US2248979A - Discharge lamp - Google Patents

Description

Julyv '15f 1941- E. FRIEDERICH Erm. 2,248,979

DISCHARGE LAMP Filed Sept. 25. 1940 l Geerv Gades,

Theil- A'tftorneg.

Patented July 15, 1941' DISCHARGE LAMP l Ernst Frlederich and Martin Reger, Berlin-Charlottenburg, Germany,

and Georg Gaidiel, Berlin-Pankow, assignors to General Electric Colnpany, a corporation of New York application september as, 1940, serial Ne. 358,022 -In Germany July 14, 1939 s claims.' (ci. 11s-124) The present invention relates to electric discharge lamps ofthe elongated, positive column,.

low gas pressure type having thermionic electrodes which are provided with heater elements similar to thosedisclosed in the United States Reissue Patent No. 19,057, issued January 23, 1934. During the starting period of the lamp, that is, when the electrodes are being heated to an .electron emitting, arc discharge supporting temperature and before the positive column discharge has started between the electrodes the electrodeheater elements are connected across the terminals of a current source. Generally the electrodes consist of an elongated hollow cylinder of sheet metal, such as nickel, having a coating of material of high electron emissivity on the outer surface thereof andthe heater elements are mounted. inside the hollow cylinder. Usually the special heater current is interrupted during the operation of the lamp and the heater elements are in series with the discharge to serve as a resistance for Hunting the discharge current.

Discharge lamps provided with electrodes of the type described above have a number of advantages. The preheating of the electrodes reduces the ignition potential of the discharge and venting hot spots thereon caused by ionic bomvide a' gaseous electric discharge lamp or the above type having a long useful life and which emits light immediately on the application of potenti-al to the lamp and before the heated electrodes have attained a discharge supporting temperature. Another object of the invention is to provide'a self-contained lamp of the above type. Still further objects and advantages of the invention will be/ apparent te those skilled in the art from the following particular description and from the appended claims.

The invention attains its objects by providing auxiliary thermionic electrodes for supporting a luminous discharge in the lamp during the interval between the application of the heater current to the heated electrodes and the attainment by said electrodes of an arc discharge supporting temperature. Preferably the auxiliary electrodes are of the lamentary type capable of attaining 4a discharge supporting temperature practically instantaneously when the heating current is applied to the main electrodes. The auxiliary electrodes are connected in series with the heating elements o! the main electrodes and means is bardment When'the discharge rst starts. During the operation of the lamp the` heater elements of the electrodes are maintained at an elevated temperature by the discharge currentA which ows therethrough and heat the electron emitting material on the electrode to a temperature such that the voltage drop at the electrode and the reignition voltage of the discharge is reduced to a minimum. Further, the resistance of the heating wires can be made of such magnitude, when desired, that 'no resistance external to the lamp is required.

A disadvantage of such lamps is the interval between the connecting of the lamp across the terminals of a current source and the emission of light by the lamp. The electrodes have an appreciable thermal capacity and do not attain an arc vdischarge supporting temperature until 20 or seconds or more have elapsed after the heating current starts to flow through the heater elements. The starting potential cannot be applied across the electrodes before the electrodes have attained a discharge supporting temperature without causing hot spots thereon due to ionic bombardment resulting Ain a short lived lamp.

The object of the present invention is to proincluded in the circuit-to break the series connection therebetween as soon as said auxiliary electrodes have attained a discharge sustaining temperature. Simultaneously a luminous discharge starts between the auxiliary electrodes and the lamp emits light before the main electrodes have attained their discharge sustaining temperature. I y

In the drawing accompanying and forming part of this specification several embodiments. of the invention are shown in which- Fig. 1 is a side elevational, partly of one embodiment ot the invention Fig. 2 is a similar view of another embodiment oi the invention and Fig. 3 is a similar view bodiment of the invention.

Referring to Fig. 1 of the drawing the gaseous electric discharge lamp comprises a tubular, vitreous envelope l, such as a glass envelope, about 1 meter in length and about 30 mm. in diameter. Said envelope I contains a luminosity producingegaseous filling. such as a ilxed gas; or a mixture of gases, a mixture of neon and argon, for example, at a pressure of about 2 to 10 mm. When desired, a vaporizable metal, such as mercury, is present in addition to the gas inthe envelope I and the vapor thereof is luminosity producing during operation. A pair of cooperating electrodes 2 are `sealed into said envelope I.v Each of said electrodes 2 consls'tff'of'a hollow, sheet sectional view of still another em-l metal cylindrical body about 2 cm. in length and about 1.5 mm. to 2 mm. in diameter having a ation of the lamp. Preferably the voltage drop.

across each of the wires 3 is 35 to 45 volts when the current value is 100 milliamperes. The lamp is then capable of operation on 220 volts without external resistance. e

An electrical conductor 4 connects said electrodes 2 in series across the terminals 'of the current source. Part of said conductor 4 is cemented to the outer surface of the envelope l. A bimetallic switch 5 andan electrical resistance 6 are connected into said conductor l and both these elements are preferably mounted outside the envelope I in a base attached to the end of the envelope I. Two auxiliary electrodes 1 and 8 are mounted inside said envelope I and are connected in series with the heater wires 8, the electrodes 2, the bimetallic yswitch 5,.the auxiliary resistance 6 and the conductor 4 across lthe terminals of the alternating current source during the starting of the lamp. The auxiliary electrodes v1 and 8 consist of a filament of high melting point `metal, such as tungsten, and a body of high electron emissivity characteristics, such as barium oxide, or thorium, mounted in heat receiving relation thereto. Said electrode 8 is wrapped around sleeve III supporting one of the electrodes 2.

When a suitable potential is applied across the terminals of the lamp a heater current ows through the shunt circuit above described. This current'is limited by the heater elements 3 and the auxiliary resistance 8 andis sumcient-to heat the electrodes 1 and 8 to an electron emitting. discharge supporting temperature almost instantaneously. that is, within a second or less.

IThe bimetallic switch l, which has a resistance heater therein, opens when the electrodes 1 and 8 have been heated to a discharge supporting temperature. The opening of the switch 5 causes a potential diierence between the electrodes 1 and B of suilicient magnitude to start an arc discharge therebetween. The lamp thus emits light almost immediately upon being connected into the current supply circuit.

The electrodes 1 and 8 support a discharge for a short time only each time the lamp is started. As a result they have a long useful life even when said electrodes have such small ther;- mal capacity that they are heated to a discharge supporting temperature almost immediately by the heating current or when they comprise elec tron emitting materials which are highly emissive but which would have a short useful life if -said electrodes 1 and 8 were used alone in the lamp for supporting the discharge'.

The auxiliary resistance 6 is constructed in such manner, when desired, that the electrical resistance thereof increases rapidly with increasing temperature. Preferably the resistance thereof increases 5 to 10 times its original value. The potential difference between the electrodes 1 and 8 is thus rapidly increased to a value such that the discharge starts therebetween and, when desired, the value of the resistance 8 is of such magnitude that the switch 5 is not necessary and is omitted. Other types of current interruptors are used in place of the switch 5 when desired. For example, a discharge device having a higher discharge maintaining voltage than the voltage available in said shunt circuit during the operation of the starting discharge in the lamp is useful.

The embodiment shown in Fig. 2 of the drawing is similar to that shown in Figure 1 except that in this embodiment the auxiliary electrode I0 is separated such a distance from the lead II connected to the conductor I that a short electric discharge takes place between these elements before the discharge starts between the electrode IB and the corresponding electrode at the opposite end of the lamp. The electrode I0 is thus rapidly heated and the starting of the discharge between said electrode I0' and the corresponding electrode at the opposite end of the lamp facilitated. `The short electric discharge is extinguished to break the shunt circuit when the dis- The arc discharge current flows through the heater elements 3 which raise the electrodes 2 to a temperature such that 'they are capable of supporting the arc discharge without the occurrence of destructive ionic bombardment thereat in about 20 to 30 seconds after the starting of the arc discharge incident at the electrodes 1 and 8. When said electrodes 2 have attained such temperature the arc discharge transfers from the electrodes 1 and 8 to the electrodes?. beca' se the distance between said electrodes 2 is shorter than i that between the electrodes 1 and 8. .The same result is attained by using materials of higher electron emissivity for the electrodes 2 than for the electrodes 1 and 8 or by using other known means for making lthe electrodes 2 more capable of supporting the discharge than the electrodes 1 and 8 after the preliminary heating of the electrodes 2.

charge starts between the electrode I0 and the corresponding electrode at the opposite end of the lamp.

The embodiment of the invention illustrated in Fig. 3 of the drawing is similar to that shown in Figs. 1 and 2 except that in this embodiment a hydrogen filled iron wire resistor II is -connected into the current leads of one of the electrodes 2 and a resistance element 9 having a negative thermal resistance characteristic, such as an oxide body, is also connected into one of said leads or into the circuit between the electrode 2 and the electrode 1. The resistance of the `'element 9 decreases as the temperature thereof increases. The resistor I I has a regulating range of about 13 to 39 volts at 100 milliamperes.

When the lamp is connected across the terminais of an alternating current source current flows through the shunt circuit including the conductor and the lamp starts into operation in the same manner as the lamp illustrated in Figs. l and 2. In this embodiment, however, during the interval between the starting of the discharge between the electrodes and 8 and that between the electrodes 2 the discharge current is limited by thc resistances 3, 9` and II. While the resistance of the elements 3 increases as the temperature thereof increases the resistance of the element 9 decreases as the temperature thereof increases and at about the same rate so that the discharge current owing through the circuit during this period is restricted to a range not exceeding the regulating range of the resistor II.

, rium, the voltage drop in the discharge is about i55\volts, that across the resistor Il is about 25 to 30 volts and that across the two filaments 3 totals about 40 volts. The lamp is thus capable of operating on potentials of 220 volts.

When desired, the envelope I of the lamps described above has a coating of luminescent material mounted in light receiving relation to the luminous discharge, such as by being applied to the inner surface of the envelope; or said envelope I consists in wholeor in part of luminescent glass.

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

l. An electric lamp comprising in combination,

a vitreous envelope, a luminosity producing gaseous lilling therein, aplurality of thermionic operating electrodes having an appreciable thermal capacity and a plurality of thermionic starting electrodes having a relatively inappreciable thermal capacity sealed into said envelope, the circuit includingthe chscharge path between said operating electrodes having a lower resistance than that including the discharge path be- I' tween said starting electrodes when all of said electrodes are at a discharge sustaining temperature, heater elements for said operating electrodes, a shunt circuit for connecting said heater elements and said starting electrodes in series for 1 heating said starting electrodes, resistance increasing means connected between said starting electrodes in said shunt circuit to increase the potential diierence between said starting electrodes to cause a'luminous discharge to start there-between before said operating electrodes have attained their operating temperature, said heater elements being connected in series with the discharge between said starting electrodes and that between said operating electrodes to 4' limit the discharge current and to raise and maintain said operating electrodes at a discharge sustaining temperature.

2. An electric lamp comprising in combination, a vitreous envelope, a luminosity producing gaseous iilling therein, a plurality of thermionic operating electrodes having an appreciable thermal capacity and a plurality of thermionic starting electrodes having arelatively inappreciable thermal capacity sealed into said-envelope, said start- 5? use 9 luminous discharge to start therebetween Gf before said operating 'electrodeshave attained their operating temperature, said vheater elements being connected in series with the discharge be- Y tween said starting electrodes-and that between said operating electrodes to limit the discharge current and to raise and maintain said operating' electrodes at a discharge sustaining temperature.

3. An electric lamp comprising in combination, a vitreous envelope, a luminosity producing gaseous lling therein. a plurality oi thermionic operating electrodes having an appreciable thermal capacity and a plurality of thermionic starting electrodes having a relativelyl inappreciable thermal capacity sealed into said envelope, said operating electrodes having a higher electron emission than said starting electrodes during operation ofy said lamp, heater `elements for said operating electrodes, a shunt circuit for connecting said heater elements and said starting electrodes in series for -heating said starting electrodes, resistance' increasing means connected' between said starting electrodes in said shunt circuit to increase the potential diierence between said starting electrodes to cause a luminous discharge to start therebetween before said operating electrodes have attained their operating temperature, said heater elements being connected in series with the discharge between said starting electrodes and that between said operating electrodes to limit the discharge current and to raise and maintain said operating electrodes ata discharge sustaining temperature.

4. An electric lamp comprising in combination, a vitreous envelope, a luminosity producing gaseous filling therein, a plurality of thermionic -operating electrodes having an appreciable thermal capacity and a plurality of thermionic starting electrodes having a relatively inappreciable ther- Q heater elements for said operating electrodes, a shunt circuit for connecting said heater elements and said starting electrodes in series for heating said starting electrodes, resistance increasing.

means connected between said starting electrodes in said shunt circuit to increase the potential diiierencefbetween said starting electrodes to cause a luminous discharge to start therebetween` before said operating electrodes have attained their operating temperature, said heater elements being connected in series with the discharge between said starting electrodes and that between said operating electrodes to limit the discharge current and to raise and maintain said operating electrodes. at a discharge sustaining temperature, and voltage regulating means connected into the current lead to one of said heater elements to minimize the eiect of line voltage fluctuations on the luminous output of said lamp.

5. An electric lamp comprising a sealed en.

velope containing a luminosity producing gaseous filling .and a plurality of thermionic electrodes, said electrodes being mounted in spaced pairs, 'one electrode of each pair having an appreciable Vthermal capacity and the other electrode a relato said discharge path, the resistance of said path i being higher than theV resistance of said shunt circuit before said electrodes ofv inappreciable thermal capacity have attained a discharge supporting temperature and lower than that of said shunt circuitafter said electrodes have lattained such temperature., p t

' ERNST FRIEDERICH.

MAR'I'INREGER.

GEORG GAl'DIES.

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