U.S. patent application number 14/017201 was filed with the patent office on 2014-01-02 for integrated led based illumination device.
This patent application is currently assigned to Xicato, Inc.. The applicant listed for this patent is Xicato, Inc.. Invention is credited to Serge J. A. Bierhuizen, Stefan Eberle, Gerard Harbers, Tyler Robin Kakuda.
Application Number | 20140003044 14/017201 |
Document ID | / |
Family ID | 49777948 |
Filed Date | 2014-01-02 |
United States Patent
Application |
20140003044 |
Kind Code |
A1 |
Harbers; Gerard ; et
al. |
January 2, 2014 |
INTEGRATED LED BASED ILLUMINATION DEVICE
Abstract
A light emitting diode (LED) based illumination device include a
plurality of LEDS mounted to mounting board and includes a
transmissive plate disposed above the LEDs. The transmissive plate
includes an amount of wavelength converting material configured to
change a wavelength of an amount of light emitted by the plurality
of LEDs. A base reflector structure is coupled to the LED mounting
board and the transmissive plate between at least two of the LEDs.
In another configuration, a dam of reflective material surrounds
the LEDs and is coupled to the LED mounting board and the
transmissive plate, while a dam of thermally conductive material
surrounds the dam of reflective material. In another configuration,
the LED mounting board has a protrusion of thermally conductive
material that surrounds the LEDs and is coupled to the transmissive
plate, and has a void on the side opposite the protrusion.
Inventors: |
Harbers; Gerard; (Sunnyvale,
CA) ; Kakuda; Tyler Robin; (Stockton, CA) ;
Bierhuizen; Serge J. A.; (San Jose, CA) ; Eberle;
Stefan; (Mountain View, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Xicato, Inc. |
San Jose |
CA |
US |
|
|
Assignee: |
Xicato, Inc.
San Jose
CA
|
Family ID: |
49777948 |
Appl. No.: |
14/017201 |
Filed: |
September 3, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61697712 |
Sep 6, 2012 |
|
|
|
61790887 |
Mar 15, 2013 |
|
|
|
Current U.S.
Class: |
362/230 |
Current CPC
Class: |
F21Y 2113/13 20160801;
F21V 29/763 20150115; F21V 29/74 20150115; H01L 2924/0002 20130101;
H01L 33/507 20130101; H01L 33/504 20130101; H01L 2924/00 20130101;
H01L 2933/0075 20130101; H01L 33/644 20130101; F21Y 2105/10
20160801; F21V 3/12 20180201; F21K 9/64 20160801; F21V 31/005
20130101; H01L 2933/0058 20130101; H01L 25/0753 20130101; F21V
7/0083 20130101; H01L 33/60 20130101; F21Y 2115/10 20160801; H01L
2924/0002 20130101; F21V 19/0015 20130101; F21V 13/04 20130101 |
Class at
Publication: |
362/230 |
International
Class: |
F21K 99/00 20060101
F21K099/00 |
Claims
1. An LED based illumination device comprising: a plurality of LEDs
mounted to an LED mounting board; a first transmissive plate
disposed above the plurality of LEDs, the first transmissive plate
includes a first amount of a first wavelength converting material
configured to change a wavelength of an amount of light emitted by
the plurality of LEDs; and a base reflector structure coupled to
the LED mounting board between at least two of the plurality of
LEDs and extending to the first transmissive plate over a contact
area.
2. The LED based illumination device of claim 1, wherein the
contact area between the base reflector structure and the first
transmissive plate is shaped as a grid pattern between the
plurality of LEDs.
3. The LED based illumination device of claim 1, wherein the
contact area between the base reflector structure and the first
transmissive plate is a matrix of contact points between the
plurality of LEDs.
4. The LED based illumination device of claim 1, further
comprising: a plurality of total internal reflection (TIR) lens
elements disposed between each of the plurality of LEDs and the
first transmissive plate, wherein each of the TIR lens elements are
disposed within the base reflector structure.
5. The LED based illumination device of claim 1, further
comprising: an encapsulant material disposed between the base
reflector structure and the first transmissive plate over the
plurality of LEDs.
6. The LED based illumination device of claim 1, further
comprising: a second transmissive plate disposed above the first
transmissive plate, the second transmissive plate includes a second
amount of a second wavelength converting material configured to
change the wavelength of a second amount of light emitted by the
plurality of LEDs.
7. The LED based illumination device of claim 1, wherein the first
transmissive plate includes a second amount of a second wavelength
converting material configured to change a wavelength of the amount
of light emitted by the plurality of LEDs.
8. An LED based illumination device comprising: a plurality of LEDs
mounted to an LED mounting board; a first transmissive plate
disposed above the plurality of LEDs, the first transmissive plate
includes a first amount of a first wavelength converting material
configured to change a wavelength of an amount of light emitted by
the plurality of LEDs; a dam of reflective material surrounding the
plurality of LEDs and coupled to the LED mounting board and the
first transmissive plate; and a dam of thermally conductive
material surrounding the dam of reflective material, wherein the
dam of thermally conductive material is coupled to the LED mounting
board and the first transmissive plate.
9. The LED based illumination device of claim 8, wherein the dam of
thermally conductive material is spaced apart from the dam of
reflective material.
10. The LED based illumination device of claim 8, wherein the dam
of thermally conductive material is in contact with the dam of
reflective material.
11. The LED based illumination device of claim 8, wherein the dam
of reflective material optically shields the dam of thermally
conductive material from the amount of light emitted by the
plurality of LEDs.
12. The LED based illumination device of claim 8, further
comprising: a plurality of total internal reflection (TIR) lens
elements disposed between each of the plurality of LEDs and the
first transmissive plate.
13. The LED based illumination device of claim 8, further
comprising: an encapsulant material disposed between the plurality
of LEDs and the first transmissive plate.
14. The LED based illumination device of claim 8, further
comprising: a second transmissive plate disposed above the first
transmissive plate, the second transmissive plate includes a second
amount of a second wavelength converting material configured to
change a wavelength of the amount of light emitted by the plurality
of LEDs.
15. The LED based illumination device of claim 8, wherein the first
transmissive plate includes a second amount of a second wavelength
converting material configured to change a wavelength of the amount
of light emitted by the plurality of LEDs.
16. An LED based illumination device comprising: a plurality of
LEDs; an optically transmissive element disposed above the
plurality of LEDs, the optically transmissive element includes a
first amount of a first wavelength converting material configured
to change a wavelength of an amount of light emitted by the
plurality of LEDs; and an LED mounting board, the plurality of LEDs
mounted on a first side of the LED mounting board, the LED mounting
board having a protrusion of thermally conductive material on the
first side of the LED mounting board surrounding the plurality of
LEDs, wherein the LED mounting board is coupled to the optically
transmissive element at the protrusion, and wherein the LED
mounting board includes a void on a second side of the LED mounting
board opposite the protrusion.
17. The LED based illumination device of claim 16, wherein the
protrusion is formed on the first side of the LED mounting board by
forming the void on the second side of the LED mounting board.
18. The LED based illumination device of claim 16, wherein the
optically transmissive element is a transmissive plate.
19. The LED based illumination device of claim 16, wherein the
optically transmissive element is a shaped lens element.
20. The LED based illumination device of claim 16, further
comprising: an encapsulant material disposed between the plurality
of LEDs and the optically transmissive element.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority under 35 USC .sctn.119 to
U.S. Provisional Application No. 61/697,712, filed Sep. 6, 2012,
and U.S. Provisional Application No. 61/790,887, filed Mar. 15,
2013, both of which are incorporated by reference herein in their
entireties.
TECHNICAL FIELD
[0002] The described embodiments relate to illumination modules
that include Light Emitting Diodes (LEDs).
BACKGROUND
[0003] The use of light emitting diodes in general lighting is
still limited due to limitations in light output level or flux
generated by the illumination devices. Illumination devices that
use LEDs also typically suffer from poor color quality
characterized by color point instability. The color point
instability varies over time as well as from part to part. Poor
color quality is also characterized by poor color rendering, which
is due to the spectrum produced by the LED light sources having
bands with no or little power. Further, illumination devices that
use LEDs typically have spatial and/or angular variations in the
color. Additionally, illumination devices that use LEDs are
expensive due to, among other things, the necessity of required
color control electronics and/or sensors to maintain the color
point of the light source or using only a small selection of
produced LEDs that meet the color and/or flux requirements for the
application.
[0004] Consequently, improvements to illumination device that uses
light emitting diodes as the light source are desired.
SUMMARY
[0005] A light emitting diode (LED) based illumination device
include a plurality of LEDS mounted to mounting board and includes
a transmissive plate disposed above the LEDs. The transmissive
plate includes an amount of wavelength converting material
configured to change a wavelength of an amount of light emitted by
the plurality of LEDs. A base reflector structure is coupled to the
LED mounting board and the transmissive plate between at least two
of the LEDs. In another configuration, a dam of reflective material
surrounds the LEDs and is coupled to the LED mounting board and the
transmissive plate, while a dam of thermally conductive material
surrounds the dam of reflective material. In another configuration,
the LED mounting board has a protrusion of thermally conductive
material that surrounds the LEDs and is coupled to the transmissive
plate, and has a void on the side opposite the protrusion.
[0006] Further details and embodiments and techniques are described
in the detailed description below. This summary does not define the
invention. The invention is defined by the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIGS. 1, 2, and 3 illustrate three exemplary luminaires,
including an illumination device, reflector, and light fixture.
[0008] FIG. 4 illustrates a perspective cut-away view of components
in an embodiment of an LED based illumination device including a
base reflector structure that physically couples a transmissive
plate and an LED mounting board.
[0009] FIG. 5 illustrates a perspective cut-away view of components
in another embodiment of an LED based illumination device including
a base reflector structure that physically couples a transmissive
plate and an LED mounting board.
[0010] FIG. 6 illustrates a perspective cut-away view of components
in another embodiment of an LED based illumination device including
a base reflector structure that physically couples a transmissive
plate and an LED mounting board.
[0011] FIG. 7 illustrates a side view of components in another
embodiment of an LED based illumination device with a total
internal reflection (TIR) lens structure to direct light emitted
from LEDs to a transmissive plate.
[0012] FIG. 8 illustrates a side view of components in another
embodiment of an LED based illumination device with a dam of
reflective material surrounding the LEDs and supporting a
transmissive plate.
[0013] FIG. 9 illustrates a side view of components in another
embodiment of an LED based illumination device with a shaped lens
disposed over the LEDs and thermally coupled to the LED mounting
board.
[0014] FIG. 10 illustrates a side view of components in another
embodiment of an LED based illumination device with multiple
transmissive plates.
[0015] FIG. 11 illustrates a side view of components in another
embodiment of an LED based illumination device with droplets of a
wavelength converting material uniformly applied to the surface of
transmissive layer.
[0016] FIG. 12 illustrates a side view of components in another
embodiment of an LED based illumination device with droplets of a
wavelength converting material applied to the surface of
transmissive layer in a non-uniform pattern.
[0017] FIG. 13 illustrates a side view of components in another
embodiment of an LED based illumination device with droplets of
different wavelength converting materials applied to the surface of
transmissive layer in a non-uniform pattern.
[0018] FIG. 14 illustrates a side view of components in another
embodiment of an LED based illumination device with a dam of
reflective material surrounding the LEDs and supporting a
transmissive plate and a dam of thermally conductive material
surrounding the dam of reflective material.
[0019] FIG. 15 illustrates a side view of components in another
embodiment of an LED based illumination device with a dam of
reflective material surrounding the LEDs and supporting a
transmissive plate and another embodiment of a dam of thermally
conductive material surrounding the dam of reflective material.
[0020] FIG. 16 illustrates a side view of components in another
embodiment of an LED based illumination device with a dam of
reflective material surrounding the LEDs and supporting a
transmissive plate and another embodiment of a dam of thermally
conductive material surrounding the dam of reflective material.
[0021] FIG. 17 illustrates a side view of components in another
embodiment of an LED based illumination device with another
embodiment of a dam of reflective material surrounding the LEDs and
supporting a transmissive plate.
[0022] FIG. 18 illustrates a perspective cut-away view of
components in another embodiment of an LED based illumination
device including another embodiment of a base reflector structure
that physically couples a transmissive plate and an LED mounting
board.
[0023] FIG. 19 is a top view of the LED based illumination device
illustrated in FIG. 18.
DETAILED DESCRIPTION
[0024] Reference will now be made in detail to background examples
and some embodiments of the invention, examples of which are
illustrated in the accompanying drawings.
[0025] FIGS. 1, 2, and 3 illustrate three exemplary luminaires,
labeled 150, 150', and 150'', which are sometimes collectively
referred to as luminaire 150. The luminaire illustrated in FIG. 1
includes an LED based illumination device 100 with a rectangular
form factor. The luminaire illustrated in FIG. 2 includes an LED
based illumination device 100' with a circular form factor. The
luminaire illustrated in FIG. 3 includes an LED based illumination
device 100' integrated into a retrofit lamp device. These examples
are for illustrative purposes. Examples of LED based illumination
devices of general polygonal and elliptical shapes may also be
contemplated, and in general, LED based illumination devices 100
and 100' may be collectively referred to as LED based illumination
device 100. As illustrated in FIG. 1, luminaire 150 includes
illumination device 100, reflector 125, and light fixture 120. FIG.
2 shows luminaire 150' with illumination device 100', reflector
125', and light fixture 120' and FIG. 3 shows luminaire 150'' with
illumination device 100', reflector 125'', and light fixture 120''.
Reflectors 125, 125', and 125'' are sometimes collectively referred
to herein as reflector 125, and light fixtures 120, 120', and 120''
are sometimes collectively referred to herein as light fixture 120.
As depicted, light fixture 120 includes a heat sink capability, and
therefore may be sometimes referred to as heat sink 120. However,
light fixture 120 may include other structural and decorative
elements (not shown). Reflector 125 is mounted to illumination
device 100 to collimate or deflect light emitted from illumination
device 100. The reflector 125 may be made from a thermally
conductive material, such as a material that includes aluminum or
copper and may be thermally coupled to illumination device 100.
Heat flows by conduction through illumination device 100 and the
thermally conductive reflector 125. Heat also flows via thermal
convection over the reflector 125. Reflector 125 may be a compound
parabolic concentrator, where the concentrator is constructed of or
coated with a highly reflecting material. Optical elements, such as
a diffuser or reflector 125 may be removably coupled to
illumination device 100, e.g., by means of threads, a clamp, a
twist-lock mechanism, or other appropriate arrangement. As
illustrated in FIG. 3, a reflector 125 may include sidewalls 126
and a window 127 that are optionally coated, e.g., with a
wavelength converting material, diffusing material or any other
desired material.
[0026] As depicted in FIGS. 1, 2, and 3, illumination device 100 is
mounted to heat sink 120. Heat sink 120 may be made from a
thermally conductive material, such as a material that includes
aluminum or copper and may be thermally coupled to illumination
device 100. Heat flows by conduction through illumination device
100 and the thermally conductive heat sink 120. Heat also flows via
thermal convection over heat sink 120. Illumination device 100 may
be attached to heat sink 120 by way of screw threads to clamp the
illumination device 100 to the heat sink 120. To facilitate easy
removal and replacement of illumination device 100, illumination
device 100 may be removably coupled to heat sink 120, e.g., by
means of a clamp mechanism, a twist-lock mechanism, or other
appropriate arrangement. Illumination device 100 includes at least
one thermally conductive surface that is thermally coupled to heat
sink 120, e.g., directly or using thermal grease, thermal tape,
thermal pads, or thermal epoxy. For adequate cooling of the LEDs, a
thermal contact area of at least 50 square millimeters, but
preferably 100 square millimeters should be used per one watt of
electrical energy flow into the LEDs on the board. For example, in
the case when 20 LEDs are used, a 1000 to 2000 square millimeter
heat sink contact area should be used. Using a larger heat sink 120
may permit the LEDs 102 to be driven at higher power, and also
allows for different heat sink designs. For example, some designs
may exhibit a cooling capacity that is less dependent on the
orientation of the heat sink. In addition, fans or other solutions
for forced cooling may be used to remove the heat from the device.
The bottom heat sink may include an aperture so that electrical
connections can be made to the illumination device 100.
[0027] Light generated by LEDs in the LED based illumination device
100, is generally color converted to generate a desirable output
light. Various embodiments are introduced herein to improve the
light extraction efficiency from LED based illumination device 100
and to improve the dissipation of heat generated by the color
conversion process. In one aspect a base reflector structure (shown
in FIGS. 4-7, as base reflector structures 171, 171', 171'', and
171', and sometimes collectively referred to herein as base
reflector structure 171) directs light emitted from LEDs 102 to a
transmissive plate 174 (shown in FIGS. 4-7) coated with at least
one wavelength converting material, illustrated as wavelength
converting materials 180 and 181, and provides a direct thermal
path between the transmissive plate 174 and an LED mounting board
104. In this manner, light extraction efficiency is improved by the
same structure that provides a direct heat dissipation path from
the transmissive plate to a heat sinking device.
[0028] FIGS. 4, 5, and 6 illustrate perspective cut-away views of
components of various embodiments of LED based illumination device
100. It should be understood that FIGS. 4-6 illustrate the LED
based illumination device 100 as having a circular form factor,
such as that illustrated in FIG. 2, but other form factors may be
used, including a rectangular form factor such as that shown in
FIG. 1. It should be understood that as defined herein an LED based
illumination device is not an LED, but is an LED light source or
fixture or component part of an LED light source or fixture. For
example, an LED based illumination device may be an LED based
replacement lamp such as depicted in FIG. 3. LED based illumination
device 100 includes one or more LED die or packaged LEDs and a
mounting board to which LED die or packaged LEDs are attached. In
one embodiment, the LEDs 102A and 102B, sometimes referred to
herein as LEDs 102 are LED die electrically and mechanically
coupled to LED board 104 in an arrangement commonly referred to as
a Chip On Board (COB) configuration. In another embodiment, the
LEDs 102A and 102B, sometimes collectively referred to herein as
LEDs 102, are packaged LEDs, such as the Luxeon Rebel manufactured
by Philips Lumileds Lighting. Other types of packaged LEDs may also
be used, such as those manufactured by OSRAM (Oslon package),
Luminus Devices (USA), Cree (USA), Nichia (Japan), or Tridonic
(Austria). As defined herein, a packaged LED is an assembly of one
or more LED die that contains electrical connections, such as wire
bond connections or stud bumps, and possibly includes an optical
element and thermal, mechanical, and electrical interfaces. The LED
chip typically has a size about 1 mm by 1 mm by 0.5 mm, but these
dimensions may vary. In some embodiments, the LEDs 102 may include
multiple chips. The multiple chips can emit light of similar or
different colors, e.g., red, green, and blue. LEDs 102 are mounted
to mounting board 104. The light emitted from LEDs 102 is directed
to transmissive plate 174. A thermally conductive base reflector
structure 171 promotes heat dissipation from the transmissive plate
174 to the mounting board 104, upon which the LEDs 102 are
mounted.
[0029] As depicted in FIGS. 4-6, base reflector structure 171 is in
physical contact with transmissive plate 174 and mounting board
104. As illustrated in FIG. 4, base reflector structure 171 is
shaped to direct light from LEDs 102 to transmissive plate 174. In
addition, base reflector structure 171 includes a feature 171A that
physically couples transmissive plate 174 and mounting board 104.
As illustrated in FIG. 4, the feature 171A is located in the center
of transmissive plate 174. Typically, the temperature is highest at
the center of transmissive plate 174. However, by thermally
coupling the center of transmissive plate 174 with mounting board
104 with base reflector structure 171, the temperature at the
center of transmissive plate 174 is reduced by inducing heat flow
from the center of transmissive plate 174 to mounting board 104.
Base reflector structure 171 may thermally couple the bottom
surface of transmissive plate 174 with mounting board 104 in any
number of locations. In some examples, a number of contact points
may be distributed over the surface of transmissive plate 174. In
these examples, locations are selected to minimize the impact on
the output beam uniformity of LED based illumination device 100
while minimizing the thermal gradient across the surface of
transmissive plate 174.
[0030] FIG. 5 illustrates LED based illumination device 100 with
the base reflector structure 171'. As illustrated, the base
reflector structure 171' includes deep reflector surfaces 171B that
direct light emitted from LEDs 102 to transmissive plate 174. In
addition, base reflector structure 171' includes a centrally
located feature 171C that thermally connects transmissive plate 174
and mounting board 104. As illustrated, base reflector structure
171' is constructed from one part to minimize manufacturing
complexity.
[0031] As illustrated in FIG. 6, base reflector structure 171''
includes a thermally conductive insert 171D that thermally couples
transmissive plate 174 and mounting board 104. In this manner, base
reflector structure may be constructed from a low cost material
(e.g., plastic) and the thermally conductive insert 171C may be
constructed from a material optimized for thermal conductivity
(e.g., aluminum or copper).
[0032] As depicted in FIGS. 4-6, base reflector structure 171 is in
physical contact with transmissive plate 174 and mounting board
104. However, in some other embodiments, base reflector structure
171 may be in physical contact with transmissive plate 174 and heat
sink 120. In this manner, a more direct thermal path between
transmissive plate 174 and heat sink 120 is realized. In one
example, elements of base reflector structure 171 may be configured
to pass through voids in LED board 104 to directly couple
transmissive plate 174 to heat sink 120.
[0033] Base reflector structure 171 may have a high thermal
conductivity to minimize thermal resistance. By way of example,
base reflector structure 171 may be made with a highly thermally
conductive material, such as an aluminum based material that is
processed to make the material highly reflective and durable. By
way of example, a material referred to as Miro.RTM., manufactured
by Alanod, a German company, may be used.
[0034] The optical surfaces of base reflector structure 171 may be
treated to achieve high reflectivity. For example the optical
surface of base reflector structure 171 may be polished, or covered
by one or more reflective coatings (e.g., reflective materials such
as Vikuiti.TM. ESR, as sold by 3M (USA), Lumirror.TM. E60L
manufactured by Toray (Japan), or microcrystalline polyethylene
terephthalate (MCPET) such as that manufactured by Furukawa
Electric Co. Ltd. (Japan), a polytetrafluoroethylene PTFE material
such as that manufactured by W.L. Gore (USA) and Berghof
(Germany)). Also, highly diffuse reflective coatings can be applied
to optical surfaces of base reflector structure 171. Such coatings
may include titanium dioxide (TiO2), zinc oxide (ZnO), and barium
sulfate (Ba5O4) particles, or a combination of these materials.
[0035] In some embodiments, base reflector structure 171 may be
constructed from or include a reflective, ceramic material, such as
ceramic material produced by CerFlex International (The
Netherlands). In some embodiments, portions of any of the optical
surfaces of base reflector structure 171 may be coated with a
wavelength converting material.
[0036] FIG. 7 is illustrative of another configuration of LED based
illumination device 100, which is similar to that shown in FIGS.
4-6, like designated elements being the same. As illustrated in
FIG. 7, LED based illumination device 100 may include a total
internal reflection (TIR) lens structure 178 to direct light
emitted from LEDs 102 to transmissive plate 174.
[0037] FIG. 8 is illustrative of another configuration of LED based
illumination device 100, which is similar to that shown in FIGS.
4-6, like designated elements being the same. As illustrated in
FIG. 8, LED based illumination device 100 includes a housing 101
including mechanical features to interface LED based illumination
device 100 with a heat sink (e.g., heat sinks 120, 120', and 120''
illustrated in FIGS. 1-3, respectively). In some embodiments
housing 101 includes a fastening means (e.g., screws, spring clips,
clamps, etc.) to fasten LED based illumination device 100 to a heat
sink. In addition to providing a means of fastening LED based
illumination device 100 to a heat sink, housing 101 also protects
sensitive components of LED based illumination device 100 (e.g.,
LEDs, electronics, etc.) from damage during installation and
operation in lighting applications. As such, housing 101 may be
constructed from a suitably durable material (e.g., metal, plastic,
fiber-reinforced plastic, etc.). As can be seen, the components of
the LED based illumination device 100 are disposed within the
housing with the transmissive plate 174 located at an output port
of the housing 101. Housing 101 may be used with any of the LED
based illumination devices discussed herein.
[0038] As illustrated in FIG. 8, LED based illumination device 100
includes a number of LEDs 102A-F, collectively referred to as LEDs
102, arranged in a chip on board (COB) configuration. LED based
illumination device 100 also includes a base reflector structure
including a reflective material 176 disposed in the spaces between
each LED and a dam of reflective material 175 that surrounds the
LEDs 102 and supports transmissive plate 174. In some examples,
reflective materials 175 and 176 are a white, highly reflective
silicone-based material. The silicone-based material is a flowable
material that is dispensed between and around LEDs 102 in a viscous
state. After curing, the material assumes a permanent shape. In
some other examples, reflective materials 175 and 176 are rigid
structural materials having highly reflective properties (e.g., a
PTFE based material, a coated aluminum material, etc.). In the
embodiment depicted in FIG. 8, the space between LEDs 102 and
transmissive plate 174 is filled with an encapsulating optically
translucent material 177 (e.g., silicone) to promote light
extraction from LEDs 102 and to separate LEDs 102 from the
environment. In the depicted embodiment, the dam of reflective
material 175 is both the thermally conductive structure that
conducts heat from transmissive plate 174 to LED mounting board 104
and the optically reflective structure that reflects incident light
from LEDs 102 toward transmissive plate 174.
[0039] In another aspect, a shaped lens element is optically
coupled to LEDs 102 and thermally coupled to LED mounting board
104. The shaped lens element may include at least one wavelength
converting material. In this manner, light extraction efficiency is
improved by the shaped lens element and heat generated by the
wavelength converting material on the shaped lens element has a
direct thermal path to a heat sinking device.
[0040] FIG. 9 is illustrative of another configuration of LED based
illumination device 100, which is similar to that shown in FIGS.
4-6, like designated elements being the same. As illustrated, LED
based illumination device 100 includes a shaped lens 172 disposed
over LEDs 102A, 102B, and 102C, collectively referred to as LEDs
102. As illustrated, shaped lens 172 includes at least one
wavelength converting material at the light emitting surface of
shaped lens 172. Shaped lens 172 is directly coupled to mounting
board 104 to promote heat flow from shaped lens 172 to mounting
board 104. In this manner, heat generated by color conversion on
surfaces of shaped lens 172 is efficiently transferred to mounting
board 104 and removed from LED based illumination device 100 via
heat sink 120. In some other embodiments, shaped lens 172 is
directly coupled to heat sink 120. In one example, elements of a
base reflector structure, such as base reflector structure 171
discussed above, may be configured to pass through voids in LED
board 104 to directly couple shaped lens 172 to heat sink 120.
[0041] LEDs 102 can emit different or the same colors, either by
direct emission or by phosphor conversion, e.g., where phosphor
layers are applied to the LEDs as part of the LED package. The
illumination device 100 may use any combination of colored LEDs
102, such as red, green, blue, amber, or cyan, or the LEDs 102 may
all produce the same color light. Some or all of the LEDs 102 may
produce white light. In addition, the LEDs 102 may emit polarized
light or non-polarized light and LED based illumination device 100
may use any combination of polarized or non-polarized LEDs. In some
embodiments, LEDs 102 emit either blue or UV light because of the
efficiency of LEDs emitting in these wavelength ranges. The light
emitted from the illumination device 100 has a desired color when
LEDs 102 are used in combination with wavelength converting
materials on transmissive plate 174 or shaped lens 172, for
example. By tuning the chemical and/or physical (such as thickness
and concentration) properties of the wavelength converting
materials and the geometric properties of the coatings on the
surfaces of transmissive plate 174 or shaped lens 172, specific
color properties of light output by LED based illumination device
100 may be specified, e.g., color point, color temperature, and
color rendering index (CRI).
[0042] For purposes of this patent document, a wavelength
converting material is any single chemical compound or mixture of
different chemical compounds that performs a color conversion
function, e.g., absorbs an amount of light of one peak wavelength,
and in response, emits an amount of light at another peak
wavelength.
[0043] By way of example, phosphors may be chosen from the set
denoted by the following chemical formulas: Y3Al5O12:Ce, (also
known as YAG:Ce, or simply YAG) (Y,Gd)3Al5O12:Ce, CaS:Eu, SrS:Eu,
SrGa2S4:Eu, Ca3(Sc,Mg)2Si3O12:Ce, Ca3Sc2Si3O12:Ce, Ca3Sc2O4:Ce,
Ba3Si6O12N2:Eu, (Sr,Ca)AlSiN3:Eu, CaAlSiN3:Eu, CaAlSi(ON)3:Eu,
Ba2SiO4:Eu, Sr2SiO4:Eu, Ca2SiO4:Eu, CaSc2O4:Ce, CaSi2O2N2:Eu,
SrSi2O2N2:Eu, BaSi2O2N2:Eu, Ca5(PO4)3Cl:Eu, Ba5(PO4)3Cl:Eu,
Cs2CaP2O7, Cs2SrP2O7, Lu3Al5O12:Ce, Ca8Mg(SiO4)4Cl2:Eu,
Sr8Mg(SiO4)4Cl2:Eu, La3Si6N11:Ce, Y3Ga5O12:Ce, Gd3Ga5O12:Ce,
Tb3Al5O12:Ce, Tb3Ga5O12:Ce, and Lu3Ga5O12:Ce.
[0044] In one example, the adjustment of color point of the
illumination device may be accomplished by adding or removing
wavelength converting material from transmissive plate 174 or
shaped lens 172, which similarly may be coated or impregnated with
one or more wavelength converting materials. In one embodiment a
red emitting phosphor 181 such as an alkaline earth oxy silicon
nitride covers a portion of transmissive plate 174 or shaped lens
172, and a yellow emitting phosphor 180 such as YAG covers another
portion of transmissive plate 174 or shaped lens 172, as
illustrated in FIGS. 4-9.
[0045] In some embodiments, the phosphors are mixed in a suitable
solvent medium with a binder and, optionally, a surfactant and a
plasticizer. The resulting mixture is deposited by any of spraying,
screen printing, blade coating, jetting, or other suitable means.
By choosing the shape and height of the transmissive plate 174 or
shaped lens 172, and selecting which portions of transmissive plate
174 or shaped lens 172 will be covered with a particular phosphor
or not, and by optimization of the layer thickness and
concentration of a phosphor layer on the surfaces, the color point
of the light emitted from the device can be tuned as desired.
[0046] In one example, a single type of wavelength converting
material may be patterned on a portion of transmissive plate 174 or
shaped lens 172. By way of example, a red emitting phosphor 181 may
be patterned on different areas of the transmissive plate 174 or
shaped lens 172 and a yellow emitting phosphor 180 may be patterned
on other areas of transmissive plate 174 or shaped lens 172. In
some examples, the areas may be physically separated from one
another. In some other examples, the areas may be adjacent to one
another. The coverage and/or concentrations of the phosphors may be
varied to produce different color temperatures. It should be
understood that the coverage area of the red and/or the
concentrations of the red and yellow phosphors will need to vary to
produce the desired color temperatures if the light produced by the
LEDs 102 varies. The color performance of the LEDs 102, red
phosphor and the yellow phosphor may be measured and modified by
any of adding or removing phosphor material based on performance so
that the final assembled product produces the desired color
temperature. In some examples, the color of an assembled LED based
illumination device is measured after final assembly and an
appropriate change in phosphor content to reach the desired color
temperature is determined based on the measured color. The
appropriate change in phosphor content can be realized by either
removing phosphor material (e.g., laser ablation, mechanical
abrasion, etc.) or by adding phosphor material (e.g., by any of
spraying, screen printing, blade coating, jetting, etc.). In some
other examples, the color of an LED based illumination device is
measured before final assembly. The appropriate change in phosphor
content can be realized by either removing phosphor material or by
adding phosphor material to the transmissive plate 174 or shaped
lens 172. After changing the phosphor content, the LED based
illumination device 100 undergoes final assembly where the
transmissive window 174 or shaped lens 172 is permanently fixed
into position.
[0047] Transmissive plate 174 and shaped lens 172 may be
constructed from a suitable optically transmissive material (e.g.,
sapphire, alumina, crown glass, polycarbonate, and other
plastics).
[0048] Transmissive plate 174 and shaped lens 172 are spaced above
the light emitting surface of LEDs 102 by a clearance distance. In
some embodiments, separation is desirable to allow clearance for
wire bond connections from the LED package submount to the active
area of the LED. In some embodiments, a clearance of one millimeter
or less is desirable to allow clearance for wire bond connections.
In some other embodiments, a clearance of two hundred microns or
less is desirable to enhance light extraction from the LEDs
102.
[0049] In some other embodiments, the clearance distance may be
determined by the size of the LED 102. For example, the size of the
LED 102 may be characterized by the length dimension of any side of
a single, square shaped active die area. In some other examples,
the size of the LED 102 may be characterized by the length
dimension of any side of a rectangular shaped active die area. Some
LEDs 102 include many active die areas (e.g., LED arrays). In these
examples, the size of the LED 102 may be characterized by either
the size of any individual die or by the size of the entire array.
In some embodiments, the clearance should be less than the size,
e.g., the length of a side, of the LED 102. In some embodiments,
the clearance should be less than twenty percent of the size of the
LED 102. In some embodiments, the clearance should be less than
five percent of the size of the LED. As the clearance is reduced,
light extraction efficiency may be improved, but output beam
uniformity may also degrade.
[0050] In some other embodiments, it is desirable to attach
transmissive plate 174 or shaped lens 172 directly to the surface
of the LED 102. In this manner, the direct thermal contact between
transmissive plate 174 or shaped lens 172 and LEDs 102 promotes
heat dissipation from LEDs 102. In some other embodiments, the
space between mounting board 104 and transmissive plate 174 or
shaped lens 172 may be filled with a solid encapsulate material. By
way of example, silicone may be used to fill the space. In some
other embodiments, the space may be filled with a fluid to promote
heat extraction from LEDs 102.
[0051] In the embodiment illustrated in FIG. 8, the surface of
patterned transmissive plate 174 facing LEDs 102 is coupled to LEDs
102 by an amount of flexible, optically translucent material 177.
By way of a non-limiting example, the flexible, optically
translucent material 177 may include an adhesive, an optically
clear silicone, a silicone loaded with reflective particles (e.g.,
titanium dioxide (TiO2), zinc oxide (ZnO), and barium sulfate
(BaSO4) particles, or a combination of these materials), a silicone
loaded with a wavelength converting material (e.g., phosphor
particles), a sintered PTFE material, etc. Such material may be
applied to couple transmissive plate 174 to LEDs 102 in any of the
embodiments described herein.
[0052] In some embodiments, multiple, stacked transmissive layers
are employed. Each transmissive layer includes different wavelength
converting materials. For example, as illustrated in FIG. 10,
transmissive layer 174 includes wavelength converting material 180
over the surface area of transmissive layer 174. In addition, a
second transmissive layer 163 is placed over and in contact with
transmissive layer 174. Transmissive layer 163 includes wavelength
converting material 181. In this manner, the color point of light
emitted from LED based illumination device 100 may be tuned by
replacing transmissive layers 174 and 163 independently to achieve
a desired color point. Although, as illustrated in FIG. 10,
transmissive layer 163 is placed over and in contact with
transmissive layer 174, a space may be maintained between the two
elements. This may be desirable to promote cooling of the
transmissive layers. For example, airflow may by introduced through
the space to cool the transmissive layers.
[0053] In some embodiments, any of the wavelength converting
materials may be applied as a pattern (e.g., stripes, dots, blocks,
droplets, etc.). For example, as illustrated in FIG. 11, droplets
of wavelength converting material 180 are uniformly applied to the
surface of transmissive layer 174. Shaped droplets may improve
extraction efficiency by increasing the amount of surface area of
the droplet.
[0054] As illustrated in FIG. 12, in some embodiments, droplets of
wavelength converting material 180 may be spaced on transmissive
layer 174 in a non-uniform pattern. For example, a group of
droplets 165 located over LED 102C is densely packed (e.g.,
droplets in contact with adjacent droplets), while a group of
droplets 164 located over a space between LEDs 102A and 102B is
loosely packed (e.g., droplets spaced apart from adjacent
droplets). In this manner, the color point of light emitted from
LED based illumination device 100 may be tuned by varying the
packing density of droplets on transmissive layer 174.
[0055] As illustrated in FIG. 13, in some embodiments, droplets of
different wavelength converting materials may be placed in
different locations of transmissive layer 174 and may also be
placed in a non-uniform pattern. For example, group of droplets 164
may include wavelength converting material 180 and group of
droplets 165 may include a combination of droplets including
wavelength converting material 181 and wavelength converting
material 182. In this manner, combinations of different wavelength
converting materials are located relative to LEDs 102 in varying
densities to achieve a desired color point of light emitted from
LED based illumination device 100.
[0056] In the illustrated embodiments, wavelength converting
materials are located on the surface of transmissive layer 174.
However, in some other embodiments, any of the wavelength
converting materials may be embedded within transmissive layer
174.
[0057] The area between LEDs 102 and transmissive plate 174 or
shaped lens 172 may be filled with a non-solid material, such as
air or an inert gas, so that the LEDs 102 emits light into the
non-solid material. By way of example, the cavity may be
hermetically sealed and Argon gas used to fill the cavity.
Alternatively, Nitrogen may be used. In other embodiments, the area
between LEDs 102 and transmissive plate 174 or shaped lens 172 may
be filled with a solid encapsulate material. By way of example,
silicone may be used to fill the cavity. In some other embodiments,
color conversion cavity 160 may be filled with a fluid to promote
heat extraction from LEDs 102. In some embodiments, wavelength
converting material may be included in the fluid to achieve color
conversion.
[0058] FIG. 14 is illustrative of another configuration of LED
based illumination device 100, which is similar to that shown in
FIGS. 8, like designated elements being the same. As illustrated,
LED based illumination device 100 includes a number of LEDs 102A-F,
collectively referred to as LEDs 102, arranged in a chip on board
(COB) configuration. In addition, LED based illumination device 100
includes a base reflector structure including a reflective material
176 (e.g., a white silicone material) disposed in the spaces
between each LED, a reflective material structure referred to
herein as a dam of reflective material 192 surrounding the LEDs 102
and supporting transmissive plate 174, and a thermally conductive
structure referred to herein a dam of thermally conductive material
190 surrounding the dam of reflective material 192. The dam of
thermally conductive material 190 is in contact with transmissive
plate 174 and is in contact with LED mounting board 104 at thermal
interface area 191. In one embodiment, the dielectric surface of
LED mounting board 104 is etched away to expose the conductive
metal substrate (e.g., copper, aluminum, etc.) over thermal
interface area 191.
[0059] In some embodiments, the dam of thermally conductive
material 190 is spaced apart from the dam of reflective material
192. The space allows excess optically translucent material 177 to
pour over the dam of reflective material 192 when transmissive
plate 174 is attached without interfering with the thermal
connection between thermally conductive material 190 and
transmissive plate 174. In some other embodiments, the dam of
reflective material is in contact with the dam of thermally
conductive material 190. In one example, the reflective material is
a flowable material (e.g., silicone based material) that is
dispensed within the dam of thermally conductive material 190. The
reflective material wicks up the edge of the dam of thermally
conductive material 190 to shield the dam of thermally conductive
material from exposure to light emitted from LEDs 102. In some
embodiments, the dam of thermally conductive material 190 envelopes
the edge of transmissive plate 174, which provides a larger surface
area of thermal contact and also allows the effective aperture of
the LED based illumination device to be defined by the dam of
thermally conductive material 190.
[0060] FIG. 15 is a diagram illustrating another configuration of
LED based illumination device 100, which is similar to that shown
in FIG. 14. However, in the embodiment depicted in FIG. 15, the dam
of thermally conductive material 193, contacts transmissive plate
174 primarily on the bottom surface, rather than wrapping around
the edge of transmissive plate 174 as described with reference to
FIG. 14.
[0061] In general, the dam of reflective material 192 is
constructed from a highly reflective material. The emphasis is on
selection of materials with high reflectivity to minimize optical
losses in LED based illumination device 100. The thermal
conductivity of the highly reflective material 192 is of secondary
importance due to the presence of the dam of thermally conductive
material 190. In contrast, the dam of thermally conductive material
190 is constructed from a material with high thermal conductivity.
The emphasis is on selection of materials with high thermal
conductivity to minimize the thermal resistance between
transmissive plate 174 and mounting board 104. The reflectivity of
the thermally conductive material 190 is of secondary importance
due to the presence of the dam of highly reflective material 192
that is in the optical path of LEDs 102. In this manner, a first
dam of material, e.g., dam of highly reflective material 192,
surrounds the LEDs 102 with the objective of minimizing optical
losses, and a second dam of material, e.g., dam of thermally
conductive material 190, surrounds the first dam with the objective
of focusing on thermal performance. Importantly, the thermal dam is
optically shielded from LEDs 102 by the optical dam; hence, the
optical performance of the thermal dam is not critical. Rather than
being forced to select a dam material that is neither optically nor
thermally optimal, this approach allows the designer to choose
separate materials, one optimized for optical performance, and the
other optimized for thermal performance for each respective dam of
material.
[0062] In some embodiments, the dam of reflective material 192 is a
highly reflective silicone, and the dam of thermally conductive
material 190 is a thermally conductive silicone. However, other
materials may be contemplated. For example, as illustrated in FIG.
16, which is similar to the embodiment illustrated in FIG. 14, the
dam of thermally conductive material 194 is a thermally conductive
metal bonded to transmissive plate 174 and mounting board 104. In
some embodiments, the dam of thermally conductive material 194 is
aluminum or copper. Other thermally conductive materials may be
contemplated. The thermally conductive metal may be bonded to
transmissive plate 174 and mounting board 104 by a solder joint, a
frit seal, an epoxy, or any other suitable bonding material.
[0063] In one example, LED based illumination device 100 is
constructed in part by bonding the dam of thermally conductive
material 190 to LED mounting board. For example, the dam of
thermally conductive material 190 is a metal structure (e.g.,
nickel plated aluminum, copper, etc.) that is bonded onto LED board
104 (e.g., reflow solder, epoxy, etc.). The LED board 104 is
populated with LEDs 102 and electrical connections are made between
the LED die and LED board 104. Flowable, reflective material is
deposited within the dam of thermally conductive material 190 and
in the space between the LEDs 102. The reflective material wicks up
the edge of the dam of thermally conductive material 190 to shield
the dam of thermally conductive material from exposure to light
emitted from LEDs 102. The transmissive plate 174 is bonded to the
dam of thermally conductive material 190 (e.g., using glue, epoxy,
etc.).
[0064] FIG. 17 is illustrative of another configuration of LED
based illumination device 100. As illustrated, LED based
illumination device 100 includes a number of LEDs 102A-F,
collectively referred to as LEDs 102, arranged in a chip on board
(COB) configuration. The spaces between each LED are filled with a
reflective material 176 (e.g., a white silicone material). In
addition, a dam of reflective material 195 surrounds the LEDs 102
and supports transmissive plate 174. The space between LEDs 102 and
transmissive plate 174 is filled with an encapsulating optically
translucent material 177 (e.g., silicone) to promote light
extraction from LEDs 102 and to separate LEDs 102 from the
environment. In the depicted embodiment, the dam of reflective
material 195 is both the thermally conductive structure that
conducts heat from transmissive plate 174 to LED mounting board 104
and the optically reflective structure that reflects incident light
from LEDs 102 toward transmissive plate 174. The dam of reflective
material 195 is generated by punching or coining the bottom surface
of mounting board 104 to create a protrusion on the top surface and
a void on the bottom surface of the mounting board 104 opposite the
protrusion. The resulting protrusion on the top surface of mounting
board 104 serves as the dam of reflective material 195 and provides
thermal conductivity between the transmissive plate 174 and the
mounting board 104. Mounting board 104 is an insulated metal
substrate (e.g., a metal core printed circuit board). By way of
non-limiting example, the metal substrate may be aluminum or
copper.
[0065] FIG. 18 is illustrative of another embodiment of a base
reflector structure 200, similar to that shown in FIGS. 4-6. As
illustrated in FIG. 18, base reflector structure 200 directs light
emitted from LEDs 102 to the transmissive plate 174 coated with at
least one wavelength converting material (illustrated as wavelength
converting materials 180 and 181) and provides a direct thermal
path between the transmissive plate 174 and an LED mounting board
104. Base reflector structure 200 is in contact with transmissive
plate 174 over an area 201. Area 201 is designed to be large enough
to dissipate a significant amount of heat, but not so large as to
block a significant portion of light transmitted through
transmissive plate 174.
[0066] FIG. 19 is a top view of the light emitting device
illustrated in FIG. 18. In the illustrated embodiment, LEDs 102
with a 1 mm.sup.2 light emitting area are arranged on LED mounting
board 104 with a spacing of approximately 4 millimeters. Base
reflector structure 200 is arranged in a grid pattern between each
LED. The contact area 201 between base reflector structure 200 and
transmissive plate 174 has a width of approximately one millimeter,
while the distance between transmissive plate 174 and LED mounting
board 104 is approximately 0.5 millimeters. In the depicted
embodiment, base reflector structure 200 is an optically reflective
silicone with a thermal conductivity of approximately 1 W/mK. This
configuration allows a significant amount of heat to be conducted
from transmissive plate 174 to LED mounting board 104 through base
reflector structure 200.
[0067] In general, base reflector structure 200 is constructed from
a reflective material with high thermal conductivity. In some
embodiments, a highly reflective, thermally conductive silicone
material is employed. By controlling the spatial distribution of
the silicone as it is dispensed on LED mounting board 104, a
cup-like shape can be formed around the LEDs 102. In this manner,
large angle light emission from the LEDs 102 is directed toward
transmissive plate 174 by base reflector structure 200.
[0068] In another aspect, transmissive plate 174 is coupled to LED
mounting board 104 by a thermally conductive structure and an
optically reflective structure to promote heat transfer from
transmissive plate 174 to mounting board 104 and to promote light
extraction from the LED based illumination device.
[0069] Although certain specific embodiments are described above
for instructional purposes, the teachings of this patent document
have general applicability and are not limited to the specific
embodiments described above. For example, although LED based
illumination device 100 is depicted as emitting from the top of the
device (i.e., the side opposite the LED mounting board 104), in
some other embodiments, LED based illumination device 100 may emit
light from the side of the device (i.e., a side adjacent to the LED
mounting board 104). In another example, any component of LED based
illumination device 100 may be patterned with phosphor. Both the
pattern itself and the phosphor composition may vary. In one
embodiment, the illumination device may include different types of
phosphors that are located at different areas of LED based
illumination device 100. For example, a red phosphor may be located
on the bottom side of transmissive plate 174 and yellow and green
phosphors may be located on the top of transmissive plate 174. In
one embodiment, different types of phosphors, e.g., red and green,
may be located on different areas on transmissive plate 174 or
shaped lens 172. For example, one type of phosphor may be patterned
on transmissive plate 174 or shaped lens 172 at a first area, e.g.,
in stripes, spots, or other patterns, while another type of
phosphor is located on a different second area of on transmissive
plate 174 or shaped lens 172. If desired, additional phosphors may
be used and located in different areas. Additionally, if desired,
only a single type of wavelength converting material may be used
and patterned on transmissive plate 174 or shaped lens 172. In
another example, LED based illumination device 100 is depicted in
FIGS. 1-3 as a part of a luminaire 150. As illustrated in FIG. 3,
LED based illumination device 100 may be a part of a replacement
lamp or retrofit lamp. But, in another embodiment, LED based
illumination device 100 may be shaped as a replacement lamp or
retrofit lamp and be considered as such. Accordingly, various
modifications, adaptations, and combinations of various features of
the described embodiments can be practiced without departing from
the scope of the invention as set forth in the claims.
* * * * *