Note: Descriptions are shown in the official language in which they were submitted.
`~ ` 2 1 37860
EMERGENCY LIGHTING SYSTEM INCORPORATING
SELECTIVE CONTROL OF FIXTURES
The invention relates generally to emergency lighting
systems having centrally located batteries and charging elements --~
remote from light sources or exit signs comprising the system,
the invention particularly relating to "central" emergency
lighting systems wherein each fixture of the system is
separately controlled.
Emergency lighting systems have long been known which
provide auxiliary power upon the loss of AC power typically
supplied by a utility. Such systems have utilized various
commonly available light sources including incandescent,
fluorescent, HID, etc. for general area lighting and further -~
inc~i.~ electroluminescent light sources, LED light sources,
etc. for exit signage which comprise a portion of the lighting
system. The most commonly available emergency lighting systems
comprise self-contained u~its which include a battery, a charging
sub-system for the battery and a logic unit which energizes
a light source upon normal power loss. These commonly
available emergency lighting systems have proven to be reliable
often through the provision of redundant features, although
some such systems have been known to produce glare and
highly concentrated hot-spot~ of illumination which render
such systems less dcsirable in use than the industry continues
to strive for. The fact that such prior systems include
2 t 378~0
large numbers of batteries and charging systems also mandates
extensive and often inconvenient maintenance. While the prior
art has attempted and continues to attempt to incorporate
emergency lighting into existing fluorescent fixtures, the
advantages which would accrue from such a practice, that is,
reduction of glare, better aesthetics, etc., are neutralized
due to the fact that operating temperatures within lighting
enclosures typically prove detrimental to battery life and
function, Accordingly, some currently available emergency
lighting systems deplo~ batteries and charging systems therefor
in a remote position relative to light sources or exit signs,
this remotely located cquipment being placed in some "central"
location which causes a system of this nature to be referred
to as a "central system". The batteries needed for emergency
power are thus located in a more suitable environment and
may be more easily maintained. Such "central~systems" still
require large banks of batteries with the output of a typical
system of this type necessarily duplicating normal AC power,
that is, 60 Hz. AC in most situations. Such systems therefore
require the use of large inverters which are typically "lossy"
and noisy in operation. Still further, such systems typically
lack provision for reduction of the clrcuit load, thereby
requiring that the system be sized for a normal load, that
is, sized for task lighting thereby resulting in vast over
sizing for emergency or "path of egress" lighting. The art
has long known that path of egress lighting may be a small
fraction of normal lightin9 levels and when provision is made
~ - 2 ~ 37860
for reducing load in such systems, a signal to reduce load
must be communicated throughout the system by a complex
methodology which can include control wiring, radio transr~lission
or powerline carrier, etc. The cost of such systems is
therefore substantially increased. In alternative arrange-
ments, separate circuits can be provided but additional
cost is also incurred in such circumstances.
A central system of the prior art is best represented
by U.S. Patent 4,349,863 to Petersen which supplies AC power
normally in a lighting system and DC power in an emergency
situation. In the DC emergency power mode of Petersen,
different circuits are utilized to alter fixture function.
The Petersen patent also describes a system which requires
electronic ballast.
Ertz describes in U.S. Patellt 4,751,398 a system
whereby normal AC power is converted to DC whereby DC is
distributed in both the normal as well as the emergency mode.
All fixtures and ballast in the circuits of Ertz must
operate on DC power. Ertz does not provide for reduction of
loads in the emergency mode such that the system and
battery requirement must be sized for full circuit conditions.
The art is thus improved by a provision of an
emergency lighting system wherein normal task lighting is
provided by AC power and emergency functions are provided
by DC power and wherein lightlng fixtures in the system
are capable of changing functlon irl the DC mode and on the
same circuit. The present emergency lighting system provides
such function, is operable with both conventional ballasts
~ 2 ~ 37860
as well as electronic ballasts, allows use of both lighting
fixtures and exit signage within the system and, upon loss
of normal AC power, is capable of load shedding in order to
conserve battery power and is still further capable of
operating exit signage at a brighter level.
The invention provides an emergency lighting system
capable of including both lighting and exit signage on the
same circuit wherein the function of those fixtures on the
circuit can be altered without resort to separate circuitry
for such function alteration. The present emergency lighting
system provides auxilliary DC power upon the loss of normal,
utility supplied AC power, the loss of AC power resulting in
a switching to a DC emergency mode with alteration of fixture
function occurring through an interface unit at each fixture.
Each interface unit comprises a simple circuit capable of
producing a change in function of the associated fixture,
such as level reduction, load shedding, etc., on the same
circuit used for power distribution.
The present emergency lighting system may be
utilized with either conventional or electronic ballasts and
Canbe}amped with incandescent, fluorescent, HID, and similar
light sources for general area lighting and may include
conventional light sources as well as electroluminescent,
LED, etc. for exit signs and the like. The system can still
further be utilized with controllable ballasts.
4-
2 1 37860
The present emergency lighting system comprises a
central system wherein batteries and charging structure
therefore are located remotely from the light sources and
signage in the system. Due to the abillty of the present
emergency lighting system to alter the functions of the
various fixtures without additional circuitry and depending
upon the presence or absence of normal utility power allows
functional changes brought about by interface units at the -
various fixtures. Accordingly, a reduced level for emergency -'
power can be accomplished without the need for the quantities
of batteries necessary in prior systems.
Accsrdingly, it is an object of the present
invention to provide an improved emergency lighting system
which may include both lighting and exit signage on the
same circuit and whereby the function of the fixtures can be
altered depending upon the presence or absence of normal
utility power and wherein functional changes in the fixtures
can be accomplished without the need for separate circuitry
or control wiring.
It is another object of the invention to provide
necessary emergency functions in an improved eme_gency lighting
system without the need for special ballasts and without
the need for large quantities of batteries and charging units
located at the fixtures themselves.
It is a still further object of the invention to
provide an improved emergency lighting system wherein AC
power is normally supplied and DC power is supplied upon
` 2 1 37860
loss of the AC source and wherein interface units are provided
for each fixture in the system circuitry which act to change
function of the fixture on the same circuit used for power
distri~utio~ changes in function including level reduction,
load shedding, etc.
Further objects and advantages of the invention
will become more readily apparent in light of the following
detailed description of the preferred embodiment.
FIGURE 1 is an idealized perspective view of a
typical installation of the present emergency lighting system;
FIGURE 2 is a schematic of the emergency power
unit which is incorporated into the present system;
FIGURE 3 is a detailed schematic of the components
of a boost converter utilized in the present system;
FIGURE 4 is a schematic of circuitry devised according
to the ivnention for differentiation between AC and DC power
and for the resulting actuation of a relay according to the
invention;
FIGURE S is a schematic of a fluorescent fixture
interface circuit according to the invention;
FIGURE 6 is a schematic illustrating the connections
of an interface unit according to the invention such as is
seen in Figure 6 to a conventional magnetic or electronic
two lamp 40 watt fluorescent ballast; and,
~ 21 37860
FIGURE 7 is a schematic of an exit interface circuit
according to the invention utilized with an electroluminescent
exit sign.
~ eferring now to the drawings and particularly
to Figure 1, the emergency lighting system of the invention
is shown generally at 10 to comprise a desired number of
lighting fixtures 12 connected in the same circuit with a
plurality of exit signs 14, the fixtures 12 and signs 14
being controlled through an emergency power unit 16 when
operating in the emergency DC power mode. A usual lighting
panel 18 functionally connects to the emergency power unit 16
such as is typical in a lighting system including emergency
features. The lighting fixtures 12 and exit signs 14 are
operated from normal AC utLlity power usually at 120 volts or
277 volts, The utility power is conventionally supplied
through the lighting panel 18 to the lighting circuitry
represented by the system 10 in a given area or zone of an
installation. The utility power is connected to the emergency
power unit 16 for supply to the lighting fixtures 12 as well
as the exit signs 14. While only one circuit is shown in
Figure 1 for simplicity, it should be understood that a
single emergency power unit 16 can be utilized to handle a
number of circuits each containing a plurality of lighting
fixtures 12 and exit signs lq depending upon the exigencies
of a typical installation. The use of a single emergency
2 1 37860
power unit 16 for a plurality of circuits depends primarily
upon circuit loading and the rating of the emergency power
unit 16. In supplying DC emergency power to the fixtures 12
and signs 14, the emergency power unit 16 typically includes
a plurality of sealed lead calcium batteries (not shown)
which are conventional in nature. A typical emergency power
unit 16 has a 450 watt capacity for emergency capacity
function and the capability for up to six 120 volt AC
circuit breakers or three 277 volt circuit breakers (not
shown). The emergency power unit 16 will be
described in more detail hereinafter.
The lighting fixtures 12 can be chosen to operate
incandescent lamps, fluorescent lamps, HID lamps, etc.,
depending upon the desired operation of the system 10.
Similarly, the exit signs 14 can be electroluminescent,
edge-lighted, incandescent, fluorescent, etc., as is
desired. Each of the lighting fixtures 12 mount and cooperate
with a fixture interface unit 20 while each exit sign 14
is associated with a sign interfact unit 22. The sign interface
unit 22 is not shown in Figure 1 since the interface unit
22 is incorporated into each exit sign 14. The sign interface
unit 22 is shown in other figures and will be described
in detail hereinafter.
Upon loss of utility AC power, each fixture inter-
face 20 is capable of operating one of the lighting fixtures
12 at a reduced output for a period of time and at a reasonably
low power consumption. As an example, each fixture interface
unit 20 is capable of operating one or two four foot fluorescent
21 37860
lamps at 30 percent light output for at least 90 minutes upon
loss of normal AC power. Alternatively, a single eight foot
fluorescent lamp can be operated at 20 per cent light output
for at least 90 minutes upon loss of normal AC power. These
lamp operations can be conducted with a consumption of
approximately 16 watts of emergency DC power. Similarly,
each sign interface unit 22 is capable of operating an
exit sign 14 with a consumption of approximately 4.5 watts
of emergency DC power and with a brighter light output.
For a conventional electroluminescent lamp, the output in the
emergency mode can be five times greater than in the normal
utility-operated mode.
in a typical installation the emergency lighting
system 10 can provide emergency power to approximately 28
fluorescent fixtures or a combination of fixtures and exit
signs for approximately 90 minutes with the use of only two
batteries tnot shown) disposed in the emergency power unit 16,
thereby protecting the batteries from high temperatures which
would be encountered if located internally of the fixtures.
As best seen in Figure 2, the emergency power unit
16 is shown to be formed of basic functional blocks which
include battery charger 24, at least one battery 26, a
transfer relay shown at 28 and a unit 30 capable of performing
supervisory and test functions. A boost converter 32 is also
preferably employed in the unit 16. When utility power is
available, the power is passed unimpeded to the load being
driven, that is, the fixtures 12 and the signs 14. The
emergency power unit 16 in the normal utility mode takes
2137860
only that power necessary to charge and maintain the battery
26 as well as a small amount of power necessary to energize
the transfer relay 28 (or transfer relays). It should be
understood at this point that many prior art emergency
systems are characterized by high power conversion losses
at all times. In the emergency power unit 16, the input at
34 is passed through the transfer relay 28 to output 36 when
the system 10 is operating in a normal utility mode.
The battery charger 24 is supplied from the normal
utility power source and may be conventional in nature.
However, due to the nature of the system 10, the battery
charger 24 may be less bulky and complex. This improvement
in the bulkiness and complexity of the battery charger 24
is brought about in part by the load shedding capability
of the system 10 and will be described hereinafter and,
secondly, by the provision of the boost converter 32. Use
of the boost converter 32 allows a step-up or a "boosting"
of the battery voltage to a level more suitable for
distribution and in line with those voltage levels normally
present. Accordingly, both emergency and normal power may
be distributed upon the same circuit wiring without the need
for separate circuits. Prior art systems typically
incorporate large battery stacks tO achieve a necessarily
higher voltage and as a consequence incur the need for
duplications in the battery charger function. As is known
in the art, large series battery strings are difficult to
maintain and charge adequately due primarily to the lessened
significance of total battery voltage as an indicator of
charge condition.
~ 2137860
As is seen in Figure 3, the boost converter 32
includes a semiconductor switching device shown at 38 to
comprise a MOSFET. When the switching device 38 is conducting
or "on", energy is stored in the inductor of the MOSFETcircuit.
During the "off" time of the switching device 38, energy is
transferred through diode 40 to output capacitor 42. The
resulting output voltage is given by the equation noted in
Figure 3 where D is the duty cycle of the switching device 38.
The duty cycle can be defined as the "on" time expressed as
a percentage of cycle time. The output of the boost converter
32 may thus be many times the input voltage.
The unit 30 which provides supervisory and test
functions can be as simple as a test switch and pilot lamp
(not shown\ but can also extend to such functions as metering
ofbattery condition, metering of output voltage and measure-
ments of current. The unit 30 may also incorporate a
preset timer ~not shown) to allow time for the entire
system operation to be observed. The functions provided by
the unit 30 are made vastly superior to that provided by
self-contained emergency lighting devices since the provision
of these functions are centralized and are not duplicated
throughout the lnstallation space.
Referring now to Figure 4, an AC/DC power
differentiation circuit is shown at 44, the circuit 44
allowing communication to the interface units 20 and 22
within the system 10 the need for a different operating
mode. Accordingly, the circuit 44 differentiates between
normal AC power and an emergency situatlon which requires
11~
2137860
DC power. In the circuit 44, a resistor 46 is used for
inrush suppression and is in fact not a necessary portion
of the circuit 44. Capacitor 48 is connected to the
resistor 16 when the resistor 16 is utilized to provide a
series impedance to AC which in turn supplies power through
diode bridge 50 to relay coil 52. Second capacitor 54
placed across the relay coil 52 provides filtering and a
stable source for the relay coil 52. Accordingly, when AC
is present, the relay coil 52 is energized and contacts 56
are in a position such that power will be passed to the
normal fixture ballast ~not shown) or load. In the case of a
sign such as one of the exit signs 14, power would be applied
to the "normal~' lamp circuit of the sign 14. It should be
understood here that the contacts 56 of the relay coil 52
will change state when power is lost and will remain in the
"power lost" state if DC power is applied, this situation
occurrinq regardless of the manner in which the fixtures 12
and/or signs 14 respond. The capacitor 48 will charge to the
line voltage initially but will block operation of the relay
coil 52 as long as DC power is present. The contacts 56
are therefore in one position when AC is present and in a
second position when DC is present and could, in this second
position, apply DC power to an altogether different circuit
or function. This change of relay state can be used, for
example, to alter the level of a controllable ballast (not
--- shown) in the event that such a ballast is incorporated into
the system 10. The present system 10 therefore provides an
extraordinary variety of function without the need for
modification of system circuitry.
2137860
- Referring now to Figure 5, a circuitry schematic
is provided illustrating the structure and operation of the
fixture interface unit 20, this interface unit 20 being
intended for use with a typical fluorescent lighting fixture
such as the fixture 12 of Figure 1. It should be under-
stood, however, that other lighting fixtures utilizing lamps such
as incandescent lamps and the like can be used in systems such
as described herein. To the left in Figure 6 is a circuit
numbered as circuit 44 in the manner of the circuit of
Figure 4 since the circuit 44 of Figure S is identical in
function to the circuit 44 of Figure 4. However, the circuit
44 of Figure S provides an additional input capacitor 58
having the purpose of accommodating higher source voltages.
With lower source voltages, only the capacitor 48 is necessary
as is shown in Figure 4. When using higher source voltages
such as 277 volts AC, jumper 60 is removed. With the jumper
60 in place as is shown in Figure 5, the circuit 44 of
Figure S is suitable for 120 volt AC power. The circuit 44
of Figure 5 is also provided with two relays, that is, relay 62
and 64 in order to provide additional relay contacts in an
economical manner. The purpose of the additional relay
contacts will become apparent through reference to Figure 6
as will be described hereinafter, the purpose generally being
to provide proper connections of the interface unit 20 to
conventional rapid-start fluorescent ballasts (not shown)
and also to electrorlic ballasts which connect in the same
manner.
13-
-2~37860
Orange lead 66 of the interface unit 20 is provided
to allow local switching of the fixture 12 or fixtures 12.
The power applied through such a switch (not shown) may be
the "system" power or may be obtained from some local source.
In any event, this power, applied to the interface unit 20
through the orange lead 66, is controlled by a first set 68
of contacts. The contact set 68 controls the input power of
ballast 70 (shown in Figure 6) which is connected to black/
yellow lead 72. It is necessary for the interface unit 20 to
be able to disconnect input power in order to test the system 10.
A second set 74 applies DC power, when present,
to inverter circuit 76. A third set 78 of contacts and a
fourth set 80 allow blue leads 82 and 84 respectively to be
interrupted so as to separate lamp 86 from the ballast 70
and therefore prevent unnecessary loading of the inverter
circuit 76. An interim circuit 88 is provided in order to
block high AC voltages from the inverter circuit 76 during
the transitional period required for the second set 74 of
contacts to change state. The lnterim circuit 88 is only
necessary when the AC voltage is much higher than the design
voltage of the inverter circuit 76. In a preferred embodiment
the interim circuit 88 is required since the interface unit
20 must accommodate 277 volt AC line voltages and the
inverter circuit 76 is designed for 120 volts DC.
Referring now to Figures 5 and 6, an external
connector or "jumper" 90 is used tO alter output of the inverter
circuit 76 so that different lamp lengths can be accommodated.
-14-
2137860
In usual situations, the jumper 90 is connected for lamps
of four foot lengths and less. In the case of longer lamps
or when two lamps are operated in series, the jumper 90 is
disconnected.
As is seen best in Figure 6, aconnector 92 can be
employed as is shown in the Figure. However, hot leads of
additional ballast (not shown) must be connected to the black/
yellow lead 72. It is also to be seen in Figure 6 that connec-
tors 94 are utilized on the blue leads 82 and 84 between the
ballast 70 and the fixture interface unit 20. Still further,
an insulation displacement connector 96 is employed for
connection of the lamp 86 tothe circuit in the emergency mode.
For the sake of brevity, Table I is now provided
for identlfication of suggested values for the components
of the fixture interface unit 20 of Figure 5. These
components and component values are identified for the
purpose of illustration only and do not limit the scope of
the invention.
2137860
TABLE I
DESIG. C~ 'ON ~T ~FSCRIPTION
58 CA Ar G , ^. ~~, 2, V
48 CA~AC-O~, 2.~ , V
C3 CA'AC_~ f, 25~
C4--C5 ~A AC-'~, 'OL~E``TER O 3-~LF, 250V
C6 1-A A-i I , y '' l ' 1 . 0~ -, 50V
C7 ~:A~A(~-G , Y~ ~O 4, - !'pF 2KVDC
C8 CA~AO-~ , O.~ R~F, 1,J~VDC
C9,Cl O CA'AC-C', ~' 00 I~LF, 2KVDC
C 1,C12 r~AG (` ., C~ Av C O.l~f ~5VDC
h1-46 - C~,c~ o~ lMt?,+l %1/2W
~3 ~ ~, L~ 1 I<.n. i s% /4W
R~,R7 -~, -Lv l oKn, _5, /4W
R~"R6 . -O, ~A 0~ lOn, i O~. 1/2W
8 -O', v coKn. i5.~ /2W
~9 .. '-O ., ` 4 Mn, + 5% 1 /4W
h O -O, - 4 .sn, i5% 1/2W
60 ''~-0, - ~ on, l/4W
D1 - 6 ~ YP- 1N~nOI
D7 - J8 ~ ~ .. P . R2.C î
D9--G 10 ~ -NER,
D1 v ~. NER ~ l~o
Q l - Q2 ., -f ~, 2.OA, ~OOV
Q3 ., 4TP ~ 60, .OA, OOV
62, - 4 AY, 1 ,~C DPDT 277VAC 5A
L C 1~ ~KE, 32. T, #30
- T ~VERTER T ANSfORMER (9 MIL GAP)
Transformer 98 of thc inverter circuit 76 is
intended to have a primary winding of 30 turns of wire size
#30. The secondary winding of the transformer 98 is intended
to have 250 turns of wire size #31. The gatewindings of the
transformer 98 is intended to have 10 turns of a wire size #30.
The core of the transformer 98 is taken to be a conventional
high frequency transformer core.
1~
-21~7860
The system 10 thus descrlbed hereinabove provides
a load shedding capability which can be understood relative
to a situation wherein the lighting fixture 12 is taken to be
a typical four lamp fluorescent fixture using commonly
available 40 watt fluorescent lamps. Such a fixture
typically consumes approximately 190 watts when ballast losses
are included. Connection of the fixture interface unit 20
as shown in Figure 6 to the lighting fixture shown generally
at 12 in Figure 6, the lamp 86 is operated in the emergency
mode with a total input to the inverter circuit 76 (see
Figure 5) of fixture interface unit 20 of only 16 watts,
a consumption of only 8.5% in the emergency mode of the power
utilized for normal system loading. Lamp 100 operates in the
normal mode and the load represented thereby is shed in the
emergency mode. Any ballast connected into the connector 92
is also shed in the emergency mode.
Referring now to.Figure 7, the sign interface unit
22 is generally seen to contain circuitry similar to that of
the fixture interface unit 20. The sign interface unit 22
of Figure 7 is particularly intended for use with an electro-
luminescent exit sign but can be used with other exit signage
and other illuminated signage. The circuitry of the sign
interface unit 22 is more simple than that of the fixture
interface unit 20 of Figure 5 since typical exit signs 14
do not require the use of ballasts or lamp filament wiring.
However, an additional impedance is represented by capacitor
102 which is jumper selected when the unit 22 is to be used
on a 277 volt AC utility li~Q This additional impedance
provides a voltage dropping function in order to operate
the electroluminescent lamp ~not Shown) of the sign 14 at
its proper voltage.
_,,",r
2137860
,. -
Circuit 104 of Figure 7 corresponds to the circuit
44 of Figure 5 with the purpose of the circuit 104 being
to discriminate between AC and DC input power and to channel
the power appropriately. First set 106 of contacts of the
sign interface unit 22 switches power to inverter circuit 108
when DC power is present. The contacts 110 act to simply
switch the lamp (not shown) from the system input to the
output of the inverter circuit 108. The components of the
inverter circuit 108 are similar to those of the inverter
circuit 76 of Figure 5. However, the requirements of an
electroluminescent lamp such as is used in the typical exit
sign 14 are such that the inverter circuit 108 operates at
a much lower frequency and voltage. Interim circuit 112
of Figure 7 is substantially identical to the interim
circuit 88 of Figure 5 and acts to perform the same blocking
function previously described relative to the circuit 88
of Figure 5.
In operation, it is usually desirable for the exit
sign 14 to become brighter in t~le emergency mode. This
function does not substantially reduce load shedding benefits
of the total system since the exit signs 14 normally constitute
only a small portion of the total load. Since one of the
exit signs 14, particularly an electroluminescent exit sign,
typically consumes less than one watt when operated on the
AC line and since the inverter circuit 108 operates an electro-
luminescent lamp up to five times brighter in the emergency
mode, only an input of approximately 4.5 watts to the inverter
circuit 108 is necessary.
_~,
`2137860
Reference to the following Table II identifies the
components of the sign interface unit 22 and suggested
component values which are for the purpose of illustration
only and not for limitation of the scope of the invention.
TABLE II
DES G. COM ~O ~ ~T ~ESCR P~
C CA~AC O, Y'- rG" ~. ~L, .2- V
C 2 CA'AC -O , Y . '~ JV
C3 CA 'AC-G, 'LECT. O .r c 47~Lf, 25V
C4--C5 CA~AC-r', ~OLYE'- _R O 33~.LF, '.~iOV
102 CA'AC-~ Yl~: 4 0."2, f, 6~0 VDC
C7 (~A~ 4 1. ,L~ 50\~
, CA -Ot~ lOn, i 7. 1/2W
R2, ~3,R8 . ~ o~ , Mn~ l ~ 1/2W
R~,~7 .~ Kn, 1 5- /4W
R~ 6 .~- o , M ~ , i S7. / W
O, M OKn, I ~S. /2W
P ~ - . O , M l Mn, I . ,~. 1 /4W
R .'` .-0 , - M 27n, i .5. 1 /2W
- J ,J2 ' ~-0', - M on l/~W
D1--~6 o~ :, ~P. 1 N40~
D7--D8 o ~ NER, lN ~ ,'B
D9 o~, .NER, lN ''.~I El
Q 1-- )2 -F, IRf612, 2.0A, ".OOV
Q_ F, MTP N60, 6.0A, 600V
RY1--~Y3 ~Y, 1 ~v DC
Ll l ~OKE, 3 25 T, #30
T1 ~VERtER TRANSFORMER
The inverter circuit 108 has an inverter transformer
which typically can be formed wlth both primary and secondary
windings having 400 turns (tap at 300) with a wire size of #34.
/9 - ' .
2137860
,,
, ... .
The gate windings of such a conventional transformer can have 50
turns with a wire size of #34. The core of such a high frequency
transformer can also be conventional.
An emergency lighting system is thus described
which is capable of including both lighting and exit signage
on the same circuit wherein the function of the lighting
fixtures on the circuit can be altered without resort to
separate circuitry for function alteration. In the present
emergency lighting system, loss of AC power resùlts in a
switching to DC emergency mode with alteration of fixture
function occurring through an interface unit at each fixture
including each exit sign as desired. The interface units at
both the lighting fixtures and at the exit signs comprise
simple circuits capable of producing changes in function of
the associated fixture or sign, such functions including
level reduction, load shedding, etc., with the changes in
function occurring on the samé circuit used for power distribution.
As has also b^en described in detail, exit signs in the
present system can be operated at higher brightness levels in
the emergency mode.
The foregoing is intended to be illustrative of
the embodiments of the invention and is not intended as
limitation to the scope of the invention such as is defined
in the appended claims.
