US2181924A - Gas and metal vapor discharge tube - Google Patents

Description

Dec. 5, 1939. H. J. SPANNER GAS AND METAL VAPOR DISCHARGE TUBE 'Filed June 16, 1937 alllllllllllllllll |lI||IIIl|lI|I|||7 INVENTOR awn... s, 1939 UNITE "STATES PATENT orrlca ApplicationJune 18, 1931, Serial No. 148,489 In Germany June 16, 1936' s Claims. (c1. 110-122) This invention relates to gas and metal vapor discharge devices designed for use as sources of visible and ultra-violet radiation, especially for illuminating purposes, therapeutic radiation, dual purpose lighting, etc. This invention deals espe-'- purposes.

These objects can be attained according to my invention, e. g., by designing the electrodes so that they convert into heat a substantial part of the electrical energy supplied thereto and of such dimensioned that they are heated thereby stantially in the total radiant emission of the device; or by providing other solid bodies of dimensions adapted to be heated to incandescence by the action of the discharge thereon. It is advantageous in a tube for motion picture projection or television that the light emitted is comparable with the white day light; therefore the electrodes and the filling of the tubes is adapted to produce together with the high pressure discharge preferablyin mercury and/or cadmium such a white light. The electrodes at present used in high pressure vapor lamps consist of twisted tungsten wires which are, coated with barium and barium compounds. During operation these electrodes have a temperature of about 700 C. and do not materially contribute, therefore, to the light emission. According to this invention the electrodes are activated with-metals and/ or metal compounds of which the work func- 40 tion is higher than three volts. Such metals are, e. g., magnesium, zirconium and others. It is also possible to use compact tungsten electrodes suitably activated as described below especially in the shape of balls. Such electrodes can consist also of other high melting materials such as tantalum, molybdenum, iridium and others or alloys suitably activated. The electrodes will be selected in accordance with their work function or according to the work function of their admixtures the temperature being that at which they emit enough electrons to keep the discharge going; one has however to select the right size for the current in question, so that the electrodes are not overloaded nor insufficiently loaded.

ing picture projection, television and advertising to a temperature at which they participate sub- Means may be provided for preventing the deposits of tungsten in the pole vessels from extending into. the discharge tube itself by providing rings or screens at the end of the pole ves= sels, but if full use is to be made of the radiation from incandescent electrodes it is important to control evaporation and sputtering by use of activation and proper dimensioning.

By using activation material like magnesium, the temperature of the electrodes is decreased to about 2000" C. The magnesium or zirconium is embodied in the high melting point metal according to the commonly known processes like that used for incorporating thorium in tungsten.

- By admixing these materials which have work functions between three and four volts the emitting temperature is lowered just enough so that the light produced by the electrodes helps to correct the blue green colour of the mercury discharge while not allowing the tungsten to vaporise to any appreciable extent.

In such discharge devices one may advantageously use all the other well known features of the modern metal vapor lamps. In many cases one might use also sodium as a metallic filling; sometimes it might not be necessary that the filling metal is brought to a high pressure. The electrodes of this invention although provided withv admixtures of activating materials can hardly be called activated in the usual sense because the starting potential of lamps in which they are used will be higher than 220 volts, even though auxiliary electrodes are used. The electrodes according to this invention can be also incorporated in types of arc discharge lamps ordinarily having tungsten electrodes and commonly shown as sunlamps, to prevent blackening of the bulbs after a short period of operation.

In the accompanying drawing:

Fig. 1 is a view in cross section of a lamp embodying my invention;

Fig. 2 is a. view partly in axial section and partly in elevation of another lamp embodying my invention;

Fig. 3 is a fragmentary sectional view showing another embodiment of my invention.

Referring firsttd Fig. 1, I have shown there a sealed envelope l0 having electrodes ll of the type described above mounted on lead wires i2 sealed through the wall of the tube. I The envelope i0 is provided with a suitable filling, e. g., of gas are described for example in my prior applications Serial No. 558,148, filed-August 19, 1931, Serial No. 744,206, filed September 15, 1934, and these electrodes by their light emission strong in the red end of the spectrum complement the emission spectrum of the mercury vapor. However, because of the geometrical separation of the electrodes giving light rich in red rays from the discharge ving colored light, e. g., of a bluegreen color, the light emitted from the new discharge tubes is not very uniformly distributedin colour over the length of the tube. Therefore one may use besides the metal or. mixed metal vapor filling, which may be present in such an amount that it is totally vaporised during high pressure or ultra high pressure operation, particles of metals 24 like tungsten, tantalum or compounds like tantalum carbide as filling to help during operation by emitting yellow red light by incandescence. These particles can be held in the discharge by magnetic influence; this influence can be produced by known methods e. g., the electro magnets I3, H, l5. One can keep the particles also on a structure of insulation materials I8 like glass wool in'the path of the discharge.

As mentioned above the discharge tubes embodying the new features of thisrinvention are especially adapted to be used where one needs white light of a high intensity.

One can use every sort of high pressure or ultra high pressure lamps for moving pictures projection. If one wants to interrupt the discharge for discontinuous exposure of the film, one should use an auxiliary discharge from at least onemain electrode to an auxiliary electrode so that the restarting of the high pressure main discharge is made possible. This auxiliary discharge is also necessary for increasing the life of the electrodeswhich cannot take the overload instantly with which the lamp is charged in a very small fraction of a second. ThisI have illustrated in Fig. 2, the auxiliary electrode 20 being mounted on inlead wires 2i and each connected to the opposite main electrode through resistors- 22, 23 respectively.

In Fig.3, I have shown a modification of the lamp illustrated in Fig. 1 in which rings or screens 30 are provided at the end of the pole vessel as described above in order to keep any deposit of vaporized metal from the electrode within the pole vessel and away from the main arcing part of the discharge tube. The auxiliary discharge nowadays used in the high pressure lamps running over a. resistance of about 50,000 ohms is not capable to prepare the electrodes for the enormous kick and for the restarting of the high pressure discharge. The auxiliary discharge according the invention has to be at least 10% as high as the main discharge would be if the lamp would be loaded normally. In these lamps for projection purposes one can use of course the barium activated electrodes such as are at present used in discharge lamps.

What I claim is:

1. A radiant electrical arc discharge device comprising an energizing circuit adapted to give a limited current loading to the discharge and a columnar discharge tube having solid electrodes positioned at opposite ends therein, capable of supporting an arc, said electrodes having a work function of 3-4 volts, and said energizing circuit being designed to give a current loading suflicient to heat the electrodes to white heat at which they operate without excessively vaporizing, and'therematerial adapted by its vaporization to convert an initial discharge into a typical high pressure arc, circuit connections for said auxiliary electrode from said energizing circuit adapted to provide current loading through the auxiliary electrode at least 10% of that supplied to the main electrode, whereby, to maintain the main electrode at arcing temperature and to maintain ionization in the tube while the discharge between the main electrodes is extinguished, whereby an arc willbe re-established between the main electrodes immediately upon theenerglzation-of the main electrodes.

3. The method of operating intermittently a discharge tube of the type in which the discharge is converted to a typical high pressure arc by vaporization of a material within said tube whereby its restarting voltage rises above the voltage normally available from a source of operating voltage, which comprises establishing amain discharge between arcing electrodes in the tube, interrupting the main discharge, but con tinuing an auxiliary discharge from at least one of said electrodes over a shorter path than the main discharge and loading said auxiliary discharge with a current at least 10% that of the main discharge, whereby to maintain the electrade in arcing condition and to maintain the ionization of the atmosphere in the tube, so that the main discharge can be restarted at a voltage near its operating voltage, and restarting the main discharge by again connecting said arcing electrodes to the source of operating voltage.

4. The method of operating intermittently a discharge tube of the type in which the discharge is converted to a typical high pressure are by vaporization of 'a material within said tube whereby its restarting voltage rises above the voltage normally available from a source of operating voltage, which comprises establishing a main discharge between arcing electrodes in the tube, interrupting the main discharge, but continuing an auxiliary discharge from each of said electrodes over a shorter path than the main discharge and loading said auxiliary discharges with a current at least 10% that of the main discharge, whereby to maintain the arcing condition of the electrodes and the ionization of the atmosphere in the tube, so that the main discharge can be restarted at a voltage near its operating voltage, and restarting the main discharge by again connecting the arcing electrodes to the source of operating voltage.

5. A radiant electrical arc discharge device which comprises an envelope, a filling within said envelope, including a vaporizable material adapted to provide a gaseous medium for the discharge and by vaporization to increase the voltage, of the discharge, an energizing, circuit adapted to give a limited current loading to the discharge, arcing electrodes spaced in said envelope, lead-in wires connecting said electrodes to said energizing circuit, and comminuted tantalum carbide adapted to be suspended in the arc stream, said com- 15 minuted tantalum carbide being adapted to become incandescent when subjected to said are stream so as to supplement the discontinuous pectrum light oi the arc with a light having a continuous spectrum, and means for suspending the comminuted tantalum carbide in the arc stream. v

8. A radiant electrical arc discharge device which comprises an envelope, a filling within said envelope, including a vaporizable material adapted to provide a gaseous medium for the discharge and by vaporization to increase the voltage of the discharge, an energizing circuit adapted to give a limited current loading to the discharge,

arcing electrodes spaced in said envelope, lead-in wires connecting said electrodes to said energizing circuit, a ball of glass wool in the arc stream. and

candescent when subjected to said arc stream so as to supplement the discontinuous spectrum light of the arc with a lightnhaving a continuous. 10

spectrum. 1 HANS J. BPANNER.

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