Note: Descriptions are shown in the official language in which they were submitted.
1;~64351
FIELD OF T~E INVENT~ON
The invention relates generally to lighting control, and more
particularly, to the automatic actuation of incandescent and fluorescent lighting
elements in response to ambient light intensity.
S BACKGROUND OF THE TNVENTION
Increasing energy costs have created a demand for devices which
automatically turn lighting off during the day when natural light is avai1able and turn
lighting on at night. For example, it is now common to actuate lights external to a
building with circuitry employing a photodetecting element responsive to ambientlight. The photodetecting device is normally mounted behind the associated lighting
element where light from the lighting element will not affect detection. Basically,
on-off oscillation is avoided by shielding the photodetective element from the lighting
element which it controls.
There is also a need for automatic lighting control indoors. Such
lighting control would not only permit energy conservation, but also theft prevention,
being used to create the impression of occupancy. At present, automatic timers are the
principal mechanism for regulating lighting in the interior of a house or building.
Photodetecting devices would provide an alternative, and in many instances much less
expensive, means of automatically controlling indoor lighting. However, conventional
photodetecting devices used in outdoor lighting control are more difficult to shield in
indoor applications, and are too readily subject to on-off oscillation.
It is accordingly one object of the invention to provide a device which
regulates the operation of a lighting element in response to ambient light intensity and
which can be operated in the presence of light generated by the lighting element itself.
It is a further object of the invention in various embodiments to provide
devices of the above nature which can automatically control either incandescent or
fluorescent lighting elements, and which can be manufactured essentially as
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two-terminal devices that may be conveniently series connected with the controlled
lighting element.
BRTEF SUMMA~Y OF THE I VENTI~N
In one aspect, the invention provides a device for controlling operation
5 of electrically powered lighting element in response to ambient light intensity, which
includes switching means adapted to conduct light through the lighting element and
requiring periodic triggering to remain in a conductive state. Light sensing means are
provided to sense and indicate ambient light intensity, and also triggering means for
periodically triggering the switching means whenever the indicated ambient light
10 intensity drops below a threshold level. Light generating means (not intended for
general illurnination of the environment) are positioned proximate to the light sensing
means, and generate light of a predetermined intensity thereby augmenting the
indicated ambient light intensity. The light generating means are actuated in response
to the conduction state of the switching means, the light generating means generating
15 light whenever the switching means are in a non-conductive state (the controlled
lighting element being off), and are otherwise inoperative (the controlled lighting
element being on).
Accordingly, the device is capable of automatically regulating operation
of an electrically powered lighting element even in the presence of the light generated
20 by the lighting element. The light generating means effectively shift the light intensity
threshold level required to trigger conduction through the switching means whenever
the lighting element is powered. Alternatively, the light generating means may be
viewed as augmenting indicated ambient light intensity, whenever the lighting element
is inoperative, to make the device effectively responsive only to components of
25 ambient light intensity other than those contributed by the lighting element.
DESCRIE~ON OF THE DRAWIN~;S
The invention will be better understood with reference to drawings
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illustrating preferred embodiments in which:
fig. 1 is a basic two-terrninal device for controlling electrically powered
lighting elements in response to ambient light intensity;
fig. 2 is a perspective view of a second device specifically adapted for
5 control of incandescent lighting; and,
fig. 3 is a schematic representation of electronic circuitry associated
with the device of fig. 2.
pESCRlPT~ON OF PREFERRED EMBODIMENTS
Reference is made to fig. 1 which illustrates a two-terminal device 20
10 series connected to a lighting element 22 that is powered by a 120 volt AC line source
at a pair of line terrninals 24. The lighting element 22 may be of either the
incandescent or fluorescent variety. The general function of the device 20 is to activate
the lighting element 22 when, for exarnple, a room in which the lighting element 22 is
located becomes dark, and to shut off the lighting element 22 when light in the room
15 from outdoors is otherwise adequate for the intended use of the room. This function is
performed while a light sensor associated with the device 20 is fully exposed to the
light generated by the lighting element 22.
The device 20 includes a bidirectional switching element, a conventional
triac 26. Conduction in the triac 26 is initiated by the voltage difference between the
20 device terminals 28, 30 and receipt of a trigger signal at its tngger terminal 32. When
triggered for conduction, the triac 26 couples the device terminals 28,30 thereby
permitting conduction of current through the lighting element 22. Triac conduction is
self-extinguishing (the triac 26 assuming a non-conductive state whenever current
through the triac 26 drops to 0 and the voltage across the triac drops to 0), and
25 accordingly the triac 26 requires triggering in each half-cycle of the AC line voltage to
remain in a substantially continuous conductive state.
The triac triggering signal is generated from the voltage difference
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between the device terminals 28,30 (or alternatively viewed, from the voltage across
the triac 26) by a capacitive voltage divider 34. The divider 34 includes a capacitor 36
series connected to a capacitor 38 at a divider node 40. The divider node 40 is coupled
to the triac trigger terminal 32 by a bidirectional serniconductor device, a diac 42,
which has a turn-on voltage of about 8 volts. Accordingly, the voltage divider 34
tends to trigger the triac 26 in each half-cycle of the AC line voltage when the voltage
difference between the device terminals 28, 30 rises to about 18 volts. A resistor 44 in
series with the capacitor 36 serves to lirnit surge currents through the capacitive Yoltage
divider 34 which are apt to occur with each reversal of the polarity of the AC line
voltage, and does not substantially affect the preselected divider ratio.
Ambient light is sensed by a photoresistor 46. The resistance of the
photoresistor 46 decreases with increasing intensity of light incident upon the
photoresistor 46, and consequently indicates ambient light intensity. The photoresistor
46 couples the divider node 40 to the device terminal 30, shunting the divider capacitor
38. When ambient lighting intensity is sufficiently great, the photoresistor 46 has a
small impedence, and effectively shorts the capacitor 38. The voltage differencebetween the divider node 40 and the device terminal 30 is consequently reduced
throughout each half-cycle of the AC line voltage to less than 8 volts, preventing
triggering of the triac 26 and illumination of the lighting element 22. However, when
ambient light intensity drops below a certain level, the resistance of the photoresistor
46 increases and the photoresistor 46 no longer significantly affects the operation of
the voltage divider 34. The triac 26 is then periodically triggered for conduction, and
the lighting element 22 illuminated.
A neon light 48 with a 68 volt turn-on threshold is positioned physically
~i 25 proximate to the photoresistor 46, and is actuated in a manner that prevents on-off
oscillation of the lighting element 22. The neon light 48 is connected in parallel with
~' the triac 26, and accordingly, is powered by the voltage difference across the triac 26
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(alternatively viewed as the voltage difference between the device terminals 28,30)
and actuated in response to the conduction state of the triac 26. When the triac 26 is in
a non-conductive state (the lighting element 22 being off) substantially all the AC line
voltage appears across the device terminals 28,30, and accordingly in each half-cycle
S of the AC line voltage the neon light 48 is actuated to generate light. When the triac 26
is in a conductive state, however, the voltage difference between the device terminals
28,30 does not exceed 2 volts, and accordingly the neon light 48 is inoperative. A
resistor 50 ensures that excessive current flow through the neon light 48 does not
occur.
The neon light 48 when actuated effectively augments the ambient light
intensity indicated by the photoresistor 46. The indicated ambient light intensity is
increased a predetermined amount, dependant principally on the relative spacing of the
photoresistor 46 and neon light 48 and on the power rating of the neon light 48. In
any given application the amount by which the indicated ambient light intensity is
15 augmented should correspond to and exceed the expected component of ambient light
intensity, at the photoresistor 46, attributable to the lighting element 22. The neon
light 48 can alternatively be viewed as effectively creating a hysteresis in the turn-off
ambient light threshold level. That threshold level is automatically increased whenever
the triac 26 is in a conductive state (the lighting element 22 being illuminated) thereby
20 making the device 20 non-responsive to the operating state of the lighting element 22.
A significant advantage of this type of operation is that both
incandescent and fluorescent lighting can be accommodated. With fluorescent lighting
the inductive load presented by associated ballasts tends to phase shift voltage and
current between the device terrninals 28,30, an the current conducted through the
25 device 20 can significantly lag the voltage appearing between the device terminals 28,
30. Thus, when an inductive load such as a fluorescent luminaire is turned on, the
device will tend to remain on even though the light contribution of the luminaire will
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decrease the resistance of the photosensor 46. The provision of the light 48 operating
as described overcomes this problem, ensuring turn off. A small inductor 52 is series
connected with the triac 26 between the device terminals 28, 30 to prevent sudden
current changes in the case of resistive loading. The inductor 52 may be eliminated
S from a device which is intended solely for use with inductive lighting elements. The
capacitor 36 and resistor 44 act as a snubber limiting rapid voltage changes in the case
of inductive loads.
Figs. 2 and 3 illustrate an alternative a device 60 adapted specifically for
control of incandescent lighting elements in response to ambient light, but providing a
number of additional control functions. The device 60 is effectively a modification of
the device 20 to permit those additional functions which include dimming, variation of
the threshold ambient light intensity for turn-on, by-passing of control in response to
ambient light intensity, and total switching off of control circuitry and the associated
lighting element. Since the device 60 is in effect an embellishment of the device 20,
1~ incorporating all components to be found in the device 20, like components have been
labelled with like reference numerals, and general operation will not be described in
detail.
A general external view of the device 60 is provided in fig. 2. The
device includes a conventional metal housing 62 which can be mounted in a wall in a
manner conventional to most light switches. Two leads 64, 65 extend from the
housing 62 to permit series connection of the device 60 with a lighting element to be
controlled. The device 60 has a plastic decorative panel 64 which during installation of
the device is mounted flush against a wall (once again in a conventional manner). On
the surface of the panel 64 are located a number of circuit components of the device
60, including a rotary switch 66 with five settings or positions, the photoresistor 46
described above, and close thereto the neon light 48. Operation of the device 60 will
be described with reference to the schematic diagram of fig. 2 representing various
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circuit components to be found within the housing 62.
The rotary switch 66 has ten poles indicated by the reference numerals
1-10 inclusive which are equally spaced-apart circumferentially in a circular
arrangement. A wiper 68 is rotatably mounted within the switch 66, and has a pair of
5 diametrically opposing, electrically insulated wiper end portions 70, 72. One wiper
end portion electrically connects one adjacent pair of poles, whenever the other wiper
end portion electrically connects another adjacent pair of poles, positioned
diametrically opposite the first pair. For example, as illustrated, the wiper end portion
70 electrically connects the poles 1, 2 while the wiper 72 electrically connects10 diametrically opposite poles 6, 7. The construction of the rotary switch 66 is
conventional.
The electrical coupling of the various poles of the rotary switch 66 is
significant, and provides a very inexpensive means for conveniently implementing the
various functions intended of the device 60. In describing the electrical connection
15 existing between the various switch poles, both in this disclosure and the appended
claims, one pole (namely pole 1) is arbitrarily designated a circumferentially first pole,
and the positions of the other poles are specified according to circumferential position
relative to the first pole . Clockwise or counterclockwise orientation of the poles
relative to the arbitrary first pole is inconsequential to proper electrical connection of
20 the rotary switch 66, so long as the pole positions are consistently designated in either
a clockwise or counterclockwise direction.
Circumferentially first and fifth switch poles 1, 5 are connected by a
diode 74. The fifth pole 5 is also electrically coupled (through the inductor 52) to the
device terrninal 28. These connections are in furtherance of an arrangement which
25 perrnits dimrning or effective by-passing of the device 60 for regular lighting control.
Circumferentially second and third poles 2, 3 are coupled by a resistor 76, which is
also series connected with the photoresistor 46 and couples the photoresistor 46 to the
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device terminal 30. pole 3 is connected to the device terminal 30, and pole 2 isconnected to the circumferentially seventh pole 6. Circumferentially fouIth, eighth,
ninth and tenth poles 4,8, 9, 10 are electrically connected together and to an output
terminal 78 (which in tum is connected to one of the leads 64, 65).
S The wiper 68, as illustrated, couples poles 1 and 2, and diametrically
opposing poles 6 and 6. Accordingly, output terminal 78 is isolated from device
terminal 28, and the lighting system including the lighting element 22 is in an off state.
The wiper 68 can be rotated clockwise to a next position in which poles
2 and 3 are electrically connected and also the diametrically opposing poles 7 and 8. In
this switch state, the resistor 76 is effectively short-circuited, the terminals 28,78
electrically coupled through the triac 26, and actuation of the lighting element 22 is
then responsive to ambient light intensity, exactly as descAbed with reference to the
device 20. Movement of the wiper 68 clockwise to a next position in which poles 3
and 4 are connected, and diametrically opposing poles 8 and 9, connected, effectively
results in a shifting of the ambient light turn-on threshold. The resistor 76 is now
series connected to the photoresistor 46, and accordingly, the triac 26 will be triggered
for conduction only in response to relatively higher ambient light intensity.
Accordingly, the sensitivity of the photodetection can be selectively increased or
decreased.
Movement of the wiper 68 clockwise to the next position, electrically
couples poles 4 and 5 and diametrically opposing poles 9 and 10, causes a by-passing
of the triac 26 and associated photodetection and triggering circuitry. In this wiper
orientation, the lighting element 22 is simply turned on, and operation is not
responsive to ambient light levels.
Rotation of the wiper 68 clockwise to the next position coupling poles 1
anfl 10 and diametrically opposing poles 5 and 6. This switch state also results in
bypassing of the triac 26 and associated photodetection and trigger circuitry, but also
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engages operation of the diode 74. In this wiper position, current through the lighting
element 22 is conducted through the diode 74 which accordingly reduces power
consumption in half, and the light element 22 is accordingly dimmed. It will be
appreciated that any two-terminal diode-type device can be substituted for the diode
5 74, and the only requirement is that the device have low power consumption andselectively pass current in response to voltages across the device.
The device 60 will accordingly be seen to provide a myriad of functions
beyond those of the device 20 without complex circuitry and costly components. In
particular, the light 22 can be switched off, turned on, dimmed, and made responsive
10 to ambient light intensity at two different threshold levels.
It will be appreciated that particular embodiments of the invention have
been described, and that modi~lcations may be made therein without departing from the
spirit of the invention or the scope of the appended claims.
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