US2341905A - Operating mechanism for discharge lamps - Google Patents

Description

Feb. 15, 1944. w. COOK 2,341,905

OPERATING MECHANISM FOR DISCHARGE LAMPS Filed 001;. 11, 1941 .76 c I as 42 47 I 36 48 as Inventor: Leonard W. Cook WW 5. His Attorney.

Patented Feb. 15, 1944 OPERATING MECHANISM FOR DISCHARGE LAMPS Leonard W. Cook, Stratford, Conn., assignor to General Electric Company, a corporation of New York Application October 11, 1941, Serial No. 414,655

7 Claims.

My invention relates to an operating mechanism for discharge lamps and more particularly to a control switch for starting and operating discharge lamps, for example, fluorescent lamps of the type now on the market.

Electric discharge lamps, such as fluorescent lamps, are formed with an elongated glass envelope containing a small quantity of mercury. the envelope being provided with filamentary electrodes at each end so that an arc discharge through the mercury vapor between the electrodes energizes a suitable phosphor coated on the inner wall of the envelope causing the lamp to light. The electrodes are usually coated with an electron emissive material to assist in striking and maintaining the arc. Such lamps are connected in circuit with a suitable ballast or reactor, together with a control switch, the arrangement being such that current passes through the filaments and the reactor to heat up the filaments to a temperature at which they become emissive; after a predetermined period of time, the circuit through the filaments is interrupted by the control switch so that the reactor provides a high voltage inductive surge of current across the filaments causing an arc to strike between them lighting the lamp. It is to a control switch of this type that my invention relates.

Control switches utilized in this manner in circuit with a fluorescent lamp have become known to the trade as starting switches or starters." For this reason, my control switch will be referred to hereafter as a "starting switch although it controls the operation of the lamp at other times than in starting, as will be manifest as the description proceeds.

In operating a fluorescent lamp of the type described, it is of paramount importance that the filamentary electrodes be heated a sufficeintly long period of time so that they reach a temperature at which they become fully emissive before the application of the high voltage surge in an attempt to start the lamp. If the high voltage is appled before the normal operating temperature of the filaments has been reached, part of the emissive coating on the filaments is likely to be sputtered off, greatly reducing the life period of the lamp. Moreover, if the filaments are too cold, the arc may not strike. My starting switch is one which closely controls the length of the period during which the filaments are heated and makes sure that they reach the proper temperature before the application of the high voltage surge under all operating conditions of the lamp.

Under certain operating conditions, fluorescent lamps are subjected to unusual extremes of ambient temperature, for example, if they are mounted in a refrigerated display cabinet. Moreover, the starting switch itself is usually subjected to the same ambient temperature as the lamp. My starting switch is so, constructed that variations in the ambient temperature to which the lamp and switch are exposed are compensated for in a manner to increase or decrease the time during which the filamentary electrodes are heated so that they reach the proper temperature before application of the high voltage current.

Under other operating conditions, relatively large variations in the voltage of the current supply to which the lamp is connected may oc cur. If the voltage is somewhat lower than the normal required for operation of the lamp, then it becomes necessary to heat the electrodes for a longer time interval to be sure that they reach the proper emissive temperature before application of the high voltage starting current. Conversely, a higher voltage will reduce the heating interval. My starting switch is so designed that the length of time during which the filaments are heated is automatically increased or decreased as the voltage of the supply current is lowered or raised.

While fluorescent lamps of the type described have an unusually long period of life, toward the end of their rated life the electrodes at opposite ends of the tubes tend to lose their emissive coating so that the electrons produced by the filaments cannot maintain an adequate are discharge. When this occurs, starting switches of the type now on the market automatically make an attempt to restart the lamp because the arc circuit is opened the same as in first starting the lamp. If the starting mechanism is successful in restarting the lamp the arc discharge will be almost immediately disrupted again due to the lack of emissive material on the electrodes. This sequence of operation causes the lamp to flicker, or, rather, to flash off and on at short intervals as the starting switch keeps restarting the lamp. In a battery of lamps this flicker may become very objectionable. While this objection may be overcome by removing the defective lamp and inserting a new one, it frequently happens that the lamp cannot be replaced immediately. Under such conditions my starting switch is so designed that after attempts have been made to restart the lamp for a predetermined time interval, it will automatically disconnect the lamp from the operating circuit so that the lamp will remain in what may be termed a locked out condition.

It frequently happens that at the first application of the high voltage inductive surge from the reactor an arc discharge will not be struck between the filaments, particularly in those cases when the induced voltage surge is low as when the circuit is opened near the zero point of the cycle of the alternating current supply. Under such circumstances, it is desirable to have the starting switch operate to make another trial as quickly as possible. The high voltage inductive current may be re-applied to the lamp almost immediately since the filaments will already be nearly at their emissive temperature. To this end, my starting switch is so designed that if the arc fails to strike between the electrodes at the first attempt, the switch will almost immediately make another attempt to strike the are by reclosing and reopening the circuit without waiting for the filaments to cool down and be re-heated.

Usually the lamp will light at the first attempt and almost certainly at the next succeeding second or third attempts. However, if the lamp is defective, it may not be possible to strike an are between the filaments. In such cases, if the arc discharge is not struck after a predetermined number of attempts or after a predetermined period of time, for example, an interval of three to four minutes, then the starting switch is so constructed that the circuit to the lamp is automatically interrupted. The lamp is then, in effect, locked out of the operating circuit.

It is an object of my invention to provide a new and improved starting switch for discharge lamps of the type described in which provision is made for insuring proper operation of the lamp irrespective of variations in the ambient temperature to which the lamp and starting switch are subjected.

It is another object of my invention to provide a new and improved starting switch for a discharge lamp whlch will insure proper starting and operation of the lamp irrespective of variations in the voltage of the supply current.

It is another object of my invention to provide a new and improved starting switch for fluorescent lamps which will quickly make repeated attempts to light the lamp in case the arc discharge is not initiated at the first trial.

A further object of my invention is the provision of a new and improved operating mechanism for discharge lamps in which a starting switch is so constructed and arranged that if an are discharge cannot be initiated or maintained in the lamp, the operating circuit to the lamp will be opened automatically, effectively disconnecting the lamp from the circuit.

In the accompanying drawing, Fig. 1 is a cross sectional view through a starting switch incorporating my invention; Fig, 2 is a diagrammatic view showing the starting switch connected together with a discharge lamp in an operating circuit, and Fig. 3 illustrates diagrammatically a modification of the starting switch.

Referring to Fig. 2 of the drawing, I have shown a starting switch Ill connected in circuit with a gaseous electric discharge lamp l I, for example, a fluorescent lamp of the type now in commercial use. Such lamp is provided with an elongated glass envelope [2 coated on the inside wall with a suitable phosphor actuated by an are struck between electrodes l3 and I4 at opposite ends of the envelope. The electrodes l3 and M are of filamentary form. They comprise tungsten wire wound in the form of a helix and coated with a suitable electron emitting material such as barium oxide or strontium oxide. A small quantity of mercury is placed within the glass envelope [2 which vaporlzes under the discharge are between the electrodes l3 and I4 so that the discharge through the mercury activates the fluorescent material on the inner wall of the envelope, lighting the lamp.

In order to connect the lamp to an operating circuit, one end of the electrode I3 is connected by a conductor IE to one side of a supply iii of alternating current, for example, an ordinary 6D cycle, -115 volt lighting circuit. The other end of the electrode i3 is connected by-a conductor ll to a contact pin l8 forming one terminal of the starting switch l0. One end of the other electrode i4 is connected by a conductor l9 to another contact pin 20 forming the other terminal of the starting switch. At its other end, the electrode I4 is connected by a conductor 2| to a reactor 22 and thence by a conductor 23 to the other side of the alternating current supply 45. A manually operable switch 24 is inserted in the circuit in conductor 23 to turn the lamp on and off.

When connected in this manner, the starting switch I0 is in circuit in series with the filaments l3 and I4 and in shunt with the path of the arc discharge between the filaments. When the circuit through the switch is closed, current flows through the filaments heating them to a point at which they become emissive. After a predetermined length of time, during which the filaments are being heated, the circuit through the starting switch is automatically interrupted. This interrupts the fiow of current through the reactor 22 which instantly provides a high voltage inductive surge of current across the filaments causing an arc to strike between them, lighting the lamp. The structure of the starting switch and the manner in which it operates to light the lamp will now be described.

The starting switch l0 includes a casing 25 formed of any suitable insulating material, such as a molded plastic, the casing being preferably formed as a cylinder the bottom wall of which carries the aforementioned contact pins i8 and 20; the upper open end of the housing is closed by a disk 26 frictionally seated in engagement with a groove 21. Disposed within the housing 25 is a plate 28 of insulating material, for example, sheet fiber, which acts as a support for the operating elements of the starting switch. A thermal member 29, shown as a bimetallic strip having a looped end, is mounted in position parallel with one side of the supporting plate 28. The looped end of the termal member is secured in any suitable manner, as by a rivet 30, to the lower end of the supporting plate; the other end of the thermal member carries a contact 3| formed with contact surfaces on opposite sides of the member. In normal position, the thermal member 29 is spring biased to an extent such that the contact 3| makes positive electrical connection with a fixed contact 32, shown in the form of a bracket, fastened to the upper end of the supporting plate in any suitable manner, as by a rivet 33. The contact 32 is spaced from the surface of the supporting plate 28, as shown by 34, so that the thermal member 29, when heated, may move between the contact surface 32 as one abutment and the supporting plate 23 as the other. When the thermal member 29 moves to a position such that it abuts against the supporting plate 28, the contact member 3| extends into an opening 35 formed in the plate 28 for a purpose to be described later.

In order to supply heat to the thermal member 29, a heater 36 in the form of a resistance is mounted at a point immediately adjacent the looped portion of the thermal member and is connected to the contact prong I6 by a conductor 31. A conductor 38 connects the other end of the resistor to the stationary contact 32 at the upper end of the supporting plate. In order to complete the circuit from the contact prong i8 through the resistor 36 and fixed contact 32, the thermal member 29 is connected by a conductor 39 to the other contact prong 20. When the thermal member 29 is in normal position in engagement with the fixed contact 32, a circuit is completed through the contact prong i8, conductor 31, resistor 36, conductor 38, fixed contact 32, contact 3|, bimetallic strip 29, conductor 39 to the other contact prong 20. This means that when the manual switch 24 is closed to light the lamp current will flow through the resistor 36, heating it to apply heat to the thermal member 29 so that the latter is moved to the left, in the view of Fig. 1, to break the circuit between contacts 3| and 32.

When the contacts 3i and 32 are opened, the circuit through the heating resistor 36 is not interrupted due to the fact that a second resistor 40 is connected in shunt with the thermal member 29 and in series with the resistor 36. The purpose of the additional resistor 40 is to provide another source of heat for operating the thermal member 29 as well as a connection for keeping the resistor 36 in circuit when the contacts 3| and 32 open. A conductor 4| connects one end of the resistor 40 to the conductor 36 while a conductor 42 connects the other end to the conductor 39. I have found that the system operates satisfactorily if the heater 36 has a resistance of approximately 20,000 ohms and the resistance of the heater 40 i made approximately 40,000 ohms.

When the switch 24 is closed, a large impulse of heat is given by the heater 36 to the thermal member 29, causing it to move to the left opening the contacts 3| and 32. When the additional resistor 40 is placed in the circuit by breaking of the contacts 3| and 32, the amount of heat generated by the heater 36 is materially reduced and the total amount of heat given out by the combined heaters 36 and 40 will be considerably less than that given out by the heater 36 alone. The manner in which this reduced amount of heat aiTects the thermal member 29 will be discussed later. However, the initial impulse of heat given by the heater 36 is sufiicient to move the bimetallic member 29 to the left notwithstanding the fact that after the circuit through the thermal member has been opened the amount of heat acting on the member is reduced.

As the thermal member 29 moves in response to the heat developed by the heater 36, the contact member 3| engages a movable contact 43, preferably made of carbon, mounted on one end of a thermal member 44 which is in the form of a bimetallic strip. The bimetallic strip 44 normally lies fiat against the wall of the supporting plate 28 on the side opposite that on which the thermal member 29 is disposed. It is secured to the plate in any suitable manner as by a rivet 46 and is connected in circuit to the contact pin II by a conductor 46 connected to the conductor 31. This thermal member 44 is self heated by the passage of current flowing therethrough. When heated, the member 44 is distorted to curve away from the supporting plate 26 opening the contacts 43 and 3|.

Upon closure of contacts 3| and 43 in the manner already described. current flows from contact pin l6 through conductor 46 to the bimetallic thermal member 44 through contacts 43 and 3| to the thermal member 29 and thence through the conductor 39 to the other contact pin 20. Simultaneously, passage of this current through the system heats up the lamp electrodes l3 and I4 so that when the thermal member 44 moves to the left, in the view of Fig. 1, to open contacts 43 and 3|, the circuit through the lamp electrodes is interrupted causing the reactor 22 to provide a voltage surge striking an arc discharge between the electrodes lighting the lamp.

A condenser C is connected across the contact members 3|, 32 and 43 for the purpose of reducing radio interference. It is connected into the circuit at one end by a conductor 41 connected to the conductor 31 and at the other end by a conductor 49 connected to the thermal member 29.

The sequence of operation of the elements of the starting switch in operating the lamp under various conditions will now be described.

Operation to start lamp when the lamp operating circuit is open, the elements of the starting switch take the position shown by Fig. 1 in which the thermal member 29 is biased toward t h e right so that the contacts 3| and 32 are firmly in engagement and the other thermal member 44 lies flat against the supporting plate 28 with the contact 43 resting within the opening 35 in the supporting plate. Upon closure of switch 24 to light the lamp, current flows from one side of the alternating current supply l6 through the conductor l5 to the lamp filament I3, through conductor i! to contact pin 8 forming one terminal of the control switch. It then flows through the conductor 31 to the heating resistor 36, through conductor 38 to the fixed contact 32, to contact 3i on the thermal member 29, through the thermal member to the conductor 39 to the other contact pin 29 forming the other terminal of the control switch, through the conductor l9 to the other lamp filament 4, through conductor 2| to the reactor 22, conductor 23, switch 24 to the other side of the alternating current supply line. This means that a circuit is completed through the starting switch and lamp filaments and since the full voltage across the lamp is applied to the switch, the heating resistor 36 produces a large impulse of heat distorting the thermal member 29 quickly to open the contacts 3| and 32 almost immediately. When this occurs, the shunt circuit through the thermal member 29 is interrupted so that the additional heater member 40 is connected in series with the heater 36 in the shunt circuit across the filaments l3 and I4; both heaters are subjected to the full voltage across the lamp. While the total output of heat generated by both heaters 36 and 49 is less than that of the heater 36 alone, the initial charge of heat developed by the heater member 36 is sufiicient to move the thermal member 29 quickly into electrical engagement with the other thermal member 44 by engagement of the contacts 43 and 3|. When this occurs, both of the heaters 36 and 40 are shunted out of the cirlighting the lamp.

An important feature of my invention is the fact that the length of time during which the filaments l3 and M are heated is controlled by the length of time that the contacts 43 and 3| are in contact with each other; this period, in turn, is controlled by the length of time it takes the current passing through the thermal member 44 to generate sufficient heat to distort it. Thus, the heating period of the thermal member 44 is very closely correlated with that of the electrodes l3 and I4. The heating period is definitely controlled by the amount of current flowing through the circuit and the length of time the circuit is closed. This becomes important in those cases where the fluorescent lamp and starting switch are subject to wide variations in ambient temperature or are connected to a source of current supply the voltage of which varies considerably.

If the lamp and starting switch are subjected to a low ambient temperature, for example, if they are placed in a refrigerator display cabinet, both the filaments and the thermal member 44 would be subject to the same low temperature and it would take the thermal member 44 a longer period of time to heat up under the influence of the current flowing therethrough than would be the case if the thermal member were in a comparatively warm ambient temperature. This means that the electrodes are likewise heated for a longer period, as would be necessary to heat them to the proper emissive condition, before the application of the high voltage surge from the reactor 22. In other words, the thermal member 44 always compensates for variations in ambient temperature because as it is cooled down or heated up by the surrounding atmosphere the length of time required for it to deflect to open the circuit is automatically varied to insure proper heating of the lamp electrodes under all conditions. It should be noted that the starting switch is customarily mounted on one of the sock ets which support each end of the lamp so that it is subjected to the same ambient temperature as the lamp,

Because both of the thermal members 44 and 23 move in the same direction in response to temperature changes, the operation of the starting switch is not affected adversely by changes in the ambient temperature. In other words, the length of time necessary for the contact 3| to break with the contact 32 and make with the contact 43 is always substantially the same. If the starting switch is subjected to an increase in temperature, then both thermal members will tend to move slightly to the left, in the showing of the drawing, so that while the biasing force of the member 29 against the fixed contact 32 is reduced increasing the speed with which the contacts 3| and 32 open, this increased speed will be compensated for by the fact that the thermal member 29 will take more time to engage the contact 43 which has been moved slightly to the left by the distorted thermal member 44. If the switch is subjected to a decrease in temperature, the thermal members tend to move in the opposite direction so that the member 44 is maintained flat against the support 28 and the thermal member 29 is biased against the contact 32 with increased force. When the circuit through the switch is closed, it will take a slightly longer time for the contacts 3| and 32 to separate due to the increasing biasing force but this will be compensated for by the increased speed with which the contacts 43 and 3| close since the contact 43 will be as close to the contact 3| as possible. By compensating the switch in this manner, it is possible to make uniform the time necessary to start heating of the filaments under all operating conditions.

If wide voltage variations in the current supply occur, the thermal member 44 still provides for proper heating of the filaments I3 and H. In case of low voltage, the heating effect of the current through the thermal member 44 would be somewhat reduced and a longer period of time would occur before the contacts 43 and 3| separated so that the current heating the filaments I3 and I4 would likewise flow for a longer period of time heating them to the proper emissive condition. Conversely, an abnormally high voltage would reduce the time necessary for heating the electrodes and, correspondingly, the thermal member would be heated more quickly and open the circuit sooner. By insuring that the lamp filaments are properly heated at all times before application of the high voltage starting current, the life of the lamp is not reduced such as would be the case if the high voltage wer applied acros improperly heated filaments.

While the thermal member 44 has been illustrated and described as a bimetallic strip heated internally by the current passing therethrough, it should be manifest that it may be replaced with a bimetallic strip distorted by a separate resistance wire or heater connected in series with the strip and the conductor 46 so that the heating effect of such resistor in distorting the strip would be controlled by the amount of current flowing through the circuit and resistor.

After the contacts 43 and 3| have separated and an arc is struck between the electrodes, lighting the lamp, the circuit through the thermal member 44 is interrupted permitting it to cool down. This it does fairly rapidly clue to the fact that it has a comparatively large surface area to dissipate heat so that the member quickly returns to normal position. In the meantime, the thermal member 29 is likewise cooled down an amount sufficient for it to move away from the thermal member 44 a distance great enough to prevent the contacts 43 and 3| from reclosing. When the lamp is running, the voltage across the filaments is reduced to approximately 50% of that prior to striking of the are. This means that when this reduced voltage is applied to the heaters 36 and 40 their heat output is reduced to about 25% of their former output permitting the thermal member 29 to cool sufficiently to move away from the thermal member 44, in the manner described.

The thermal member 29 does not move back to its starting position in engagement with the fixed contact 32 because the combined heat output of the heaters 36 and 40, under the reduced voltage incident to operation of the lamp, is suflicient to keep it distorted in position approximately midway between the fixed contact 32 and the contact 43 on the thermal member 44. Since the thermal members move in the same direction under ami .P in" Mrs Iw-rar bient temperature changes, in the manner already described, the thermal member 29 will be maintained substantially in the mid-position irrespective of variations in the ambient temperature since the spacing between the thermal members in the operating condition of the lamp will be maintained substantially constant.

Should the switch be subject to an unusually low ambient temperature, the thermal member 29 may be cooled and distorted to the right sufficiently to touch the contact 32. This simply shunts the heater 40 out of the circuit so that the heat generated by the resistor 36 is increased to move the thermal member away from the contact 32 immediately reinserting the heater 40 in the circuit. This same operation takes place if the voltage of the supply source is suddenly reduced since the heat output of the resistors 36 and 40 is decreased. In either case, closure of contacts 3| and 32 has no effect on the operation of the lamp and cannot produce a flicker since the resistor 36 prevents any appreciable amount of current from the flowing to short circuit the arc path.

When. the lamp is operating the heaters 36 and 40 are connected continuously in series in a circuit including the conductors l1 and 9 across the lamp electrodes. However, the resistance path through these heaters is very high compared with that across the arc path between the lamp electrodes so that only a very small current will flow through this shunt circuit, the power loss through the circuit being on th order of V6 watt. For this reason, there is no danger of the discharge are being short circuited by the shunt circuit through the heaters.

Under certain conditions, for example, if the contacts 43 and 3| open at a low point on the cycle of the alternating current, the voltage surge supplied by the reactor 32 will be insufilcient to light the lamp. In this event, it is desirable to have the starting switch mak another attempt to start the lamp as quickly as possible. My switch is designed to do this.

Since the filaments l3 and I4 have already been heated to an emissive condition, it i not necessary to wait a comparatively long time interval for them to heat up as is the case when starting with a cold lamp. As already described, the thermal member 44 cools off much more quickly than the thermal member 29 so that as soon as the contacts 43 and 3| are separated. the member 44 tends to cool an move back to reolose the contacts. When the arc through the lamp fails to strike, the voltage across th filaments is not reduced as when the lamp is running; consequently, the heaters 36 and 40 are operating under full voltage and produce enough heat to maintain the thermal member 29 in distorted position, whereas if the arc had struck, the heaters would be operating at reduced voltage and would not produce sufficient heat to prevent the thermal member 29 from cooling to an extent such that it would move away from the thermal member 44. Since the thermal member 29 is held in distorted position, contact 43 again engages the contact 3| to re-establish the circuit through the thermal member 44 causing it to heat up again and move to the left to open the contacts. Further heating of the thermal member 44 is facilitated by the arcing taking place at the carbon contact 43 which generates sufficient heat to assist in heating up the thermal member 44. When the thermal member 44 is again heated to an extent sufflclent to separate contacts 43 and 3|. which will take place in a relatively short period of time, the shunt circuit between the filaments l3 and I4 is again interrupted so that a high voltage surge is supplied by the reactor 22. If the lamp does not light on the second attempt, the starting switch will repeat this sequence of operation as many times as necessary to start the lamp. However, if the lamp will not start after a predetermined number of attempts, or after a predetermined time interval, the starting switch will automatically disconnect the lamp from the circuit and no further attempts will be made to start the lamp. This disconnecting or look out" operation will be described later.

If the manual switch 24 is opened and then suddenly reclosed, as when a person leaves the room and turns off the lights and then suddenly enters the room turning the lights on again, it

is desirable to have the lamp relight or restart as quickly as possible. When the circuit is interrupted and again established, as by opening and closing the manual switch 24, the heaters 36 and 40 will be subjected to the full line voltage across the filaments and will move the thermal member 29 into engagement with the contact 43 without first waiting for the thermal member to cool down to reengage the fixed contact 32. For this reason, the time interval required to restart the lamp is materially reduced over that which would be required if it were necessary for the thermal member 29 to cool down to engage contact 32. As soon as the contacts 3| and 43 are closed. the starting switch makes an attempt to light the lamp in the manner already described.

Operation of switch to lockout lamp If a lamp is defective or if for any reason it cannot be started it is desirable to have it locked out of the operating circuit. This is particularly true in those cases where the lamp has reached the end of its normal rated life and is in a condition such that an arc is momentarily struck every time an attempt is made to start the lamp, causing the lamp to flicker. Such flashes of light may be very objectionable. Moreover, by electrically disconnecting the lamp from the operating circuit a saving in power is effected and the life of the starting switch is increased because it will not wear itself out trying to start a defective lamp. To this end, my starting switch is so designed that after attempts have been made to start the lamp for a predetermined period of time, for example, during a period of three or four minutes. the switch will automatically lock the fluorescent lamp out of the operating circuit.

During the time that the switch is attempting to start the lamp, the heaters 36 and 40 are connected in series in the shunt circuit and are subjected to the full voltage between the electrodes in the unlighted condition of the lamp, so that they tend to keep the thermal member 29 in distorted position against the face of the supporting plate 28 with the contact 3| disposed in the opening 35. During this restarting period, the other thermal member 44 is moving into and out of engagement with thermal member 29 by making and breaking the circuit through the contacts 43 and 4|. After a predetermined eriod of time, th heat generated by the resistors 36 and 40 will become suillcient to not only act on the thermal member 29 but to likewise act on the thermal member 44. The heating action of the resistors 36 and 40 on the thermal member 44 is made more effective by the fact that the heat is confined within the housing so that after this predetermined period of time, the ambient temperature within the housing is raised sufilciently to cause the thermal member 44 to move to the left to open circuit position and to remain in such position by virtue of the high temperature existing in the housing.

Although the high temperature within the housing moves both of the thermal members 44 and 29 to the left, as shown in Fig. 1, the thermal member 29 cannot engage the other thermal member 44 because its movement is limited by the supporting plate 28. Thus, if the starting switch is unable to start the lamp, it will shortly reach a condition in which the thermal member 29 is pressed tightly against the support 28 and the thermal member 44 is distorted to maintain the contact 43 out of engagement with contact 3|. This maintains the shunt circuit across the filaments I3 and I4 in open circuit condition with the exception of the small amount of current passing through the heaters 36 and 40. When in locked out condition, the lamp is effectively disconnected from the operating circuit and no intermittent flow of current will take place through the electrodes l3 and H to heat them up at frequent intervals in an attempt to start the lamp. Since the total resistance of the heaters and is on the order of 60,000 ohms, the power loss through these elements will be negligible and will be on the order of /3 watt. This is the amount of power necessary to maintain the lamp in locked out position and represents a considerable saving over the power that would be expended if the electrodes were periodically re-heated in an attempt to start the lamp.

When the defective lamp is replaced by a good one, the filaments are taken out of the circuit automatically upon removal of the lamp from the mounting sockets so that the shunt circuit through the heater members 36 and 40 is broken. This causes the thermal members 44 and 29 to cool and return to their normal position, as shown in Fig. 1, with the contact 3| in engagement with the fixed contact 32 so that the switch is in condition to start the replacement lamp.

While two heaters comprising the resistors 36 and 40 have been provided to supply heat to the thermal members 29 and 44, I have found that in some cases the resistor 40 may be omitted, thereby simplifyin the construction. This modified form of starter is shown by Fig. 3. It eliminates the shunt connection around the thermal member 29. Otherwise the structure of the modified form of starter is the same as that already described. The operation of this modified form of my invention will now be described.

Operation of modified switch of Fig. 3

Generally speaking, the operation of the modifled form of my starting switch is the same as that of the preferred embodiment of the invention with the exception that the heater 36 alone is designed to operate the thermal member 29. The resistance of the heater is reduced somewhat to increase the momentary heat output; it may be as low as approximately 6,000 ohms.

When the manually operable switch 24 is closed, current flows from one filament through resistor 36, the contacts 3| and 32, thermal member 29 to the other filament so that the heater 36 provides a high impulse of heat moving the thermal member 29 to open the contacts 3| and 32 and close the contacts 3| and 43 so that the lamp filaments begin to heat up. The contact 43 is then moved away from the contact 3| by the thermal member 44 which is distorted by the filament heating current flowing therethrough so that a high voltage inductive surge of current is provided to strike an are between the filaments lighting the lamp. When contacts 3| and 32 separate, the heater 36 is out of the circuit so that the thermal member 29 will cool down and tend to return to a position in which the contact 3| will just engage the contact 32. By properly proportioning the resistor 36 and the thermal member 29, the member 29 can be heated sufiiciently so that it will remain in distorted position for a short period of time permitting the thermal member 44 to move into and out of engagement therewith several times in the event that the lamp does not light on the first attempt. The heating action of the carbon contact will assist in keeping the thermal member 29 heated for this short interval.

As soon as contacts 3| and 32 close, the heater 36 is again placed in the circuit and supplies an impulse of heat to move the thermal member 29 to open contacts 3| and 32. However, the impulse of heat given ofi by the heater 36 will not be sufficient to move the thermal member 29 to a position at which it will again engage the contact 43 because the voltage across the filaments which is applied to heater 36 is substantially less in the running condition of the lamp than in the starting condition. This means that as long as the lamp is lighted, the heat given off by the heater 36 is insufficient to distort the thermal member 29 to close the contacts 3| and 43. Whenever the contacts 3| and 32 are opened, the heater 36 is disconnected from the circuit so that the thermal member 29 cools ofi and again engages the stationary contact 32. The thermal member will thus flex slowly into and out of engagement with the fixed contact 32 as long as the lamp is lighted. This periodic opening and closing of the contacts 3| and 32 will not affect the operation of the lamp because the circuit through these contacts across the lamp filaments includes the high resistance 36 permitting only very small currents to flow through this circu1 If the lamp fails to light, even after several openings and closings of contacts 43 and 3| by the thermal member 44, the heater 36 will generate another large impulse of heat as soon as the thermal member 29 has cooled down enough to re-engage with the fixed contact 32, since the full voltage across the filaments is applied to the heater. When this occurs, the thermal member is again moved into engagement with the contact 43 and the thermal member 44, and another attempt is made to light the lamp. If the lamp will not light, several attempts will be made in this manner after which suflicient heat will have been generated by the heater 36 and stored within the housing 25 to deflect the thermal member 44 out of the path of contact 3| so that the lamp will, in effect, be disconnected or locked out of the circuit in the manner previously described in connection with the device of Fig. 1.

The modified form of my starting switch, shown by Fig. 3, has the advantage that it restarts the lamp more quickly than the switch shown by Fig. 1. This is due to the fact that the thermal member 29 will be just moving into or out of engagement with the fixed contact 32, and, in any event, will be very close to this contact so that as soon as the operating circuit is opened and reclosed by switch 24, the thermal member will almost immediately engage contact 32 causing the heater 36 under full voltage across the electrodes to give member 29 a high impulse of heat. This quickly moves the thermal member 29 into engagement with contact 43 so that the thermal member 44 may function to start the lamp.

My switch is one which is easy to assemble and which may be manufactured at low cost since the supporting plate 28 serves both as a support for the thermal members 29 and 44 and as a limit stop for the thermal member 29. It should be manifest, however, that a separate limit stop might be provided for the thermal member 29 and provision made for engaging the contacts 3| and 43 by extending them beyond the outer edge of the supporting plate or in some other manner. However, by mounting the thermal members in parallel relationship on opposite sides of the insulating supporting plate and providing an opening through which the members cooperate a starting switch is obtained which is very compact and which is well adapted for use in the confined space of a lighting fixture.

The heaters 36 and 40 are supported in the assembly by the various conductors which join them to the other elements so that no separate supporting means is necessary for these elements. The whole assembly, comprising the supporting plate, thermal members and heaters, is supported within the housing 25 by the conductors fastened to the contact pins l8 and 20.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. A thermal switch comprising a plurality of cooperating contacts, a thermal member responsive to an increase in temperature thereof for causing said contacts to engage each other and a thermal member responsive to the heating effect of current flowing in a circuit closed by said contacts for causing said contacts to disengage each other.

2. A thermal switch comprising a plurality of cooperating contacts, a thermal member responsive to an increase in temperature thereof for causing said contacts to engage each other and a thermal member connected in series with said contacts and constructed to cause them to disengage each other in response to the heating of the member by current flowing therethrough when the contacts are in engagement.

3. A thermal switch connected in a cricnit for controlling the current flow therein comprising a plurality of thermal members each having a contact, a resistance heater connected across said contacts, one of said members being responsive to heat from said heater for moving its contact into engagement with the other contact, and the other member being arranged to move its contact away from the contact of said one member in response to the heating effect of current flowing through the contacts.

4. A thermal switch connected in a circuit for 6 controlling the current flow therein comprising a. plurality of thermal members each having a contact, a resistance heater connected across said contacts, one of said members being responsive to heat from said heater for moving its contact 10 into engagement with the other contact, and

the other member being connected in said circuit in series with said contacts and constructed to move its contact out of engagement with the contact of said one member in response to the ii ating effect of current flowing through it.

,5. A thermal switch connected in a circuit for i/controlling the current flow therein comprising a plurality of thermal members each having a contact, a resistance heater connected across said contacts, one of said members being respofisive to heat from said heater for moving its contact into engagement with the other contact, the' other member being connected in said circuit in series with said contacts and constructed to move its contact out of engagement with the contact of said one member in response to the heating effect of current flowing through it, and means responsive to the initial movement of the contact moved by said other member for opening the circuit of said heater.

6. A starting switch for an electron discharge device comprising a plurality of cooperating contacts, a two-part resistance heater connected across said contacts, a thermal member responsive to heat from said heater for causing said contacts to engage each other, means operative in the unheated position of said member to short circuit one of said heater parts and means responsive to the initial engaging movement of one of said contacts for opening said short circuit.

7. A starting switch adapted to be connected between the electrodes of an electron discharge device comprising a plurality of thermal members having cooperating contacts, a two-part resistance heater connected across said contacts,

one of said members being responsive to heat from said heater for moving its contact into engagement with the contact of the other member, means operative in the normal position of said switch for short circuiting one part of said heater, means responsive to the initial closing movement of said switch for opening said short circuit, the other of said members being heated by current flow therethrough when said contacts are in engagement and being constructed to bend in a direction to move its contact away from the other contact.

LEONARD W. COOK.

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