U.S. patent application number 13/867691 was filed with the patent office on 2013-11-07 for thermal management of led-based lighting systems.
The applicant listed for this patent is Albeo Technologies, Inc.. Invention is credited to Jeffrey Bisberg, Neil Cannon, Tracy Earles, Peter Van Laanen.
Application Number | 20130294060 13/867691 |
Document ID | / |
Family ID | 41341979 |
Filed Date | 2013-11-07 |
United States Patent
Application |
20130294060 |
Kind Code |
A1 |
Van Laanen; Peter ; et
al. |
November 7, 2013 |
Thermal Management Of LED-Based Lighting Systems
Abstract
An LED lighting element for use in a fluorescent lighting
fixture includes first and second end caps formed as printed
circuit boards for connecting with and obtaining physical support
from respective first and second sockets of the fluorescent
lighting fixture, and a blade supporting one or more LEDs between
the first and second end caps. The blade includes a first
compartment that contains high voltage circuitry, a second
compartment, separated from the first compartment, that contains a
low voltage assembly including the one or more LEDs, and a third
compartment forming an optical cavity. The element also includes a
power converter, located in one or both of the first and second end
caps, that converts power from the fluorescent light socket into
power for operating the LEDs.
Inventors: |
Van Laanen; Peter; (Boulder,
CO) ; Bisberg; Jeffrey; (Boulder, CO) ;
Cannon; Neil; (Boulder, CO) ; Earles; Tracy;
(Boulder, CO) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Albeo Technologies, Inc. |
Boulder |
CO |
US |
|
|
Family ID: |
41341979 |
Appl. No.: |
13/867691 |
Filed: |
April 22, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12431674 |
Apr 28, 2009 |
8425085 |
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13867691 |
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|
11735903 |
Apr 16, 2007 |
7806574 |
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12431674 |
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|
11959335 |
Dec 18, 2007 |
8506121 |
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12431674 |
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60744935 |
Apr 16, 2006 |
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60984075 |
Oct 31, 2007 |
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60870607 |
Dec 18, 2006 |
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60870608 |
Dec 18, 2006 |
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61048469 |
Apr 28, 2008 |
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61048461 |
Apr 28, 2008 |
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Current U.S.
Class: |
362/218 ;
362/221 |
Current CPC
Class: |
F21V 3/02 20130101; Y02B
20/386 20130101; H05K 1/0203 20130101; H05K 2201/10106 20130101;
F21V 29/83 20150115; F21V 29/506 20150115; F21V 21/00 20130101;
F21Y 2115/10 20160801; H05K 2201/0969 20130101; F21V 29/507
20150115; F21V 3/04 20130101; Y02B 20/30 20130101; H05K 1/181
20130101; H05K 3/0061 20130101; H05K 2203/1572 20130101; F21V 29/70
20150115 |
Class at
Publication: |
362/218 ;
362/221 |
International
Class: |
F21V 29/00 20060101
F21V029/00; F21V 21/00 20060101 F21V021/00 |
Claims
1. An LED lighting element for use in a fluorescent lighting
fixture, comprising: a first end cap formed as a printed circuit
board for connecting with and obtaining physical support from a
first socket of the fluorescent lighting fixture; a second end cap
formed as a printed circuit board for connecting with and obtaining
physical support from a second socket of the fluorescent lighting
fixture; a blade supporting one or more LEDs between the first and
second end caps, the blade comprising a first compartment that
contains high voltage circuitry, a second compartment, separated
from the first compartment, that contains a low voltage assembly
including the one or more LEDs, and a third compartment forming an
optical cavity; and a power converter, located in one or both of
the first and second end caps, that converts power from the
fluorescent light socket into power for operating the LEDs.
2. The system of claim 1, the two or more blades being
substantially `L` shaped.
3. The system of claim 1, wherein the LEDs mount on a back surface
of a first portion of the blade, the first portion being
substantially perpendicular to a second portion of the blade.
4. The system of claim 1, wherein the LEDs mount on a front surface
of a first portion of the blade, the first portion being
substantially perpendicular to a second portion of the blade.
5. The system of claim 1, wherein each blade forms a first portion
and a second portion coupled with the first portion and
substantially perpendicular to the first portion, and the venting
space is limited by respective second portions and one of the first
portions, of two blades nearest the venting space.
6. A flow-through LED lighting system, comprising: a housing; and
two or more substantially flat blades disposed with the housing, at
least one of the blades having a plurality of LEDs mounted
therewith such that light emits from the LEDs substantially
perpendicularly to a plane of the blade, and further comprising at
least one optical element for dispersing the light parallel to the
plane of the blade.
7. The system of claim 6, the optical element comprising a
reflective surface, and the at least one of the blades being
disposed with the housing such that when the system is in an
operational position, (a) the plane of the blade is substantially
vertical, and (b) the optical element disperses the light
downwardly.
8. The system of claim 6, each blade being separated from an
adjacent blade by a venting space that is rectangular in cross
section, such that the blade and the adjacent blade form two
opposing sides of the venting space, and portions of the housing
form two other opposing sides of the venting space.
9. A light-emitting diode ("LED") based lighting system, comprising
one or more light bars, each of the one or more light bars having a
plurality of LEDs mounted proximate to a bottom surface thereof,
each of the one or more light bars having a height to width aspect
ratio of 3:1 to 6:1.
10. The LED based lighting system of claim 9, wherein each of the
one or more light bars has a height to width aspect ratio of about
4:1.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation application of U.S.
patent application Ser. No. 12/431,674, filed 28 Apr. 2009, which
is a continuation-in-part application of U.S. patent application
Ser. No. 11/735,903, filed 16 Apr. 2007, now U.S. Pat. No.
7,806,574, which claims priority to U.S. Provisional Patent
Application No. 60/744,935, filed 16 Apr. 2006. U.S. patent
application Ser. No. 12/431,674 is also a continuation-in-part
application of U.S. patent application Ser. No. 11/959,335, filed
18 Dec. 2007, which claims priority to U.S. Provisional Patent
Applications Nos. 60/984,075, filed 31 Oct. 2007; 60/870,607, filed
18 Dec. 2006; and 60/870,608, filed 18 Dec. 2006. U.S. patent
application Ser. No. 12/431,674 also claims the benefit of priority
of U.S. Provisional Patent Applications Nos. 61/048,469, filed 28
Apr. 2008 and 61/048,461, filed 28 Apr. 2008. All of the
above-identified patent applications are incorporated herein by
reference in their entireties.
BACKGROUND
[0002] Light-emitting diode ("LED") based lighting systems are
currently increasing in popularity for a number of reasons.
Compared to incandescent lighting (based on filament heating),
LED-based lighting systems are much more efficient at conversion of
input power to light energy. Compared to fluorescent lighting
(based on absorption and reemission of photons generated by a
plasma), LED-based lighting systems have longer lifetimes, operate
without noticeable flickering and humming, can be dimmed by
reducing the operating current thereto, and do not require high
voltage electronics.
[0003] Efficient removal of heat is important in LED-based lighting
systems. Despite its efficiency, heat is generated by an LED during
operation, and concentrates in a small volume, potentially
increasing the LED's operating temperature significantly. The
operating lifetime of an LED is often strongly correlated to its
operating temperature, such that a small increase (e.g., a few
degrees Celsius) in operating temperature may degrade operating
lifetime by hundreds or thousands of hours.
[0004] FIG. 1 shows a portion of a prior art LED-based lighting
system 10. LEDs 20 and other circuit components 30 mount on a
printed circuit board ("PCB") 40, which in turn mounts on a heat
sink 60 (not all LEDs 20 and components 30 are labeled in FIG. 1
for clarity of illustration). PCB 40 includes a metal core 45. A
front side 42 of metal core PCB 40 has a dielectric layer 50 and
conductors 55 that electrically connect LEDs 20 with circuit
components 30 and with external power supplies. The metal core of
PCB 40 facilitates heat transfer such that heat generated by LEDs
20 flows through PCB 40 (from front side 42 to a back side, hidden
in the perspective of FIG. 1) to heat sink 60. System 10 may also
include thermal grease (hidden in the perspective of FIG. 1)
between the back side of PCB 40 and heat sink 60 to further
facilitate heat transfer.
[0005] In a thermal test of system 10, with LEDs 20 being 1/2 watt
LEDs and operated at a given test current, a .DELTA.T (difference
in temperature) of 5 to 6 degrees Celsius was measured between
metal leads of LEDs 20 and heat sink 60.
[0006] Another PCB substrate material that has been utilized for
LED-based lighting systems is ceramic material, which can be costly
and can introduce manufacturing difficulties, such as low yield
when substrates are singulated (separated into single units during
fabrication) and difficulty in reworking of mounted components.
SUMMARY
[0007] In an embodiment, an LED-based lighting system includes a
housing forming one or more apertures, a printed circuit board
("PCB") having conductors on a front-side thereof; and one or more
LEDs mounted with the conductors. The PCB is mounted with the
conductors proximate to and thermally coupling with a surface of
the housing such that the LEDs emit light through the apertures.
Heat generated by the one or more LEDs primarily dissipates through
the conductors to the housing.
[0008] In an embodiment, an LED-based lighting system includes a
housing forming one or more apertures, and one or more LEDs mounted
in the one or more apertures to emit light through a front surface
of the housing. A printed circuit board controls the LEDs, is
mounted on a back surface of the housing, and includes one or more
electrical conductors that supply power to the one or more LEDs.
The one or more electrical conductors thermally couple directly
with the housing such that more heat generated by the LEDs
dissipates through the one or more electrical conductors into the
housing as compared to dissipation through other thermal paths.
[0009] In an embodiment, a retrofit apparatus for a light fixture
includes a printed circuit board having electrical conductors on
its front-side, and one or more LEDs mounted with and powered
through the one or more electrical conductors. A mounting bracket
is configured for attaching to the light fixture, such that when
the bracket attaches to the light fixture, heat generated by the
one or more LEDs is primarily communicated from the LEDs through
the one or more electrical conductors and the mounting bracket to
the light fixture.
[0010] In an embodiment, a method of retrofitting a light fixture
with LEDs includes mounting to the light fixture a printed circuit
board having electrical conductors on a front-side thereof, and
LEDs mounted with the electrical conductors on the printed circuit
board front-side. The electrical conductors are in thermal contact
with the light fixture. The LEDs emit light through apertures of
the light fixture, and the electrical conductors and light fixture
form a thermal path that dissipates more of the heat from the LEDs
than other thermal paths.
[0011] In an embodiment, a method of retrofitting a light fixture
with LEDs includes mounting a bracket in thermal contact with a
housing of the light fixture. The bracket has a printed circuit
board that has conductors on a frontside thereof and LEDs mounted
with the conductors on the frontside. The bracket also has
electronics mounted therewith, for supplying power to the LEDs. The
conductors are in thermal contact with the bracket. The conductors
and the bracket form a primary heat dissipation path from the LEDs
to the housing.
[0012] In an embodiment, an LED based retrofit apparatus for a
light fixture includes a bracket configured for attachment to the
light fixture. Electronics mounted with the bracket convert AC line
voltage power to low voltage DC power. A printed circuit board has
one or more LEDs mounted thereon, and mounts with the bracket such
that when the printed circuit board is supplied with the low
voltage DC power, the LEDs primarily emit light upwardly into the
light fixture, and the light reflects from one or more surfaces and
exits the light fixture downwardly.
[0013] In an embodiment, an LED based lighting system, comprising
one or more light bars, each of the one or more light bars having a
plurality of LEDs mounted proximate to a bottom surface thereof.
Each of the one or more light bars has a height to width aspect
ratio of 3:1 to 6:1. Heat dissipation from the plurality of LEDs is
dependent on the height to width aspect ratio.
BRIEF DESCRIPTION OF DRAWINGS
[0014] Embodiments herein may be understood by reference to the
following detailed description, with reference to the drawings
briefly described below.
[0015] FIG. 1 shows a portion of a prior art LED-based lighting
system.
[0016] FIG. 2 shows an LED-based lighting system 100 in accord with
an embodiment.
[0017] FIG. 3 shows an exploded view of a portion of LED-based
lighting system of FIG. 2.
[0018] FIG. 4 shows a back side of a PCB of the system of FIG. 3,
with components mounted thereto.
[0019] FIG. 5 is a schematic cross-section showing primary heat
dissipation for an LED-based lighting system, in accord with an
embodiment.
[0020] FIG. 6 is a schematic cross-section showing primary heat
dissipation for another LED-based lighting system, in accord with
an embodiment.
[0021] FIG. 7 is a schematic cross-section of a troffer type
LED-based lighting system, in accord with an embodiment.
[0022] FIG. 8 shows details of one region the troffer type
LED-based lighting system of FIG. 7, in accord with an
embodiment.
[0023] FIG. 9A is a schematic cross-section of a retrofit apparatus
mounted with a portion of a housing, in accord with an
embodiment.
[0024] FIG. 9B is a schematic cross-section of a retrofit apparatus
mounted with a portion of a housing, in accord with an
embodiment.
[0025] FIG. 9C is a schematic cross-section of a retrofit apparatus
mounted with a portion of a housing, in accord with an
embodiment.
[0026] FIG. 10A is a schematic cross-section of an LED-based
lighting system that includes two of the retrofit apparatuses of
FIG. 9A, retrofitted into an existing housing, in accord with an
embodiment.
[0027] FIG. 10B is a schematic cross-section of an LED-based
lighting system that includes two of the retrofit apparatuses of
FIG. 9B, retrofitted into an existing housing, in accord with an
embodiment.
[0028] FIG. 10C is a schematic cross-section of an LED-based
lighting system that includes two of the retrofit apparatuses of
FIG. 9C, retrofitted into an existing housing, in accord with an
embodiment.
[0029] FIG. 11A is a schematic cross-section of a retrofit
apparatus that may be retrofitted to an existing housing, in accord
with an embodiment.
[0030] FIG. 11B shows a light fixture in which a housing has been
retrofit with the retrofit apparatus of FIG. 11A.
[0031] FIG. 11C shows a bottom view of the light fixture of FIG.
11B, to further illustrate mounting hardware utilized in attaching
the retrofit apparatus of FIG. 11B with a housing.
[0032] FIG. 12A is a schematic cross-section of a retrofit
apparatus that may be retrofitted to an existing housing, in accord
with an embodiment.
[0033] FIG. 12B shows a light fixture in which a housing has been
retrofit with the retrofit apparatus of FIG. 12A.
[0034] FIG. 13 shows a light fixture in which a housing has been
retrofit with a retrofit apparatus, in accord with an
embodiment.
[0035] FIG. 14 is a schematic cross-section of a light bar 730(1)
that may be a component of an LED-based lighting system, in accord
with an embodiment.
[0036] FIG. 15 depicts magnitude of heat transfer to ambient air at
representative locations of light bars of varying aspect ratios,
each such light bar having LED light and heat sources near a bottom
thereof, in accord with an embodiment.
DETAILED DESCRIPTION OF DRAWINGS
[0037] In the following description, specific instances of elements
may be described with reference subnumerals in parentheses (e.g.,
brackets 538(1), 538(2)) while elements that may be any of such
individual elements may use numerals without subnumerals (e.g.,
brackets 538 may be any of brackets 538(1), 538(2)).
[0038] FIG. 2 shows an LED-based lighting system 100. System 100
includes a structural element 160 that provides structural support
for a PCB (hidden by structural element 160 in the perspective of
FIG. 2) on which LEDs 120 are mounted. Structural element 160 may
be, for example, a metal rail that readily transfers heat from heat
sources to a surrounding environment (e.g., air). Each LED 120 is
centered within an aperture 165 formed by structural element 160 so
that light emanates from each LED 120 and away from system 100 (not
all LEDs 120 and apertures 165 are labeled in FIG. 2 for clarity of
illustration). As used herein, the term "LED" includes
light-emitting diodes and other devices based thereon, such as for
example superluminous diodes and laser diodes.
[0039] FIG. 3 shows an exploded view of a portion of LED-based
lighting system 100. LEDs 120 mount to conductors 155 on a
front-side 142 of a PCB 140, which may include a substrate of epoxy
glass circuit board material (not all conductors 155 are labeled in
FIG. 3 for clarity of illustration). A dielectric film 170
electrically isolates PCB 140 from structural element 160.
Dielectric film 170 may optionally be absent if conductors 155 are
otherwise isolated from structural element 160, for example when
conductors 155 are covered by a solder mask layer (not shown).
Alternatively, a structural element 160 formed of aluminum may be
anodized to isolate PCB 140 from structural element 160. However,
dielectric film 170 may be formed independently of a PCB or rail
fabrication process, so that any shorting defects remaining after
soldermask or anodizing processes are insulated by dielectric film
170. Dielectric film 170 may be for example a 4 mil film of
Kapton.RTM., although other thicknesses may be utilized, and other
dielectrics such as polyester may be utilized. Dielectric film 170
may also be more ductile than a solder mask layer or an anodized
layer, so that it conforms to topology of PCB 140 to promote heat
transfer between conductors 155 and structural element 160, while
ensuring electrical isolation therebetween. In one embodiment,
dielectric film 170 covers areas of PCB 140 where a solder mask
layer is not present so that components are solderable to
through-holes of PCB 140, and so that inclusions or irregularities
in conductors 155 that the solder mask does not cover are
insulated. Dielectric film 170 and/or a solder mask layer are
advantageously thin enough so as not to significantly impede
transfer of heat where conductors 155 face structural element 160
(that is, where conductors 155 are immediately adjacent to
structural element 160 except for intervening solder mask and/or
dielectric layers).
[0040] PCB 140 is fastened to structural element 160 using screws
180, or equivalent fasteners such as clips or nuts and bolts.
Dashed lines show positions of screws 180 and LEDs 120 with respect
to PCB 140 and structural element 160 in the exploded view of FIG.
3.
[0041] Conductors 155 are configured such that heat generated by
LEDs 120 dissipates first into conductors 155 and then into
structural element 160. Conductors 155 are formed of metal (e.g.,
copper) that may be thicker than required for electrical purposes
alone, to facilitate heat transfer away from LEDs 120. That is, it
is understood that "conductors" herein refers to materials and
items formed thereof that are thermally conductive as well as
electrically conductive. For example, standard PCBs may have
conductor thicknesses of about 0.55-1.25 oz/ft.sup.2 in order to
accommodate typical current requirements, but conductors 155 may
have conductor thicknesses of about 2.0-2.5 oz/ft.sup.2 or more to
facilitate this heat dissipation. Also, conductors 155 may be laid
out on PCB 140 so as to occupy as much area of PCB 140 as possible.
For example, conductors 155 may occupy more than 50%, 70% or even
95% of a surface area of front-side 142 of PCB 140. In the layout
shown in FIG. 3, conductors 155 occupy about 74% of the front-side
142 area of PCB 140. Furthermore, the area of conductors 155 may be
arranged so as to maximize area of conductors 155 that faces
structural element 160 when assembled.
[0042] The thickness and large percentage of front-side PCB area
occupied by conductors 155, and the proximity of conductors 155 to
structural element 160, facilitate thermal coupling so that heat
generated by LEDs 120 primarily dissipates through conductors 155
and structural element 160. That is, more heat generated by LEDs
120 dissipates through this heat dissipation path as compared to
other thermal paths (e.g., through a back-side of PCB 140 to air or
to other parts of a light fixture). When assembled to structural
element 160, the large area of conductors 155 is separated from
structural element 160 only by thin layers such as soldermask of
PCB 140 and optional dielectric layer 170, so that such layers do
not significantly impede heat transfer from conductors 155 to
structural element 160.
[0043] In a thermal test of the configuration shown in FIG. 3, with
LEDs 120 being 1/2 watt LEDs operated at the same test current as
used to test system 10 (discussed above), a .DELTA.T between metal
leads of LEDs 120 and structural element 160 of 3 to 4 degrees
Celsius was measured.
[0044] Use of epoxy glass as substrate material for PCB 140 may
have certain advantages as compared to the metal core material used
in PCB 40 of system 10. Epoxy glass PCBs are inexpensive, and are
widely available from a large selection of suppliers, whereas metal
core and ceramic PCBs are costly and are available from fewer
suppliers. Inner layers can be readily incorporated into epoxy
glass PCBs to facilitate electrical or thermal connections, but
such layers currently cannot be incorporated into metal core PCBs.
Epoxy glass PCBs are readily singulated (that is, separated into
single PCBs during fabrication) whereas metal core and ceramic PCBs
are more difficult to singulate. Rework of components mounted to
epoxy glass PCBs is relatively easy, whereas rework of components
mounted to metal core or ceramic PCBs is more difficult. Epoxy
glass PCBs are lighter (per unit area) than metal core and ceramic
PCBs.
[0045] Having LEDs 120 on front-side 142 of PCB 140, while
components 130 are on back-side 144 (FIG. 4) may also provide
certain advantages. For example, limiting the mounting of
components 130 to back-side 144 facilitates a sleek appearance of
system 100 wherein LEDs 120 emit light through structural element
160 while components 130 remain hidden from view. By comparison,
prior art system 10 (FIG. 1) mounts components 30 along with LEDs
20 on front side 42 of PCB 40, necessitating extra structure if
hiding components 30 from view is desired. Also, lack of non-LED
components allows front-side 142 to present a planar surface except
at LEDs 120; since LEDs 120 fit into apertures 165, the remaining
planar surface of front-side 142 readily mounts to an inner surface
of structural element 160, facilitating heat transfer. Furthermore,
lenses, protective covers or other aesthetic or practical structure
may optionally mount to structural element 160 with ease in the
vicinity of LEDs 120, since structural element 160 presents an
easily used substrate for mounting of such structure. Mounting
similar extra structure to system 10 is more difficult since all of
conductors 55, LEDs 20 and components 30 compete for space on the
same front side 42 of PCB 40.
[0046] FIG. 4 shows a back-side 144 of PCB 140 with components 130
mounted thereto (not all components 130 are labeled in FIG. 4, for
clarity of illustration). System 100 (FIG. 3) dissipates more power
as heat through LEDs 120 than through components 130, such that
thermal management of components 130 is not as critical to
reliability of system 100.
[0047] FIG. 5 is a schematic cross-section showing primary heat
dissipation paths 210 for an LED-based lighting system 200. System
200 includes a PCB 240 having conductors 255 that are at least
partially covered by a solder mask layer 257. A dielectric layer
270 provides additional electrical isolation between PCB 240 and a
structural element 260, but does not significantly impede thermal
transfer therebetween. An LED 220 emits light that passes through
an optional lens 290.
[0048] A PCB may include structure for conducting heat from a front
side to a back side of the PCB, to further improve heat dissipation
from the LEDs. For example, the PCB may include vias filled with
metal to facilitate heat transfer from a front-side to a back-side
of the PCB, as now discussed in FIG. 6.
[0049] FIG. 6 is a schematic cross-section showing primary heat
dissipation paths 310 for an LED-based lighting system 300. System
300 includes a PCB 340 having conductors 355. An LED 320 emits
light and generates heat that passes into conductors 355.
Metal-filled vias 325 facilitate heat transfer from conductors 355
to back-side conductors 330 (not all vias 325 are labeled in FIG. 6
for clarity of illustration). Metal-filled vias 325 may be formed
at the time of PCB fabrication--for example, as vias that are
through-hole plated--or may be formed after fabrication--for
example, by filling holes of PCB 340 with solder, or mechanically
by inserting or screwing metal rods or screws through PCB 340.
Back-side conductors 330 may dissipate heat into a surrounding
medium (e.g., air) directly. Alternatively, conductors 330 may
facilitate heat transfer to optional heat sinks 360, which may
include passive structures (e.g., radiating structures) and/or
active devices (e.g., fans).
[0050] The above description of thermal dissipation paths for
LED-based lighting systems thus provide one set of methods for
generating thermal dissipation paths. Such methods include
specifying PCB conductors that are thicker than required to supply
current to the LEDs and that occupy 50% or more of PCB area, and
configuring the conductors in close proximity to structural
elements so as to dissipate heat away from the LEDs. Further
methods for generating thermal dissipation paths include utilizing
different structural elements to conduct heat away from LEDs, and
to encourage convective cooling, as described below.
[0051] FIG. 7 is a schematic cross-section of a troffer type
LED-based lighting system 400. System 400 includes a troffer
housing 460 and an optional diffuser 490. Electronics 410 form a
power supply for LEDs (e.g., by converting incoming AC line voltage
power to low voltage DC power, and optionally controlling dimming
of the LEDs) and connect to PCBs 440 through wiring 415 (wiring 415
is shown schematically as a single line, but may include multiple
wires). LEDs 420 mount with PCBs 440, which respectively mount with
an outer surface 462 of housing 460. In use, LEDs 420 project light
through apertures 465 of housing 460. (Apertures 465 are shown in
FIG. 7 as interruptions in housing 460, but housing 460 may connect
about apertures 465 outside the cross-sectional plane shown in FIG.
7.)
[0052] PCBs 440 are in intimate thermal contact with troffer
housing 460 to provide effective conduction of heat away from LEDs
420 and into housing 460, as discussed below in connection with
FIG. 8. Additionally, housing 460 may form optional vent apertures
467, and optional diffuser 490 may form optional vent apertures
495. Vent apertures 467 and/or 495 encourage convection of ambient
air through system 400, such as a flow represented by arrows 499,
for convective cooling of housing 460. Details of a region denoted
by A in FIG. 7 are shown in FIG. 8.
[0053] It is appreciated that the number and location of elements
shown in FIG. 7 and FIG. 8 may differ from those shown. For
example, LEDs 420 and their associated PCBs 440 and apertures 465
may be entirely in a top surface of housing 460, rather than on
both the top surface and side surfaces, as shown. Vent apertures
467 and/or 495 may vary in placement and number. Electronics 430
may mount at other locations on housing 460 than the location
shown, or may be remote from housing 460 (e.g., one set of
electronics may connect to several systems 400 with wiring 415.
[0054] FIG. 8 shows details of region A of FIG. 7. PCB 440 includes
conductors 455 that make electrical and thermal contact with LED
420, and which facilitate heat transfer from LED 420 to housing 460
along paths 480. Conductors 455 may be thicker than required for
electrical purposes alone, to facilitate the heat transfer. A
dielectric layer 470 (e.g., a solder mask layer) electrically
isolates housing 460 from conductors 455, but does not
significantly impede thermal transfer therebetween.
[0055] FIG. 9A is a schematic cross-section of a retrofit apparatus
500(1) mounted with a portion of a housing 560. Retrofit apparatus
500(1) includes a thermally conductive mounting bracket 538(1). In
one embodiment, thermally conductive mounting bracket 538(1)
supports a PCB 540 with LEDs 520. Bracket 538(1) mounts with
housing 560 and may be located proximate a location intended for a
fluorescent bulb. Bracket 538(1) provides a relatively large area
of thermal contact with housing 560. Bracket 538(1) may be a
unitary bracket, or bracket 538(1) may be provided in segments.
Bracket 538(1) may be fixed when connecting system 500(1) with
housing 560(1), or bracket 538(1) may include rotating or sliding
segments that move relative to one another to allow a user or a
motor to tilt apparatus 500(1), for example to direct output light.
Bracket 538(1) thus provides a thermal path from LEDs 520 to
housing 560, for example via thermal contact with conductors of PCB
540. Wiring 515 (shown schematically as a single line, but
understood to include one or more wires) facilitates connection
between PCB 540 and an external power source, such as a wall socket
or battery.
[0056] It is contemplated that mounting bracket for a retrofit
system may have physical dimensions that enable certain types of
light fixtures to be retrofitted therewith, and/or that produce
certain results or visual effects when used. For example, FIG. 9B
is a schematic cross-section of a retrofit apparatus 500(2) mounted
with a portion of housing 560. Retrofit apparatus 500(2) includes a
thermally conductive mounting bracket 538(2) that is substantially
similar to bracket 538(1) (FIG. 9A) except that bracket 538(2) is
longer in a vertical direction, thereby allowing use with a deeper
housing 560, or bringing LED 520 further down within housing 560
(e.g., see FIG. 10B). FIG. 9C is a schematic cross-section of a
retrofit apparatus 500(3) mounted with a portion of housing 560.
Retrofit apparatus 500(3) includes a thermally conductive mounting
bracket 538(3) that is substantially similar to bracket 538(1)
(FIG. 9A) except that bracket 538(2) is more compact in a vertical
direction, and thus may be suitable for a lower profile housing 560
(e.g., see FIG. 10C).
[0057] The thermal coupling provided by brackets 538 enables
superior performance of lighting systems that utilize any of
retrofit apparatuses 500 (e.g., apparatuses 500(1)-(3) shown in
FIGS. 9A-9C), by providing for operation of LEDs 520 at a low
operating temperature, which leads to high efficiency operation.
Furthermore, a retrofit apparatus 500 can be retrofitted into
existing housings 560, as described in connection with FIGS.
10A-10C below. In one embodiment, bracket 538 and the components
mounted thereon, along with a power supply and a connector to
wiring 515, are provided as a retrofit apparatus for easy
installation with an existing fluorescent fixture. Bracket 538 fits
with an existing housing 560 via mechanical fasteners such as
screws, pegs, clips, one or more braces or other known fasteners
(not shown) or may utilize such fasteners as magnets or adhesives,
that fix or brace bracket 538 with housing 560. In one aspect,
these fasteners work with bracket 538 to hold apparatus 500 firmly
in place, yet allow for removal of apparatus 500 for service (if
necessary) or if a substitute apparatus 500 is desired. Magnets
integrated with bracket 538 may be a particularly useful choice for
connecting bracket 538 with housing 560. For example, many magnets
are good thermal conductors, and can be utilized as part of a
primary thermal dissipation path. Also, in certain embodiments
magnets may support bracket 538 without fixing its position with
respect to housing 560, such that bracket 538 may be repositioned
without drilling holes, applying adhesive or otherwise altering
bracket 538 or housing 560 in a manner that would be difficult to
undo.
[0058] Bracket 538 may be coated with or otherwise incorporate a
highly conductive material or combination of materials. In one
embodiment, bracket 538 is made with copper. In another embodiment,
bracket 538 includes a copper/diamond combination. In still another
embodiment, bracket 538 includes aluminum, magnesium, and/or alloys
thereof. Further exemplary materials that may be incorporated in
bracket 538 include (but are not limited to) those listed below in
Tables 1-3.
TABLE-US-00001 TABLE 1 First Generation Thermal Management
Materials Specific Thermal Thermal Conductivity k CTE Density
Conductivity Reinforcement Matrix (W/m-K) (ppm/K) (g/cm.sup.3)
(W/m-K) -- Aluminum 218 23 2.7 81 -- Copper 400 17 8.9 45 -- Invar
11 1.3 8.1 1.4 -- Kovar 17 5.9 8.3 2.0 -- Cu/I/Cu 164 8.4 8.4 20 --
Cu/Mo/Cu 182 6.0 9.9 18 -- Cu/Mo--Cu/Cu 245 to 280 6 to 10 9.4 26
to 30 -- Titanium 7.2 9.5 4.4 1.6 Copper Tungsten 157 to 190 5.7 to
8.3 15 to 17 9 to 13 Copper Molybdenum 184 to 197 7.0 to 7.1 9.9 to
10.0 18 to 20 -- Solder - 50 25 8.4 6.0 Sn63/Pb37 -- Epoxy 1.7 54
1.2 1.4 E-glass Fibers Epoxy 0.16 to 0.26 11 to 20 2.1 0.1
Properties of traditional first-generation thermal management
materials. From: Zweben, Carl, "Thermal Materials Solve Power
Electronics Challenges," Feb. 1, 2006, available at:
http://powerelectronics.com/thermal_management/heatpipes_spreaders/power_-
thermal_materials_solve/
TABLE-US-00002 TABLE 2 Second Generation High-Performance Thermal
Materials Through- Specific Inplane Thickness Inplane Thermal
Thermal Inplane Thermal Conductivity Conductivity CTE Density
Conductivity Reinforcement Matrix (W/m-K) (W/m-K) (ppm/K)
(g/cm.sup.3) (W/m-K) Natural Epoxy 370 6.5 -2.4 1.94 190 Graphite
Continuous Polymer 330 10 -1 1.8 183 Carbon Fibers Discontinuous
Copper 300 200 6.5 to 9.5 6.8 44 Carbon Fibers SiC Particles Copper
320 320 7 to 10.9 6.6 48 Continuous SiC 370 38 2.5 2.2 170 Carbon
Fibers Carbon Foam Copper 350 350 7.4 5.7 61 Properties of advanced
second-generation thermal management materials with high thermal
conductivities and low coefficients of thermal expansion (300
.ltoreq. k < 400). From: Zweben Carl, "Thermal Materials Solve
Power Electronics Challenges," citied above
TABLE-US-00003 TABLE 3 Third Generation High-Performance Thermal
Materials Through- Specific Inplane Thickness Inplane Thermal
Thermal Inplane Thermal Conductivity Conductivity CTE Density
Conductivity Reinforcement Matrix (W/m-K) (W/m-K) (ppm/K)
(g/cm.sup.3) (W/m-K) -- CVD 1100 to 1800 1100 to 1800 1 to 2 3.52
310 to 510 Diamond -- HOPG 1300 to 1700 10 to 25 -1.0 2.3 565 to
740 -- Natural 150 to 500 6 to 10 -- -- -- Graphite Continuous
Copper 400 to 420 200 0.5 to 16 5.3 to 8.2 49 to 79 Carbon Fibers
Continuous Carbon 400 40 -1.0 1.9 210 Carbon fibers Graphite Hake
Aluminum 400 to 600 80-110 4.5 to 5.0 2.3 174 to 260 Diamond
Aluminum 550 to 600 550 to 600 7.0 to 7.5 3.1 177 to 194 Particles
Diamond and Aluminum 575 575 5.5 -- -- SiC Particles Diamond Copper
600 to 1200 600 to 1200 5.8 5.9 102 to 203 Particles Diamond Cobalt
>600 >600 3.0 4.12 >145 Particles Diamond Silver 400 to
>600 400 to >600 5.8 5.8 69 to >103 Particles Diamond
Magnesium 550 550 8 -- -- Particles Diamond Silicon 525 525 4.5 --
-- Particles Diamond SiC 600 600 1.8 3.3 182 Particles Properties
of advanced third-generation thermal management materials with
ultrahigh thermal conductivities and low coefficients of thermal
expansion (k .gtoreq. 400). From: Zweben, Carl. "Thermal Materials
Solve Power Electronics Challenges," cited above
[0059] Materials listed in Tables 1-3 may, for example, be extruded
to form bracket 538, such that PCB 540 spans a length of the
extrusion and incorporates any number of LEDs 520.
[0060] FIG. 10A is a schematic cross-section of an LED-based
lighting system 600(1) that includes two apparatuses 500(1) (FIG.
9A) retrofitted into an existing housing 560(1). System 600(1)
includes electronics 510 that connect with wiring 515 of
apparatuses 500(1), as shown. Electronics 510 form a power supply
for LEDs (e.g., by converting incoming AC line voltage power to low
voltage DC power, and optionally controlling dimming of the LEDs).
Apparatuses 500(1) are in intimate thermal contact with housing
560(1) to provide effective conduction of heat away from LEDs 520
(see FIG. 9A). Heat generated by LEDs 520 passes into thermally
conductive PCB layers in PCB 540 (FIG. 9A, heat travels in the same
manner as illustrated in FIG. 8), then to bracket 538(1) (FIG. 9A)
and to housing 560(1).
[0061] To further facilitate heat transfer away from LEDs 520,
housing 560(1) may form optional vent apertures 567, and an
optional diffuser 590 may form optional vent apertures 595. Vent
apertures 567 and/or 595 encourage convection of ambient air
through system 600(1), such as flows represented by arrows 599, for
convective cooling of housing 560. Vent apertures 567 may be part
of an original configuration of housing 560(1), or they may be
added (e.g., by drilling or punching) when apparatuses 500(1) are
retrofitted into housing 560(1). Similarly, vent apertures 595 may
be part of an original configuration of the lighting system before
apparatuses 500(1) are retrofitted, or apertures 595 may be added
at the time of retrofitting apparatuses 500(1), or retrofitting may
include installing a diffuser 590 that was not previously
present.
[0062] FIG. 10B is a schematic cross-section of an LED-based
lighting system 600(2) that includes two apparatuses 500(2) (FIG.
9B) retrofitted into existing housing 560(1) (e.g., having the same
dimensions as housing 560(1) of FIG. 10A). Apparatuses 500(2)
utilize brackets 538(2) (FIG. 9B) that are taller in a vertical
direction than brackets 538(1) (FIG. 9A) such that for housing
560(1), LEDs 520 (FIG. 9B) are closer to diffuser 590 than when
apparatuses 500(1) are used.
[0063] FIG. 10C is a schematic cross-section of an LED-based
lighting system 600(3) that includes two apparatuses 500(3) (FIG.
9C) retrofitted into a low profile housing 560(2). As compared with
apparatuses 500(1) and 500(2), vertically compact apparatuses
500(3) are retrofittable into low profile housing 560(2) to form
system 600(3) that may be advantageously used, for example in
applications where limited vertical space is available for a
lighting system. Alternatively, apparatuses 500(3) may be utilized
in a relatively deep housing, in order to provide a significant
space between LEDs 520 and a diffuser of the system.
[0064] FIG. 11A is a schematic cross-section of a retrofit
apparatus 700(1) that may be retrofitted to an existing housing
(e.g., a troffer). Retrofit apparatus 700(1) includes a thermally
conductive bracket 650(1) configured for mounting to the housing,
that provides both structural support and an efficient thermal
dissipation path for LED based lighting mounted thereon. Bracket
650(1) supports electronics 610 and PCBs 640 that emit light from
LEDs thereon (the LEDs are not individually labeled in FIG. 11A,
for clarity of illustration, but are mounted with PCBs 640 in like
manner as shown in FIG. 8). Electronics 610 form a power supply for
LEDs (e.g., by converting incoming AC line voltage power to low
voltage DC power, and optionally controlling dimming of the LEDs).
Bracket 650(1) may be formed, for example, of aluminum, magnesium,
copper, alloys thereof and/or any of the materials listed in Tables
1-3 above. PCBs 640 may be strips that mount along a length of
element 650(1) (e.g., in and out of the plane of the page where the
cross-section is taken) such that each PCB 640 may include multiple
LEDs thereon. Two PCBs 640(1) direct light upwardly that is
diffused or reflected from the existing housing to exit downwardly
therefrom, while a PCB 640(2) directs light downwardly; a
collective effect of the light from PCBs 640(1) and 640(2) is
therefore one of "direct/indirect" lighting. Wiring 615 transmits
electrical power from electronics 610 to each PCB 640. An optional
diffuser 690, through which the LED light passes before it exits
the light fixture, may be included in retrofit apparatus 700(1)
along with element 650(1) and the electronics and PCBs mounted
thereon. Retrofit apparatus 700(1) may be advantageous for
retrofitting light fixtures because the necessary electronics that
provide power to LEDs, and the LEDs themselves, are physically
integrated into a single unit, providing for simpler field
retrofits as compared to apparatuses that require installing
multiple components.
[0065] FIG. 11B shows a light fixture 705(1) in which a housing 660
has been retrofit with retrofit apparatus 700(1). Housing 660 may
be, for example, a troffer. LEDs associated with each PCB 640 emit
light designated by light rays 645. PCBs 640(1) are mounted such
that light rays 645 are directed upwardly towards housing 660,
where they impinge on an inner surface 662 of housing 660. Surface
662 may be reflective or coated with a reflective color (e.g.,
white) so that light from the outwardly facing PCBs is efficiently
reflected downwards from housing 660. PCB 640(2) that is
approximately central within housing 600 directs light rays 645
downwardly. Optional diffuser 690 may be utilized to help blend and
diffuse light generated by the LEDs (e.g., to minimize user
discomfort and/or distraction that may be associated with LEDs that
are bright point sources of light). Bracket 650(1) may form a
primary thermal path for conducting heat generated by the LEDs,
away from PCBs 640 to housing 660.
[0066] FIG. 11C shows a bottom view of light fixture 705(1) of FIG.
11B, to further illustrate mounting hardware utilized in attaching
retrofit apparatus 700(1) with housing 660. Dashed line 11B-11B
indicates the cross-section along which the view of FIG. 11B is
taken. Electronics 610 are shown in dashed outline, as they are
hidden within bracket 650(1) in the view of FIG. 11C. Also shown in
dashed outline are eight fasteners 670 that attach bracket 650(1)
with housing 660. As noted above, fasteners such as mechanical
fasteners, magnets and/or adhesives may be utilized as fasteners
670. Fasteners 670 may include slots or tabs of bracket 650(1)
and/or housing 660 that mate with one another. Fasteners 670 may
advantageously facilitate heat dissipation from bracket 650(1) to
housing 660. Also, although eight fasteners 670 are shown, it is
contemplated that other numbers and arrangements of fasteners may
be utilized in embodiments.
[0067] It is contemplated that a unitary retrofit apparatus may be
configured with differing numbers, types and/or arrangements of
LEDs, and differing diffuser configurations, than are shown in FIG.
11A and FIG. 11B. For example, FIG. 12A is a schematic
cross-section of a retrofit apparatus 700(2) that may be
retrofitted to an existing housing. Retrofit apparatus 700(2)
includes a thermally conductive bracket 650(2) configured for
mounting to the housing, that provides both structural support and
an efficient thermal dissipation path for LED based lighting
mounted thereon. Bracket 650(2) supports electronics 610 and PCBs
640 that emit light from LEDs thereon (the LEDs are not
individually labeled in FIG. 11B, for clarity of illustration, but
each PCB 640 includes multiple LEDS that are mounted with PCBs 640
in like manner as shown in FIG. 8). Bracket 650(2) may be formed,
for example, of aluminum, magnesium, copper, alloys thereof and/or
any of the materials listed in Tables 1-3 above. In retrofit
apparatus 700(2), PCBs 640(3) mount in pairs along upwardly facing
sides of element 650(2) (e.g., the strips extend in and out of the
plane of the page where the cross-section is taken, as illustrated
in FIG. 11C) and a pair of PCB 640(4) mounts downwardly, as shown,
to create an effect of "direct/indirect" lighting. Wiring 615
transmits electrical power from electronics 610 to each PCB 640.
Optional diffusers 690, 692 and 694 may be included in retrofit
apparatus 700(1) along with element 650(2) and the electronics and
PCBs mounted thereon. Optional diffuser 694 is shown as a concave,
downwardly facing element that primarily reflects and may also
diffuse light emitted from LEDs of PCBs 640(3). Diffuser 694 is
shown extending across a top surface of bracket 650(2) but is
configured for minimal thermal impedance between element 650(2) and
a housing. For example, diffuser 694 may have open areas that allow
direct contact between element 650(2) and a housing, or may be very
thin, or may be provided in sections that attach to sides of
element 650(2) but do not extend between element 650(2) and the
housing Like retrofit apparatus 700(1), retrofit apparatus 700(2)
may be advantageous for retrofitting light fixtures because the
necessary electronics that provide power to LEDs, the LEDs
themselves, and optional diffusers may be physically integrated
into a single unit, providing for simpler field retrofits as
compared to apparatuses that require installing multiple
components.
[0068] FIG. 12B shows a light fixture 705(2) in which housing 660
has been retrofit with retrofit apparatus 700(2). LEDs associated
with each PCB 640 emit light designated by light rays 645. Four
PCBs 640(3) mount such that light rays 645 are directed upwardly
towards housing 660, where they impinge on an inner surface 662 of
housing 660, unless optional diffuser 694 is installed, in which
case light rays impinge on diffuser 694. Diffuser 694 need not
completely reflect light incident thereon (e.g., diffuser 694 may
be made of a translucent material) and surface 662 may be
reflective or coated with a reflective color (e.g., white) so that
any light from PCBs 640(3) that transmits through diffuser 694 is
efficiently reflected back downwards from housing 660. PCBs 640(4)
mount approximately central within housing 660 and direct
respective light rays 645 downwardly.
[0069] Whether light emitted by PCBs 640(3) reflects from inner
surface 662 or optional diffuser 694 or both, blending and
diffusion associated with such reflections helps to minimize user
discomfort and/or distraction that may be associated with LEDs that
are bright point sources of light. Optional diffuser 690, through
which the LED light passes before it exits the light fixture, may
be utilized to help further blend and diffuse light emitted by PCBs
640(3); such two stage diffusion may be particularly helpful in
minimizing user discomfort and/or distraction. Optional diffuser
692, when present, further blends and diffuses light from PCBs
640(4); thus when utilized with optional diffuser 690, the light
from PCBs 640(4) is also blended and diffused in two stages.
Bracket 650(2) may form a primary thermal path for conducting heat
generated by the LEDs, away from PCBs 640 to housing 660.
[0070] FIG. 13 shows a light fixture 705(3) in which a housing 660
has been retrofit with a retrofit apparatus 700(3). LEDs associated
with each of two PCBs 640(5) emit light designated by light rays
645. In light fixture 705(3), a bracket 650(3) spans a full width
of housing 660 and reflects and diffuses light rays 645; an
optional diffuser 690 may also be added, in the same manner as
optional diffuser is used in retrofit apparatuses 700(1) and 700(2)
(FIG. 11A, 12A respectively). Fasteners 770 may be used to secure
bracket 650(3) to top and/or side surfaces of housing 660, as
shown. As discussed with respect to fasteners 670 (FIG. 11C),
fasteners 770 may be mechanical fasteners, magnets, adhesives,
and/or arrangements whereby slots or tabs of bracket 650(3) and/or
housing 660 that mate with one another. Fasteners 770 may
advantageously facilitate heat transfer from bracket 650(3) to
housing 660.
[0071] Typically, when heat is generated by a lighting fixture, the
heat transfers from point to point within the fixture (and/or
objects with which it may be in thermal contact) until the heat
eventually transfers to ambient air. Radiative heat transmission
from a light fixture to air may therefore play an important role in
managing temperature of the fixture and components therein. FIG. 14
is a schematic cross-section of a light bar 730(1) that may be a
component of an LED-based lighting system. Light bar 730(1) has a
width w and a height h as shown; for light bar 730(1), h and w are
equal, that is, light bar 730(1) has a height to width aspect ratio
of 1:1. An exemplary PCB 740 and LED 720 are shown proximate to a
bottom surface 734 of light bar 730(1); since the view shown in
FIG. 13 is a cross-section, light bar 730(1) represents a tube
extending in and out of the page while PCB 740 is a strip running
along such tube, and having LEDs 720 at intervals thereon. When LED
720 is on, light is emitted downwardly therefrom, as indicated by
light rays 745. Heat is generated by LEDs 720 (and/or by other
components on PCB 740) and at least some of the heat transfers to a
side surface 732 of light bar 730(1) near bottom surface 734.
Arrows 750 indicate the magnitude of heat transfer to ambient air
at representative locations of side surface 732 (heat transfers
from many locations of light bar 730(1); arrows designate only two
such locations, for clarity of illustration). When LEDs 720 are on,
heat dissipated from LED 720 will raise temperatures at locations
adjacent to LED 720 the most, and as the heat spreads, other areas
will correspondingly increase in temperature. Since heat transfer
is proportional to temperature difference between adjacent points,
heat transfer to air will therefore be highest near bottom surface
734 and will diminish further up on side surface 732.
[0072] FIG. 15 shows arrows 750 designating magnitude of heat
transfer to ambient air at representative locations of light bars
730(1)-730(4), each such light bar having LED light (and heat)
sources near a bottom thereof, like LED 720 shown in FIG. 14 (the
LED(s) are not shown in FIG. 14, for clarity of illustration). As
noted for FIG. 14, light bar 730(1) has a height to width aspect
ratio of 1:1; light bars 730(2), 730(3) and 730(4) have height to
width aspect ratios of 2:1, 4:1 and 8:1 respectively. Arrows
750(1)-750(4) illustrate the respective magnitudes of heat transfer
to ambient air at representative locations of light bars
730(1)-750(4). It can be seen that net heat transfer (visualized as
a sum of arrows 750) increases significantly with height to width
aspect ratio for light bars 730(1)-730(3), but for light bar 730(4)
with a height to width aspect ratio of 8:1, incremental heat
transfer near a top of the light bar is small. Since volume,
material used, and therefore weight of a light fixture will vary
with height to width aspect ratio of light bars used, increasing
height to width aspect ratio up to 4:1 (e.g., the aspect ratio of
light bar 750(3)) may be advantageous in terms of reducing
operating temperature, but increasing height to width aspect ratio
to 8:1 may negate this advantage due to such aspect ratio
generating an excessively large and heavy fixture without
significant further temperature reduction. Accordingly, height to
width aspect ratios ranging from 3:1 to 6:1 may be useful choices
for light bars 730, and a height to width aspect ratio of 4:1 may
be approximately optimal. A height to width aspect ratio such as
4:1 may also have other advantages, such as generating a high ratio
of side surface to top and bottom surface of a light fixture.
Since, over time, dust and/or other contaminants may settle on a
top surface of a light fixture, minimizing top and bottom surface
area relative to side surface area may be advantageous.
[0073] Changes may be made in thermal management of the LED-based
lighting systems described herein without departing from the scope
hereof. It should thus be noted that the matter contained in the
above description or shown in the accompanying drawings should be
interpreted as illustrative and not in a limiting sense. The
following claims are intended to cover all generic and specific
features described herein, as well as all statements of the scope
of the present method and system, which, as a matter of language,
might be said to fall there between.
* * * * *
References