Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02792187 2014-05-14
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LIGHT-GENERATING SYSTEM
FIELD OF THE INVENTION
[0001] The present invention is a light-generating system.
BACKGROUND OF THE INVENTION
[0002] As is well known in the art, light-emitting diodes ("LEDs") are
more efficient than
incandescent light bulbs, i.e., more light is produced per watt by an LED than
by an incandescent
bulb. Other known electrically-powered light sources, e.g., fluorescent light
bulbs, have a
number of disadvantages, as is well known in the art. For example, fluorescent
light bulbs are
required to be replaced relatively frequently. Where they are used in
streetlights, this can involve
significant expenses.
[0003] LEDs have a number of additional advantages. However, as is
well known in the art,
LEDs require relatively close control of voltage and current and also heat
management. For
example, because current through the LED is dependent exponentially on
voltage, voltage should
be closely controlled. Also, the voltage supplied should be sufficient, at a
minimum, to cause
current to flow in the proper direction (i.e., from p-type to n-type
material). In addition, the
ambient temperature of the operating environment can significantly affect the
performance of
LEDs.
[0004] Although LEDs have certain advantages when compared to incandescent or
fluorescent bulbs (e.g., lower power consumption, and longer operating time)
LEDs also have
certain disadvantages, as noted above.
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SUMMARY OF THE INVENTION
[0006] For the foregoing reasons, there is a need for an improved light-
generating system, in
which one or more of the disadvantages of the prior art are addressed or
mitigated.
[0007] In its broad aspect, the invention provides a light-generating
system for consuming
input electrical power from a power source to generate light. The light-
generating system
includes a LED load array with a plurality of light-emitting diodes, the light-
emitting diodes
having an operating temperature when energized, and a heat sink on which the
LED load array is
mounted, the heat sink being adapted for absorbing and dissipating heat energy
generated by the
light-emitting diodes when energized. The heat sink includes a body portion to
which the light-
emitting diodes are attached, and a finned portion connected to the body
portion, for dissipation
of heat energy transferred thereto at least partially via conduction from the
light-emitting diodes,
to cool the light-emitting diodes. The system also includes a power control
unit electrically
connected to the power source and the LED load array, for converting the input
electrical power
to an output electrical power and controlling voltage and current of the
output electrical power
provided by the power control unit to the LED load array. In addition, the
system includes a
temperature detector subassembly operatively connected to the power control
unit, the
temperature detector subassembly being adapted for sensing a heat sink
temperature of the heat
sink at one or more predetermined locations thereon.
[0008] The temperature detector subassembly is adapted to compare the heat
sink temperature
to one or more preselected temperatures within a preselected temperature
range, and to transmit a
control signal to the power control unit upon determining that the heat sink
temperature differs
from said at least one preselected temperature by more than a preselected
minimum difference.
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[0009] Upon receipt of the control signal, the power control unit changes
the voltage of the
output electrical power, to modulate the performance of the light-emitting
diodes such that the
heat sink temperature is within the preselected temperature range.
[0010] In one of its aspects, the preselected temperature includes an upper
limit preselected
temperature, and the preselected minimum difference includes an upper limit
minimum
difference.
[0011] In another aspect, upon the temperature detector subassembly
determining that the
heat sink temperature is greater than the upper limit preselected temperature
by at least the upper
limit minimum difference, the temperature detector subassembly sends the
control signal to the
power control unit, for causing the power control unit to decrease the output
electrical power to
lower the heat sink temperature until the heat sink temperature is within the
preselected
temperature range.
[0012] In yet another aspect, the control signal causes the voltage of the
output electrical
power to decrease to an extent required by the control signal.
[0013] In yet another of its aspects, the power control unit of the
invention includes a
microprocessor and a current sensor, for determining current data associated
with the output
electrical power and communicating the current data to the microprocessor.
[0014] In another aspect, the invention additionally includes an ambient
light controller for
controlling the electrical power provided to the LED load array, in indirect
proportion to ambient
light intensity.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] The invention will be better understood with reference to the
attached drawings, in
which:
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[00161 FIG. 1A is an isometric view of an embodiment of a light-generating
system of the
invention;
[0017] FIG. 1B is a side view of the light-generating system of FIG. 1A;
[00181 FIG. 2 is an exploded view of the light-generating system of FIG.
1A;
100191 FIG. 3A is a plan view of a bottom plate subassembly of the light-
generating system
of FIG. 1A, drawn at a larger scale;
10020] FIG. 3B is a schematic illustration of the light-generating system
of FIG. 1A;
[0021] FIG. 4A is a schematic diagram illustrating the light-generating
system of FIGS. 1A-3;
[0022] FIG. 4B is a schematic diagram illustrating an alternative
embodiment of the light-
generating system of the invention;
[00231 FIG. 5 is a schematic illustration of another alternative embodiment
of the light-
generating system of the invention;
[00241 FIG. 6 is an isometric view of an alternative embodiment of the
light-generating
system of the invention, drawn at a smaller scale;
[00251 FIG. 7 is an end view of a base of the light-generating system of
FIG. 6, drawn at a
larger scale;
[0026] FIG. 8A is a side view of selected elements of the light-generating
system of FIG. 6,
drawn at a smaller scale; and
[0027] FIG. 8B is an end view of a cover of the light-generating system of
FIG. 6, drawn at a
larger scale.
DETAILED DESCRIPTION OF THE INVENTION
[00281 In this specification and in the claims that follow, "LED" means a
light-emitting diode.
In the attached drawings, like reference numerals designate corresponding
elements throughout.
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,
'
Reference is first made to FIGS. 1A-4A to describe an embodiment of a light-
generating system
of the invention indicated generally by the numeral 20. The light-generating
system 20 is for
consuming input electrical power from a power source (not shown) to generate
light. Preferably,
the light-generating system 20 includes a LED load array 22 with a number of
light-emitting
diodes 23, which have an operating temperature when energized. The system 20
also preferably
includes a heat sink 24 on which the LED load array 22 is mounted. The heat
sink 24 is adapted
for absorbing and dissipating heat energy generated by the light-emitting
diodes 23, when they
are energized. It is preferred that the heat sink 24 includes a body portion
25 to which the light-
emitting diodes 23 are attached, and a finned portion 26 connected to the body
portion 25, for
dissipation of heat energy transferred thereto at least partially via
conduction from the light-
emitting diodes 23, to cool the light-emitting diodes 23. In addition, the
system 20 preferably
includes a power control unit 28 electrically connected to the power source
and the LED load
array 22, for converting the input electrical power to an output electrical
power, and for
controlling voltage and current of the output electrical power provided by the
power control unit
28 to the LED load array 22. In one embodiment, the system 20 preferably also
includes a
temperature detector subassembly 30 operatively connected to the power control
unit 28. The
temperature detector subassembly 30 is adapted for sensing a heat sink
temperature of the heat
sink 24 at a predetermined location thereon. As will be described, the
temperature detector
subassembly 30 preferably is also adapted to compare the heat sink temperature
to one or more
preselected temperatures within a preselected temperature range, and to
transmit a control signal
to the power control unit 28 upon determining that the heat sink temperature
differs from the
preselected temperature by one or more preselected minimum differences. Upon
receipt of the
control signal, the power control unit 28 changes the voltage of the output
electrical power, to
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modulate the performance of the light-emitting diodes so that the heat sink
temperature is within
the preselected temperature range.
[0029] As can be seen in FIGS. 1A-3A, in one embodiment, the body portion
25 of the heat
sink 24 preferably includes first and second end plates 32, 34 to which the
finned portion 26 is
attachable (FIG. 2). Preferably, the end plates 32, 34 are substantially round
in plan view thereof,
with substantially the same diameter. As shown in FIG. 2, it is preferred that
the finned portion
26 includes first and second parts 36, 38 which, when attached to the end
plates 32, 34, define a
generally cylindrical shape overall. Each of the first and second parts 36, 38
includes an interior
surface 40, 42 (FIG. 2). It will be understood that, when the heat sink 24 is
assembled, the
interior surfaces 40, 42 and the end plates 32, 34 at least partially define a
cavity 44 in which
certain elements (e.g., the power control unit 28) are positionable. For
instance, as schematically
illustrated in FIG. 3B, the power control unit 28 preferably is mounted on one
or more of the
interior surfaces 40, 42.
[0030] The heat sink 24 preferably includes any suitable heat dissipation
means. For example,
depending on the application, one or more heat pipes may be suitable. However,
it is preferred
that the heat sink 24 includes fins 45 which extend outwardly from the finned
portion 26 for heat
exchange with the ambient atmosphere, to dissipate heat to the ambient
atmosphere. Preferably,
the fins 32 are formed for optimal heat transfer characteristics. It will be
appreciated by those
skilled in the art that the heat sink preferably is made of material with
relatively high thermal
conductivity. For example, the heat sink 24 preferably is made of extruded
aluminum.
[0031] It is preferred that the power control unit 28 includes a
microprocessor 46 and a
current sensor 48, for determining current data associated with the output
electrical power and
communicating the current data to the microprocessor 46 (FIG. 4A).
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[0032] The power control unit 28 preferably provides a current-regulated
and voltage-
regulated power supply to the LED load array 22. Preferably, the components of
the power
control unit 28 are included in a highly integrated single power/controller
board design (i.e., a
printed circuit board ("PCB")), which is a microprocessor-based control system
that fits within
the heat sink 24. In one embodiment, the power control unit 28 and other
elements of the light-
generating system 20 preferably are adapted for 50 W or 100 W rated output, as
selected by the
user. Preferably, the power control unit 28 is set for either 50 W or 100 W
when it is
manufactured. This arrangement reduces manufacturing costs. Other possible
power outputs will
occur to those skilled in the art.
[0033] It is also preferred that the system 20 includes a connector 50, for
electrically
connecting the LED load array 22 to the power control unit 28. The connector
50 preferably is
adapted for quick connection and disconnection, to permit relatively quick
replacement of a used
LED load array 22.
[0034] The light-generating system 20 preferably includes continuous
diagnostics for supply,
lamp load condition and system functionality. The power measurement and
control capability of
the power control unit 28 leads to a relatively longer operational life of the
LED load array 22.
[0035] Preferably, the microprocessor 46 is for monitoring and controlling
various aspects of
the performance of the power control unit 28 and/or the light-generating
system 20 overall. In
particular, the microprocessor 46 receives data about the current and voltage
provided to the
LED load array 22, compares such measured current and voltage to rated current
and voltage,
and initiates appropriate action if the measured current and voltage vary from
the rated values
therefor by more than predetermined differences respectively. Preferably, the
output electrical
power is controlled via pulse width modulation. It is preferred that voltage
is monitored within
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the microprocessor 46. Current preferably is sensed by the sensor 48, and data
in this regard is
provided to the microprocessor 46. The microprocessor 46 then directs the
pulse lengths
accordingly. The microprocessor 46 continuously processes such data at very
short time
intervals.
[0036] The LED driver 28 sets the voltage applied to the LED load array 22
in a variable
fashion, where the microprocessor 46 adjusts the voltage slightly up or down
within a given
range in order to sense the predetermined current flow. The current flow is
measured by a very
low resistance power resistor (usually 0.1 Ohms) sensing a very small voltage
drop across it (in
milli-volts). This measurement is then amplified and put on a feedback to the
microprocessor 46
so that it can adjust the potential of the pulses it feeds the output to
attempt to match the pre-
determined voltage drop across the current sensing resistor.
[0037] From the foregoing, it can be seen that the power control unit 28 is
used to control the
voltage applied to the LED load array 22. However, unlike traditional
supplies, an absolute
output voltage is not set, but instead the applied voltage is set relative to
the drop across a
current-sensing resistor, as described above.
[0038] In addition, the light-generating system 20 has an overall power
efficiency of at least
86 percent, a relatively high efficiency. (Prior art units typically average
from 70 percent to 75
percent power efficiency.) The light-generating system 20 preferably has the
full operational
input range of 85-480 VAC.
[0039] In one embodiment, the light-generating system 20 preferably is
adapted to
automatically shut itself down immediately upon sufficiently unusual
conditions being detected.
For example, as the system 20 includes elements thereof adapted for
measurement of current and
voltage, if the current or voltage supplied is not within predetermined
ranges, then the system 20
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shuts down upon detection of the unusual conditions. If the applied voltage
does not remain
within its regulation parameters, then the system is shut down. Similarly, if
the current supplied
by the pulsing is insufficient to power the load, then the system 20 shuts
itself down. Insufficient
current may indicate that the system has a short circuit condition.
[0040] In addition, the light-generating system 20 preferably includes an
automatic recovery
function, pursuant to which the system 20 reboots itself if necessary. For
instance, in the event of
a complete failure of the power supply to the light-generating system 20, the
system 20 reboots
itself once the power supply is restored.
[0041] In one embodiment, the light generating system 20 preferably
includes the temperature
detector subassembly 30 (FIG. 4A) operatively connected to the power control
unit 28 via a
thermal feedback network 52 (FIG. 4A). Those skilled in the art will be aware
that the
temperature detector subassembly may include various temperature-detecting
elements. It is
preferred that the temperature-detecting element in the temperature detector
subassembly 30 is a
thermistor. The temperature detector subassembly 30 is for sensing a
temperature of the heat sink
24. If the temperature differs from a preselected temperature by more than a
predetermined
extent, then the thermistor 30 provides an increasing signal to the power
control unit 28, for
increasing the electrical power supplied to the LED load array 22, or the
thermistor 30 provides a
decreasing signal to the power control unit 28, for decreasing the electrical
power supplied to the
LED load array 22, as the case may be. The thermistor 30 is adapted to take
the ambient
temperature into account. Because the thermistor 30 is included in the system
20, a somewhat
smaller heat sink 24 may be used than otherwise would be selected for the
light-generating
system.
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[0042] It will be understood that, in practice, the location on the heat
sink 24 at which the
temperature thereof is detected preferably should be relatively proximal to
the light-emitting
diodes 23. For instance, it is preferred that the thermistor 30 is connected
to the heat sink 24 for
detection of the temperature thereof at the end plate 32. Those skilled in the
art will appreciate
that, in determining the temperatures which trigger the generation of control
signals, the thermal
conductivity of the heat sink 24 and the distance of the location at which
temperature is detected
is from the light-emitting diodes is taken into account.
[0043] In general, the power control unit 28 is required to lower the
temperature of the heat
sink. In one embodiment, the preselected temperature is an upper limit
preselected temperature
and/or a lower limit preselected temperature. Also, it is preferred that the
preselected minimum
difference is, when compared to the upper limited preselected temperature, an
upper limit
minimum difference, and when the operating temperature is compared to the
lower limit
preselected temperature, a lower limit minimum difference.
[0044] Preferably, upon the temperature detector subassembly 30 determining
that the heat
sink temperature is greater than the upper limit preselected temperature by at
least the upper limit
minimum difference, the temperature detector subassembly 30 sends the control
signal to the
power control unit 28, to cause the power control unit 28 to decrease the
output electrical power
to lower the heat sink temperature until the heat sink temperature is within
the preselected
temperature range. The control signal preferably causes the voltage of the
output electrical power
to be decreased to an extent required by the control signal.
[0045] Preferably, upon the temperature detector subassembly 30 determining
that the heat
sink temperature is less than the lower limit preselected temperature by at
least the lower limit
minimum difference, the temperature detector subassembly sends the control
signal to the power
CA 02792187 2012-10-12
control unit 28, to cause the power control unit 28 to increase the output
electrical power to raise
the heat sink temperature until the heat sink temperature is within the
preselected temperature
range. The control signal preferably causes the voltage of the output
electrical power to be
increased to an extent required by the control signal.
[0046] It will be appreciated by those skilled in the art that the light-
generating system 20
may be mounted in any suitable manner. Although many alternative arrangements
are possible,
in one embodiment, the system 20 preferably includes a hook element 54, to
enable the system
20 to be suspended by the hook element 54 attached to a suitable part of a
building or other
structure (not shown). Input electrical power preferably is provided via any
suitable means, e.g.,
a suitable insulated power cord (not shown). As can be seen in FIGS. 1A-2, the
system 20
preferably includes a connection box 56 secured to the heat sink 24 in which
the wiring (not
shown) for connection with outside feed is located. In one embodiment, the
hook element 54 is
attached to the connection box 56. It is preferred that the system not be
mounted directly into a
standard socket (e.g., a socket for accepting an E39 base) due to a
requirement for a standards
body's approval of both the socket and the light-generating system mounted in
such socket.
[0047] In use, the system 20 is positioned as required, e.g., suspended by
the hook element
54, and the input electrical power is provided to the system 20 via any
suitable means therefore.
The light-emitting diodes preferably are fitted with one or more suitable
lenses (not shown) for
any particular application. For example, in view of the distance above a floor
at which the light-
emitting diodes are positioned, and the area to be illuminated, lenses with
certain characteristics
would be preferred. Once connected, the input electrical power is provided to
the power control
unit 28. The power control unit 28 controls the voltage and current of the
electrical power which
is provided to the LED load array, so that it is within the appropriate
parameters for safe
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operation of the LED load array. Among other things, if the input electrical
power is AC, then
AC current is rectified (to DC current) by the power control unit. Once the
LED load array is
operating, the heat sink dissipates heat, to provide a temperature within a
pre-determined
operating range of the LED load array.
[0048] As described above, the thermistor preferably provides signals to
the power control
unit 28 to control the voltage of the output electrical power provided to LED
load array 22, in
order to maintain the heat sink temperature within a predetermined range, in
real time.
[0049] The light-generating system 20 is relatively robust, as all wiring
and connectors are
generally located inside the heat sink 24, except for the power cord or other
wiring for
connection to an external power source. The heat sink 24 preferably also acts
as a heat sink for
the power control unit 28. Preferably, the power control unit 28 is attached
directly to an interior
surface of the heat sink 24, and positioned in the cavity 44 inside the heat
sink 24.
[0050] For reliability, it is preferred that the light-omitting diodes 23
are divided into a
number of pairs of individual light-emitting diodes connected in series, and
the pairs are
connected in parallel. For example, in one embodiment, the LED load array 22
preferably
includes 54 light-emitting diodes 23 divided into 27 pairs, and the 27 pairs
are connected in
parallel. This arrangement is intended to result in greater reliability. If
one light-emitting diode
fails, then only the other light-emitting diode in that pair ceases to
function as a result, because
only such other light-emitting diode in that pair is connected in series to
the failed light-emitting
diode.
[0051] In one embodiment, the light-generating system 120 preferably
additionally includes
an ambient light controller 160 for controlling the electrical power supplied
to the LED load
array 122, in indirect proportion to ambient light (FIG. 4B). The ambient
light controller 160
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preferably includes an ambient light sensor 162 and a photo feedback network
164. The sensor
162 notifies the feedback network 164 of changes in ambient light, and this
data is provided to
the microprocessor 146. The microprocessor 146 is adapted to compare ambient
light levels to
predetermined light levels and to determine whether additional electrical
power is required to be
provided to the LED load array 122 (i.e., if ambient light is below a
predetermined lower level)
or, alternatively, whether the electrical power supplied to the LED load array
122 should be
decreased (i.e., if ambient light is greater than a predetermined upper
level). (It will be
understood that "ambient light" to which a particular light-generating system
120 is exposed
would also include, for instance, light produced by the LEDs in other light-
generating systems
positioned nearby.) Preferably, the power control unit 128 (FIG. 2B) includes
the pulse width
modulator in the microprocessor 146 for "slowing down" (or, if necessary,
"speeding up") the
current provided to the LED load array 122, thereby causing the LED load array
122 to provide
less or more light, i.e., as required in indirect proportion to the ambient
light.
100521 In short, where the system of the invention includes an ambient
light controller, the
electrical power provided to the LED load array via the power control unit is
controlled, in
indirect proportion to ambient light. Accordingly, the light-generating system
122 has complex
dimming and startup functionality, thereby providing improved efficiency in
mornings, evenings,
and at other times when the ambient light is changing.
[0053] An alternative embodiment of the light-generating system 220 of the
invention is
shown in FIG. 5. As can be seen in FIG. 5, in the light-generating system 220,
a LED load array
222 is mounted on a side 268 of the heat sink 224. The light-generating system
220 is intended
for use where the light fixture (not shown) in which the light-generating
system is to be used
positions the light-generating system so that light is directed from the light-
generating system in
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a direction which is substantially transverse to the axis (identified as "X"
in FIG. 5) defined by
the heat sink 224, e.g., for "cobra" style streetlights or parking lot lights.
[0054] An alternative embodiment of a light-generating system 320 of the
invention is
illustrated in FIGS. 6-8B. As can be seen in FIG. 6, the light-generating
system 320 includes a
base 369 with a heat sink 324 on which a power control unit 328 (including a
printed circuit
board 370) is positioned. Preferably, the light-emitting diodes 323 in a LED
load array 322 are
positioned on the printed circuit board 370, at suitable intervals along the
length of the base 369.
The light-generating system 320 also includes end caps 372 positioned at each
end of the base
369.
[0055] Each end cap 372 preferably includes a body portion 373 positioned
to assist in
holding a cover 374 in position. Preferably, each end cap 372 includes two
prongs 378, 380
extending from the body portion 373. The prongs 378, 380 are formed to be
receivable in the
holes in a typical light fixture for a fluorescent light tube (not shown). It
will be understood that
the prongs 378, 380 are made of an electrical insulator (e.g., a suitable
plastic, such as
polyethylene), and so the prongs 378, 380 do not conduct electricity. The
connection of the
system 320 to a power source (not shown) preferably is via wires 382.
[0056] Preferably, the light-generating system 320 is formed to fit into a
conventional
fluorescent tube light fixture. Accordingly, the heat sink 324 is elongate,
and the LED load array
322 is positioned on the PCB 370 which preferably is secured directly to the
heat sink 324 so that
the LED load array 322 will direct light downwardly from the conventional
light fixture, when
the system 320 is positioned in the conventional fixture (not shown) and
energized. As can be
seen in FIG. 7, the base 369 preferably includes a finned portion 326, with
fins 345 extending
outwardly, for heat dissipation. The heat sink preferably includes
substantially flat regions 384A,
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384B on which the PCB 370 is attachable. It is preferred that the base 369
also includes a
channel 385 positioned centrally along the length of the base 369, between the
flat regions 384A,
384B. The channel 385 is at least partially defined by walls 393, 394, 395
(FIG. 7). Certain
elements of the power control unit 328 (e.g., the microprocessor) preferably
are positioned in the
channel 385, to protect such elements, and also for dissipation of heat
therefrom. The light-
emitting diodes 323 preferably are mounted on a strip (not shown) which
preferably is also at
least partially positioned in the channel 385, for dissipation of heat
therefrom.
[00571 Preferably, the base 369 also includes side portions 386 with
transverse parts 388 at
ends 390 of the side portions 386. As can be seen in FIG. 6, the light-
generating system 320
includes the substantially transparent cover 374 which is held in position on
the heat sink 324
between the side portions 386. The cover 374 preferably is made of any
suitable flexible
transparent or translucent material such as those skilled in the art would be
aware of. Preferably,
the cover 374 is made of a suitable acrylic. However, if the system is to be
used in a harsh
environment, the cover 374 preferably is made of polycarbonate, which would
withstand shocks
better than acrylic.
[0058] It is also preferred that the cover 374 (also shown in FIGS. 8A and
8B) is formed so
that it is subjected to tension when folded (as shown in FIG. 8B) and held
between the side
portions 386. Because the cover 374 is subjected to tension when it is held in
this way between
the side portions 386, the cover 374 is held in position when the light-
generating system 320 is in
position in the conventional fluorescent light tube fixture. The cover 374 is
also partially held in
place on the base 369 by the transverse parts 388, which engage the cover 374.
(It will be
understood that the end caps 372 are intentionally omitted from FIG. 8A for
clarity of
illustration.)
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[0059] In operation, the light-generating system 320 functions generally
the same as the
system 20, described above. Input electrical power, if AC, is rectified by the
power control unit
328, and the output electrical power is changed or modified by the power
control unit 328 in
response to information provided by a thermistor (not shown), which monitors
temperature of the
heat sink 324 at a predetermined location. Optionally, the light-generating
system 320 may
additionally include an ambient light controller (not shown), functioning as
in the system 120,
described above.
[0060] As noted above, the light-generating system 320 preferably is
configured to fit into a
conventional fluorescent light tube fixture, although the power supply is not
provided via such
fixture. It will be appreciated by those skilled in the art that the system
320 may be conveniently
used to retrofit with LEDs, with minimal rewiring required.
[0061] It will be appreciated by those skilled in the art that the
invention can take many
forms, and that such forms are within the scope of the invention as described
above. The
foregoing descriptions are exemplary, and their scope should not be limited to
the preferred
versions provided therein.
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