U.S. patent number 3,873,882 [Application Number 05/403,948] was granted by the patent office on 1975-03-25 for auxiliary lighting system for a gaseous discharge lamp.
This patent grant is currently assigned to Leviton Manufacturing Co., Inc.. Invention is credited to Bernard J. Gershen.
United States Patent |
3,873,882 |
Gershen |
March 25, 1975 |
**Please see images for:
( Certificate of Correction ) ** |
Auxiliary lighting system for a gaseous discharge lamp
Abstract
An emergency or auxiliary lighting system for a gaseous
discharge lamp is provided with an auxiliary lamp controlled by a
switch which is biased to remain in a closed position. A control
circuit, responsive to the voltage across the gaseous discharge
lamp, produces a voltage proportional thereto which is opposed to
the biasing control. During any time that the gaseous discharge
lamp provides more than a minimum adequate light output, the
control circuit voltage becomes greater than the biasing control to
open the switch. Also, in the event of a power interruption, the
control circuit closes the switch.
Inventors: |
Gershen; Bernard J.
(Centerport, NY) |
Assignee: |
Leviton Manufacturing Co., Inc.
(Little Neck, NY)
|
Family
ID: |
23597528 |
Appl.
No.: |
05/403,948 |
Filed: |
October 5, 1973 |
Current U.S.
Class: |
315/92; 315/120;
315/91; 315/135 |
Current CPC
Class: |
H03K
17/725 (20130101); H02J 9/02 (20130101) |
Current International
Class: |
H02J
9/00 (20060101); H03K 17/725 (20060101); H02J
9/02 (20060101); H03K 17/72 (20060101); H05b
041/46 (); H05b 037/04 () |
Field of
Search: |
;315/88,91,92,119,120,121,127,129,130,131,135,178,182 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Rolinec; R. V.
Assistant Examiner: LaRoche; E. R.
Attorney, Agent or Firm: Hamilton; Hanse H.
Claims
What is claimed is:
1. An auxilairy lighting system for use with a primary lighting
system having a gaseous discharge lamp and a ballast connecting the
gaseous discharge lamp to an alternating current source of voltage
for igniting and operating said gaseous discharge lamp, said
auxiliary lighting system comprising:
a. an auxiliary light source;
b. switch means connected in series with said auxiliary light
source and an output from a ballast;
c. said switch means comprising an SCR and a bridge rectifier;
d. biasing means connected in series with said switch means and
said auxiliary light source for producing an output voltage acting
on said switch means and maintaining said switch means in a
conductive condition;
e. said biasing means including a resistor connected between a gate
electrode of said SCR and a source of positive voltage; and
f. control means responsive to a voltage across the discharge lamp
for producing an output proportional to said lamp voltage and
opposing the output voltage of the biasing means;
g. said control means includes a transformer and a rectifier
connected across a gaseous discharge lamp for producing a negative
output voltage proportional to the voltage applied to said
discharge lamp;
h. said output voltage from the transformer and rectifier being
connected to the gate electrode of the SCR;
i. said control means having an output voltage which is greater in
magnitude than said output voltage from the biasing means during a
period of time when said gaseous discharge lamp is operating at
full illumination and said SCR is in a non-conductive condition,
and causing said SCR to become conductive in response to
application of a starting voltage to said gaseous discharge
lamp;
j. said control means also including a filter circuit and a
breakdown device connected between the output of the transformer
and the rectifier and the gate electrode of the SCR;
k. said breakdown device producing a fixed low voltage after
application of a high voltage thereto in response to the
application of a starting voltage to the discharge lamp.
2. An auxiliary lighting system as defined in claim 1, in
which:
a. the bridge rectifier is connected to the alternating current
source of voltage and produces a positive voltage applied at the
resistor of the biasing means;
3. An auxiliary lighting system as defined in claim 1, wherein:
a. said transformer has a primary connected across the gaseous
discharge lamp and a secondary having ends interconnected at a
first terminal;
b. said secondary having an intermediate tap providing a second
terminal;
c. said filter circuit comprising capacitors and resistances
connected across said first and second terminals of the transformer
secondary.
4. An auxiliary lighting system as defined in claim 3, wherein:
a. said breakdown device comprises a silicon unidirectional switch
connected in parallel with one of the filter capacitors.
5. An auxiliary lighting system as defined in claim 3, which
includes:
a. a limiting resistor serially connected between the gaseous
discharge lamp and the primary of said transformer.
6. A lighting system, which comprises:
a. a gaseous discharge lamp;
b. a ballast connnected to said gaseous discharge lamp and to a
source of alternating current voltage for igniting and operating
said discharge lamp;
c. an auxiliary light source;
d. rectifier means connected across said gaseous discharge
lamp;
e. said rectifier means producing an output;
f. reed switch means comprising an electromagnetic coil enclosing a
pair of movable contact elements;
g. said electromagnetic coil being connected to the output from
said rectifier means in parallel with a filter capacitor;
h. said movable contact elements being connected in series with a
limiting resistor between an anode and a gate electrode of a
semi-conductor switch;
i. said contact elements when closed supplying a voltage to said
gate electrode and causing said semi-conductor switch to become
conductive; and
j. permanent magnet means positioned adjacent said electromagnetic
coil and acting on the movable contact elements to hold the
contacts closed;
k. said electromagnetic coil when energized producing a magnetic
field in opposition to the magnetic field of the permanent
magnet;
l. said coil and said permanent magnet having a net field holding
the contacts in engagement after a power interruption and during a
warm-up period of the lamp;
m. said net field permitting the contacts to separate under
conditions when the lamp is operating and producing an acceptable
level of illumination.
Description
BACKGROUND OF THE INVENTION
This invention relates to an emergency lighting system, and more
particularly to an auxiliary lighting circuit for use with a
primary lighting system.
Gaseous discharge lamps, such as mercury arc lamps, metal arc lamps
and similar type lamps, have long been used in industrial lighting
facilities as well as on highways because of their extremely high
efficiency when compared to other sources of light. This type of
lamp has the property of requiring a relatively high voltage for
striking the arc to light the lamp, and requires a relatively lower
voltage for maintaining the arc. These requirements are handled by
various types of ballasts which are commercially available.
One of the problems in using such gaseous discharge lamps resides
in the fact that, upon interruption of power for a few cycles, the
lamp will become extinguished and restriking of the arc within the
lamp will not occur immediately upon restoration of the power
source. One reason for this is that the striking potential of a hot
lamp is much higher than the striking potential when the lamp is
cool. Thus, when the gaseous discharge lamp is initially turned on
while in a cool state, the ballast will provide sufficient voltage
to strike an arc in the lamp. After the lamp has been operating for
a length of time, it heats up and should a power interruption
occur, a return of power to the line of the hot lamp will require a
greater striking potential than the ballast is capable of
providing. The lamp will therefore not immediately strike and may
require as much as fifteen minutes to cool sufficiently before the
ballast voltage will restrike the arc. If this should occur in a
factory or office, a safety hazard may very well result. Similarly,
when used in highways the absence of sufficient lighting for a
length of time may contribute to the occurrence of accidents or
other resulting emergencies.
An additional problem which occurs when using gaseous discharge
lamps resides in the fact that once the arc is struck there is an
initial warmup of the gaseous discharge until the potential across
the lamp provides adequate lighting output.
To facilitate the use of gaseous discharge lamps it is desirable to
provide an emergency or auxiliary lighting circuit in conjunction
with the gaseous discharge lamp to provide illumination during the
off and warm-up periods of the lamp. While various circuits have
been suggested in the past for providing such emergency
illumination, such circuits have in general been relatively
complicated, expensive, inefficient, and have employed many
components.
Many of the circuits available in the prior art only provide
auxiliary lighting which will solve the first of the aforementioned
problems. Namely, the auxiliary lighting circuits will be only
turned on after a power interruption while the gaseous discharge
lamp is cooling off awaiting restriking by the ballast output
voltage. However, these prior art circuits will turn off as soon as
the gaseous discharge lamp has been restruck. Therefore, during the
period of time that the gaseous discharge lamp has not reached
sufficient illumination to provide normal desired lighting output,
the auxiliary circuit will not provide any assistance to compensate
for such lack of proper illumination.
Other known devices do provide auxiliary lighting which will
respond to both aforementioned problems. Namely, in addition to the
auxiliary lighting being turned on following a power interruption,
this auxiliary lighting will also remain on during the warm-up
period until the gaseous discharge lamp reaches the normal desired
illumination output level. However, most of these circuits make use
of relays involving a relay coil in series or in parallel with the
ballast output. This requires stringent manufacturing restrictions
on the design of the relay coil such that it will not have an
adverse effect on the gaseous discharge lamp wattage. Furthermore,
the use of relay coils necessarily involves an electromechanical
device which is not always reliable. In addition, these prior art
circuits generally require two switching devices wherein one of the
switching devices controls the turning on of the auxiliary lighting
during the initial warm-up period, while the second switching
device serves to disconnect the first switching device during power
interruption such that the auxiliary lighting will remain turned
on.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a
novel emergency or auxiliary lighting system for gaseous discharge
lamps which avoids the aforementioned problems of the prior art
devices.
Another object of the invention is to provide an emergency lighting
circuit for gaseous discharge lamps which does not contain relay
switches.
Yet another object of the invention is to provide an emergency
lighting system for gaseous discharge lamps which uses a single
switching element to provide auxiliary illumination both during
initial warmup of the gaseous discharge lamp as lamp as during the
cooling off period required after a power interruption of the
gaseous discharge lamp.
Still a further object of the invention is to provide an emergency
lighting system for gaseous discharge lamps which is relatively
inexpensive and uncomplicated as well as highly efficient.
These and other objects of the present invention will be apparent
from a reading of the following description and accompanying
drawings. In accordance with one aspect of the present invention an
emergency or auxiliary lighting circuit is provided in conjunction
with a gaseous discharge lamp which includes a single switch means
characterized by the absence of solenoid operated contacts. The
switch is biased in a normally closed position. A control circuit
is provided for the switch which operates in opposition to the bias
means. The output voltage of the control circuit is proportional to
the voltage across the lamp and thus increases as the lamp warms
up. As this output voltage reaches a predetermined value,
corresponding to the voltage across the gaseous discharge lame when
the lamp reaches the desired output illumination, the control
circuit dominates over the biasing means and opens the switch
means, thereby turning off the auxiliary light sourse. The control
circuit senses the high voltage output of the ballast which occurs
when power is restored after an interruption and the gaseous
discharge lamp is cooling off prior to being restruck by the
voltage output from the ballast. This insures that the auxiliary
light device will remain on during the cooling off period until the
gaseous discharge lamp is restruck. Immediately following the
restriking of the lamp, however, as the gaseous discharge lamp
again warms up to provide the desired illumination output, the
auxiliary lighting circuit will also remain on under control of the
biasing means.
In a preferred embodiment of the invention the switch means is a
reed switch controlled by an electromagnetic coil and includes a
permanent magnet biasing the reed switch into closed position. The
flux from the electromagnetic coil is fixed to operate in a
direction opposite to that of the magnetic field provided by the
permanent magnet.
In a second embodiment the switch is an SCR having its gate
positively biased and having the voltage across the gaseous
discharge lamp transformer coupled, rectified and inverted to serve
as a negative control voltage acting in opposition to the positive
bias on the gate. A unidirectional switch is used as the high
voltage sensing device which overrides the negative control
voltage, thereby permitting the biasing voltage to hold an SCR in a
conducting state until after the striking of the arc in the gaseous
discharge lamp has occurred.
BRIEF DESCRIPTION OF THE DRAWINGS
This invention will be more clearly understood by referring to the
drawings wherein similar reference characters denote similar
elements throughout the views, and in which:
FIG. 1 is a graph illustrating the voltage across the gaseous
discharge lamp as a function of time.
FIG. 2 shows the on and off state of the auxiliary lamp device as a
function of time.
FIG. 3 is a schematic diagram illustrating one embodiment of the
emergency lighting system in accordance with the present
invention.
FIG. 4 is a schematic diagram of an emergency lighting system in
accordance with another embodiment of the present invention.
DESCRIPTION OF THE INVENTION
FIG. 1 illustrates a graph of the lamp voltage plotted as a
function of time which will be useful in understanding the present
invention. It is assumed, by way of example, that the circuit
contains a gaseous discharge lamp with a ballast providing voltage
there-across with a maximum voltage of approximately 250 volts.
When the lamp is initially turned on at time T1, the ballast
provides 250 volts to strike an arc in the cold lamp. The ballast
provides its full output voltage at this point which, in turn,
ionizes or breaks down the arc, causing it to strike. As soon as
the arc is struck the voltage across the lamp drops to
approximately 25 volts. As the arc heats up between times T1 and
T2, there is a relatively low light output as the voltage increases
across the lamp to approximately 85-90 volts at the time T2. At
this point there is a minimum acceptable light output from the
lamp. However, the light intensity, as well as the voltage,
continues increasing until time T3 at which time the normal
operating condition for the lamp is reached. At time T3 the voltage
across the lamp is approximately 135 volts with the lamp in a
normal fully on condition.
Assume next that a power interruption occurs at time T4. This
interruption may result from an opening of the power source by
tripping of a circuit breaker due to momentary overloading
conditions, etc. Assume further that the power is turned on again
at T5 following the interruption which occurred at T4. Immediately
the ballast potential rises to 250 volts. The lamp however does not
light because it is still in a hot condition and its hot striking
potential is higher than 250 volts. The unlit lamp therefore begins
to cool and after a certain length of time, until T6, the lamp has
cooled sufficiently for the 250 volts provided from the ballast to
restrike the arc. When this occurs, the operation of the lamp
repeats similarly to that described for a cold start wherein the
time interval from T6 to T7 reflects the warmup time required for
the lamp voltage to rise to approximately 85 volts. During the time
interval from T7 to T8, there is minimal desired or acceptable
light output until the normal operating condition for the lamp is
reached.
As is evident from the graph of FIG. 1, during the time interval
between T1 and T2, although the lamp is struck, there is in fact
insufficient light output from the lamp. Furthermore, following a
power interruption such as that illustrated during the time
interval between T5 to T6, the lamp will remain totally in an off
state without providing any light. Thereafter, again, an
insufficient illumination will be provided by this lamp between
times T6 and T7.
In order to alleviate the problem resulting from the use of gaseous
discharge lamps it would be beneficial and it is within the scope
of this invention to provide an auxiliary lighting system which is
capable of turning on during the time following a power
interruption. As is generally well known in the art, an
incandescent lamp has been typically used for auxiliary systems,
since such lamps can be turned on immediately without any delay. It
is therefore necessary to provide a switch for use in conjunction
with the incandescent lamp in a configuration wherein the switch
operates during the required time periods. Referring now to FIG. 2,
it can be seen that it is necessary that the switch operate in an
"on" state between times T1 and T2 during the warmup time of the
gaseous discharge lamp when there is insufficient light output.
Similarly, between times T5 and T6 following power interruption the
incandescent lamp should remain "on" and should continue in this on
state until time T7 when the gaseous discharge lamp has reached its
minimal acceptable light output and whereupon the incandescent lamp
can then turn off.
Referring to FIG. 3, a schematic diagram is shown illustrating one
embodiment of the emergency lighting system in accordance with the
present invention. The main lighting system includes a gaseous
discharge or arc lamp 10 connected to the output terminals of a
ballast 12 which is, in turn, supplied with a source of power from
an AC (alternating current) supply 14. The ballast need not be of
any special type such as a lead or lag type ballast device, but any
standard ballast can be used. The voltage across the gaseous
discharge is also placed across a rectifier 16 which is shown by
way of example as a diode bridge rectifier. Capacitor 18 in series
with the rectifier 16 acts as a voltage limiting device. While the
diode bridge rectifier has been shown, it is to be understood that
other types of devices coming within the scope of this invention
may be used, such as, for example, a transformer with a pair of
appropriately poled diodes in its secondary circuit.
The output from the rectifier is applied to the electromagnetic
coil 20 of a reed switch shown generally at 22. Capacitor 24 is
connected in paralled relationship with respect to the rectifier
output to filter the rectifier output.
One contact of the reed switch 22 is connected to the gate
electrode of triac 30. A triac, as is well known, is an alternating
current semiconductor controlled switch having a single control or
gate electrode and a proper signal when applied to the gate causes
the triac to conduct current. As long as the signal is present
feeding the gate, the triac will remain in a conducting condition.
A resistor 32 is connected in series with the gate of the triac and
limits the gate current to a safe value.
The auxiliary lamp 34 is connected in series with the triac 30 to
one side of the AC supply. Thus, when the triac is in a conductive
condition, the auxiliary lamp will be turned on. This condition
will exist whenever the reed switch is closed.
The reed switch 22, as is well known, usually contains two opposing
flat reeds 20A and 20B of magnetic material which are supported as
cantilevers with their free ends overlapping and separated by a
small gap. Surrounding the reeds 20A and 20B is the electromagnetic
coil 20 so placed that the magnetic field of the coil encloses the
reeds. When the coil 20 is energised, its magnetic flux pulls the
reeds 20A and 20B together bringing them into contact and
completing the circuit to the gate of the triac 30. The flux can be
in either direction but must be of sufficient magnitude to cause
the reeds to close. As shown in FIG. 3, a permanent magnet 36 is
located adjacent to the reed switch structure and provides a fixed
magnetic bias, thereby keeping the reed switch in a closed
condition. Thus, in the presence of low voltage across the arc lamp
terminals, the reed switch will remain in a closed condition and
the auxiliary lamp will be turned on. The electromagnetic coil 20
is in such a position, and is connected in such a direction, that
the magnetic field produced by it opposes the permanent bias magnet
field.
In operation, during the time period from T1 to T2, as the voltage
is increasing across the gaseous discharge lamp, the
electromagnetic coil 20 is energized and produces a flux opposing
the permanent bias magnet field. However, voltage is low and the
resulting electromagnetic field is insufficient to overcome the
field of the permanent magnet. Therefore, the reeds in the switch
remain closed and the auxiliary lamp remain, on. At time T2,
however, a sufficient voltage is present across the gaseous
discharge lamp to cause the coil 20 to produce a field which
balances the field produced by the permanent bias magnet 36, but
which is in an opposite direction. As a result, there is no net
magnetic field enclosing the reeds and the contacts of the reed
switch 22 open. From time T2 to T3, the voltage continues to
increase across the gaseous discharge lamp and the magnetic field
from the electromagnetic coil 20 continues to increase in a
direction opposite to that of the permanent bias magnet. However,
the total net field produced in a single direction acting upon the
reed switch contacts is insufficient to cause them to close. The
reed switch therefore remains open and the auxiliary lamp remains
in an "off" condition. This phenonenon continues from time T3 to T4
wherein the electromagnetic field remains constant but yet
sufficient to cause the reed switch to close.
At time, T4, we can assume for purposes of illustration that the
power is interrupted and the electromagnetic field produced by the
coil 20 will be reduced to zero, permitting the permanent bias
magnet to take over closing the reed switch. However, at T5, if the
power is restored, although the gaseous discharge lamp remains off,
the ballast voltage is relatively high (250 volts), and as a
result, the field produced by the electromagnetic coil 20 is high
enough to overcome the permanent bias magnet field and to reclose
the reed switch. It is to be remembered that the reed switch will
close with a flux in either direction. Thus, even though the flux
in this case is opposite to that of the flux from the permanent
bias magnet, the reed switch responds to a sufficient difference in
the magnetic flux and will close in response thereto. The reed
switch remains closed and the triac conducts current from time T5
until time T6 when the gaseous discharge lamp is restruck. At that
time, the voltage across the gaseous discharge lamp is suddenly
reduced to a very low value (30 volts). The field from the
electromagnetic coil 20 is therefore also reduced to a low value.
However, at this time the flux from the permanent bias magnet
controls and the reed switch will remain closed under the influence
of the permanent bias magnet. As the control of the switch
transfers from the flux in one direction from the electromagnetic
coil to the flux in opposite direction from the permanent bias
magnet, a flicker of the incandescent lamp 34 may occur. The slight
flicker however can be reduced by increasing the size of the filter
capacitor 24 thereby increasing its energy storage capability to
prevent noticeable flicker of the auxiliary lamp 34. The auxiliary
lamp remains in its on state until time T7 when the gaseous
discharge lamp has sufficient voltage across it to provide
acceptable illumination.
Although the circuit has been shown including the triac 30, it is
to be understood that the triac 30 may be eliminated and the
current flowing through the reed switch may feed directly to the
auxiliary lamp. However, because of the restricted current carried
by the reed switch 22, this could restrict the voltage of the
auxiliary lamp 34. It is nevertheless seen however, that a single
switch element, namely the reed switch 22, can be used to detect
both the conditions of high voltage and low voltage across the
gaseous discharge lamp which occur during its operation.
Referring now to FIG. 4, there is shown another embodiment of this
invention where the gaseous discharge lamp 40 is placed across the
output of the ballast 42 which is, in turn, energized by an AC
source 44. Connected to the output of the gaseous discharge lamp 40
is a transformer 46 having a primary 46a and a secondary 46b with
appropriately poled diodes 48, 50 connected to the secondary. If
desired, a current limiting resistor 47 may be connected in series
with the primary 46a. Although a transformer is shown it is to be
understood that a rectifier diode bridge may also be used as well
as an auxiliary winding on the ballast to monitor the lamp voltage.
The ends of the secondary of the transformer are interconnected at
terminal 52 and the output is connected through limiting resistor
54 to one side of capacitor 56. The other side of capacitor 56 is
connected to a tapped mid-point 58 of the secondary of the
transformer 46. Thus, the voltage at point 60 will be negative with
respect to the voltage at point, 62. A resistor 64 is connected to
the resistor 54 and to the capacitor 56 to filter the output from
the diodes 48 and 50. The magnitude of the voltage across the
capacitor 56 will be proportional to the voltage across the gaseous
discharge lamp, but will be a negative voltage.
The AC source 44 is also connected across opposite terminals of a
rectifier containing a diode bridge arrangement 66. The opposite
arms of the diode bridge are connected to a series circuit
containing a quick starting auxiliary lamp 68 in series with the
anode and cathode of an SCR 70. The gate of the SCR is connected
through a resistor 72 to a positive voltage from the diode bridge
66. It is also coupled to the negative voltage signal from the
capacitor 56 through a resistor 74 and an additional capacitor 76.
A unidirectional switch 78 is also connected in parallel across the
capacitor 56 and the resistor 64 and receives the negative voltage
therefrom.
As is well known in the art, the unidirectional switch 78 operates
such that for voltages lower than its breakdown voltage, the switch
does not conduct and thus for all practical purposes is not seen by
the circuit. When the breakdown voltage of the switch 78 is
reached, the device goes into an avalanche mode of operation and
can support only a relatively low voltage across it. When it is in
the avalanche mode of operation, should current through the device
drop below a specified holding current, the device reverts back to
its non-conducting state.
In operation, from the time T1 to T2, when the gaseous discharge
lamp is in the warmup stage, there is a relatively low voltage
across the lamp. Thus, the magnitude of the negative voltage
feeding the gate of SCR 70 will be less than the positive bias
voltage from the resistor 72 and the SCR will be in a conducting
state, thereby keeping the auxiliary lamp 68 on. As the voltage
across the gaseous discharge lamp continues to increase between
time T2 and T3, the magnitude of the negative voltage feeding the
gate of SCR 70 increases greater than the positive bias from the
resistor 72 and will turn off the SCR 70, thereby extinguishing the
auxiliary lamp 68. The auxiliary lamp 68 will remain off between
times T3 and T4 or until a power interruption occurs.
At time T4, when the power is momentarily interrupted, the entire
system is in off or a dark state. However, at time T5 when the
power is restored, the gaseous discharge lamp will not restrike
immediately, but there is a very high voltage (approximately 250
volts) across it. Normally, the high voltage should cause the
negative voltage feeding the gate of the SCR to be much greater
than the positive bias voltage and should turn the SCR off.
However, the voltage from the transformer is now greater than the
breakdown voltage of the unidirectional switch 78 and causes it to
breakdown and go into its avalanche mode of operation whereby only
a low voltage can be supported across it. Thus, there will only be
a low negative voltage feeding the gate of the SCR 70 and the
positive bias voltage from resistor 72 will in fact control the
SCR. This keeps the SCR in a conducting state and causes auxiliary
lamp 68 to remain on.
The various resistors in the circuit are set at specific values to
proportionately relate the voltage across the gaseous discharge
lamp to appropriate voltages for the various circuit elements such
as the SCR 70 and the unidirectional switch device 78. It is to be
noted, while generally SCR circuits are triggered by a pulse, the
present circuit does not use a trigger pulse but rather a constant
DC bias on the gate. When using a trigger pulse the appropriate
timing of the trigger pulse is of critical importance. In the
present case, however, such timing is not necessary since the
constant DC bias on the gate no longer makes the timing a critical
factor. When the auxiliary light is no longer required, the DC bias
is simply removed and the lamp extinguishes.
It is therefore seen that in the present invention a single switch
element is used to detect both the very low voltage during the
warmup period of the gas discharge lamp to turn the auxiliary lamp
on, as well as the very high voltage after a power interruption to
turn the auxiliary lamp on. No electromechanical relays are
employed and no additional parallel circuitry is necessary to
shortout or disconnect the main switch element by means of a
secondary switching element. In addition, no special ballasts are
required for operation in connection with the circuit. In each
case, the single switching element is biased to keep the suxiliary
lamp on and the gaseous discharge lamp voltage is used to provide a
voltage opposite to the biasing voltage to turn off the auxiliary
lamp during normal operation of the gaseous discharge lamp.
While the present invention has been described with reference to
particular embodiments thereof, it will be understood that numerous
modifications may be made by those skilled in the art without
actually departing from the scope of the invention.
* * * * *