U.S. patent number 3,739,226 [Application Number 05/178,636] was granted by the patent office on 1973-06-12 for emergency light unit for mounting to an electrical wall outlet.
This patent grant is currently assigned to SAID Christensen, by said Seiter. Invention is credited to Calvin J. Christensen, William A. Seiter.
United States Patent |
3,739,226 |
Seiter , et al. |
June 12, 1973 |
EMERGENCY LIGHT UNIT FOR MOUNTING TO AN ELECTRICAL WALL OUTLET
Abstract
This invention relates to an emergency light unit of a size for
plugging into a standard electrical wall outlet. The unit is
self-contained and includes means for energizing the light when the
main electrical power fails and the ambient light in the area in
which it is mounted is below a prescribed level. The light is
powered during emergency conditions from rechargeable batteries
which are continuously and automatically charged when the main
power is operational. All of the components of the unit, including
the batteries, are mounted in a casing of unitary construction at
the front of which are exposed light bulbs for supplying the
emergency light, the light-sensitive surface of a photocell for
sensing the ambient light level in the area, and an electrical
utility outlet. Means accessible from the front of the unit are
also provided for testing its operability. The unit is plugged into
a standard electrical wall outlet with the cover plate removed and
is secured in the same manner as a conventional cover plate.
Inventors: |
Seiter; William A. (Fenton,
MO), Christensen; Calvin J. (Fenton, MO) |
Assignee: |
SAID Christensen, by said
Seiter (N/A)
|
Family
ID: |
22653305 |
Appl.
No.: |
05/178,636 |
Filed: |
September 8, 1971 |
Current U.S.
Class: |
315/86; 174/53;
174/56; 307/66; 315/88; 315/135; 315/156; 340/663; 362/20; 320/128;
174/66 |
Current CPC
Class: |
F21V
23/0442 (20130101); F21S 9/022 (20130101) |
Current International
Class: |
F21S
9/00 (20060101); F21S 9/02 (20060101); H05b
037/04 () |
Field of
Search: |
;315/86,87,149-159
;320/9,10 ;340/333 ;307/66 ;240/2S,2SP,10.6,1.6CH,37.1
;174/53,54,55,56 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Kominski; John
Claims
What is claimed is:
1. A combination emergency light unit and wall plate for mounting
to a standard electrical wall outlet of a building, the outlet
having a plurality of electrical receptacles and being supplied
with main power from the building, the unit comprising a casing
covering the areas between the electrical receptacles and the
surrounding wall so as to provide an attractive finishing plate for
the outlet, a lamp means for supplying the emergency light, means
for mechanically mounting the lamp means so that its light emanates
from the front of the casing, electrical circuit means housed
within the casing, plug terminals electrically and mechanically
connected to the electrical circuit means and extending rearwardly
of the casing, the plug terminals being adapted to plug into one of
the electrical receptacles to supply main power to the unit, said
casing having an opening in front of at least one of the other
receptacles for accessibility for other use, emergency power supply
means mounted in the casing, means associated with the electrical
circuit means for sensing a power failure in the main power supply
of the building, means for supplying electrical power from the
emergency power supply means to the lamp means when a main power
failure is sensed, thereby energizing the lamp means, whereby the
emergency light unit plugs into an electrical receptacle of a
standard electrical wall outlet for ease in assembly, provides a
cover plate for the outlet, and provides accessibility to another
receptacle of the outlet for use as desired.
2. The emergency light unit of claim 1 including photosensitive
means for detecting the ambient light level in the immediate area
outside the unit, and means associated with the electrical circuit
means and responsive to the photosensitive means for supplying
power from the emergency power supply means to the lamp means only
when the light in the room is below a prescribed level.
3. The emergency light unit of claim 2 wherein the emergency power
supply means includes rechargeable batteries, and including means
associated with the electrical circuit means for charging the
batteries whenever the main power is on.
4. The emergency light unit of claim 1 wherein the casing defines
cavities around the opening, and wherein the emergency power supply
means includes rechargeable batteries mounted in said cavities.
5. The emergency light unit of claim 4 wherein the cavities for the
batteries are located at the sides and end of the casing around the
opening.
6. The emergency light unit of claim 1 including switch means
mounted in the wall of the casing and actuatable from outside the
unit, and means associated with the electrical circuit means and
responsive to actuation of the switch means for testing the
operability of the unit.
7. The emergency light unit of claim 6 wherein the actuation of the
switch means simulates a power failure, thereby causing the lamps
to light if the unit is operational.
8. The emergency light unit of claim 6 wherein the switch means is
actuated by axial movement of a spring bias rod, the rod being
reciprocally mounted in a wall of the casing with one end exposed
at the outer surface of the unit and the other end contacting the
switch means for actuation thereof as the rod is moved
rearwardly.
9. The emergency light unit of claim 1 wherein the unit casing is
approximately 41/2 inches long, 3 inches wide, and 1 inch deep.
10. The emergency light unit of claim 1 wherein except when the
lamp means is energized, the maximum current drain on the emergency
power supply means in only approximately 1 milliamp.
11. The emergency light unit of claim 3 wherein when the main power
is on, all but approximately 1 milliamp of charging current
produced from the main power supply is delivered to charge the
emergency power supply batteries, the circuit means offering a
relatively high impedance path for the charging current except
through the emergency power supply batteries.
12. The emergency light unit of claim 11 wherein the main power is
approximately 110 volts, AC, 60 Hertz, and including means for
converting the main power to rectified power of a maximum current
capacity of approximately 60 milliamps, whereby approximately 59
milliamps are delivered to charge the batteries, and only
approximately 1 milliamp is lost in operating the remainder of the
electrical circuit means.
Description
BACKGROUND OF THE INVENTION
Various types of emergency light devices have been developed for
supplying light to an area, such as the room of a building, when
the building's main power fails. Such devices may also include
means for energizing the light only when the light in the room is
below a prescribed level, and for automatically recharging
emergency power batteries when the main power is on. Examples of
these are found in U.S. Pat. Nos. 3,159,755; 3,294,977; and
3,486,068. Such devices, however, are relatively large, requiring
sophisticated installation for mounting in the wall or ceiling of a
room, and even where mounted externally on the wall or ceiling,
requiring special wiring. Hence, the prior art devices are not
readily adaptable for installation in buildings initially
unequipped for their use.
It is therefore desirable to provide an automatic device for
supplying emergency light to the room in which it is installed
during a main power failure, and which is relatively low in cost,
attractive, and easy to install even in buildings initially
unequipped for its use. This invention is such a device.
SUMMARY OF THE INVENTION
The emergency light unit of this invention is a completely
self-contained unit which is made to mount to a standard electrical
wall outlet. The front of the unit is a combination face plate and
casing for holding a lamp which provides the emergency light, the
light-sensitive end of a photocell for sensing the ambient light
level in the room, and a test switch actuating rod used for testing
the operability of the unit. An opening in the unit provides access
to one of the outlet receptacles for conventional use. The
dimensions of the unit are approximately those of a standard wall
switch or wall receptacle cover plate although thicker to house
emergency power batteries and other electrical and mechanical
components of the unit.
For electrical connection and mounting to an electrical wall outlet
only the wall face plate need be removed and the unit substituted
therefor. Hence, even in buildings not designed for emergency light
units, the unit of this invention can be easily installed, and
without complete loss of the outlet.
Electrical circuit means are contained in the casing for
automatically sensing a main power failure and the ambient light in
the room, and for energizing the emergency light when the main
power fails and the ambient light is below a prescribed level.
Means are also provided for testing the unit's operability, and,
except during periods of power failure, automatically recharging
its emergency power batteries from the main electrical power. The
unit includes novel structural and circuit design features which
provide exceptional long, trouble free, reliable operation.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a front elevational view at approximately full scale of
the emergency light unit of this invention;
FIG. 2 is a view in section taken along the line 2--2 of FIG. 1
including the major internal components of the unit;
FIG. 3 is a view in section taken along the line 3--3 of FIG. 1
including the major internal components of the unit;
FIG. 4 is a view in section taken along the line 4--4 of FIG. 1
including the major internal components of the unit;
FIG. 5 is a rear elevational view of the unit with part of the back
cover plate broken away;
FIG. 6 is a view in section taken along the line 6--6 of FIG. 1
including the major internal components of the unit.
FIG. 7 is a rear elevational view of the unit casing with the back
cover plate and components removed.
FIG. 8 is a front elevational view of the circuit board used in the
unit of this invention; and
FIG. 9 is a schematic drawing of the circuit of this invention.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
There is shown in the drawing the emergency light unit 20 of this
invention plugged into a standard electrical wall outlet 21 having
an upper receptacle 22 and a lower receptacle 23. The outlet 21 is
mounted in a standard electrical wall box 25 by means of mounting
screws 26 and 27. The electrical box 25 in turn is shown mounted in
a wall 28, which could be a wall in any room in which the unit 20
is to be mounted. The electrical outlet 21 and box 25 are of types
commonly known in the art for providing an electrical wall
terminal, and are of sizes very nearly to that shown in the
drawings (approximately 4 1/2 inches long, 3 inches wide, and 1
inch deep). In fact, with the exception of FIG. 9 each of the
figures is drawn to approximately full scale to better illustrate
the actual sizes of the components involved. It is one of the
primary novel features of this invention that the emergency light
unit 20 is of a size small enough to be directly connected to a
standard electrical wall outlet in place of the face plate, greatly
facilitating installation of the unit.
A suitable power cable 30 including a ground lead 31 and conductors
32 and 33 extends through an appropriate electrical cable connector
35 mounted in an aperture in the box 25 with the electrical leads
31, 32, and 33 connected to terminals 40, 41, and 42, respectively,
of the outlet 21 by means of terminal screws 43. The power
transmitted through the cable 30 is 110 volt AC, 60 cycle, with a
safety ground connection.
The emergency light unit 20 of this invention generally includes a
unitary casing 45 having a front wall 47, a top wall 48, a bottom
wall 49, and side walls 50 and 51. The casing 45 can be thought of
as having an upper portion 55 in which light bulbs and certain
other electrical components are mounted as will be described, and a
lower portion 57 having inner walls 58, 59, 60, and 61 defining an
opening 63 for access to the lower receptacle 23. The inner wall
59, front wall 47, and bottom outer wall 49 further define a cavity
portion 65 for housing a battery 66; the inside wall 60, front wall
47, and outer side wall 50 define a cavity portion 68 for housing a
battery 69; and the inner wall 61, front wall 47, and outer side
wall 51 define a cavity portion 71 for housing a battery 72.
The front wall 47 of the casing 45 is substantially thicker in the
center as at 75 just above the opening 63. Directly in the center
of the casing and through the thickened portion 75 is a bore 77 for
receiving a screw 78 for mounting the unit 20 to the electrical
outlet 21. The thickened portion 75 is formed in a ledge 80 just
above the bore 77 on which is mounted one end 82 of a circuit board
84 by means of a mounting screw 86 extending through an aperture 87
in the board 84 and into the thickened portion 75. The circuit
board 84, as shown in FIG. 8, has mounted thereon the electrical
circuit components of this invention.
The other end 88 of the circuit board 84 is mounted to another
thick front wall portion 90 centrally located near the top of the
unit 20 by means of a mounting screw 92 extending through an
aperture 93 in the board 84 and into the thickened portion 90. The
upper thickened portion 90 has two relatively large apertures 94
and 95 into which the ends of a pair of bulb sockets 96 and 97,
respectively, extend, the other ends of the bulbs sockets 96 and 97
being mounted both physically and electrically to the circuit board
84 in accordance with the electrical circuit to be described. Light
bulbs 98 and 99 of the appropriate sizes shown in FIG. 3 and having
voltage ratings of approximately 3.6 volts, are mounted in the
sockets 96 and 97, respectively.
As best shown in FIG. 2 the casing directly above the apertures 94
and 95 is formed to define a cylindrical housing 101 extending
parallel to the apertures 94 and 95 toward the circuit board 84 and
in which a rod 102 is mounted, the rod having a head portion 103
which acts to limit the forward movement of the rod. A test switch
105, for testing the operability of the emergency unit, is mounted
at the top of the circuit board 84 as best shown in FIG. 2, with
its spring biased push-type actuating arm 106 extending forward of
the circuit board 84 and into contact with the head portion 103 of
the rod 102. The switch 105 is of a type that, when the rod 102 is
pushed rearwardly with an appropriate instrument, the actuator arm
106 is pushed against its spring bias to close the switch.
Preferably, the switch contacts are gold plated for long wear.
Symmetrically on either side of the apertures 94 and 95 in which
the bulb sockets 96 and 97 are mounted, are parallel elongated
vertical slots 110 and 111. A dome cover 112, shaped as shown in
FIGS. 1, 2, and 3, has rearwardly extending snap arms 114 and 116
which fit into the slots 110 and 111, respectively, for mounting
the dome over the bulbs 98 and 99. The snap arms 114 and 116 have
shoulders 117 and 118 which engage the inside surface of the casing
as best shown in FIG. 3 to hold the dome in position. The dome may
be either clear or translucent to diffuse the light from the bulbs
98 and 99.
Centrally located in the top wall 48 of the casing 45 is an
aperture 122. A photocell 124 is mounted in the aperture 122 with
its light-sensitive surface 125 exposed to the ambient light
surrounding the unit. The back end of the photocell 124 is
electrically and mechanically connected to the circuit board 84.
Its purpose is to measure the ambient light in the room in which
the emergency light unit is mounted to insure that the bulbs 98 and
99 light only when the ambient light level is below a prescribed
value as will be described in more detail in connection with the
circuit of FIG. 9.
The batteries 66, 69, and 72 are rechargeable and are preferably of
the nickel-cadmium type. They are mounted between suitable battery
terminals 130, 131, 132, 133, 134, and 135, the terminals 130 and
135 being electrically and mechanically connected to the circuit
board 84. As will be explained in describing the circuit of FIG. 9,
the batteries power the lights 98 and 99 when there is main power
failure and the ambient room light is below a prescribed level as
sensed by the photocell 124, and are charging whenever the main
power is on.
The rear of the casing 45 is formed in an inwardly extending ledge
137 at the top and bottom of the casing on which is mounted a
backplate 140 which encloses the back of the casing 45 and which
has an opening 142 through which the front portion 143 of the lower
receptacle 23 protrudes.
A pair of plug terminals 145 and 146 are electrically and
mechanically attached to the circuit board 84 and extend through
the back plate 140. The plug terminals 145 and 146 plug into the
upper receptacle 22 of the outlet 21 to supply main power for
charging the batteries 66, 69, and 72. Other than the batteries the
electrical components, as represented on the circuit board 82 of
FIG. 8 and shown schematically in FIG. 9, are mounted in front of
the circuit board 84 in the areas around the bulb sockets 94 and
95.
INSTALLATION OF THE UNIT
The emergency light unit 20 is installed by removing the cover
plate of any standard electrical wall outlet in an area where the
unit is to be used. With the cover plate removed, the plug
terminals 145 and 146 are plugged into the upper receptacle 22 such
that access can be had to the lower receptacle 23 through the
opening 63 formed by the unit casing, thereby supplying main power
to the unit. The receptacle 23 is used as a spare receptacle as
desired. The unit is held firmly in this position by the mounting
screw 78 which screws into the same hole in the outlet 21 as the
screw for holding the cover plate. The unit is now operational.
ELECTRICAL OPERATION OF THE EMERGENCY UNIT
Referring to the schematic of FIG. 9, the electrical operation of
the emergency unit 20 of this invention will be explained. There is
shown schematically the terminals 145 and 146 which plug into the
upper electrical receptacle 22 of the outlet 21. Power is supplied
to the outlet 21 through the cable 30 and conductors 31, 32, and 33
from the main power of the building. Hence, whenever power is
delivered through the cable 30, the receptacles 22 and 23 are
operational for use in supplying electrical power as an ordinary
wall outlet. The other electrical components of the unit 20 are
connected as shown schematically in FIG. 9, and consist of
resistors 160, 161, 162, variable resistor 163, and resistors 164,
165, 166, and 167, capacitors 170 and 171, transistors 172, 173,
and 174, the switch 105, the photocell 124, the lamps 98 and 99,
the batteries 66, 69, and 72, and a diode bridge 175.
The resistors 160 and 161, capacitor 170, and diode bridge 175 are
connected as shown to form a fullwave rectifier circuit 176 for
converting the main AC power to charging power for the batteries
66, 69, and 72. Basically, the unit of this invention is designed
to provide emergency light for the room in which it is mounted only
when the main power to the room fails and the ambient light in the
room is below a prescribed level, and to charge the batteries 66,
69, and 72, which supply emergency power for the lights, whenever
the main power is on. Furthermore, the unit includes means for
testing its operability. Therefore, the device actually has five
modes of operation as follows:
Mode 1 -- Ambient light above the prescribed level, power on,
lights off;
Mode 2 -- Ambient light above the prescribed level, power off,
lights off;
Mode 3 -- Ambient light below the prescribed level, power on,
lights off;
Mode 4 -- Ambient light below the prescribed level, power off,
lights on; and
Mode 5 -- Test mode.
MODE 1 -- Ambient light above the prescribed level, power on,
lights off
With the AC power on, the rectified voltage from the full wave
rectifier 176 appears across the resistor 164 which is of a
relatively high value for purposes which will be explained, the
switch 105 being open except in the test mode. With the ambient
light in the room above the prescribed level, which in this
described embodiment is set to approximately 1 foot candle by
appropriate setting of the variable resistor 163, the photocell 124
has a relatively low resistance which applies enough of the voltage
from the batteries 66, 69, and 72 across the resistor 163 to bias
the transistor 172 to the "on" condition.
With the transistor 172 on, the resistors 164 and 165 drive the
collector of the transistor 172 to a very low voltage, this voltage
being insufficient to turn on the transistor 173. With the
transistor 173 "off", there is no bias current for the transistor
174 so that the transistor 174 remains off, keeping the lights 98
and 99 from turning on. While the batteries 66, 69, and 72 are
supplying only a very little current (probably in the microamp
range) through the resistors 162 and 163 to bias the transistor 172
to the on condition, the batteries 66, 69, and 72 are being charged
by the rectified power from the diode bridge 175 with the positive
side of the rectified power applied directly to the positive side
of the batteries, and the negative side of the rectified power
supplied through the resistor 165 and collector and emitter of the
transistor 172 to the negative side of the batteries. The resistor
164 is relatively large and the resistor 165 relatively small so
that most of the rectified power goes to charge the batteries with
very little loss through the resistor 165 and transistor 172.
MODE 2 -- Ambient light above the prescribed level, power off,
lights off
With the AC power off, the only power to the circuit is from the
batteries 66, 69, and 72 which, of course, is of a relatively low
voltage (approximately 3.6 volts) compared to the rectified voltage
from the rectifier network 176. With the ambient light in the room
above the prescribed level, the resistance of the photocell 124 is
relatively low so that most of the voltage of the batteries 66, 69,
and 72 appears across the resistor 163 to turn on the transistor
172. With the transistor 172 on, the transistors 173 and 174 and
the lamps 98 and 99 are off as heretofore described in connection
with Mode 1 operation. Of course, since the power is off, there is
no rectified power to charge the batteries. However, the battery
energy is being used very sparingly as the lamps 98 and 99 are off,
and as previously described only a few microamps are used from the
batteries to turn on the transistor 172. Also, as previously
described, the resistor 164 is relatively large to offer a high
impedance path through the transistor 172 across the batteries,
keeping the current drain very low. Under this condition, the
batteries will last for many hours and still have plenty of power
to operate the lamps 98 and 99, should the ambient light become
lower than the prescribed level.
MODE 3 -- Ambient light below the prescribed level, power on,
lights off
Just as with the operation in Mode 1, the rectified power from the
diode network 175 appears across the resistor 164. However, because
the ambient light in the room is below the prescribed level as set
by the variable resistor 163, the resistance of the photocell 124
is extremely high so that the biasing voltage across the resistor
163 is insufficient to turn on the transistor 172. If the AC power
were not on, the batteries 66, 69, and 72 would supply enough
voltage across the resistor 165 to turn on the transistors 173 and
174 and the lamps 98 and 99. However, with the AC power on, the
power supply network 176 of the circuit is trying to deliver as
much charging current as required up to a maximum of 60 milliamps,
the maximum current capacity of 60 milliamps being determined by
the values of the resistors 160 and 161 and the capacitor 170. With
the power supply of the circuit trying to deliver the required
charging current, the potential at the junction between the
resistors 164 and 165 becomes negative with respect to the emitter
potential of the transistor 173, the emitter of the transistor 173
being at the same potential as the negative side of the batteries
66, 69, and 72. When the potential across the base-emitter junction
of the transistor 173 drops to approximately -8 volts, the
transistor 173 goes into a reverse bias Zener mode, causing current
to flow from emitter to base in the transistor 173, thus providing
a complete path for supplying the rectified charging power from the
network 176 to the batteries 66, 69, and 72. With the base-emitter
junction of the transistor 173 reverse biased and operating in a
reverse Zener mode, the transistor 173 is off so that the
transistor 174 and lamps 98 and 99 are also off.
MODE 4 -- Ambient light below the prescribed level, power off,
lights on
With the ambient light in the room below the prescribed level, the
transistor 172 is off as heretofore described in connection with
Mode 3 operation. With the transistor 172 off and with the power
supply network 176 of the circuit supplying no rectified power to
create a reverse Zener condition in the transistor 173, current
supplied by the batteries 66, 69, and 72 is fed through the
resistors 164 and 165 to bias the transistor 173 to an on
condition. With the transistor 173 on, the transistor 174 is biased
to an on condition, and with the transistor 174 on, sufficient
current (approximately 350 milliamps) is supplied from the
batteries 66, 69, and 72 through the emitter-collector junction of
the transistor 174 to light the lamps 98 and 99.
MODE 5 -- Test Mode
To operate in the test mode, the operator simply simulates the
conditions of Mode 4 by covering the light-sensitive surface 125 of
the photocell 124 to simulate a darkened condition in the room,
while simultaneously depressing the rod 102 to close the switch
105, which in effect shorts out the rectified power supply. This
causes the lamps 98 and 99 to light as described in regard to the
operation of the circuit in Mode 4.
By way of example, the following chart gives values for the circuit
components of FIG. 9 for one embodiment of the invention:
COMPONENT VALUE 160 1 ohm, 1/4 W 161 20 K, 1/2 W 162 18K, 1/4 W 163
500 K, Pot. 164 5.6 K, 1/4 W 165 470 ohm, 1/4 W 166 150 ohm, 1/4 W
167 18K, 1/4 W 170 1.5 microfarad, 200 V, mylar 171 0.68
microfarad, 50V, ceramic 172 2N 3704 NPN, general purpose 173 2N
3704 NPN, medium power 174 2N 3055 PNP, medium power 66, 69, and 72
each 1.24V., 600 mah, nickel cadmium 124 5K at 2 ft. candles 98 and
99 each pilot lamp No. 13, gold plated contacts
The circuit of this invention has several unique features. As the
current in the collector of the transistor 174 decreases due to a
decrease of power from the batteries 66, 69, and 72, the resistance
in the emitter-collector junction of the transistor 174 decreases
producing more voltage across the lamps 98 and 99 thus acting as a
compensating device to maintain the light output of the lamps
constant with slight variations in battery power. Actually the
nickel-cadmium batteries used in this described embodiment of the
invention sustain their power very well over the two hours of
operation. Not until the last five or ten minutes of operation does
their power diminish rapidly.
Another feature is the use of NPN and PNP type transistors for the
transistors 173 and 174. With these transistors connected as shown,
the only time there is a heavy drain on the batteries (500
milliamps) is when the lamps are on. In all other modes the battery
drain is perhaps 1 milliamp. The batteries themselves are
rechargeable hundreds of times and will power the lamps
continuously for about 2 hours.
Another unique feature is that nearly all of the charging current
from the power supply is supplied across the batteries. Because the
batteries require a maximum charging current of approximately 60
milliamps, the current capacity of the power supply need be only
approximately 60 milliamps, which allows the capacitor 170 to be a
non-polarized, non-electrolytic type for much longer life. If the
circuit were designed, as many of the prior art devices, with
considerable current loss, the power supply current capacity would
have to be much higher to provide sufficient charge for the
batteries. This in turn would require the capacitor 170 to be much
larger so that a non-electrolytic type capacitor could not be
used.
Along these same lines, the purpose of the capacitor 171 is to
filter out ripple at the base of the transistor 173 that might
otherwise cause the light to come on inadvertently, such as in Mode
1 or Mode 3 operation. Because the current at base of the
transistor 173 is in the microamp range, the capacitor 171 can be
much smaller than if the current were 50 milliamps as in some prior
art devices, again allowing for the use of a non-polarized,
non-electrolytic capacitor. Hence, the circuit design allowing the
capacitors 170 and 171 to be small and therefore non-electrolytic
is considered very important in providing a reliable, long life,
emergency light unit. In fact, it is contemplated that the design
of this described embodiment could be guaranteed to operate
trouble-free for a period of 10 years.
Thus, there has been described a self-contained emergency light
unit of a size that can be easily mounted at a standard electrical
wall outlet in a matter of minutes to provide emergency light when
there is a power failure and when the ambient light in the room is
below a prescribed level.
Various change and modifications may be made within this invention
as will be readily apparent to those skilled in the art. Such
changes and modifications are within the scope and teaching of this
invention as defined by the claims appended hereto.
* * * * *