US2729769A - Starting and operating circuits for fluorescent lamps - Google Patents

Description

Jan. 3, 1956 w, s, HAMlLTON 2,729,769

STARTING AND OPERATING CIRCUITS FOR FLUORESCENT LAMPS 2 Sheets-Sheet 1 Original Filed June 6,' 1951 INVENTOR! )Vi/b'am 5. A. Ham/Won ATTORNEY.

1956 w. s. H. HAMILTON 2,729,769

STARTING AND OPERATING CIRCUITS FOR FLUORESCENT LAMPS Original Filed June 6, 1951 2 Sheets-Sheet 2 WM/[am J. H Ham/W017, 431" ATTORNEY United States Patent "cc .,,,,,,f,;??;122

STARTING AND OPERATING CIRCUITS FOR FLUORESCENT LAMPS William S. H. Hamilton, Larchmont, N. Y.

Original application June 6, 1951, Serial No. 230,185. Divided and this application February 18, 1953, Serial No. 337,487

4 Claims. (Cl. 315-100) This application is a division of my prior application Serial No. 230,185, filed June 6, 1951.

This invention relates to starting and operating circults for fluorescent lamps, and particularly for alternating current and direct current fluorescent lamps which are more or less diflicult to start and require an inductive kick to start them.

The primary object of the present invention is to provide in a starting circuit wherein the preheating circuit is interrupted with unusual rapidity so as to provide an extremely high voltage impulse for starting the lamp, a cut-out or lock-out mechanism which is reliable and effective, to prevent further operation of the starting mechanism in case the lamp fails to start after a reasonable number of firing attempts have been made.

A further object of my invention is to provide a starting and cut-out system having a rapid response in restarting a lamp which has been switched out of operation.

Another object of the invention is to provide a starting and cut-out circuit which can be embodied in the usual starter container and which can be reversed in its socket.

A still further object of the invention is to provide a starting and cut-out system which will effectively start lamps at low temperatures, such for example as 0 F. and below.

In the accompanying drawings, forming part of this specification,

Figs. 1, 2 and 3 are diagrammatic views of diflereht forms of circuits for D. C. or A. 0-D. C. use and which employ a starter embodying the quick restarter and the lock out means of the character described.

Fig. 4 is a diagrammatic view of a circuit similar to that of Fig. 3 but adapted solely for A. C. use.

Fig. 5 is a diagrammatic view of another circuit for use on A. C., in which special provision for starting, at cold temperatures, such as 0 F. and below, is provided.

Figs. 6, 7 and 8 are schematic obverse, reverse and side elevational views of a starter embodying the quick restarter and the lock-out means and showing only the basic features of the starter and omitting the wiring connections.

In the schematic showing of the starters A in Figs. 6, 7 and 8, A designates an insulated base carrying contact pins 1, 2, 3, 4, and an insulated upright A", which in practice are enclosed in a housing or casing, not shown. On this upright are mounted a relay coil C, a spring retracted relay armature switch S1, two thermally responsive or thermostatic switches S2, S3 and heaters H1 and H2 for the switches, which are connected in the manner shown in the disclosed circuits employing the switch S3 and its heater H2 for a lock-out action, which switch and its'heater may be omitted from a starter designed for general use but used most commonly in circuits not employing a lock-out action, the inclusion or omission of such switch and its heater-involving merely changes in the wiring arrangements.

The switches, which are of self-closing type and normally closed are not physically coupled for conjoint action, but are independently movable, switch S1 under action of the coil C and switches S2, S3, in response to their heaters, with the exception that a quick restarter in the form of a mechanical interlocking connection (controlled by the armature actuated by the coil and generally designated MIC in Figs. 1 to 5) is interposed between switches 51' and S2, and is provided for holding switch S2 open together with switch S1 under the electromagnetic attraction of the coil C when the latter is energized. Coil C when energized acts only to pull switch S1 open after switch S2 has been thermally opened, and in such action moves the interlocking connection into position to hold switch S2 in its open position.

This connection comprises an insulated arm A4 carried by the armature switch S1 which is free from connection with and normally allows full opening movement of switch S2, but which moves into engagement at its free end with switch S2 when switch S1 is opened to hold switch S2 open, this holding action being due to the magnetic attraction of the coil. A condenser C omitted in Figs. 6, 7 and 8, but shown in the disclosed circuits, is included in the starter to reduce the arcing at the contacts in accordance with customary practice. A stop A5 is provided to limit the travel of thermal switch S3 when heated.

In the drawings I have shown various types of circuits for fluorescent lamps in which the starter A, in the forms disclosed, or by simple changes in the wiring arrangements of parts, may be used to secure prompt and reliable starting and rapid restarting actions of a lamp in good order and which may be used to secure a lockout action to avoid undue repetitive starting attempts if the lamp is defective or has reached the end of its useful life period.

Referring to Fig. 1, showing a circuit for operation of D. Clamps, 5 designates the lamp having a filamentary electrode 6 and a cooperating electrode 7, and 8b and 9b designate the input and output line leads or conductors extending from the positive and negative line terminals to the starter terminals 1 and 3. The input and output portions of the circuit include an inductive reactor R and ballast lamp BL located in the conductor 8b ahead of the terminal 1, a conductor 10b leading from the starter terminal 2 to the input end of the filament 6, a conductor 11b leading from the output end of the filament 6 to the starter terminal 4, and a conductor 8b at a point between the ballast lamp BL and starter terminal 1 to the electrode 7 which'is shown as being shortcircuited.

Between the terminals 1 and 2 of the starter are serially arranged a portion or input part of the starter switch circuits which includes the conductors 12b, 13b, a magnetically operated switch S1, and a thermostatic or thermally responsive cut-out switch S3. Extending across this part of the starter circuit between conductors 12b, 13b is a heater H2 for the switch and an arc suppressing condenser C. Heater H1 may be an open coil heater of 5-10 ohms resistance, while heater H2 is preferably 0 I a carbon rod resistor of approximately 30,00050,000 ohms. With the arrangement described the switch S3 and its heater H2 are connected across the lamp electrodes so as to be responsive under certain conditions to unduly prolonged application of abnormal voltages acrossthe electrodes when the lamp, after a number of attempts, refuses to fire, to cause said switch S3 to open and stop the operation of the starter.

Another portion or output part of the starter switch circuits includes the conductors 15b, 15b, the thermostatic switch S2, and a magnetic coil or winding C which controls the magnetic switch S1. Switch S2 is normally closed and, when closed, connects the conductors 15b, 15b in series with th e conductors 11b and 9b to complete the output portion pf the preheating circuit, during 2 which it shunts the coil out of this circuit and renders the coil inactive. The parts just described as forming the output portion of the Starter preheating circuit are connected in series with the input portion of the starter preheating circuit when all the switches are closed, ready for preheating the filament when the line circuit is closed. Conductors 8b, 8b, the lamp electrodes, the gas of the lamp, conductor 11 b, coil C and conductor 9b form the component parts of the lamp operating circuit of the lamp.

In starting, preheating current flows from the positive side of the line,- through the reactor, through the ballast lamp to terminal 1 of the starter, through thermal switch S3, through heater H1, through switch S1, to terminal 2 of the starter, to and through the negative filament 6 of the fluorescent lamp, thence to terminal 4 of the starter, through thermal switch S2 to terminal 3 of the starter, and thence to the negative side of the line. During this time thermal switch S2 keeps coil C short circuited, and heater H2 is effectively short circuited due to its being much higher in resistance than heater H1.

It will be noted in this circuit the ballast lamp is in the circuit during preheating and regulates the preheating current, as well as the operating current after the lamp has fired.

Preheating current continues to flow until heater H1 heats up sufficiently to cause the thermal switch S2 to open its contacts. This cuts coil C into the circuit, which opens switch S1 by magnetic action, thus breaking the preheating circuit rapidly, and causing the lamp if it is a good one to fire.

After the lamp fires, operating current flows from the positive side of the line, through the reactor and ballast lamp to the positive filament 7 of the fluorescent lamp, through the gas in the lamp itself to the negative filament 6, thence to terminal 4 of the starter, through relay coil C to terminal 3 of the starter, and thence to the negative side of the line. The current flowing through coil C holds switch S1 open by magnetic action and thermal switch S2 is held open by the mechanical interlock MIC.

During normal operation, heater H2 is connected across the fluorescent lamp itself, but the voltage drop across the lamp is not suflicient to cause it to heat up sufiiciently to cause thermal element S3 to open its contacts.

If the line circuit is opened, switches S1 and S2 reclose immediately, so that the starter is ready for another starting action as soon as the line circuit is reclosed.

Should the lamp not fire on the first attempt however, it will make several other attempts to fire, and each time that it does, the voltage applied across heater H2 will be greater with switch S1 open while the lamp has not fired than if it had fired, this voltage being substantially line voltage, instead of lamp voltage. After a number of attempts to start, heater H2 will be heated sufficiently to cause the thermal switch S3 to open its contacts. This interrupts the circuit to the lamp, except for the very small amount of current flowing through heater H2, which will be substantially equal to line voltage being applied across heater H2, and which will be ample to hold switch S3 in its open position and cut out the starter although switches S1 and S2 will reclose.

Under this condition, an appreciable time delay will be required (several minutes), when the circuit is opened for heater H2 to cool ofl suflicie'ntly to allow the contacts of thermal switch S3 to reclose, so that the starter is ready to restart the lamp.

However, this delay can be avoided by replacing the defective fluorescent lamp andthe starter at the same time. The starter can then be used in some other circuit later, as it will not have been damaged in any way.

The circuit shown in Fig. 2 is generally similar to that of Fig. 1 except that conductor 80' leading to the cpeii-eircnited electrode 7 is directly connected with conductor 140, that a current limiting resistance R1 is provided in conductor 1%, and that a conductor 17, connecting conductor 8c with starter terminal 1, is connected directly to the reactor ahead of the ballast lamp.

Thus while this circuit employs a multiple action lockout feature, the ballast lamp is not in the circuit during preheating, which allows the preheating current to: be adjusted separately by resistor R1. Also in order to get the heater H2 across the lamp voltage after the lamp has fired, it is necessary to use a special terminal, as indicated at 4'.

In this circuit when starting, preheating current flows from the positive side of the line through the reactor, to terminal 1 of the starter, through thermal switch S3, through heater Hi, through switch S1, to terminal 2 of the starter, through the resistor R1, through the negative filament 6 of the fluorescent lamp, to terminal 4 of the starter through thermal switch S2, to terminal 3 of the starter, and thence to the negative side of the line. A connection is also made from the low side of the ballast lamp to terminal 4 of the starter and throughconductor tie to the positive filament. 7 of the fluorescent lamp, which in this case is not short-circuited. In the above described starting action, heater H2 is eflectively short-circuited by switch S1, heater H1 and the switch S3.

Preheating current continues to flow' until heater H1 heats thermal switch S2 sufiiciently to cause it to open its contacts. When this occurs, coil C is energized by preheating current flowing through negative filament 6 of the lamp, causing it to open switch S1 and break the preheating circuit rapidly, thus firing the lamp, if in normal condition. After the lamp has fired, coil C is kept energized by current flowing through the lamp.

The operating circuit is from the positive side of the line, through the reactor, through the ballast lamp, to the positive filament 7 of the fluorescent lamp, through the gas in the lamp to the negative filament 6, thence to terminal 4 of the starter, through coil C to terminal 3 of the starter, and thence to the negative side of the line.

Heater H2 being connected between terminals 2 and i of the starter, has only the voltage drop across the fluorescent lamp itself applied to it, and as in the case of Fig. 4 this voltage does not heat heater H2 enough to cause thermal switch S3 to open its contacts.

This modified form of starter cannot be changed in its position in the socket due to the special 5-contact base, so that there is no danger of interchanging any of the above connections.

If the line circuit is opened, switches S1 and S2 immediately reclose and the starter is ready for another starting action.

If, however, the lamp does not fire on the first attempt, it will make several other attempts, and each time that switch S1 opens and the lamp does: not fire, substantially line voltage will be applied to heater H2, so that it will heat up and cause thermal switch S3 to open. When switch S3 opens, current is removed from the lamp, except for the small amount of current that flows through heater H2 which is of high resistance. Switches S1 and S2 reclose, but as long as the line circuit is closed heater H2 holds switch S3 open.

With this condition, an appreciable time delay will be required (several minutes) when the line circuit is opened for heater H2 to cool oif suflicie'ntly to allow thermal switch S3 to reclose its contacts.

This time delay can be avoided, however, by replacing the defective fluorescent lamp and the starter at the same time. The starter can then be used in some other circuit later, as it will not have been damaged in any way.

Lamps used in D. C. circuits having two filamentary electrodes, only one of which is preheated to start the lamp, may have the positive filament of the lamp short annexes circuited as in Fig. 4, or open-circuited as in Fig. 5, depending on the type of lamp and other characteristics of the circuit.

The circuit shown in Fig. 3 varies from'those shown in Figs. 1 and 2, in that one line conductor'sd is connected by a conductor 82 with one terminal of electrode 7, the other terminal of which is connected by a conductor d with starter terminal 2, while a conductor 10:: containing a current limiting resistance R1, connects the starter terminal 1 with the input terminal of electrode 6, the arrangement of the switches S1, S2 and S3 and coacting parts of the starter being otherwise the same as that shown in Fig. 1.

This circuit is suitable for operating fluorescent lamps on either A. C. or D. C. When used on D. C., it has the disadvantage of having the ballast lamp in the circuit during starting. When used on A. C., the ballast lamp and resistor R1 can be omitted if the other re quirements of the circuit permit it.

In this circuit when starting, preheating current flows from one side of the line through the reactor, through th ballast lamp (if used), through filament 7 of the fluorescent lamp to terminal 2 of the starter, thence through switch S1, heater H1 and thermal switch S3 to terminal 1 of the starter, and through resistance R1 and filament 6 of the fluorescent lamp to'terminal 4 of the starter, through thermal switch S2 to terminal 3 of the starter, and thence to the other side of the line. In this connection it should be borne in mind that on A. C. circuits, resistance R1 might be zero and there might not be a ballast lamp, but the circuit path would be the same.

As in the preceding circuits, preheating current continues to flow until heater H1 heats up sufficiently to cause thermal switch S2 to open its contacts, which cuts coil C into the preheating circuit and causes switch S1 to open magnetically, thus breaking the preheating circuit rapidly and causing the lamp to fire if it is in good condition. While the lamp is operating (or running) normally, coil C is kept energized by current flowing through the lamp and holds switch S1 open by magnetic action and thermal switch S2 open by means of the mechanical interlock MIC.

While the lamp is operating normally, heater H2 is connected across the lamp voltage, which is not enough to heat it sufiiciently to cause the thermal switch S3 to open.

The operating circuit is from one side of the line, through the reactor, through the ballast lamp (if used), to filament 7 of the fluorescent lamp, through the gas of the lamp itself to the other filament 6, thence to terminal 4 of the starter, through coil C to terminal 3 of the starter and back to the other side of the line. If while the lamp is operating normally, the line circuit is opened, switches S1 and S2 will reclose immediately, ready for another starting action. V

If the lamp does not start, however, the starter will make successive attempts to start it, and each time switch S1 opens and the lamp does not fire, essentially line voltage is applied across heater H2. The repeated application of this higher voltage causes. heater H2 to heat up sufficiently to cause thermal switch S3 to open, which cuts off all current to the lamp except the small amount passing through heater H2 which is of high resistance. Switches S1 and S2 reclose under this condition.

As in the other circuits employing the multiple action lockout feature and appreciable time delay (several minutes) will be required for heater H2 to cool ofi sufficiently to allow thermal switch S3 to reclose after'the line circuit is opened. However, this time delay can be avoided by replacing the defective fluorescent lamp and the starter at the same time. The starter can then be used in some other circuit, as it will not have been damaged in any way.'

Fig. 4 shows an operating circuit for short A. C. lamps and having the multiple lock-out feature and which is substantially the same as the circuit shown in Fig. 3 with the exception of the omission of all features pertaining to D. C. operation. The operation is the same as that of circuit of Fig. 3 and hence need not be described in detail.

An advantage of this circuit is that it can be used satisfactorily for relatively short A. C. fluorescent lamps that do not have suificient voltage applied to them (particular ly when they have not fired) to cause current flow at low values after thermal switch S3 has opened its contacts. With the connections shown, line voltage is still applied across the fluorescent lamp itself, even after thermal switch S3 has opened its contacts.

Fig. 5 shows an operating circuit for A. C. fluorescent lamps using a starter with the lockout construction in which the parts are so arranged that the preheating or starting current and the operating current may be separately adjusted. Thisis desirable in the case of lamps that are to fire and operate at low temperatures (0 F. and below). The starter here shown is generally similar to that shown in Figs. 1, 3 and 4, with a certain change in construction, and with certain changes in the circuit. As shown, the switches S1, S2 and conducting connections 13b, 12b, 15b, 15b, and 14b are similarly arranged to correspondingly functioning parts shown in Figs. 1 and 3, but there are changes and additions in the circuit connections.

Conductors 9b and 11b are here arranged as in Figs. 1, 2, 3 and 4, but a conductor 8m extends from line terminal B to one terminal of electrode 7, having its opposite terminal connected to starter terminal 2, while a conductor 10f connects starter terminal 1 with the input terminal of electrode 6. Resistance R1 is used in this circuit to control the preheating current, and the ballast lamp BL and a resistance R2 are provided in a connection across the starter terminals 3, 4 to control the operating current. A resistance R3 is also added in series with the coil C in order to have it operate properly across the increased voltage drop of resistance R2 and the ballast lamp after the lamp is started into operation.

In this circuit when starting, preheating current flows from terminal B of the line through the reactor, through filament 7 of the fluorescent lamp to terminal 2 of the starter, through switch S1, through heater H1, through switch S3, to terminal 1 of the starter, through resistance R1, through the filament 6 of the fluorescent lamp to terminal 4 of the starter, through the contacts of thermal switch S2 to terminal 3 of the starter and thence back to the other line terminal line W. During the starting action, thermal switch S2 contacts short-circuit the relaycoil C and resistance R3, as well as the ballast lamp and resistance R2.

The flow of preheating current continues until heater H1 has heated thermal switch S2 sufliciently to cause it to open its contacts. When this occurs, coil C is cut into the preheating circuit, which opens contacts S1 by magnetic action, breaking the preheating currentrapidly and causing the lamp if in good condition to fire.

After the lamp has fired, operating current flows from one side B of the line through the reactor, to filament7 of the fluorescent lamp, through the gas in the lamp itself to the other filament 6, thence to terminal 4 of the starter, where it divides, part flowing through coil C and resistance R3 to terminal 3 of the starter, and the other part through the ballast lamp and resistance R2 connected across the same terminals of the starter, thence to the other side W of the line. Ballast lamp BL and resistance R2 can be selected to provide the proper operating (running current) thus permitting the reactor to be made of less reactance than would usually be the case, in order to allow more current to flow during preheating and make starting of the fluorescent lamp easier at low temperatures, such as 0 F. and below.

As in the other circuits previouslydescribed, if the line circuit is opened while the lamp is operating normally, coil C of the relay is tie-energized, allowing switches S1 and S2 to reclose immediately ready for another starting action.

During a normal starting action, heater H2 is efiectively short-circuited and takes no part in it. After the lamp has fired,- heater H2 is connected across lamp voltage but this does not produce enough heat in it to cause thermal switch S3 to open its contacts.

It the lampdoes not fire on the first attempt, however, the starter will make a number of other attempts to do so. Each time that switch S1 is opened with the lamp not having fired, essentially line voltage is impressed across the heater H2, finally heating it sufiiciently to cause thermal switch S3 to open its contacts.

In the open position of thermal switch S3, heater H2 is practically across line voltage and this opens the circuit through the lamp,- except for" the small amount of current passing through heater H2. Switches S1 and S2 reclose under this condition. Line voltage is applied across the lam terminals in the cut-out position.

As in the case of the other circuits previously described having the multiple action lockout feature, an appreciable time delay will be involved after the line circuit is opened for heater H2 to cool oil sufficiently to allow thermal switch S3 to reclose its contacts.

This time delay can be avoided by replacing the defective fluorescent lamp and the starter at the same time as has been previously described.

This circuit of Fig.- 5, as stated, has the desirable feature that the starting current may be adjusted to a higher value than normal in order to effect starting at low temperatures, and that the reactor R may be of a lower reactance than that which would normally be used in the circuit when operated at room temperatures in order to secure this higher starting current.

The heater H2 for thermal switch S3 is shown in Figs. 1 and 4 as being connected directly across the lamp electrodes 6 and 7, while in Figs. 2, 3 and 5 heater H3 is connected across the electrodes 6 and 7 and the resistance R1 in series therewith. However, since the value of resistance R1 is low its presence does not affect to any appreciable extent the voltage impressed across heater H3, and it will be understood that the expression across the electrodes, as used in the appended claims, includes either of these circuit arrangements.

A starter embodying the present invention has the following two major advantages over prior starters, to wit, (1) The preheating orstarting circuit is broken rapidly by the opening of switch Si by magnetic means. This causes the reactor to give a higher inductive kick than that obtained from the slower opening of straight thermal or glow switch starters when used in the same circuits. The higher inductive kick not only makes the firing more certain, but will also effect the firing of lamps that might be discarded under the impression that they had reached the end of their useful life period. (2) In all normal operation of lamps, due to the switch S1 being held open magnetically by the coil C by the flow of current through the lamp, the switch will open immediately if the line circuit is opened, and in so doing allow switch S2 to also reclose, so that the starter is ready for another starting'action as soon as the line circuit is reclosed. This is not so in the case of a straight thermal starter, where it is necessary for the heater to cool cit before its contacts can reclose.

This ability of obtaining a quick resetting action of the parts to obtain an immediate restart applies,- of course, to the starters used with the lock-out feature and when the starter is used with a good lamp. In the case of the use of a starter having the lock-out feature, however, the thermal units used for the lock-out action if they come into action take an appreciable length of time (several minutes) to cool off before restarting action can again take place. However, this delay can be avoided, as pre- 8 viously pointedout,- when applying a new lamp in place of the defective lamp, by removing the staiter which has been in use and applying a new starter, in which case the starter removed may be used as soon as it cools off in some other circuit.

From the foregoing description, taken in connection with the drawings, the construction and operation of the starter and various circuits disclosed will be readily understood without a further and extended description, and it will be seen that the invention provides a starter of simple and economical type which facilitates and renders easier the starting of hard starting lamps, and one which, if desired, provides means for locking out the starter from continuous or undesired repeating actions to prevent damage to the starter or other components of the circuit inthe case of a defective lamp, or a lamp which has reached the end of its useful life. While the constructions shown for these purposes are preferred, it is to be understood that they are merely exemplificative, and that changes in the form, construction and arrange ment of parts, falling within the scope of the appended claims, may be made Without departing from the spirit of the invention;

Having thus described my invention 1 claim:

1. In a system for starting and operating electric discharge devices comprising a gaseous electric discharge device of the low pressure type having two electrodes at least one of which is constructed to receive preheating current, a supply circuit, a normally closed thermally responsive shunting switch having an operating heater, a normally closed electromagnetic starting switch having an operating winding, means including an inductive reactance device and the winding of said starting switch for connecting said electrodes to said supply circuit, a preheating circuit capable of producing firing temperature electrode heating, said circuit extending from one side of a voltage source to the opposite side of said source and including in series connection said inductive reactance device and the heater for said shunting switch and at least one of said electrodes and said starting and shunting switches, said shunting switch being connected in shunt with the winding of said starting switch so that the opening of said shunting switch causes the energization of said winding and the consequent opening of said starting switch thereby causing the discharge device to fire by an inductive voltage kick, said starting switch being connected in shunt with said electrodes, and mechanical means o'peratively interconnecting said starting and shunting switches to hold the shunting switch open after the heater therefor cools, the operating current of said discharge device continuing to energize said winding and hold both of said switches open during the operation of the discharge device, the combination with said system of a normally closed thermally responsive cut-out switch included in the said preheating circuit, and a heater therefor connected at all times across the electrodes of the discharge device.

2. In a system for starting and operating electric discharge devices as set forth in claim 1 in which the heater for the cut-out switch is connected across the electrodes of the discharge device and in parallel with a circuit including in series connection the starting and cut-out switches and the heater for the shunting switch so that when the c'ut-out switch opens the heater therefor is connected in series with the starting switch winding, the

said heater not allowing sufiicient current to flow to operate the startingswitc'h.

3. In a system'tor starting and operating electric discharge devices comprising a gaseous electric discharge device of the low pressure type having two electrodes constructed to receive preheating current, a supply circuit, a normally closed thermally responsive shunting switch having an operating heater; a normally closed electromagnetic starting switch having an operating winding, means including an inductive reactan'ce device and the "new.

winding of said starting switch for connecting said electrodes to said supply circuit, a preheating circuit capable of producing firing temperature electrode heating, said circuit extending from one side of a voltage source to the opposite side of said source and including in series connection said inductive reactance device and the heater for said shunting switch and said electrodes and said starting and shunting switches, said shunting switch being connected in shunt with the winding of said starting switch so that the opening of said shunting switch causes energization of said winding and the consequent opening of said starting switch thereby causing the discharge device to fire by an inductive voltage kick, said starting switch being connected in shunt with said electrodes, and mechanical means operatively connecting said starting and shunting switches to hold the shunting switch open after the heater therefor cools, the operating current of said discharge device continuing to energize said winding and hold both of said switches open during the operation of said discharge device, the combination with said system of a normally closed thermally responsive cut-out switch and a heater therefor, said cut-out switch being connected in that portion of the preheating circuit extending from one electrode through the heater for said shunting switch and thence through the starting switch to the opposite electrode, and said cut-out switch heater being connected at all times across said electrodes.

4. A system for starting and operating electric discharge devices as set forth in claim 3 in which the shunting switch is connected in shunt with a circuit including the winding of the starting switch and a current limiting resistance arranged in series connection, and a circuit is connected in shunt with said circuit which comprises a ballast lamp connected in series with a current controlling resistance.

References Cited in the file of this patent UNITED STATES PATENTS 2,339,051 Cates Jan. 11, 1944 2,341,520 Babb Feb. 15, 1944 2,438,557 Hehenkamp Mar. 30, 1948

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