherein the homogenizer housing
structure further defines a homogenizer cavity about the
homogenizer.
12. The optical system of claim 11, further comprising a lens
housing, wherein the lens housing comprises a portion that forms
the second optical element.
13. The optical system of claim 12, wherein the lens housing
further comprises an outer wall defining a homogenizer housing
structure cavity to receive the homogenizer housing structure.
14. The optical system of claim 12, further comprising a second
lens structure having a portion that forms the second lens.
15. The optical system of claim 14, wherein: the lens housing
defines a lens cavity surrounding the second optical element; the
lens housing comprising a lens cavity wall; and the lens cavity
wall supports the second lens structure with the second lens
axially aligned with the first lens.
16. The optical system of claim 15, wherein the homogenizer is
separated from the LED by an air gap.
17. An optical system to emit light in an emission beam angle
comprising: a source, further comprising an LED; a homogenizer with
a high numerical aperture relative to the source; a high numerical
aperture imaging multi-element optical stack having an entrance
aperture and exit aperture, the multi-element optical stack
comprising: a series of lenses optically coupled to the
homogenizer, wherein lenses in said series of lenses are
configured, in combination, to successively reduce a beam angle of
light from a first beam angle to the emission beam angle and emit
in the emission beam angle at least 80% of the light entering the
series of lenses.
18. The optical system of claim 17, wherein the series of lenses
comprise: a first lens optically coupled to and axially aligned
with the homogenizer and positioned to receive light from the
homogenizer in the first beam angle; a second lens axially aligned
with the first lens and more distal from the LED than the first
lens, the second lens configured to emit light in the emission beam
angle and defining the exit aperture, wherein the exit aperture has
at least a minimum area necessary to conserve radiance for the
emission beam angle in air.
19. The optical system of claim 18, wherein the second lens is
optically coupled to the first lens through one or more
intermediate lenses in the series of lenses.
20. The optical system of claim 17, further comprising phosphors
disposed between the LED and the homogenizer.
21. The optical system of claim 17, wherein the homogenizer
comprises an entrance face separated from the LED by an air
gap.
22. The optical system of claim 17, wherein the multi-element
optical stack has a numerical aperture of greater than 0.85.
Description
RELATED APPLICATIONS
[0001] This application is a continuation of, and claims a benefit
of priority under 35 U.S.C. 120 of the filing date of U.S. patent
application Ser. No. 13/243,052, filed Sep. 23, 2011, entitled
"High NA Optical System and Device," which in turn claims the
benefit of priority under 35 U.S.C. .sctn.119(e) to U.S.
Provisional Patent Application No. 61/386,050, filed Sep. 24, 2010,
entitled "High NA Refractive LED Secondary Optic," U.S. Provisional
Patent Application No. 61/406,503, filed Oct. 25, 2010, entitled
"High NA Refractive LED Secondary Optic," U.S. Provisional Patent
Application No. 61/479,661, filed Apr. 27, 2011, entitled "High NA
Refractive LED Secondary Optic," and U.S. Provisional Patent
Application No. 61/487,511, filed May 18, 2011, entitled "LED
Homogenizer," each of which is fully incorporated by reference
herein.
TECHNICAL FIELD
[0002] Embodiments described herein are related to optics for
directing light into a desired beam angle. More particularly,
embodiments described herein are related to using high numerical
aperture ("NA") optics to project light from a light source into a
narrow beam angle.
BACKGROUND
[0003] Various solutions have been attempted to direct light into a
desired beam angle. Condenser lenses have been used in the
illumination industry to collect light for centuries. The drawback
of condenser lenses is that they have relatively low collection NA.
As LEDs have become more prevalent in the illumination industry,
new optics have been developed to shape the light beam. The
majority of these rely on reflection to control the light
distribution. Whether the reflection is off a metal (Ag, Al, alloy,
etc.) or because of total internal reflection ("TIR"), the optic
relays the source aperture to a virtual or physical plane. Other
systems use a combination of reflective, refractive and/or
diffusing elements to control distribution.
[0004] Narrow full beam angles are difficult to achieve. U.S.
patent application Ser. No. 12/788,094, which is hereby fully
incorporated by reference herein, describes a reflective optic that
exhibits superior beam shaping capabilities and higher efficiencies
in a small package. However, in order to achieve high efficiencies
at narrow beam angles, the reflective optic becomes relatively
large. This may be undesirable in some applications.
[0005] Therefore, a small, efficient optic for projecting light
into narrow beam angles is needed.
SUMMARY
[0006] Embodiments described herein provide an optical system to
create a high collection NA imaging optic that projects the emitted
photons into the desired intensity distribution while reimaging the
entrance aperture. The optical system's exit aperture (area over
which the optical system emits light) is derived from the
brightness equation. The optical power of the system is determined
by the number of elements and the curvature of each element. The
overall height of the optical stack is a function of the number of
elements and optical power of the system.
[0007] Conservation of radiance limits the minimum size of an
optic's exit aperture for a given source brightness and for a
desired emission angle. While the exit aperture is preferably at
least some minimum size to conserve radiance, the height of the
optic can be manipulated through the selection of lenses. By
utilizing multiple optical elements, embodiments described herein
offer an optical solution that can conserve brightness and project
light into a narrow beam angle with a relatively low height and
system volume.
[0008] According to one embodiment, an optical system to emit light
in an emission beam angle is provided. The optical system comprises
an LED and a high numerical aperture multi-element optical stack.
According to one embodiment, the multi-element optical stack can be
a multi-element optical stack that reimages the entrance aperture
of the optical stack in far field.
[0009] The multi-element optical stack can include a number of
optical elements forming a series of lenses. The series of lenses
comprises, a first lens positioned to receive light emitted in a
first beam angle and a second lens more distal from the LED than
the first lens, the second lens defining a second lens exit
aperture that has at least a minimum area necessary to conserve
radiance for the emission beam angle in air. The lenses in said
series of lenses are configured, in combination, to successively
reduce a beam angle of light from the first beam angle to the
emission beam angle. The lenses in said series of lenses can be
configured, in combination, to emit in the emission beam angle at
least 80% of the light entering the multi-element optical
stack.
[0010] The series of lenses can comprise additional lenses, such as
one or more intermediate lenses between the first lens and the
second lens. In one such embodiment, the first lens reduces the
beam angle of light from a first beam angle to a second beam angle,
the intermediate lens reduces the beam angle of light from the
second beam angle to a third beam angle and the second lens reduces
the beam angle from the third beam angle to the selected beam
angle. The lenses can have a variety of spacings and
configurations.
[0011] The optical system can also include a homogenizer having an
entrance face and a set of sidewalls extending from the entrance
face to a distal end of the homogenizer. The entrance face of the
homogenizer can be separated from the LED by an air gap. The distal
end of the homogenizer can be located at an entrance surface to the
first lens. The homogenizer can have a straight optical axis
aligned with the optical axis of the first lens. The area of the
distal end of homogenizer may be substantially smaller than the
entrance surface of the first lens.
[0012] The homogenizer can have an entrance face (physical or
virtual) of a first shape and an exit face (physical or virtual) of
a second shape with the sidewalls of the homogenizer transitioning
from the first shape to the second shape (e.g., from a square to a
circle). In one embodiment, the sidewalls of the homogenizer can
comprise a set of facets corresponding to the shape of the entrance
face and one or more additional sets of facets corresponding to one
or more transition shapes. In a particular embodiment, the
sidewalls comprise a set of facets corresponding to a square shape
and a set of facets corresponding to a hexadecagon shape.
Preferably, the half angle of light exiting the homogenizer is at
least 80% to equal to the half angle of light entering the
homogenizer.
[0013] Another embodiment can comprise an optical system to emit
light in a selected emission beam angle, the optical system having
an LED, a homogenizer and a high numerical aperture imaging
multi-element optical stack having an entrance aperture and exit
aperture. The multi-element optical stack comprises a series of
lenses optically coupled to the homogenizer that are configured, in
combination, to successively reduce a beam angle of light from a
first beam angle to the emission beam angle and emit in the
emission beam angle at least 70% of the light entering the
multi-element optical stack.
[0014] According to one embodiment, the series of lenses comprise a
first lens optically coupled to and axially aligned with the
homogenizer and positioned to receive light from the homogenizer in
the first beam angle. The series of lenses also comprise a second
lens optically coupled to and axially aligned with the first lens
and more distal from the LED than the first lens. The second lens
can be configured to emit light in the emission beam angle. The
second lens defines the exit aperture such that the exit aperture
has at least a minimum area necessary to conserve radiance for the
emission beam angle.
BRIEF DESCRIPTION OF THE FIGURES
[0015] A more complete understanding of various embodiments of
optical systems and devices and the advantages thereof may be
acquired by referring to the following description, taken in
conjunction with the accompanying drawings in which like reference
numbers indicate like features and wherein:
[0016] FIG. 1 is a diagrammatic representation of one embodiment of
an optical system;
[0017] FIG. 2 is a diagrammatic representation of another
embodiment of an optical system;
[0018] FIG. 3 provides a diagrammatic representation of one
embodiment of positioning a lens relative to a source;
[0019] FIG. 4 is a diagrammatic representation of another
embodiment of positioning a lens relative to a source;
[0020] FIG. 5 is a diagrammatic representation of another
embodiment of an optical system;
[0021] FIG. 6 is a diagrammatic representation of yet another
embodiment of an optical system;
[0022] FIG. 7 is a diagrammatic representation of one embodiment of
an optical device;
[0023] FIG. 8 is a diagrammatic representation one embodiment of an
LED housing;
[0024] FIGS. 9A-D are diagrammatic representations of one
embodiment of a homogenizer housing structure;
[0025] FIGS. 10A-C are diagrammatic representations of one
embodiment of a lens housing;
[0026] FIG. 11 is a diagrammatic representation of one embodiment
of a lens structure;
[0027] FIG. 12 is a diagrammatic representation of another
embodiment of a homogenizer housing structure;
[0028] FIGS. 13A-B are diagrammatic representations of one
embodiment of a homogenizer;
[0029] FIGS. 14A-B are diagrammatic representations of ray tracing
models for one embodiment of an optical system;
[0030] FIG. 15 is a diagrammatic representation of an intensity
distribution for one embodiment of an optical system;
[0031] FIG. 16 is a chart of radiant intensity versus beam angle
for one embodiment of an optical system;
[0032] FIG. 17 is a diagrammatic representation illustrating the
advantage of a high percentage of light in beam;
[0033] FIG. 18 is a diagrammatic representation of a ray tracing
model for one embodiment of an optical system;
[0034] FIG. 19 is a chart of radiant intensity versus beam angle
for one embodiment of an optical system;
[0035] FIGS. 20A and 20B are diagrammatic representations of
intensity distributions for one embodiment of an optical
system;
[0036] FIG. 21 is a diagrammatic representation of one embodiment
of a downlight or spotlight;
[0037] FIG. 22 is a diagrammatic representation illustrating one
embodiment of color mixing;
[0038] FIG. 23 is a table for one embodiment of a lens
prescription.
DETAILED DESCRIPTION
[0039] The disclosure and various features and advantageous details
thereof are explained more fully with reference to the exemplary,
and therefore non-limiting, embodiments illustrated in the
accompanying drawings and detailed in the following description.
Descriptions of known starting materials and processes may be
omitted so as not to unnecessarily obscure the disclosure in
detail. It should be understood, however, that the detailed
description and the specific examples, while indicating the
preferred embodiments, are given by way of illustration only and
not by way of limitation. Various substitutions, modifications,
additions and/or rearrangements within the spirit and/or scope of
the underlying inventive concept will become apparent to those
skilled in the art from this disclosure.
[0040] As used herein, the terms "comprises," "comprising,"
"includes," "including," "has," "having" or any other variation
thereof, are intended to cover a non-exclusive inclusion. For
example, a process, product, article, or apparatus that comprises a
list of elements is not necessarily limited to only those elements
but may include other elements not expressly listed or inherent to
such process, product, article, or apparatus. Further, unless
expressly stated to the contrary, "or" refers to an inclusive or
and not to an exclusive or. For example, a condition A or B is
satisfied by any one of the following: A is true (or present) and B
is false (or not present), A is false (or not present) and B is
true (or present), and both A and B are true (or present).
[0041] Additionally, any examples or illustrations given herein are
not to be regarded in any way as restrictions on, limits to, or
express definitions of, any term or terms with which they are
utilized. Instead these examples or illustrations are to be
regarded as being described with respect to one particular
embodiment and as illustrative only. Those of ordinary skill in the
art will appreciate that any term or terms with which these
examples or illustrations are utilized encompass other embodiments
as well as implementations and adaptations thereof which may or may
not be given therewith or elsewhere in the specification and all
such embodiments are intended to be included within the scope of
that term or terms. Language designating such non-limiting examples
and illustrations includes, but is not limited to: "for example,"
"for instance," "e.g.," "in one embodiment," and the like.
Furthermore, any dimensions, materials or other such
characteristics are provided by way of example and not
limitation.
[0042] Numerical aperture (NA) is a number that characterizes the
range of angles over which an optical element can collect light.
Embodiments described herein provide a multi-element imaging
optical stack to collect light at high NAs (greater than 0.8 to
approaching unity). The multi-element imaging optical stack relays
an image from the entrance aperture to far field with a desired
distribution. These results can be achieved with a small form
factor, including the smallest form factor required to conserve
brightness.
[0043] FIGS. 1 and 2 are diagrammatic representations of
embodiments of optical systems 100 having a light source 105 used
in combination with a multi-element imaging optical stack 110. In
general, light source 105 is any component(s) that provide light to
multi-element optical stack 110. Light source 105 may include, for
example, LEDs or an array of LEDs used with or without phosphors.
In this context, LED can refer to the LED chip with a cover, such
as a dome, or the LED chip itself. In another example embodiment,
light source 105 may be the end of a fibre optic cable or
homogenizer that provides light or multi-element optical stack
110.
[0044] Multi-element optical stack 110 comprises a series of
optical elements that form a series of lenses that act in
combination to provide a high NA optical system that directs light
into a controlled beam angle and relays an image of the entrance
aperture of the multi-element optical stack into the far field. The
optical elements can be individual lenses or optical elements that
form doublets, triplets or other lens structures.
[0045] In the embodiment of FIG. 1, multi-element optical stack 110
includes first lens 112 (the lens in multi-element optical stack
most proximate to source 105), second lens 114 (the lens in
multi-element optical stack 110 most distal from source 105) and
intermediate lens(es) 116. According to one embodiment, the lenses
are formed of clear plastic, glass or other optically transparent
material. Lenses 112, 114 and 116 may have multiple refractive
indexes and can have a variety of shapes including, but not limited
to, spherical lenses, aspherical lenses, Fresnel lenses,
diffractive lenses or combinations thereof. The lenses may be
formed of the same or different materials and may contain coatings
or scattering features. The optical system can use a variety of
optical elements to control system aberrations. Each lens in
multi-element optical stack 110 can be optically coupled to
adjacent lenses or can be separated from adjacent lenses by a gap.
Each lens has an optical axis (e.g., a line that defines the path
along which light propagates through the lens). In general, though
not necessarily, the optical axis of a lens is coincident with the
rotational or mechanical axis of the lens. Preferably, the axes of
the lenses in multi-element optical stack 110 are aligned with each
other. Furthermore, light source 105 can be aligned with the
optical axis of lens 112. In other embodiments, the source is not
aligned with the optical axis to create a skewed distribution.
[0046] Each lens can have a lens entrance aperture and a lens exit
aperture. The lens entrance aperture is the area over which light
enters the lens and the lens exit aperture is area over which light
exits the lens. The entrance aperture of first lens 112 is the
entrance aperture of multi-element optical stack 110 and the exit
aperture of second lens 114 is the exit aperture 118 of
multi-element optical stack 110.
[0047] The optical stack is important to achieving high collection
efficiency in the system (high NA). First lens 112 is in proximity
of the source and can be formed in such a way that all the light
from every point on the source passes through the lens.
Multi-element optical stack 110 defines an exit aperture. (FIG. 2
illustrates the outer rays 119 projected by second lens 114), which
can be selected so that for a given entrance aperture for
multi-element optical stack 110, radiance is conserved in
multi-element optical stack 110.
[0048] In order to conserve radiance, the size of exit aperture 118
of the system can be calculated using the Conservation of Radiance
equations:
.phi. n 2 A .OMEGA. = .phi. ' n '2 A ' .OMEGA. ' [ EQN . 1 ] A ' =
n 2 A .OMEGA. n '2 .OMEGA. ' [ EQN . 2 ] ##EQU00001##
wherein .OMEGA. is the effective solid angle light enters, .OMEGA.'
is the effective solid angle whereby light leaves multi-element
optical stack 110, A is the area of the entrance aperture of
multi-element optical stack 110, n is the refractive index into
which the source emits, n' is the refractive index of material into
which the optical stack emits.
[0049] Since the intensity distribution out of the exit aperture is
typically in air, the n' value is approximately 1. Furthermore, if
there is a gap between the source and optical device, n is also
approximately 1. Since LEDs are extended sources, the value for
.OMEGA. is .pi.. With these conditions, the brightness equation
reduces to:
A ' = n 2 A .OMEGA. n '2 .OMEGA. ' [ EQN . 3 ] A ' = A .pi. .OMEGA.
' [ EQN . 4 ] ##EQU00002##
[0050] Thus, for a projected beam angle of 10 degree, the solid
angle is approximately .pi. sin(5deg) 2 for a circular beam.
Methods for determining the solid angle for a square or rectangular
beam are described in U.S. patent application Ser. No. 12/788,094,
which is hereby fully incorporated by reference herein. For an
initial entrance aperture of 1.5 mm.times.1.5 mm, the exit aperture
has to be approximately 296 mm 2 to project all of the light into
the 10 degree full beam angle (full width half maximum).
[0051] The above example assumes a source emission angle of pi
steradians (solid angle), but in cases where the source emission
angle is different, the equation still applies. For instance, if
the source only emits into a 60 degree full cone, then A' is equal
to A Pi( )3/.OMEGA.'.
[0052] The size of the exit aperture 118 can be selected based on
conservation of radiance to achieve high efficiency. According to
one embodiment, multi-element optical stack 110 can be formed so
that exit aperture 118 is (within manufacturing tolerances) or is
at least the size necessary to conserve radiance for a given system
in a particular medium (e.g., air or other medium). In another
embodiment, exit aperture 118 can be between 95-105% of the size
necessary to conserve radiance. In other embodiment, the exit
aperture 118 can be at least some percentage (e.g., 70%, 75%, 80%,
85%, 90% or 95%) of the size necessary to conserve radiance. Having
a smaller exit aperture 118 reduces brightness. However, this may
result in a desired intensity distribution yielding softer
illumination edges. Thus, the selection of exit aperture can be
made to balance size, profile and brightness.
[0053] In order for brightness to be conserved (or be within some
percentage of being conserved) an appropriate amount of light must
be relayed from each lens to the next. To relay light from first
lens 112 to second lens 114, the projected beam angle of each lens
can within the acceptance cone of the next more distal lens.
According to one embodiment, the projected beam angle of a lens is
smaller than the projected beam angle of light emitted by the next
more proximal lens. Thus, for example, in FIG. 2, the projected
beam angle of intermediate lens 116 can be less than that of first
lens 112 and the projected beam angle half angle of second lens 114
can be less than that of lens intermediate lens 116.
[0054] To conserve radiance at each lens, the exit aperture of each
lens can be selected based on the entrance aperture of that lens,
the solid angle of light entering the lens and the solid angle of
light exiting the lens. By selecting appropriate aperture sizes for
each lens in multi-element optical stack 110, a series of lenses
can be selected to successively reduce beam angle, while conserving
radiance (or achieving other high transmission efficiency).
[0055] According to one embodiment, the multi-element optical stack
can include a series of lenses that work in combination to relay
approximately 100% or other percentage of light entering first lens
112 to far field. In some embodiments approximately 100%, or other
high percentage (e.g., 70%, 75%, 80%, 85%, 90% or 95%) of the light
entering lens 112 is relayed.
[0056] Furthermore, the lenses of multi-element optical stack 110
can work in combination to achieve a high percentage of light in
beam. That is, for a given projected beam angle, a high percentage
of the light emitted from second lens 114 is in that beam angle
(e.g., greater than 70%, 75%, 80%, 85%, 90%, 95% or 98% of light in
beam).
[0057] FIGS. 3 and 4, are diagrammatic representations of
embodiments of positioning first lens 112 relative to source 105.
In the embodiments of FIGS. 3 and 4, source 105 comprises LED chip
200 surrounded by phosphor particles 201 distributed in encapsulant
203 and disposed in cavity 202. In the embodiments of FIGS. 3 and
4, source 105 has a generally flat emitting surface (e.g., emitting
plane 209, which in this case is parallel to the primary emitting
face of the LED, represented at 207), though source 105 could have
other shapes. The cavity can be defined by or lined with a
reflective material, such as TiO.sub.2 and can have a variety of
shapes. The phosphor particles 201 can be disposed in the
encapsulant 203, coated on top of the encapsulant, coated on the
LED or otherwise disposed between LED 200 and the entrance face of
first lens 112. The entrance aperture 117 (which indicates the
object plane) of multi-element optical stack 110 is defined by exit
aperture of the source, in this example, the cavity exit.
[0058] One difference between FIGS. 3 and 4 is that, in FIG. 3,
first lens 112 is separated from the emitting surface of source 105
by an air gap 212, whereas, in FIG. 4, first lens 112 directly
contacts the emitting surface of source 105 (i.e., the surface of
the encapsulant). For purposes of the following discussion, the
embodiment of FIG. 3 will be referred to as "non-coupled," while
the embodiment of FIG. 4 will be referred to as "coupled." The use
of the phrase "non-coupled," in this context, merely means that a
gap exists between the exit aperture of source 105 and entrance
face of first lens 112 (or homogenizer as illustrated in later
embodiments), though the source and lens are still operatively
coupled to source 105. In general, the size of the gap in the
non-coupled solution can be selected so that the NA remains high
relative to the source. By way of example, but not limitation, the
gap is preferably less than 500 microns and can be approximately
100-200 microns.
[0059] Whether first lens 112 is coupled or non-coupled can affect
the size of the exit aperture 118 of multi-element optical stack
110. The above example in which the exit aperture 118 was
approximately 296 mm 2 for an entrance aperture of 1.5 mm.times.1.5
mm was for a configuration in which light entered first lens 112
from air. If the source of FIG. 4 emits directly into first lens
112, (assuming the encapsulant has a similar index of refraction as
first lens 112) the size of the exit aperture 118 of multi-element
optical stack 110 will increase by the refractive index of
encapsulant 203 (i.e., n.sup.2 as the source emits directly into
encapsulant 203 before first lens 112). If the source is embedded
into the first element, then the index of the first element would
determine, in part, exit area necessary to conserve brightness as
shown above in Equation 2. In other words, if the source aperture
is emitting into a medium with a higher index of refraction than
air, then the exit aperture has to increase to account for the
index change.
[0060] While the non-coupled solution offers the advantage of a
smaller exit aperture, the non-coupled solution may experience some
losses. FIG. 3 illustrates several possible light paths that result
in losses. At the phosphor to air interface, two events are
possible. The ray refracts into air, with corresponding Fresnel
reflection, or the light is reflected back into the encapsulant due
to total internal reflection ("TIR"). Because phosphor is an
ergodic system, rays that are reflected will have a probability of
being scattered into a non-trapping mode. This continues until the
light eventually escapes into the air interface between the
phosphor and the optical element or is absorbed by the LED chip,
the cavity walls, etc. Fresnel reflections at the phosphor to air
interface will experience the same dynamics as the totally
internally reflected light. At the air to optical element
interface, the light may refract into the optical element. Fresnel
reflections off this interface will experience the same dynamics as
the totally internally reflected light. Therefore, according to one
embodiment, the cavity walls, chips and everything within the
cavity should be as non-absorptive as possible.
[0061] AR (anti-reflective) coatings may be beneficial on the exit
face of the primary optical element (e.g., first lens 112) and any
subsequent optical elements to reduce Fresnel reflections and
increase system throughput. An AR coating at the entrance face of
first lens 112 will be less beneficial unless the AR coating is
omni-directional. A traditional multilayer coating reduces
reflections over specific angles. Outside of these angles, the
reflectivity increases. Since this interface contains light at all
angles, traditional AR coatings may not be effective, though can be
included if desired. Texturing, such as Motheye surface texturing,
or other omni-directional method can be applied to any of the lens
surfaces to reduce Fresnel reflections.
[0062] In the coupled solution, light will typically not experience
TIR at the phosphor lens interface as the materials of first lens
112 and encapsulant 203 can be selected to prevent or reduce this
phenomenon as well as Fresnel reflection. Thus, while the coupled
solution may require a larger exit aperture, the coupled solution
can be overall more efficient. It is estimated that the difference
in total emitted flux between coupling and not coupling may be
small (5-30%). The loss is dependent on the type of chip or the
geometry of the source. Thus, the selection of a coupled or
non-coupled system can depend on the tradeoffs between exit
aperture size (system volume) and losses in total emitted flux.
[0063] FIG. 5 is a diagrammatic representation of another
embodiment of an optical system including light source 105 and a
multi-element optical stack 110 having first lens 112 and a second
lens 114 used in combination with a homogenizer 120. Homogenizer
120, according to one embodiment, transfers optical stack 110's
high NA to source 105.
[0064] Homogenizer 120 includes an entrance face 122 that defines
the entrance aperture of multi-element optical stack 110 and an
exit face 124 (physical or virtual), which, if the homogenizer 120
and first lens 112 are a unitary piece, is a virtual exit face
defined at the intersection of homogenizer 120 and first lens 112.
According to one embodiment, exit face 124 is parallel to the
primary emitting plane of light source 105, so that homogenized
light is emitted in a plane parallel to the emitting plane of light
source 105. Homogenizer 120 can have a variety of shapes such as
tapered or untapered. According to one embodiment, the entrance
face 122 of homogenizer 120 can have a different shape than the
exit face 124.
[0065] In general, the purpose of a homogenizer is to allow light
to bounce multiple times as it propagates along the homogenizer,
causing spatial variation in the source to be reduced so that the
flux at any point exiting the homogenizer is preferably very
uniform. By way of example, but not limitation, homogenizer 120 can
homogenize light so that the peak to valley variation in flux per
unit area is less than 10% or other percentage (e.g., 5%).
[0066] According to the embodiment of FIG. 5, homogenizer 120 is a
rectangular homogenizer with an exit face 124 at the plano surface
of first lens 112. A homogenizer in which the entrance face 122 and
exit face 124 have the same area does not alter the angular
distribution of the light, just the spatial distribution. That is,
the homogenizer essentially moves the source aperture but does not
alter the angular distribution. However, if the exit face 124 is
larger than the entrance face 122, the half angle of light leaving
the exit face 124 will be smaller than the half angle of light
entering entrance face 122. According to one embodiment, the shape
of homogenizer can be selected so that the half angle of light
emitted from the homogenizer at the physical or virtual exit face
is from 80% to equal to the half angle of light entering
homogenizer 120.
[0067] For a given entrance face 122 size, the exit aperture 118 of
multi-element optical stack 110 can be determined from EQN. 1-4.
Each lens 112 and 114 can be configured to successively reduce beam
angle while conserving radiance to achieve the desired beam angle
for multi-element optical stack 110.
[0068] Multi-element optical stack 110 can include imaging optics
to relay an image from the entrance aperture of multi-element
optical stack 110 to far field. Homogenizer 120 essentially relays
an image from the entrance face 122 to the exit face 124.
[0069] Exit face 124 of homogenizer 120 and entrance face of lens
112 can be coupled together (e.g., as an integrated piece, using an
optical adhesive or otherwise coupled) or can be separated by an
air gap. When homogenizer 120 and first lens 112, the exit face 124
of homogenizer 120 can define the entrance aperture 117 of
multi-element optical system 110. Optical stack 110 is arranged to
have a high NA (e.g., an NA of greater than 0.8 to approaching
unity). Consequently, multi-element optical stack 110 can have a
high NA relative to source 105, even though multi-element optical
stack 110 is, to some extent, remote from source 105.
[0070] FIG. 6 is a diagrammatic representation of another
embodiment of an optical system 100 having a light source 105, a
multi-element imaging optical stack 110 and a homogenizer.
According to one embodiment, multi-element optical stack 110
includes a first optical element 125, a second optical element 127
and a third optical element (represented as second lens 114). First
lens 112, in this embodiment, is a doublet formed from optical
element 125 and optical element 127. Optical element 125 and
homogenizer 120 are integrated in a homogenizer housing structure
150 that includes optical element 125 portion and a homogenizer 120
portion. In the embodiment of FIG. 12, homogenizer 120 and optical
element 125 are an integrated component, while optical elements 125
and 127 are coupled together (e.g., using optical adhesive or other
joining mechanism). Entrance face 122 defines the entrance aperture
of multi-element optical stack 110, while second lens 114 defines
the exit aperture. Entrance face 122 of homogenizer 120 can be
sized and positioned so that all or substantially all the light
emitted by source 105 enters entrance face 122. The geometries of
each lens 112, 114 (and, in one embodiment, each optical element of
a lens) can be selected to successively reduce the beam angle of
light from that received at entrance face 122 to a selected beam
angle while conserving radiance.
[0071] In the embodiment illustrated in FIG. 6, optical element 125
comprises a first surface 151 facing source 105 and a second
surface 152 on the opposite side of lens 112 (an "exit surface"
152). Surface 151 can be flat or have other desired shape. Exit
surface 152 of first lens 112 is concave and compliments convex
entrance surface 154 of optical element 127. The surface of optical
element 127 on the opposite side of optical element 127 from the
source (i.e., exit surface 156 (the exit surface of first lens
112)) is also convex. The surface of lens 114 facing the source
(i.e., entrance surface 158) is slightly concave, while the surface
of lens 114 facing away from the source (i.e., exit surface 160) is
convex.
[0072] According to one embodiment, first optical element 125 and
second optical element 127 are formed of materials that have a
sufficient difference in abbe numbers to substantially reduce or
eliminate visible color aberration. In some embodiments, optical
element 125 may be manufactured with a low abbe number (for more
dispersion) and optical element 127 may be manufactured with a high
abbe number (for less dispersion). According to one embodiment, the
abbe number of optical element 125 is under 30 and the abbe number
of optical element 127 is above 50 so that the difference in abbe
numbers is greater than 20, and even more preferably greater than
30, though other embodiments may use smaller differences.
Furthermore, it is preferable that the material of homogenizer 120
have a softening temperature that is above the operating
temperature of source 105, which can be around 150 C if phosphors
are used. To meet these criteria, one embodiment includes a
homogenizer 120 and optical element 125 formed of PMMI and an
optical element 127 formed of acrylic. PMMI has a softening
temperature of approximately 170 C and an abbe number of 22.97,
while optical grade acrylic has a softening temperature near 85-95
C and an abbe number of 55.31. Lens 114 can be formed of a material
having a similar abbe number as optical element 127.
[0073] The surfaces of the optical elements/lenses may be coated,
textured or patterned to achieve desired results. For example,
homogenizer entrance face 122, intermediate lens exit surface 156,
second lens entrance surface 158 and/or second lens exit surface
160 can be coated with an AR coating or patterned with an AR
pattern, such as moth eye. In one embodiment, surface 160 can be
textured to provide more diffuse light. As another example,
surfaces 156 and 160 can be patterned with diffractive optical
elements. Diffractive optical elements (DOEs) are optical
components that spatially vary a lens thickness to change the
optical path length that the wavefront experiences at various
points along a lens. DOEs are typically patterned micro-structures
on the surface of a lens. In one embodiment, a DOE is selected to
control color, such as for reducing blue-red separation or
chromatic aberration. FIGS. 7-12 are diagrammatic representations
of one embodiment of an optical device 161 comprising an LED
housing 162, a homogenizer housing structure 150, a lens housing
164 and second lens portion 155. Optical device 161 incorporates an
embodiment of the optical system of FIG. 6, with homogenizer
housing structure 150 having a homogenizer 120 portion and a first
optical element 125 portion and lens housing 164 integrating second
optical element 127. Optical element 125 and optical element 127
are arranged as a doublet to form first lens 112.
[0074] LED housing 162 defines a cavity 166 (see FIG. 8) in which
an LED chip is disposed. The base of cavity 166 can be formed by a
heat sink 168, such as a copper plug or other heat sink that passes
through LED housing 162. A set of alignment walls 170 extending
upwards from around the edges of the cavity can aid in aligning the
homogenizer 120 over the LED with an air gap between the LED and
entrance face 122 of homogenizer 120. According to one embodiment,
the opening to cavity 166 and homogenizer 120 are approximately the
same size.
[0075] LED housing 162 can also include alignment features to help
ensure homogenizer housing structure 150 is properly aligned with
LED housing 162. As one example, LED housing 162 can include bosses
172 extending from the upper surface of LED housing 162 that are
received by corresponding cavities in homogenizer housing structure
150.
[0076] Homogenizer housing structure 150 comprises a portion
forming optical element 125, a portion forming homogenizer 120 and
a support member 174 formed of unitary piece of material or
multiple parts coupled together. Optical element 125 comprises a
first surface 151 facing source 105 and a second surface 152 on the
opposite side of optical element 125 (an "exit surface" 152).
Surface 152 is concave with a geometry such that light optical
element 127 in the acceptance angle of optical element 127. Surface
151 can be flat or have other desired shape.
[0077] Homogenizer 120 extends from surface 151 to entrance face
122, preferably parallel to and coaxially with the optical axis of
lens 112. Homogenizer 120 can be straight or tapered and may be
configured to shape light into a square, rectangle, circle or other
shape (including arbitrary images and letters).
[0078] Homogenizer housing structure 150 can further include a
support member 174, such as an annular wall, extending from surface
151 to LED housing 162. Support member 174 can include boss
receiving cavities 176 to receive bosses 172. Support member 174
creates a homogenizer cavity 177 around homogenizer 120. Typically,
the cavity will be filled with air to promote TIR in homogenizer
120, though other medium may be used.
[0079] Lens housing 164, according to one embodiment, forms an
integrated housing and optical element 127. Lens housing 164, in
the embodiment of FIG. 5, is shaped to form a first cavity 178 (the
"lens cavity") and a second cavity 180 (the "doublet cavity") (see
FIGS. 10A and 10B) on obverse sides of optical element 127. Lens
cavity 178 is defined by cavity walls 182 and a cavity base surface
184 that extends across the base of cavity 178. Cavity walls 182
extend upward from base surface 184 in a direction away from LED
housing 162. The ends of cavity walls 182 are spaced so that lens
114 can rest with surface 158 of lens 114 contacting surface 156 of
lens 116 or separated from surface 156 a selected distance. Thus,
lens housing 164 can be used to set the focus of optical device
161. Additionally, cavity walls 182 can be spaced from the edge of
lens 116 so that all or substantially all the light projected from
optical element 127 can enter lens 114 without hitting the cavity
walls 182.
[0080] Housing support member 186 extends from base surface 184
toward LED housing 162. According to one embodiment, housing
support member 186 can comprise an annular wall that partially
defines doublet cavity 180. Doublet cavity 180 is shaped to receive
homogenizer housing structure 150 so that concave first lens exit
surface 152 contacts entrance surface 154 of optical element 127
(the surface of optical element 127 facing the source).
[0081] Lens housing 164 can include features corresponding to
alignment features of homogenizer housing structure 150. For
example, lens housing 164 can include alignment recesses 188 to
receive extensions 190 of homogenizer housing structure 150.
Preferably, the corresponding alignment features provide a
mechanism to axially optical element 125 with optical element
127.
[0082] Second lens portion 155 of FIG. 7 includes lens 114 having a
slightly concave surface 158 on one side and a convex surface 160
on the other side. Additionally, second lens portion 155 includes
an annular flange 191 extending outward from lens 114 perpendicular
to the optical axis of second lens 114. Flange 191 can rest on
cavity wall 182 or other shoulder defined by lens housing 164. In
other embodiments, lens 114 can be supported by other mechanisms,
such as discontinuous tabs that extend outward. A portion of lens
114 extends downward from flange 191 to overlap the inside of
cavity wall 182. This can aid in aligning lens 114 so that lens 114
is axially aligned with lens 112. Adhesive can be used to join
second lens portion 155 to lens housing 164.
[0083] FIG. 8 is a diagrammatic representation of another view of
one embodiment of LED housing 162. As illustrated in FIG. 7, the
inside surfaces 192 of alignment walls 170 can be tapered so that
homogenizer 120 settles in the proper position. The walls can be
shaped so that homogenizer 120 is separated from the LED by a small
gap.
[0084] FIGS. 9A-D are diagrammatic representations of one
embodiment of homogenizer housing structure 150. FIG. 9A is a view
of homogenizer housing structure 150 looking into exit face 152 of
optical element 125, FIG. 9B is a cross-section along line B-B of
FIG. 9A and FIG. 9C is a cross-section along line A-A of FIG.
9A.
[0085] According to one embodiment, homogenizer housing structure
comprises 150 a generally cylindrical structure extending from a
first end to a second end. Homogenizer housing structure 150 may
taper outward from the first end to the second end. A surface 152
at the first end defines the exit face of optical element 125 and
acts as a refractive surface to emit light in a selected beam
angle. At the second end, the homogenizer housing structure defines
a passage 194 open at the second end of the homogenizer housing
structure 150 and extending across the homogenizer housing
structure lateral to the optical axis of homogenizer housing
structure 150. Lateral passage 194 can be sized to accommodate the
width of LED housing 162. Homogenizer housing structure 150 further
defines homogenizer cavity 177 open to lateral passage 194 and
extending a distance into the homogenizer housing structure surface
151 that, in this embodiment, extends generally lateral to the
optical axis of homogenizer housing structure 150. Generally
lateral surface 151 extends laterally from an annular sidewall
(e.g., support member 174) to homogenizer 120.
[0086] Homogenizer housing structure 150 further comprises
homogenizer 120 extending a length parallel to the optical axis
from lateral surface 151 a distance to homogenizer entrance face
122, defined in a plane perpendicular to the optical axis.
Homogenizer 120 transitions into lens 112, which extends from
surface 151 to the exit face 152 of the optical element 125.
[0087] Homogenizer housing structure 150 further comprises
extensions 190 extending laterally outward from the annular
sidewalls of homogenizer housing structure 150. Extensions 190 can
be in-line with lateral passage 194. Extensions 190 can include a
curved outer surface or other shaped surface.
[0088] Homogenizer housing structure 150 can also define boss
receiving cavities 176 that extend into homogenizer housing
structure 150 from the second end. Boss receiving cavities 176 can
be shaped to receive bosses 172 of LED housing 162. Boss receiving
cavities 176 may be partially defined in extensions 190.
[0089] FIGS. 10A-C are diagrammatic representations of one
embodiment of lens housing 164. According to one embodiment, lens
housing 164 can comprise a generally cylindrical shape extending
from a first end to a second end. Lens housing 164 defines a lens
cavity 178 open to the first end. The sides of the lens cavity can
be defined by an annular lens cavity sidewall 182 that extends from
the first end to a surface to a lens cavity base 184. Lens cavity
base 184 can include a first portion that extends inwardly from the
sidewall 182, perpendicular to the optical axis, and a second
portion that is shaped to form the refractive optical surface that
acts as exit surface 156 of optical element 127.
[0090] At the second end, lens housing 164 defines a passage 196
open at the second end of lens housing 164 and extending across
lens housing 164 lateral to the optical axis of lens housing 164.
Lens housing lateral passage 196 can be sized and shaped to
accommodate the width of the LED housing. Lens housing 164 further
defines a homogenizer housing structure cavity 180 open to lateral
passage 196 and extending a distance into the lens housing parallel
to the optical axis. According to one embodiment, the homogenizer
housing structure cavity is defined by an annular sidewall (e.g.,
support structure 186) and a surface that acts as the entrance
surface 154 of lens 116. Homogenizer housing structure cavity 180
can be shaped and sized to accommodate homogenizer housing
structure 150, such that surface 154 of optical element 127 abuts
surface 152 of optical element 125 and optical element 125 and
optical element 127 are axially aligned. Additionally, lens housing
164 defines recesses 188 extending laterally outward from
homogenizer housing structure cavity 180 to receive extensions 190
(or other alignment feature) of homogenizer housing structure 150
to align lens housing 164 relative to homogenizer housing structure
150.
[0091] In the embodiment of FIGS. 10A-10C, housing support member
186 is formed by an annular wall. In other embodiments, housing
support member 186 can comprise legs or other structures. The inner
surfaces 197 of housing support member 186 that define homogenizer
housing structure cavity 180 can taper outwards such that the width
of homogenizer housing structure cavity 180 is greater proximate to
the LED than at optical element 127.
[0092] According to one embodiment, lens housing 164 and
homogenizer housing 150 and lens housing 164 can be coupled
together using adhesive between surfaces 152 and 154. Lens housing
164 can include one or more channels (illustrated as a vertical
channel in FIG. 10C) running along the walls of homogenizer cavity
180 from the end proximate to the source to the end distal from the
source. The channels can provide a route for excess adhesive and
bubbles to evacuate when surfaces 154 and 152 are coupled together.
The channels help minimize adhesive thickness and bubbles.
[0093] FIG. 11 is a diagrammatic representation of one embodiment
of second lens portion 155 having lens 114 with an annular flange
191 extending radially outward at the sides of lens 114. Lens 114,
in the embodiment of FIG. 11, includes a concave entrance surface
158 and convex exit surface 160.
[0094] In the embodiments of FIGS. 7-11, lens 112 and 114 are
imaging lenses, meaning that they relay the image from the entrance
aperture of lens 112 (the virtual exit face of homogenizer) to far
field. Furthermore, because the entrance and exit faces of
homogenizer 120 are the same, homogenizer 120 relays the image from
entrance face 122 to the virtual exit face 124, meaning that the
image at entrance face 122, typically the image of the source, is
reimaged in far field, but with spatial variation homogenized.
Furthermore, homogenizer 120 is positioned to have a high NA
relative to the LED chip (or other source) and all the light
emitted by homogenizer 120 is collected by optical stack 110.
[0095] FIG. 12 is a diagrammatic representation of another
embodiment of homogenizer housing structure 150. The embodiment of
FIG. 12 is similar to that of FIGS. 9A-D, except that homogenizer
120 is configured such that exit face 124 has a different shape
than entrance face 122. In the embodiment of FIG. 12 homogenizer
120 is configured to convert a square illumination pattern into a
circular illumination pattern. In this case, multi-element optical
stack 110 will reimage in far field what appears at the entrance
aperture 117 (i.e., what appears at the virtual exit face 124 of
homogenizer 120).
[0096] FIGS. 13A-B are diagrammatic representations of one
embodiment of a homogenizer 120 for converting from a square to
circular illumination pattern. FIG. 13A is view of homogenizer 120
looking at entrance face 122 and FIG. 13B is a diagrammatic
representation of a side view of homogenizer 120. Homogenizer 120,
in FIGS. 13A-B, comprises entrance face 122, exit face 124 and
sidewall(s) 204 extending from entrance face 122 to exit face 124.
The shape of exit face 124 is selected to have at least the same
area as entrance face 122. In this example, the diameter of exit
face 124 is approximately equal to the diagonal of entrance face
122, making exit face 124 slightly larger than entrance face 122.
Because of the difference in shape, sidewalls 204 are slightly
tapered.
[0097] The sidewalls 204 of homogenizer 120 are shaped to
transition from the shape of the entrance face to the shape of the
exit face (e.g., from a square entrance face 122 to a round exit
face 124 or between other geometric or arbitrary shapes). The
sidewalls 204 comprise multiple sets of facets, curves or other
transition features. According to one embodiment a first set of
facets 206 correspond to a shape of the entrance face while a
second set of facets 208 correspond to a transition shape between
the shape of entrance face 122 and exit face 124 (that is, a shape
that begins to more closely approximate the shape of exit face
124). Additional sets of facets can correspond to any number of
other shapes between the shape of entrance face 122 and exit face
124. In the embodiment of FIGS. 13A-13B, facets 206 correspond to a
square shape and facets 208 correspond to a hexadecagon.
[0098] The shape of homogenizer 120 can be formed using a base
shape having the appropriate size and shape for exit face 124. For
the example of FIGS. 13A-13B, the base shape is a cylinder. Facets
206 are formed based on an extruded cut made with the shape of the
entrance face 122, with the cut tapering outward along a defined
angle. Thus, facets 206 correspond to a square shape extruded cut
(regardless of whether homogenizer 120 is actually formed by
cutting, molding or some other process). Even more specifically, in
the example of FIGS. 13A-13B, facets 206 correspond to a square
shape making an extruded cut with a taper angle 7.25 degrees such
that the entrance face 122 has the desired shaped and size and the
sidewalls taper outwards. Facets 208 are formed based on an
extruded cut made using a hexadecagon with a taper angle of 1
degree.
[0099] In other embodiments, facets can correspond to other shapes.
For example, to transition from a square to a circle, facets can be
formed based on extruded cuts using hexagonal, octagonal and or
other shapes. The sidewalls 204 may include any number of different
sets of facets formed based on any number of shapes between the
shape of entrance face 122 and exit face 124.
[0100] Furthermore, while in the embodiment of FIGS. 13A-13B the
transition features are formed based on straight extrusion cuts
corresponding to geometric shapes, other embodiments can include
transition features corresponding to arbitrary shapes. Furthermore,
the transition features may include simple or complex curves to
transition from the shape of entrance face 122 to exit face
124.
[0101] In one embodiment, a homogenizer that transitions from a
first shape to a second shape can be modeled in a 3-D modeling
program such as SOLIDWORKS by Dassault Systemes SolidWorks Corp. of
Concord, Mass. and the resulting shape can be entered in a ray
tracing program, such as ZEMAX by Radiant ZEMAX LLC of Bellevue,
Wash. Ray tracing can be performed to determine the flux per unit
area given by a particular shape. Iterative adjustment of the shape
can be performed until a satisfactory output is determined.
Preferably, the homogenizer is selected so that the difference in
half angle of light emitted from exit face 124 and the half angle
of light entering homogenizer 120 is less than 20%. Furthermore,
the homogenizer is preferably configured so that the peak to valley
difference of flux per unit area of light emitted is less than
10%.
[0102] With or without a homogenizer, various embodiments of
optical systems can be configured so that greater than 75%,
including greater the 95%, of the light entering lens 112 is
projected into far field (referred to herein as transmission
efficiency) in a desired beam angle (referred to as percent in
beam), not counting Fresnel losses. However, even at lower
transmission efficiencies and percent in beam, optical devices of
the present application provide superior beam shaping capabilities.
If a smaller percent in beam is desired, tradeoffs between the exit
aperture and the percent in beam may also be made. Lenses can be
formed to account for this tradeoff per the system requirement.
[0103] FIG. 14A is a diagrammatic representation of a ray tracing
model for rays 210 in one embodiment of a multi-element optical
stack 110. FIG. 14B illustrates the ray tracing at air gap 212. The
ray tracing was performed using Zemax software. The model considers
a non-coupled system having the properties given in Table 1 below
for a 1 mm.sup.2 source:
TABLE-US-00001 TABLE 1 Prescription radius conic thickness material
semi dia Obj 0 0 0 air 0 Lens 112 surf1 0 0 5 Acrylic 4 surf2 -3.25
-0.6 1 air 4 Lens 114 surf1 0 0 5 Acrylic 5.5 surf2 -5.5 -0.4 inf
air 5.5
[0104] The size of second lens 114 is selected so that the exit
aperture 118 of the multi-element optical stack is large enough to
conserve radiance for a 10 degree beam angle (5 degree half angle).
The shape of second lens 114 is selected to receive light in a beam
angle from first lens 112 and shape the light into the desired 10
degree beam angle with a desired distribution profile. The size,
shape and position of first lens 112 are selected to be large
enough to collect almost all light emitted by the source (e.g., to
provide an NA approaching unity) and to reduce the beam angle of
light into a beam angle within the acceptance cone of second lens
114.
[0105] In operation, light rays 210 refract into first lens 112
from air gap 212. First lens 112 emits light in the acceptance cone
of second lens 114. Second lens 114 emits the light received from
first lens 112 in the desired full beam angle (e.g., 10 degrees)
while conserving radiance.
[0106] FIG. 15 illustrates a model illumination pattern of light
emitted by the optical device of FIGS. 14A and 14B. As can be seen
in FIG. 15, the illumination profile within the selected angle can
be highly uniform. Of 5,000,000 rays traced, greater than 4,910,000
rays (98% of the rays) arrive on the far field detector plane,
indicating near conservation of radiance in the multi-element
optical stack. FIG. 16 is a chart of radiant intensity (y-axis)
versus beam angle (x-axis) and illustrates that the system of FIGS.
14A and 14B acts to create a "digital" light distribution in which
greater than 80%, and in this case greater than 90%, of the light
is within the desired beam angle and the remaining light is within
a very small range to create a sharp cutoff.
[0107] FIG. 17 illustrates the advantage of high light in beam. A
high light in beam means that there is much less wasted light
outside of desired projected beam angle. In FIG. 17, the beam
difference between a system that provides 28% Lumens in Beam versus
a system that provides 90% of Lumens in Beam to illustrate the
advantages of embodiments described herein.
[0108] FIG. 18 is a diagrammatic representation of one embodiment
of a model of a multi-element optical stack comprising a CVI Melles
Griot LAG-15.0-12.0-C(Former Melles Griot Part No. 01 LAG 001)
Aspheric Glass Condenser Lens, FL:12 mm; EPD: 15 mm as first lens
112 (from CVI Melles Griot of Albuquerque, N. Mex.) and an Edmunds
Optics NT66-013 TECHSPEC Plastic Aspheric Lens, FL 17.5 mm, EPD:25
mm second lens 114 from Edmund Optics, Inc. of Barrington N.J. In
the embodiment of FIG. 18, light from an LED or array of LEDs is
directed to first lens 112 through a homogenizer 120 and directed
to second lens 114 as discussed above. According to the embodiment
of FIG. 18, which is for a 7 degree beam angle system, the lenses
are 10 to 12 mm apart, plano surface to pseudo plano
surface--mounting points on the lenses. The air gap point-to-point
between the lenses is about 6.3 mm+/-1 mm. Again, however, it
should be understood that the foregoing ranges are provided by way
of example and not limitation.
[0109] The modeled performance of such a system is that 90% of the
emitted light is within a 7 degree full beam angle. FIG. 19 is a
chart of radiant intensity (y-axis) versus beam angle (x-axis) and
illustrates the digital light distribution with around 90% of the
light in the full beam angle of 7 degrees. FIG. 20 illustrates
modeled illumination patterns of light emitted by the system of
FIG. 17.
[0110] FIG. 21 is a diagrammatic representation of an embodiment of
a lighting system 220 having an array of second lenses 114. The
secondary optics, according to one embodiment, can be formed from a
single plate of material. Similar plates can be positioned below,
internal to lighting system 220, to create a multi-element optical
stack. Embodiments described herein can be formed with a tightly
packed array of sources within one package. Array of second lenses
114 can be arranged so that the illumination patterns emitted by
the secondary optics overlap. Since the intensity distribution of
each optic system is the same, the overall illumination spot
remains the relatively the same in the far field. The intensity of
the distribution increases by the number of LEDs/optic system.
Because the illumination patterns of the individual devices can be
highly uniform, the overall illumination pattern can also be highly
uniform.
[0111] Light to a multi-element optical stack can be provided by a
single LED or an array of LEDs. If an array is used, the various
LEDs can be controlled to emit a desired color of light so that a
single optical system can emit various colors of light.
Additionally, the illumination patterns of various optical systems
can overlap to cause color mixing. FIG. 22, for example,
illustrates that overlapping illuminated areas 225 that can be
illuminated with a mix of color temperatures providing an overlap
area 226 of very uniform color. As the distance between the
illuminated surface and an array of optical systems grows, the
width of the border area 227 stays the same size while the
illuminated area grows. At far field, border area 227 becomes
unnoticeable.
[0112] Multiple optical systems can be arranged such that the
border areas overlap to create more uniformity in the border areas,
leading to a larger illuminated area having a uniform profile. Due
to the square or rectangular shape of the illuminated area created
by an optical system, multiple arrays can be spaced at desired
distances to provide uniform lighting over large areas. The overlap
illuminated area will not have light and dark regions.
[0113] Thus, one embodiment can include an array of optical
systems. Each optical system can be configured such that light is
emitted with a uniform profile in a desired half angle with a hard
cut off or a soft cut off. The optical systems can be configured to
project an overall illumination pattern having an illuminated area
with an overlap area and a border area. The overlap area can have a
uniform profile, while the border area can have a different
intensity than the overlap area. The size of the overlap area with
uniform profile is dependent on the target surface (e.g., screen)
to lens distance such that the size of the illuminated area grows
as the target surface to lens distance grows. The width of the
border area is not dependent on the target surface to lens
distance. Consequently, as the target surface to lens distance
increases the percentage of the overlap area having a uniform
profile approaches 100%.
[0114] The color of the overlap area 226 can depend on the color
emitted by each lens which, in turn, can depend on the color of
light emitted by each source. For an LED source, the color can
depend on the LEDs and phosphor selected. According to one
embodiment, each LED can be a blue or ultraviolet LED used in
conjunction with a pure phosphor or blend of phosphors so that the
corresponding lens emits a desired color light. In other
embodiments, some or all of the LEDs selected may emit a desired
color light without using a phosphor coating. Thus, for example,
some of the LEDs in the array can be blue or ultraviolet (or other
color) LEDs used in conjunction with phosphors while other LEDs can
be red (or other color) LEDs used without phosphors. The LEDs can
be controlled so that the combined output in overlap area 226 has a
desired spectral power distribution and color coordinates.
[0115] According to one embodiment the light sources can be
selected to achieve desired x and y values in the 1931 CIE
chromaticity diagram. In particular, the color coordinates of an
array of optical systems can lie on or near the Planckian locus,
thereby producing various shades of white light (e.g., "cool"
white, "neutral" white, or "warm" white). While desirable regions
around the Planckian locus in the chromaticity diagram are defined
by the ANSI C78.377-2008 chromaticity standard, over a range of
correlated color temperature (CCT) values, embodiments described
herein may be used to achieve other color coordinates.
[0116] Embodiments of the present disclosure can achieve a high
percentage of light the full beam angle, including at narrow
angles. Additionally, optical elements can be selected to achieve a
higher percent in beam (e.g., greater than 50%, greater than 60%,
greater than 70% to greater than 90% and approaching 100%). In some
embodiments, a high percent in beam can be achieved at narrow beam
angles (e.g., full beam angles of 1-25 degrees). The optical
elements can be further selected to have a high NA of greater than
0.85 to approaching unity. In a particular embodiment, an optical
element stack can be selected to have an NA of greater 0.95 and an
exit aperture having the minimum size necessary to conserve
brightness for a narrow beam angle (e.g., a full beam (full width
half maximum) angle of 10 degrees) while achieving greater than 95%
efficiency and greater than 90% of light in beam.
[0117] Returning briefly to the embodiment of FIG. 7, first optical
element 125, second optical element 127 and second lens 127 can
have a variety of configurations. One embodiment of prescription is
illustrated in FIG. 23. It should be understood that FIG. 23 is
provided by way of example and not limitation.
[0118] Those skilled in the arts will appreciate after reading this
disclosure that dimensions and other data provided herein are
exemplary and that embodiments disclosed herein may be manufactured
according to other dimensions or data without limiting the scope of
the disclosure.
[0119] Embodiments described herein are provided by way of example.
Embodiments described herein may be used to create light output of
a desired shape. For example, the desire may be to create a more
circular distribution, a more trapezoidal distribution, or a more
rectangular distribution. This may be done through one or more
optical elements to purposefully distort the image. For instance, a
cylindrical lens may be added to focus in only one dimension
yielding a more rectangular distribution. Freeform optics may be
incorporated to generate other types of distributions.
[0120] Although embodiments have been described in detail herein,
it should be understood that the description is by way of example
only and is not to be construed in a limiting sense. It is to be
further understood, therefore, that numerous changes in the details
of the embodiments and additional embodiments will be apparent to,
and may be made by, persons of ordinary skill in the art having
reference to this description. It is contemplated that all such
changes and additional embodiments are within scope of the
disclosure and its legal equivalents.
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