Note: Descriptions are shown in the official language in which they were submitted.
3~363
POWER DISTRIBUTION SYSTEM
Summary of the Invention
This invention deals generally with systems for
electric lamp and discharge devices and more specifically
with a power distribution system for gaseous discharge lamps
which operate at low voltage and with limited power.
One need only walk into a typical large office building
to appreciate the great amount of power consumed by lighting.
In most buildings virtually the entire ceiling of each floor
is covered by row upon row of fluorescent light fixtures.
Unlike residential lighting where specific work areas are lit
by individual, moveable, lamps, most usable commercial space
is usually lit to full work level light intensity required
by the most demanding task.
This is necessary because when the building is first con-
structed the lighting designer cannot anticipate the exact loca-
tions where light is needed, and yet in commercial and in~ustrial
areas only trained electricians are permitted to install standard
ceiling lighting fixtures operating at rated electrical power.
The designer, therefore, fully lights the entire area
363
-- 2
r
rather than force the later occupant to become involved
with formal restructuring of the lighting systems. Such
procedures lead to energy wasted by using excess lighting.
One approach to saving more of this energy has
been to circulate the heat generated by the lighting
system to use it for building heat, but such solutions
gain nothing in those localities and seasons when
cooling rather than heating is required.
The present invention approaches the problem
from a different aspect, that of using a distribution
system which can easily and safely be rearranged by
non-electricians. Such a system brings to lighting
systems what has existed in wall structures for many
years. Most large office complexes use moveable room
dividers to permit flexibility of office arrangements.
However, prior to the present invention, no rearrange-
ment of lighting was possible without using the services
of a trained electrician for revising the lighting--the
equivalent of moving permanently fixed walls.
The present invention is a unigue distribution
system which permits changes of lighting arrangements in
a much more casual manner, and is particularly
advantageous for use with suspended ceilings. In such
installations, the lighting fixtures themselves are
typically supported by the ceiling grid and can be
removed and relocated easily. In the prior art, however,
the fixtures are wired with permanently attached armored
cables connecting the fixtures to electrical power, so that
the simple mechanical installation is completely negated by
the semirigid electrical hook-up.
The present invention uses flexible cable and
plug-in electrical connections, but does so in a safe
manner, which protects against fire and shock hazards.
This new system of power distribution is such that it
would prevent shock and fire hazards even in the familiar
:
g ~3~ 3
~ 3 --
context of a typical residence. For instance, one
embodiment is designed so that even if a child were to
insert a metal object into the power receptacle and
touch it, no harm would likely result.
Moreover, all embodiments of the present
invention furnish fire protection from a short circuit.
Again, in the context of a typical residence, if the
flexible cable of the present invention were used as an
extension cord, but, contrary to all safety considerations,
placed under a high traffic area of carpet where damage
to the cable insulation was likely to occur, nevertheless,
there would be little risk of fire even if a short circuit
did occur.
These results are supported by information
from the National Electrical Code which permits the use
of certain limited voltage and limited power systems
which are considered to be free of shock ha~ard and free
of fire hazard according to Articles 725 and other of the
National Electrical Code published by National Fire
Protection Association, Quincy, Massachusetts~ Typical
familiar applications which fall into this category are
door bell circuits, ringing circuits in telephone systems,
and fire alarm systems.
The present invention therefore furnishes a safe,
versatile lighting system for use in commercial and industrial
locations. This is accomplished by limiting the lighting
system power to specific predetermined values which have
been generally accepted for other low power circuits by
the National Electrical Code, and thereby enabling the use of
a flexible cable in systems which are fire and/or shock hazard
free. A plug-in connecting system is also used for the cabIes.
In the National Electrical Code, Class 2 power
limited circuits, which are considered shock and fire hazard
free, include circuits in which the open circuit voltage does
not exceed 30 volts and having load currents inherently
limited to 8.0 amperes, or, if not inherently limited to that
~23~63
-- 4
value but including overcurrent protection, such protection
must interrupt the curxent at 100 divided by the maximum
voltage.
Such Class 2 circuits are premitted by the Code -to
5 use flexible cable wiring on the load side o the circuit.
The flexible cable assembly used in the present
invention meets the National Electrical Code standards, and
is generally conventional plastic covered multi-conductor
cable. Class 2 circuits require only that the conductors and
10 insulation be "suitable for thé particular application," while
r Class 3 specifies certain material (copper) and insulation
sizes, which are not very stringent by industry standards.
Class 3 circuits, which are considered only fire
hazard free, also permit flexible cables, and are defined to
15 include voltages up to 150 volts, providing the overcurrent
protection interrupts the circuit current at one ampere.
Below 100 volts, Class 3 circuits which are inherently current
limited to 1000 divided by the maximum voltage must also have
overcurrent protection set at 1/10 this value. Class 3
20 circuits with inherent current limitation of 150 divided by the
maximum voltage need no overcurrent protection.
Both classes limit the volt-amperes (VA) of the
load to 100.
The present invention, although not specifically
25 covered by the Code, operates within the limits set by Class 2
and Class 3 operation to yield a system which permits
relocation of suspended ceiling light fixtures safely without
special tools or experience and with little danger of shock
or fire.
As will be apparent from the following and detailed
description-s, the specific limits for voltage and current
parameters can be adjusted by the seLection of specific
component values. Thus, reduced fire hazard can be accomp-
lished by the use of components which limit the voltage and
power to certain values, and reduced fire and reduced shock
hazard can be accomplished by selecting components to further
.q
c
- 5 - ~Z34~63
:
-~ limit the voltage and power.
In both situations, the basis of the presen-t
invention remains the same, to limit the voltage and -the
power to levels which will prevent fire and shock hazard
while still assuring sufficient voltage and powar to
opera-te the light fixtures.
The invention uses a power limited source -to
operate gaseous discharge lamps with sufficient light
output for commercial and industrial installations. One of
the means of accomplishing this is raising the frequency
above power line frequencies.
In the invention herein, "power limiting means"
defines an element or elements which will limit power to no
more than a predetermined output, herein 100VA. A fuse is
not a power limiting means because it will deliver in excess
of its rating for a finite period before it interrupts.
Such above definition is in conformity with the National
Electric Code.
All embodiments of the invention use power 10 from
rated voltage electrical lines, 120 volts, 240 volts, 277
volts, etc. In one embodiment, these sources are connected
to a number of rated voltage operated inverter power
supplies, each such power supply providing for a plurality of
outputs, with each such output being of limited power and of
relatively high frequency. This goal is aided by a sub-
stantial inductive internal impedance, which is operative
to limit the output current from each individual output to
a maximum not exceeding a predetermined valueO The invention
will limit power output regardless of the electrical power
source capacity. The invention will limit output power to
not exceed a predetermined value regardless of the load
conditions including short circuit.
The outputs of the inverter power supply,
supplying high frequency~ but voltage and current limited
power, are connected ~o a plurality of paris of
~23~
-- 6 --
- flexible conductor wires which are pr~vided With easy
plug-in connection at each of the several outputs of the
individual inverter power supplies.
The flexible conductor wires connect to and
feed the high frequency, limited voltage and current
power to a plurality of fluorescent lighting units, each
such unit comprising one or more fluorescent lamps and a
matching network operative to derive the requisite lamp
operating voltages and currents from one of the
inductively current limited, high frequency, limited
voltage outputs of one of the inverter power supplies.
The power provided to each lighting unit is
provided at a high power factor, thereby permitting a
power level of nearly 100 Watts to be provided to each
lighting unit, which, with the indicated high frequency
operation and with presently available high-effici~llcy
fluorescent lamps, can provide nominal light O~ltpUt.
The invention therefore furnishes a versatile
lighting system in which several permanently wired and
located inverter power supplies can supply power to a
multitude of relocatable fluorescent light fixtures,
each connected to an inverter by flexible cable and
plug-receptacle combinations, but safely detachable and
relocatable without experienced electricians.
The present invention, then, in one aspect,
resides in a lighting system adapted to be powered from
an ordinary electric utility power line and comprising:
a central power conditioner adapted to ~onnect
with said power line and comprising a plurality of se~arate
output means, each such output means having current
limiting means and being operative to provid~ an e~sctrical
output that is individually and manifestly limited in terms
of continuously available electric power to a leveI that
is substantially lower than the electric power available
directly from said power line~ said level being low enough
to be considered to be reasonably safe from a fire
initiati~n viewFoint;~
123~63
-6a-
a plurality of lighting units, each lighting
unit comprising an electric lamp and having electric input
means operable to receive the electrical output from one
of said output means; and
a flexible cord and connect means for each
lighting unit, said cord and connect means being operative
to provide aisconnectable connection between one of said
output means and the input means of one of said lightiny
units whereby each individual lighting unit is connectable
directly with the central power conditioner;
thereby permitting a lighting unit to be moved
and re-located relative to, as well as to be removed and/or
disconnected from, said power conditioner.
In another aspect, the present invention resides
in a lighting system adapted to be powered from an
ordinary electric utility power line and comprising:
a number of power conditioners connected with
said power line at different spaced-apart points
therealong, each of said power conditioners having a
2~ plurality of separate power-limited outputs, each such
output being limited in terms of maximum power extractable
therefrom on a continuous basis to about 100 Watt or less;
a set of lighting fixtures for each power
conditioner, each lighting fixture having: (i) an electric
lamp, ii) matching means operative to match the input
characteristics of said lamp to the output characteristics
of one of said outpu~s, and iii) terminal means connected
with said matching means and operative to receive the
output from one of said outputs; and
connect cords operative to provide connection
between said lighting fixtures and said power-limited
outputs, with each one of these connect cords being used
! for connecting between one of said outputs and said
terminal means of one of said lighting fixtures wher by
each said individual lighting fixture is connected
directly with one of the central.power conditioners.
~3~ 3
-6b-
The present invention urther provides a lighting
system for a suspended ceiling, said suspended ceiling
having a grid structure and being suspended below a
permanent ceiling, said system comprising:
a numher of central power conditioners mounted some
distance apart on said permanent ceiling, each of these power
conditioners being connected with an ordinary electric
utility power line and having a plurality of separate Volt-
Amp-limited power outputs, with each such power output
current limiting means and being operative to supply an AC
output current that is manifestly limited in magnitude to
a degree such that the maximum energy flow extractable from
each such power output stays below a level that is
considered hazardous from a fire initiation viewpoint;
a set of lighting fi~tures for each central power
conditioner, each of said lighting fixtures being mounted
in said grid structure and having: i) an electric lamp,
ii) matching means operative to match the electrical input
characteristics of said lamp with the electrical output
characteristics of said power outputs, and iii) electrical
terminal means connected in circuit with said matching
means and operable to receive power from one of said power
outputs; and
for each lighting fixture, a connect cord by which
to connect that lighting fixture to one of said Volt-Amp-
limited power outputs whereby each said individual lighting
fixture is connected directly with one of the central
power conditioners.
Bri~f Description of the Draw~ngs
FIG. 1 schematically illustrates, from an
overall systems viewpoint, the preferred embodiment of
the invention; and shows a plurality of rated voltage
operated inverter power supplies, each providing
powerline isolated, current limited, high frequency AC
voltage for operation of a number of individual gaseous -
discharge lighting units.
~23~863
-6c-
FIG. 2 schematically illustrates the first
embodiment of one of said plurality of rated voltage
operated power supplies and its multiple current limited
outputs and corresponding individual connections with a
number of gaseous discharge lighting units.
FIG, 3 schematically illustrates electrical
- 7 ~ ~234~63
circuit details of a first embodiment of a fluorescent
lighting unit usable within the system shown in PIGS. 1
and 2.
FIG. 4 is a simplified schematic diagram of an
alternate embodiment of a resonant circuit system for use
in the described system.
FIG. 5 is a simplified schematic diagram of a
third alternate embodiment of a resonant circuit system
for use in the described system.
FIG. 6 is a simplified schematic diagram of a
system of power limitation operable directly at rated
power line frequencies.
Detailed Description of the Invention
The preferred embodiment for the invention is
shown in simplified block diagram form in FIG. 1.
In FIG. 1, a source 12 of rated voltage is
applied to a pair of power line conductors 14 and 16.
Connected at various points along this pair of power
line conductors are a number of power line operated inverter
power supplies 18, 20 and 22.
To each such rated voltage operated power supply
are connected a number of gaseous discharge lighting units
24, 26 and 28. The number may be different for different
power supplies at different system arran~ements.
FIG. 2 illustrates in further detail one of the
typical power supplies of FIG~ 1 and its associated li~hting
units.
This typical power supply 18 is powered from
power line conductors 14 and 16.
Inside 18, power line conductors 14 and 16 are
directly connected with a rectifier-filter combination 30,
the substantially constant DC output voltage of which is
applied to an inverter 32.
The output from inverter 32 is a 30 kHz AC
voltage, which AC voltage is applied to the primary
winding 38 of an isolation transformer 34.
12~ 3
-- 8
The output o transformer 34 is provided from
its secondary winding 36 and is a 30 kHz AC voltage of
approximately 30 Volt RMS magnitude. Secondary winding
36 is electrically isolated from primary winding 38.
By way of a number of inductor means 40, 42
and 44, this transformer output voltage is supplied to a
number of power output receptacles 46, 48 and 50,
respectively.
By way of male plugs 52, 54 and 56 conduction
wire-pairs 58, 60 and 62 and female plugs 64, 66 and 68,
the output receptacles 46, 48 and 50 are connected with
input receptacles 70, 72 and 74 on lighting units 76, 78
and 80, all respectively.
The assembly consisting of rectifier and filter
means 30, inverter 32, transformer 34 and the output
receptacles 46, 48 and 50 is referred to as power supply
18.
FIG. 3 illustrates one of the typical lighting
units referred to in FIG. 2 as 76, 78 and 80. This
20 typical lighting unit is referred to as 76 and has a power
input receptacle 70.
Inside lighting unit 76 is a voltage step-up
auto-transformer 82, the input side of which is directly
connected with input receptacle 70 and the output side
. 25 of which is directly connected across a series combination
of two f~uorescent lamps 84 and 86.
Fluorescent lamp 84 has two cathodes 88 and 90;
and fluorescent lamp 86 has two cathodes 92 and 94.
Auto-transformer 82 has three secondary windings
30 96, 98 and lOO, all of which are electrically isolated
r from one another as well as from the input side of auto-
transformer 82.
Secondary winding 96 is directly connected with
cathode 88; secondary winding 98 is directly connected
35 with a parallel-connection of cathodes 90 and 92, and
secondary winding 100 is directly connected with cathode 94.
, .
- 9 - ~3L23~363
Capacitor 102 is connected directly across the
output side of auto-transformer 82.
Operation of the First Embodiment
The operation of the system and circuits
illustrated in FIGS. 1 to 3 may be explained as ollows:
In FIG. 1, the pair of powerline conductors 1
and 16 provides rated voltage power to each and every
inverter power supply: 18, 20 and 22.
Each inverter power supply converts its raked
input voltage to a plurality of powerline isolated power
limited, high frequency, limited magnitude AC voltage
outputs. Each such AC voltage output is directly connected
with a lighting unit, powering this lighting unit by way
of said power limited, high frequency, limited magnitude
AC voltage.
FIG. 2 shows how said powerline isolated, power
limited, high frequency, limited magnitude AC voltage
outputs are obtained.
The powerline voltage is applied to a rectifier-
filter combination of a conventional construction; and theoutput from this rectifier-filter combination is a sub-
stantially constant DC voltage. This DC voltage is
inverted by conventional inverter 32, as described in
U. S. Patent No. ~,184,128, to a 30 kHz AC voltage of
essentially squarewave shape.
This 30 kHz squarewave inverter output voltage
is applied to the primary winding of voltage step-down,
high frequency transformer 34; which transformer is of
conventional construction.
This transformer also pxovides for electrical
isolation between its primary and secondary windings,
thereby providing for the extra safety of powerline
isolation of the AC voltage outputs from power supply 18.
The output of the secondary winding 36 of
transformer 34 is a 30 kHz unlimited power, essentially
squarewave shaped AC voltage with a substant~ially constant
- 10 -
~23~3
RMS magnitude of about 30 Volts; which AC voltage is
provided to the power output receptacles 46, 48 and 50 of
power supply 18 by way of inductors 40, 42 and 44.
Thus, the magnitude of the current avallable at
any one of these power output receptacles is limited by
the reactance of the inductor connected in series circuit
with that receptacle. .The magnitude of the reactance of
this inductor is chosen such that the current resultiny
when a given output receptacle is short circuited is no
higher than 8 Amp RMS.
. The high frequency AC voltage output from each
of the power output receptacles is applied to a fluorescent
lighting unit by way of a conduction wire pair and its
associated male plug and female receptacle.
FIG. 3 shows how the individual lighting units
work and more particularly, how the ballasting of the
fluorescent lamps is accomplished in conjunction with series
inductances 40, 42 and 44.
The output from one of the output receptacles of
power supply 18 is applied by way of a conduction wire pair
to p3~er input receptacle 70 of lighting unit 76, from where
it is applied directly to a voltage step-up transformer 82,
the output of which is applied directly across two series
connected fluorescent lamps 84 and 86.
The actual ballasting of the two fluorescent lamps
is accomplished by way of resonant interaction between
capacitor 102 which is connected in parallel across the two
series connected fluorescent lamps 84 and 86 and the
particular inductor 40 located in the power supply 18
feeding power to the lighting unit 76.
In other words, part of the ballasting function
for the two fluorescent lamps 84 and 86 of lighting unit 76
is accomplshed by way of inductor 40 within the power
supply 18.
The rest of the circuit functions within
lighting unit 76, such as the provision of cathode heating
.... .
. ~L23~363
by way of the three secondary windings on transformer 82,
is accomplished in manners well understood by those skilled
in the art.
It should be noted that any one of the lighting
units, such as lighting unit 76, may consist of any number
or types of lamps; and that these lamps might.even be
mounted in different locations or located in diferent
lighting structures or fixtures. However, within the
context of the present invention, it is important that all
the lamps powered from a single output from any of the
inverter power supplies, be ballasted as a single entity
and that the aggregate Volt-Ampere product drawn from
this output not exceed 100 VA.
It should also be noted that, due to the
resonant matching of the fluorescent lamp loads to the
source of high frequency power, the current drawn from
the inverter power supplies by the different lighting
units will be nearly sinusoidal in waveshape; and it will
be substantially in phase with the fundamental component
of the .squarewave AC voltage outputs provided by these
power supplies. As a result, the power drawn by the
lighting units is drawn with a high power factor, which
implies a maximization of the power available within a
set limit of Volt-Amperes. Moreover, resulting electro-
magnetic interference by radiation from lamps andconductor wires is minimized.
Yet another thing that should be noted is the
fac~ that capacitor 102, which is shown in FIG. 3 as
being connected across the primary side of transformer 82,
may just as well be connected across the secondary side of
transormer 82. In fact, to provide for the desired power
factor correction, capacitor 102 may even be connected in
series with the output or input side of transformer 82.
FIG. 4 depicts an alternate embodiment of a
resonant circuit ballast in simplified schematic form.
This ballast circuit, like that shown in FIG. 3, is used
- 12 _ 1234~3
with inverter 3~, series inductor 40, output receptacle
46, male plug 52, wire-pair 58, female plug 64 and input
receptacle 70, in a system as previously described in
regard to FIGS. 1 and 2.
Fixture 104 of FIG. 4 however diff~rs from
fixture 76 depicted in FIG. 3 in that, in addition to the
direct wire connection between the primary windiny of
transformer 82 and secondary winding 96, the direct wire
connection is supplemented by capacitor 106 connected
between thP primary winding and secondary winding 100.
; The circuits of ~IG. 3 and FIG. ~ both operate
in the following manner. Before lamps 84 and 86 ignite
the voltage supplied by inverter 32 across input receptacle
70 is near-resonant because of the combination of inductor
40 and capaci or 102. As a result, because of Q-multiplica~
tion, the voltage developed across capacitor 102, and
therefore across lamps 84 and 86 as well, is ver~ high
causing ignition of the discharge in lamps 84 and 86.
Upon ignition, the resonant circuit of inductor 40 and
capacitor 102 will become loaded which reduces the
Q-multiplication, which causes the voltage across receptacle
70 to be reduced.
It should be n~ted that the safety goals of
the circuits are met in all conditions since detaching
any of the plug-receptacle combinations, or even breaking
the flexible cable, terminates the resonant condition and
leaves the open circuit condition as one with low voltage
and power limitation through inductor 40.
The difference in operation of the circuit of
FIG. 4 caused by the addition of capacitor 106 is that
capacitor 106 adds phase correction and power factor
improvement. Without capacitor 106, if the unloaded
inductor 40 and capacitor 102 combination is substantiaIly
resonant, then the loaded combination, with the load in
parallel with capacitor 102 is necessarily inductive
rather than resonant. The addition of capacitor 106
- 13 ~3~3
neutralizes this inductive factor and greatly improves the
power factor. Moreover, it should be noted that capacitor
106 is only effective when the lamps are operative and
therefore does not affect the resonant starting.
In both FIG. 3 and FIG. 4, however, the cathode
heating circuits have a decided ef~ect in the starting
operation. Initially, before cathodes 88, 90, 92 and 94
have reached their normal operatlng temperature, and are
therefore relatively low in resistance, they create a
heavier current load on the circuit. Through transformer
82 they therefore load the resonant circuit of inductor 40
and capacitor 102, similar to the action described above
during lamp operation; and the voltage a~ross the lamp is
momentarily limited on start-up untll the cathodes have
reached operating temperature. As the cathode temperatures
increase, their resistances increase, the currents decrease,
and the loading action on transformer 82 diminishes, thereby
permitting the Q-multiplication to increase. The voltage
across capacitor 102 therefore does not instantaneously
jump on start-up and, more importantly, it does not subject
the lamps to a higher voltage until the cathodes are
properly heated. This action, which may be called "soft"
starting, increases the life and reliability of lamps 84
and 86.
FIG. 5 depicts another embodiment which is a
highly simplified version of the present invention. This
embodiment, which can also be used in the system shown in
FIGS. 1 and 2, includes ballast circuit 108 as shown in
U. S. Patent 3,710,177 which, operating in conjunction
with source limiting inductor 40 of the present lnvention,
operates single lamp 110, but as described previously
assures that voltage and power levels are always within
the limits for shock and fire safety. In FIG. 5, when
voltage is applied to lamp 110 by inverter 32 through
limiting inductor 40, capacitor 112, in series combination
with limiting inductor 40, causes the circuit to resonate
~" . ~
- 14 - ~ ~3~3
and a high voltage is impressed across lamp 110. Also,
the high resonant current passes through cathodes 11~ and
116 to overheat them and encourage fast starting~ When
the discharge is establishe~ withln lamp 110, the discharge
current acts as a shunt resistance across capacitor 112
shifting the operation point somewhat and reducing both
the voltage across the lamp and the current through
cathodes 114 and 116. Capacitor 118 is an optional addition
to the patented circuit to better adjust it ~or optimum
operation.
When the current operates at or near resonance,
power factor is optimized, and, because of the sinusoidal
current, radio frequency interference is also reduced. An
additional advantage of the configuration of FIG. 5 is the
self compensation of cathode heating current with lamp
output, providing for decreased cathode current when cathode
heating is provided by the discharge current. Lamp voltage
is characteristically inversely proportional to discharge
current. As such, increasing discharge current is
accompanied by decreasing lamp and capacitor ~oltage,
which results in diminished cathode current and increased
lamp efficacy. Conversely, as lamp output and the
discharge current decrease, cathode filament heating
current will increase, and provide additional cathode
heating to compensate for the reduction in heating resulting
from the diminished discharge current.
FIG. 6 is a further embodiment of the present
invention and is perhaps the simplest of all. Most
important, it uses conventional power source 120 operating
at rated power line frequency and voltage and also uses
conventional fluorescent lamp fixture 126. It differs
~rom conventional plug-in fluorescent lamp circuits,
however, in that, because of proper choice of value for
inductors 122 and 123,-located within power supply 121,
all circuit elements on the load side of inductors 122
and 123 are protected from shock hazard and ~ire hazard.
- 15 _ ~234~3
Capacitor 124 is located in series with
limiting inductor 122 and selected so that, considering
inductive components in standard lamp fixture 126, it will
cause the entire circuit to resonate at the frequency of
power supply 120. Thus the series circuit of limiting
inductor 122, capacitor 124 and lamp fixture 126,
includiny reactances within the fixture and from the
system wiring, are designed to be resonant at the power
supply frequency, even though that frequency is as low as
60Hz. Inductor 122 is also selected with the criteria
that its reactance must be such that, if a short circuit
occurs on its load side, the ampere output will be
limited to a safe valve. It should be noted that part of
the inductance of the resonant circuit can be located
other than within power supply 121.
In specific terms, that means that for the fire
safety case, the reactive impedance of induc~or 120 must
be at least 120 ohms for a 120 volt rated power source,
and at 60Hz that requires an inductance of approximately
0.32 Henries. Capacitor 124, to resonate the circuit,
assuming no additional inductance in lamp fixture 126,
must have a value of approximately 22 microfarads.
The shock safety case requires a lower voltage
of 30 volts maximum and therefore requires only a 0.9 ohm
inductive reactance. At 60Hz this is available from an
approximately .0024 Henries inductance which would require
an approximately 2900 microfarad capacitance for resonance.
Such values could therefore ~urnish a safe,
versatile lighting system which can be rearranged by
virtually anyone.
It is to be understood that the form of this
; invention as shown is merely a preferred embodiment.
Various changes may be made in the function and arrange-
ment of parts; equivalent means may be substituted for
those illustrated and described; and certain features may
be used independently from others without departing from
- 16 _ ~23~3
the spirit and scope of the invention as defined in the
following claims.
For example, sodium vapor lamps may be used in
plaee of conventional fluorescent lamps, and multiple
lamps may be located in a single ixture with eaeh lamp
separately powered by a circuit sueh as that shown in
FIG. 5. Conversely, multiple lamps in a eireuit sueh as
that shown in FIG. 3 could each be plaeed in different
localities but be interconnected. Moreover, in many of
the embodiments, the locations of inductive and capacitive
reactances could be interchanged and resonanee and power
limitation could be maintained. This is particularly so
for the circuit of FIG. 6.
