US2462336A - Electric discharge device and method of operation - Google Patents

Description

Feb. 22, 1949. RUFF 2,462,336

ELECTRIC DISCHARGE DEVICE AND METHOD OF OPERATION Filgd April 10, 1946 FIG 1 iii-k2 6 J il- 5 FIG 3 a IIF INVENTOR: HAROLD R. RUFF, BY MM HIS ATTORNEY Patented Feb. 22, 1949 ELECTRIC DISCHARGE DEVICE AND METHOD OF OPERATION Harold Robert Ruff, Rugby, England, assignor to General Electric Company, a corporation oi New York Application April 10, 1946, Serial No. 660,879 In Great Britain May 18, 1945 6 Claims.

My invention relates to electric discharge devices and more particularly to electric discharge lamps of the fluorescent type, and methods of starting and operating such devices.

In the field of electric discharge devices, such as fluorescent lamps, there has been evidenced a decided and continuing need for improved constructions and methods of operation whereby the starting of such devices may be improved without employing starting voltages considerably in excess of the operating voltages, and wherein the desired positive initiation of operation and starting is not sacrificed.

Heretofore it has been considered important in operating such devices or lamps, before applying operating voltages between the electrodes, to preheat the electrodes to an operating temperature, and then to produce a voltage peak materially in excess of the operating voltage between the electrodes to cause the electric discharge to start. The voltage peak has usually been produced by suddenly interrupting the starting operation of such a lamp, by first connecting the electrodes in series relation across the source or supply circuit and in series relation with a stabilizing reactor, bymeans of 'a switch having its contacts in shunt relation with the discharge space, and then opening the switch at the termination of the preheating period whereupon the voltage surge is produced due to the presence of the series reactor which is suflicient to initiate the discharge between the electrodes.

In accordance with the teachings of my invention described hereinafter, I provide improved constructions and methods of operating such discharge devices, whereby considerable improvement is made in the structural features and. ability to withstand rough usage, with particular reference to the simplicity of the associated energizing circuits or equipment.

It is an object of my invention to provide new and improved electric discharge devices.

It is another object of my invention to provide new and improved methods of operating electric discharge devices.

It is a further object of my invention to provide new and improved electric discharge lamps of the fluorescent type.

It is a still further object of my invention to provide new and improved methods of operating low pressure positive column electric discharge lamps of the fluorescent type.

Briefly stated, in accordance with my invention, I provide new constructions and methods of operating low pressure positive column electric discharge devices, such as fluorescent lamps, whereby the starting voltage is not substantially in excess of, or may be no greater than, the operating voltage. This improvement is incident to the conjoint effects of certain structural features and the manner of operation whereby a positive initiation or establishment of an arc discharge is effected between thermionic electrodes without applying starting voltages disproportionally great with respect to the operating voltages.

More particularly, the above described results are accomplished by arranging or designing the electrodes in such manner that the voltage-drop across the electrodes or parts thereof under the influence of preheating current of predetermined value is such as to produce ionization across portions or terminals thereof lying within the receptacle or envelope, and by providing an electrically conductive path preferably adhering to the exterior surface of the envelope and which extends into proximity to the electrodes at each end thereof. The preheating current to the electrodes may be transmitted simultaneously with, or prior to, the impression of voltage across the electrodes. In either case, the establishment of the are discharge takes place when the electrodes assume a temperature at which sufiicient electron emission is present; which factor in conjunction with the electric fleld gradient incident to the impressed voltage and as modified and accentuated by the conductive starting strip, causes sufficient ionization of the medium or working substance to establish and support an arc discharge between the electrodes.

If desired, in carrying out other method aspects of my invention, I may employ energizing circuits for the discharge devices which are compact in construction and arrangement and which do not employ elements having moving parts such a switches and the like. For example, in one aspect, I contemplate methods and circuits for energizing discharge lamps of the above described nature wherein after initiation of the are dis-- charges within the lamps, the magnitude of the preheating or heating current transmitted to the electrodes, and the voltage across the pair of electrodes, are reduced thereby improving the operating efficiency in comparison to what it would be if the heating current were maintained at the higher value during operation.

For a better understanding of my invention reference may be had to the following description taken in connection with the accompanying drawing and its scope will be pointed out in the appended claims. Fig. 1 diagrammatically illustrates an embodiment of my invention as applied to a low pressure positive column fluorescent lamp provided witha starting strip of conductive material and which employs a suitable transforming arrangement and reactor for effecting reduction of the operating voltage and heating current after initiation'of an arc discharge. Fig. 2 diagram-. matically illustrates in somewhat more detailed form my invention as applied to a fluorescent lamp and wherein the exteriorly placed conductive strip is provided with a lead or contact whereby it may be grounded through an associated socket (not shown). Fig. 2 illustrates another circuit arrangement comprising an autotransformer and reactor for impressing operating voltage across electrodes of a lamp and which is also employed to supply preheating or energizing current to the thermionic electrodes. Fig. 3 is a modification of the circuit arrangement shown in Fig. 2.

Referring now,more particularly to Fig. 1 my invention is there illustrated as applied to an electric discharge device of the low pressure positive column type, such as a fluorescent lamp, comprising an envelope i preferably constructed of glass and having therein a plurality of electrodes 2 and 3, at least one of which is of the thermionic type. These electrodes, if desired, may be con structed in filamentary form each having terminations l and lying within the enclosure provided by envelope I. I have found that my invention is particularly applicable to thatform of electric discharge device or lamp in which the axial dimension, or distance between electrodes, is substantially greater than a transverse dimension of the envelope, uch as tubular envelopes in which the electrodes are positioned in the ends thereof. The invention described herein may be applied with equal facility to low pressure positive column discharge devices generally, and I have chosen to illustrate certain features thereof with particular reference to low pressure positive column fluorescent lamps. When applied to lamps, which may be of the type designed to supply ultraviolet radiation, visible radiation or a combination of both, the structural features and operating circuit described hereinafter may be applied. When used in conjunction with a fluorescent lamp, a layer or inner coating of a suitable phosphor or fluorescent material 6 may be applied to the inside surface of the envelope I in a usual manner.

Within the envelope I there is provided an ionizable medium or atmosphere which maycontain a starting gas such as argon at a pressure of a few mm., for example from 2 to mm., and a vaporizable and ionizable substance such as mercury. A supply of mercury, which may exceed the amount which would be vaporized during operation of the lamp is indicated by a drop 7 inside the envelope i. p

In order to augment or accentuate the distribution of the electric field intensity within the vicinity of the electrodes 2 and 3, and which is incident to the applicationof a voltageacross these electrodes, I provide an electrically conductive path along the envelope i' and extending into the viclnities of or or in proximity to the electrodes 2 and Sat each end thereof. This strip is of conductive material and may be relatively narrow in width, and may be constituted of metal particles rendered adherent to the surface of the envelope. I have illustrated a metallic strip I, having a. width of approximately /4 inch, adherent to the exterior surface of the envelope l and which may be applied in a variety ofways. For example, the exterior surface of the envelope may be roughened in a narrow strip corresponding to the desired width of the resultant conductive path and extending between the ends of the envelope.

A preferable method of applying the conducting strip or path is to heat the envelope to a temperature somewhat inexcess of 300 C. and then to spray the metal onto the heated glass through a 'mask. On subsequent cooling of the envelope the metal will be found to be securely adherent to the glass.

I provide, in connection with the electrodes 2 and 3, constructions thereof which upon the transmission of energizing or preheating current in predetermined amount to raise the voltage appearing across portions thereof, such as terminals 4 and 5, to values suflicient to establish localized regions of ionization within the vicinities of the electrodes. Such localized regions of ionization, produced in the neighborhoods of the respective electrodes on the passage of current therethrough to heat the electrodes to electron emissive temperatures, in conjunction with the effective shortening of the discharge path or space between the electrodes caused by the presence of the electrically conductive strip'l, enables the electric discharge to start in the absence of the application of a voltage peak heretofore required. It has been found that these two features in combination in a lamp, which in the absence of an electrically conductive path'would require a voltage materially in excess of the normal operating voltage to initiate a discharge between the preheatedelectrodes, will render the lamp conductive upon the application of the normal operating voltage between the electrodes after the electrodes have been preheated to a suitable operating temperature.

As means for energizing the electrodes 2 and I and for impressing starting and operating voltage thereacross I provide a pair of circuits including conductors 8 and II, and Ii and II, which serve as preheating circuits for the electrodes 2 and I and which also serve to impress starting and operating voltages across the electrodes. One way in which these circuits may be energized from an alternating current supply circuit II is through a transformer ll comprisinga primary winding II and a second winding ll having terminal connections I1 and II and taps or intermediate connections is ad 20. The portion of the secondary winding voltage between connections I! and ll,

and is and 2|, serve to apply preheating or energizing current to the filamentary electrodes 2 and 3 respectively, and the resultant terminal voltage appearing across the secondary winding ll serves as starting and operating voltage which is impressed across electrodes 1 and I. I may also employ a suitable current limiting impedance such as a reactor 2| which I connect in series relation between the supply circuit II and the primary winding II of transformer ll. of course, I may also employ a suitable starting switch I! for starting and maintaining operation of the lamp.

Fig. 2 illustrates another modification of my invention wherein the features of the fluorescent lamp are illustrated somewhat in detail and corresponding elements have been assigned like reference numerals. In the arrangement of Fig. 2 the lamp may comprise a pair of similar thermionic electrodes positioned at the ends of the envelope, and these electrodes are supported by suitable base constructions 23 and 24 which may the electrodes described immediately hereinafter are merely exemplary of one suitable form. Each base construction supports a stem press 28 conwhich that electrode is positive with respect to the other electrode.

I have found that his desirable in many instances to ground the metal strip 8. One way in which this maybe effected is by means of a suitable contact member 33 which is constructed of metal and constitutes an extension of the strip 8 and extends along the exterior of the base 24 to place it in a position easily engageable by a suitable contact which may be provided by an associated socket for supporting the lamp and which in turn provides a connection to ground.

An autotransformer 34 is employed to supply preheating current and starting and operating voltage to the lamp which is shown in the arrangement of Fig. 2. The primary winding section of the autotransformer 34 may constitute an electrically symmetrical section of the autotransformer winding 35 and the circuits comprising conductors 9 and I0, and H and I2 may be connected to terminals 36 and 31 and intermediate connections 38 and 39 so that relatively small voltages are impressed across the filamentary electrodes in comparison to the starting or operating voltages.

Upon closing switch 22, effecting energization of autotransformer 34, preheating current and starting voltage are simultaneously supplied to the lamp. I choose the value of voltage impressed across the respective electrodes, and which is transmitted thereto by circuits comprising conductors 9, i0 and ii, l2, to have such a value so that the voltage difference between portions of the electrode structure reaches a value upon heating of the electrode to produce local regions of ionization. For example, these local regions of ionization may be established between the terminals of the coiled coil 30, or between parts thereof and the wires 3| and 32. The initiation of the main discharge between the electrodes is efiected by the conjoint action of the local regions, the electric field incident to the impressed voltage, and the modification of such field by virtue of the grounded conductive strip 3. Upon establishment of the discharge between the electrodes the increased current flow through the reactor 2i effects a reduction in the voltage supplied to the autotransformer 3E and consequently eflects a reduction not only in the voltage which is supplied to the respective filamentary electrodes but also reduces the. voltage impressed across the electrodes.

Fig. 3 illustrates a still further modification of the circuit for supplying preheating current and operating and starting voltages to the lamp. This circuit is similar in many respects to that illustrated in Fig. 2 and corresponding elements have been assigned like reference numerals. The autotransformer 34' is shown as being arranged in a manner so that the alternating supply voltage is impressed across the electrodes of the lamp and the voltage for supplying heating current to the electrodes is obtained from extensions.

43 and ll of the autotransformer winding.

Although in the above described embodiments of my invention I have chosen to illustratevarious aspects thereof wherein the lamps are energized from an alternating current supply circuit it will readily be appreciated that certain structural features and principles of operation are applicable to electric discharge devices and lamps arranged for operation from direct current circuits, in which case only one of the electrodes need be of the filamentary type having features and characteristics suitable for operation as a cathode. It is to be understood that the general features of the above described methods of operation are also applicable to electric discharge devices and lamps intended for operation on direct current circuits.

While I have shown and described my invention as applied to particular systems of connections and as embodying various devices diagrammatically shown, it will be obvious to those skilled in the art that changes and modifications may be made without. departing from my invention, and I, therefore, aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

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

1. In an electric lamp of the discharge type comprising a pair of thermionic electrodes of the filamentary type spaced apart in an envelope, an ionizable atmosphere comprising a rare gas at a pressure of a few mms. and a small quantity of mercury which supplies mercury vapor during operation of the lamp, said electrodes being arranged so that the voltage drop across terminations thereof within said envelope under the influence of preheating current of predetermined value is such as to produce local regions of ionization between said terminations, a layer of fluorescent material on the inside surface of said envelope, a strip of conductive material on said envelope extending along the discharge path and terminating in the vicinities of said electrodes to assist in the establishment of an arc discharge therebetween by co-operating with the regions of ionization appearing across the terminations of the filamentary electrodes.

2. In an electric lamp of the discharge type comprising an envelope having therein an ionizable atmosphere comprising a rare gas at a pressure of a few mms. and a small quantity of mercury which supplies mercury vapor during the operation of the lamp, a layer of fluorescent material on the inside surface of said envelope, a strip of conductive material on said envelope extending along a discharge path within saidv envelope, and a pair of thermionic electrodes of the filamentary type and each comprising terminations within said envelope, said electrodes being arranged to produce under the influence of rated heating current local regions of ionization across said terminations and which in conjunction with the eflect of said strip upon application of voltage across said electrodes assist in the establishment of an arc discharge therebetween.

3. The method of starting and operating an electric discharge lamp of the fluorescent type including a pair of thermionic electrodes spaced apart in an envelope containing an ionizable atmosphere. which comprises transmittal of heating sumcient to increase the voltage across the terminations of said electrodes in said envelope to a;

value which produceslocal regions of ionization, impressing a starting voltage across said electrodes and modifying the electric field distribution therebetween which, in conjunction with said local regions of ionization, establish a discharge between said electrodes, and reducing the voltage impressed across said electrodes and the voltages impressed across the individual electrodes.

4. The method of starting and operating an electric lamp of the discharge type including an envelope containing an ionizable atmosphere and having a pair of thermionic electrodes positioned therein and a strip of conductive material extend ing an appreciable distance therebetween, which comprises transmitting to said electrodes an appreciable starting current to raise the temperature thereof and to produce across terminations lyingwithin said envelope voltages of suiflcient magnitude to cause local regions of ionization, impressing across said electrodes a startingvoltage of a magnitude which is suflicient in cooperation with the effects of said local regions of ionization and said strip to initiate the establishment of an arc discharge between said electrodes, and subsequently reducing the voltage impressed across the electrodes and the voltages impressed across the individual electrodes.

5. The method of starting an electric discharge lamp of the fluorescent type including an envelope having therein an ionizable medium, a pair of thermionic electrodes and a strip of conductive material extendin an appreciable distance between said electrodes, which method comprises transmitting current to said electrodes of suflicient magnitude to produce across portions thereof positioned within said envelope voltage diflerences which establish local regions of ionization, impressing across said electrodes a starting voltage of a magnitude sumcient in conjunction with the eilects of said local regions of ionization and said strip to initiate an arc discharge between said electrodes, and simultaneously reducing the voltage impressed across the electrodes and the voltages impressed acrossthe individual electrodes after the initiation of an arc discharge between the electrodes.

Number Name Date 7 1,915,019 Ewest et al June 20, 1933 5 2,094,647 Freitag et al Oct. 5, 1937 2,146,579 Inman Feb. 7, 1939 2,181,294 Biggs Nov. 28, 1939 2,182,732 Meyer Dec, 5, 1939 2,249,672 Spanner July 15, 1941 40 2,259,040 Inman (b) Oct. 14, 1941 2,264,055 Stocker Nov. 25, 1941 2,307,971 Stirnkorb Jan. 12, 1943 FOREIGN PATENTS Number Country Date 623,532 Germany Dec. 27, 1935 8. The method oi. starting electric discharge lamp of the fluorescent type including an envelope having an ionizable medium therein, a pair of thermionic electrodes of the filamentary type and a strip of conductive material terminating within the vicinities of said electrodes, which method comprises the simultaneous application or voltage across said electrodes and the transmittal of heating current to said electrodes, the time of initiation or an arc discharge between said electrodes being determined by the conjoint 'eflect of voltage gradient incident to the voltage across said electrodes, the modification of the gradient due to said strip and the eflect of local regions of ionization within the vicinities of said electrodes caused by the transmittal of heating current oi a value sumcient to produce across portions or said electrodes within said envelope voltage difierences which produce said local regions 0! ionization, and substantially simultaneously reducing the voltage impressed across said electrodes and the voltages impressed across the individual thermionic electrodes upon the establishment of an arc discharge between said electrodes.

HAROLD ROBERT RUFF.

REFERENCES CITED The following references are of record in the file of this patent:

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