US2625671A - Electrical discharge lamp - Google Patents

Description

Jan. 13, 1953 H. E. KREFFT 2,625,671

ELECTRICAL DISCHARGE LAMP 2 SHEETS-SHEET 1 Filed July 19, 1949 Tic'll. 52/256 19 w /'14, 1 13 8 [20 r W 4 9 Wtiqu 4 12 F 1a 3 43 6 A 19 INVENTOR. HERMANN E ARD KREFFT ,4 TTOPNE'Y Patented Jan. 13, 1953 ELECTRICAL DISCHARGE LAMP Hermann Eduard Kreift, Buenos Aires- Belgrano, Argentina Application July 19, 1949, Serial No. 105,526

The present invention relates to electrical discharge lamps of the high pressure type and more particularly to super high pressure lamps operated under pressures exceeding ten atmospheres which have more than two operating electrodes.

Super high pressure lamps containing mercury vapor, or a mixture of mercury vapor with other vapors, or rare gases under high pressures, are sources of radiation of very high brightness particularly adapted to the uses in projection and searchlights. The manufacture of such lamps, especially for high wattage, however, is extremely difilcult as they must be supplied with quartz glass seals and electrodes capable of carrying high currents. The mechanical strength of'these seals and of the quartz glass discharge container generally used is not suflicient to allow a safe operation of these lamps the container and seals of which are exposed to high pressures at high temperatures. Moreover, the operation characteristics of these lamps possess many disadvantages mainly connected with the difficulty of starting the are when the lamp is under pressure.

It is one object of my invention to provide a super high pressure lamp for safe operation. Another object is a lamp with improved operation characteristics. Still another object is a source of light of suitable shape. A further object is a super high pressure lamp of high wattage which can be made with precise dimensions and in large numbers at comparatively low cost. Other objects and advantages of this invention will become apparent from the description hereinafter following and the drawings forming part hereof in which:

Figure 1 is a longitudinal sectional view of a super high pressure lamp constructed in accordance with my invention,

Figure 2 is another sectional view of a lamp according to the invention,

Figure 3 is a transverse sectional view taken on the line 2-2 of Figure 1 illustrating the construction of the seal,

Figure 4 is a diagrammatic section along the line 3-3 of Figure 1 showing the electrode arrangement,

Figure 5 is a schematic representation of a circuit according to the invention,

Figure 6 illustrates a modification of the electrode arrangement for a lamp according to the invention,

Figure 7 is a diagrammatic sectional viewv taken on the line 4-4 of Figure 6 showing the electrode arrangement,

7 Claims. (Cl. 31549) Figure 8 is a schematic representation of another electrode arrangement, and

Figure 9 is a diagrammatic sectional view taken on-the line 55 of Figure 8 illustrating the electrode arrangement.

According to Figure 1, a lamp embodying my invention comprises a discharge container l, pref erably made of quartz glass, and having, a wall thicknessof two to three millimeters, provided with short necks 2 and, 3 the ends of which are closed by seals 4 and 5, which are, preferably, also' made of quartz glass and are firmly welded thereto. Each seal is composed of a plurality of seal elements 6 containing metallic conductors 1 which are electrically connected to the electrodes 8. These electrodes are mechanically supported by discs 9 which are connected to the seals 4 and 5 by means of rods l0 shown in Figure 2. Electrical connection between the seal conductors and the wires or rods H carrying the electrodes is made by a series of flexible strips or coils I2 which consist of a metal of high melting point. I g

The discharge container is filled with arare gas and a limited quantity of mercury which, under full operation of the lamp, is entirely evaporated and produces a pressure of at least about ten atmospheres. The lamp may also contain limited quantities of other vaporizable metals, or it may contain rare gases only at a pressure exceeding ten atmospheres when the lamp is in operation, or a mixture of such gases at high pressure with metal vapors the pressure of which is not higher than that of the rare gases.

As shown in Figure 2, a lamp according to the invention is also provided with a starting electrode [3 connected to a seal element, e. g. seal element l5, and with a pair of auxiliary electrodes or pilot electrodes l4 and I4. These pilot electrodes are supported in a similar manner as the main electrodes, and connected to seal elements, e. g. seal elements [6 and I6 respectively. The seals 4 and 5 are also provided with exhaust tubes IT.

The discharge container 1 is a spherical or cylindrical body of uniform wall thickness which is preferably blown in a mold, and advantageously consists of quartz glass. As this material attains maximum mechanical strength at temperatures around 800 C., which is also the operating temperature of the bulb, and since its wall contains no elements like exhaust tubes or seals, it has a considerable mechanical strength sufflcient to withstand internal pressures three to four times the operation pressure of .the lamp.

short necks 2 and 3 which form part of the bulb, are cut precisely at right angles to the main axis of the bulb, and their edges are smoothly ground and possess a profile i8, as indicated in Figure 1, which is essential for a good weld with the seals. Into these neck openings, the molded quartz glass discs IQ of the lamp seals fit precisely, and to this end their edges are also accurately ground and" provided with a-profile;cor-- responding to the profiles of the necks. The

manufacture of these seals which are composed of a plurality of seal elements, and their construction, is described in my co-pending patent application Serial No. 105,525 of even date here.-

with. The metallic conductors which are fused.

into the seal elements consist of metallic strips,

e. g. molybdenum strips, which, underconditions described in my co-pending application, form: a vacuum tight seal with the quartz glass. One

type of arrangement. of the. seal elements 5, l5,

and I '6 on the seal'isillustratedby Figure 3 which. also shows thepositions ofthe suppotringrods it, and of. the. exhaust tube. II;

The electrode arrangement is illustrated by Figure. 4 showing. one set of. main. electrodes 8, which supply the main. arcs while the lamp is in full normal operation, and one of the pilot electrodes M, which are used for starting the lamp and to maintain a pilot. arc which keeps the lamp warmed up and. ready for. instant operation of the main arcs. The main. electrodes consist of tungsten bodies, made. e. g. by coiling. tungsten wire of circular or square cross-section, or by sintering pure tungsten powder, previously pressed in the desired shape, at high temperatures. These electrodes may be of. the nonactivated type, or they may contain a body of activating material which, preferably, consistsessentially of thorium oxide. The. pilot. electrodes are of similar construction, but may be smaller in size, and they are activated by a. storage body composed of a mixture of thorium. oxide and the. oxides of barium, calcium, and strontium. For either' electrode, when of the.

activated electrode type, any other suitable. activationmaterialmay be used, in. the form of oxides or other suitable compounds or in the metallic form. Figure 4. also shows the supporting wire 29 of the starting electrode which is arranged in'the spacebetween. the mainv electrodes, as shown in Figure 2.

The electrodes are" carried by tungsten wires or rods H. which are firmly connected to the supporting structures 9. These may consist of refractory or ceramic material sintered at high temperatures, like zirconium. oxide, as they are exposed to high temperatures when the lamp is operated. Preferably, the supporting wires II are sinteredinto this material. Depending on the electrode arrangement these supporting structures have the shape of a disc, or a ring, or they may be rectangular in shape. They may consist also of a metal, like sheet of molybdenum or tantalum, and in this case, the electrode supporting Wires H from the conducting material of the supports 9. These. elements are firmly connected to the seals 4 and 5 by rods Ill, preferably made of quartz glass and forming part of the seals.

Electrical connection between the conductors of the seal elements and the electrodes is produced by strips or coils [2 which are welded to the molybdenum foils of the seals and to the wires carrying the electrodes. These strips or coils consist of metals of high melting point,

must be insulated ill like tungsten, molybdenum or tantalum, and their lengths and cross sections are conveniently chosen so that a certain amount of heat is produced by the electrical current conducted to the electrodes, sufiicient, if necessary, to beat them to incandescence and to warm up the necks of the lamp, and to accelerate the building up of. the requiredhigh vapor pressure. in the lamp.

During manufacture. of the. lamp, the seals consisting of the molded quartz glass discs I9, the seal elements 6, i5 and IS, the rods I0, and the exhaust tubes 11, as illustrated by Figure 3, are assembled and welded to form one solid body. Then an. electrode supporting structure 9,. already provided with supporting wires II, and electrodes 8 and I 4, is fastened on to the rods I0, and finally the connecting strips or coils I2 are welded to the electrode wires and the molybdenum strips. of the seal elements. The supporting wire 29 of the starting electrode is fastened in a different way as it is convenient to weld it directly to the conductor of the seal element I5, and thus forms part of this elementassembled with the seal. This wire is insulated by a quartz'glass tube 2| which is welded to the seal, as a high voltage is applied to the starting electrode I3 when the lamp is started under high pressure conditions. After the electrode structure of the lamp is completely assembled in this way, the seals are welded onto the neck openings of the bulb. In order to produce a good weld, both the discs of the seals and the openings of' the necks are previously given precise dimensions by grinding, and in this way the weld can be made in a; high temperature electrical furnace and/or by means. of a hydrogen-oxygen flame without appreciable deformation of the quartz material. During this process, the electrode structure is protected against oxidation by an inert. atmosphere. seals have been welded, the lamp, which is preferablyprovided with two exhaust tubes in order to improve, pumping speed and permit continuous flushing, with. a rare gas during the exhaust process, is degassed by application of heat, bombardment of. the electrodes, and running of a discharge, and finally filled with a rare gas and the desired vaporizable metal or metals, and finally sealed off.

As the mechanically weakest. part of the lamp container is the seal and the weld between the seals and the necks, these welds must be made very carefully and speciaLcare must be taken that. no. sharp. angles are formed or remain in.-

ternally, which would lower the mechanical.

strength of this part of the. container. A. good weld is. obtained if, as illustrated in Figure 1, the discs 19 of the seals are givenv a cup like shape so that after the weld has been made, the inside surface obtains a round and smooth curvature as shown in Figure 2. As the spherical or cylindrical bulb itself has a much higher mechanical strength than this weld and the seal, an accidental explosion of the lamp can only start here. In order to prevent the main body of the container from being afiected in such a case, it has been found useful to provide the necks, near the seal weld, with a slight rib or constriction which will stop cracks developing in the weld.

The strips or coils I2 are preferably made of tantalum as an absorbing or gettering material used at an adequate temperature has been found to improve very considerably both starting of the discharge and lamp life.

When both If the lamp is to be used as a rare gas super high pressure lamp, krypton or xenon are preferably filled into the container at pressures above ten atmospheres. In the case of mercury, or of mercury containing some additions like cadmium, zinc, or thallium, a limited quantity is introduced into the container sufiicient to produce vapor pressures above atmospheres, preferably in the range of twenty to thirty atmospheres when under full operation of the lamp all the material, or at least the mercury, is evaporated. Such metal vapor super high pressure lamps usually also contain a small amount of a rare gas for starting the discharge, but it has been found advantageous to fill such metal vapor lamps with rare gases under pressures of several atmospheres as the warmingup time is considerably reduced. The vapor pressurethen may be adjusted somewhat lower than the rare gas pressure.

Lamp dimensions, for a given wattage, depend on optical requirements and the electrical characteristics demanded. Furthermore, stability of the arc and good operating characteristics must be considered. Since the general theory of super high pressure lamps, with respect to the mechanical and gas discharge problems involved, is sufiiciently known, dimensions can be computed and adapted to practical conditions by experiment. As a general rule, the relation between lamp watts and surface of the bulb should be 30 watts per square centimeter if the lamp is operated without forced cooling. A practical range for the arc length is five to twenty millimeters. If forced cooling with com pressed air is used, the surface load may be raised to near 100 watts per square centimeter.

From the viewpoint of lamp operation, the principal problem of super high pressure vapor lamps is starting under high pressure, and when starting a cold lamp, the production of a high pressure atmosphere within a sufiiciently short time.

According to my invention, this problem is solved in the lamp construction already described by providing the lamp with a pair of special electrodes or pilot electrodes. When starting the lamp, a discharge is produced between these electrodes until sufficient metal vapor has developed. Once this arc exists, the main arcs between the main electrodes can be produced any time without the use of high voltage, as the existence of one are is sufiicient, provided this arc, or pilot arc, is not too far away from the main discharge path. In this way, a super high pressure lamp can be kept ready for quick operation either by warming up through the pilot are or by maintaining this are immediately after the main arcs have been interrupted. If the pilot arc is not operated during full operation of the lamp, care must be taken that it is produced prior to the interruption of the main discharge.

In the case of a lamp which is provided with four pairs of main electrodes one of these may be used as pilot electrodes, but the use of a special pair of electrodes has many advantages, as size, position, and activation of these electrodes can be chosen according to their special functions. However, a part of the main arcs may be left operating in such cases where an immediate full operation of the lamp is desired. But initial starting and warming up of the lamp should be done always with the pilot electrodes,

6. as the main electrodes are not adapted to operation under such conditions.

The starting electrode 13, which is built for high voltage operation, is required in such cases when the pilot discharge has been interrupted accidentally, or for initial starting of lamps containing rare gases under high pressure.

The circuit shown in Figure 5 illustrates schematically the operation of a lamp which has four pairs of main electrodes 8 arranged in two sets, one pair of pilot electrodes [4 and I 4', and one starting electrode IS. The electrodes 8 and M are connected through ballasts or resistances 22 and 23, and switches 24 and 25, in parallel to a source of voltage 26 supplying single phase alternating or direct current at or 220 volts. The starting electrode I3 may consist of pure tungsten and is connected to the secondary coil of a transformer 21 the primary coil of which is connected to the source of voltage through the switch 28.

The lamp is started by closing only those switches of 24 and 25 which lie in the circuit of the pilot electrodes l4, while the circuits of the main electrodes 3 remain open. If necessary, a high voltage is impressed on the starting electrode by closing the switch 28 for a short time. The discharge produced between the pilot electrodes warms up the lamp and raises the vapor pressure to a value suificient for the operation of the main arcs, which are started by closing the corresponding switches 25 and 25. The main arcs are thus formed at once as the discharge path of the pilot arc transfers itself to the other electrodes as soon as their circuits are closed. As the lamp is now fully operated the final vapor pressure of more than ten atmospheres is soon produced by total evaporation of the metal. While the main arcs are operating the pilot arc can be switched ofi and stay so as long as the other arcs exist. The pilot arc, however, must be switched on again before the main arcs are interrupted, if the lamp is to be kept ready for further use. When the pilot arc is maintained alone, the vapor pressure will fall off to a certain extent, but the lamp is kept ready for instant starting, as already described, and full vapor pressure can be obtained again within a very short time.

In metal vaporv lamps containing a rare gas at low pressure, the starting electrode and its operation with a high voltage of several thousand volts is required only if all the arcs have been interrupted accidentally, and immediate starting of the hot lamp is required. However, the starting electrode is essential when the lamp contains rare gases under high pressure.

The present invention is not restricted to the one example of a lamp containing four pairs of main electrodes arranged in two sets, and in one plane. Obviously, the number of main electrodes may be larger or smaller, and each set of electrodes can be arranged to form two rows, a triangle, or a square. The lamp can also have but one neck, and in this case all the electrodes would be mounted on one seal, or the bulb is provided with three or four necks and a corresponding number of seals carrying more than two electrode sets. As there are many possibilities for the construction of lamps according to my invention, any desired geometrical combination of arcs can be produced by suitable electrode arrangements. My invention is also not limited to the use of single phase alternatin currents.

A modification of a lamp according to my invention is shown in Figure 6. The discharge container of this lamp is provided with two seals 4 and 5 of which each carries three pairs of main electrodes 29, 30, 3'! and 33, 34, 35 respectively, which are arranged in a triangle, as illustrated by Figure 7. Ihe pilot electrodes 32 and 35, are arranged in the axis of the lamp, and closer to the seals than the main electrodes.

When this lamp is operated with a circuit similar to the one shown in Figure 5, four arcs can be formed between corresponding main electrode pairs and the pilot electrodes. However, if three phase voltage is used for the operation of the lamp a larger number of arcs can be produced. In the case of a three phase four wire system, when the neutral conductor is connected to the pilot electrodes while the phases are connected through ballasts to the main electrodes, phase displaced arcs are produced within each electrode set and the corresponding pilot electrode, and between the two sets also wherever potential differences between electrodes exist. It is often advantageous to use two separate three phase systems which are electrically independent from each other, as in this case the are between the pilot electrodes can be produced, or arcs within each set and the pilot electrode only, or arcs between the two sets without the other arcs.

The use of pre-heated electrodes as pilot electrodes is illustrated by Figure 8 which shows schematically the electrode arrangement of a super high pressure lamp provided with two pairs of main electrodes 37, 38 and 39. id and with one pilot electrodes 4!, and 42, which are of the pre-heated type, and therefore possess two leading-in conductors each. The electrode arrangement of this lamp is further illustrated by the transverse view of Figure 9. Starting of this lamp, and the production of a metal vapor atmosphere of sufiicient pressure for the operation of the main arcs, is particularly facilitated as the heating of the electrodes will both lower the starting voltage and contribute to the warming up of the necks and seals of the lamp. Under high pressure, however, as already explained, one arc must be maintained always for instant operation of the lamp.

Super high pressure lamps of high wattage have been made up to now with one arc only, and for this reason they had to be supplied with large electrodes and seals of high current capacity both of which are diiiicult to make and lead to constructions of the discharge container of reduced mechanical strength. They are not adapted to economical and large scale manufacture,

and their operating characteristics are little satisfactory, as a heavy electrode is hard to start and cannot be operated reasonably under very different conditions of current and vapor pressure.

What I claim is:

1. A high pressure electrical discharge lamp comprising in combination a glass vessel having an opening, a glass seal member engageable with the walls of said opening to close said opening to form a gaseous discharge envelope, an ionizable gas filling within said envelope, said seal member having secured therethrough a plurality of substantially elongated glass seal elements each containing an electrical conductor leading to the discharge chamber of said envelope, a plurality of pairs of spaced electrodes within said envelope for maintaining a plurality of discharge arcs, each of said electrodes bein electrically connected to one of said seal element conductors, at least a pair of said electrodes operable as main electrodes for full operation of said lamp, another pair of said electrodes each being adjacent to one of said main electrodes and of smaller mass than said main electrodes and operable as pilot electrodes to maintain a pilot discharge arc to keep the lamp ignited and ready for instantaneous full operation of said lamp, each pair of are maintaining main electrodes being electrically and independently connectable in parallel to a source of current, switch means for each of said parallel connections.

2. A high pressure electrical discharge lamp comprising in combination a quartz glass vessel having an opening, a quartz glass seal member engageable with the walls of said opening to close said opening toform a gaseous discharge envelope, an ionizable gas filling within said envelope, said seal member having secured therethrough a plurality of substantially elongated quartz glass seal elements each containing an electrical conductor leading to the discharge chamber of pairs of said envelope, a plurality of spaced electrodes within said envelope for maintaining a plurality of discharge arcs, each of said electrodes being electrically connected to one of said seal element conductors, at least a pair of said electrodes operable as main electrodes for full operation of said lamp, another pair of said electrodes each being adjacent to one of said main electrodes and of smaller mass than said main electrodes and operable as pilot electrodes to maintain a pilot discharge are to keep the lamp ignited and ready for instantaneous full operation of said lamp, each pair of arc maintaining main electrodes being electrically and independently connectable in parallel to a source of current, switch means for each of said parallel connections, an incandescible conductor electrically connected intermediate of said main electrodes and a seal element conductor.

3. A high pressure electrical discharge lamp comprising in combination a quartz glass vessel having axial openings, a glass seal member for each of said openings and engageable With the walls thereof to close said openings to form a gaseous discharge envelope, an ionizable gas filling within said envelope, said seal member having secured therethrough a plurality of substantially elongated glass seal elements each containing an electrical conductor leading to the discharge chamber of pairs of said envelope, a plurality of spaced electrodes within said envelope for maintaining a plurality of discharge arcs, each of said electrodes being electrically connected to one of said seal element conductors, at least a pair of said electrodes operable as main electrodes for full operation of said lamp, another pair of said electrodes each being adjacent to one of said main electrodes and of smaller mass than said main electrodes and operable as pilot electrodes to maintain a pilot discharge are to keep the lamp ignited and ready for instantaneous full operation of said lamp, each pair of are maintaining main electrodes being electrically and independently connectable in parallel to a source of current, switch means for each of said parallel connections.

4. A high pressure electrical discharge lamp according to claim 1, comprising a starting electrode of tungsten wire electrically connected to one of said seal element conductors and positioned in the path of an are between said main electrodes.

5. A high pressure electrical discharge lamp according to claim 1, wherein said main electrodes consist of tungsten bodies and said pilot electrodes consist of activated tungsten bodies.

6. A high pressure electrical discharge lamp comprising in combination a quartz glass envelope having a substantially short opened neck, a molded quartz glass seal member in welded engagement with said neck to provide a sealed envelope, an ionizable gas filling within said envelope, said seal element having secured and sealed therethrough a plurality substantially elongated of quartz glass seal elements each containing an electrically conductive metallic strip leading to the discharge chamber of pairs of said envelope, a plurality of spaced electrodes within said envelope for maintaining a plurality of discharge arcs, each of said electrodes being electrically connected to one of said metallic strips of said seal elements, at least a pair of said electrodes operable as main electrodes for full operation of said lamp, another pair of said electrodes each being adjacent to one of said'main electrodes and of smaller mass than said main electrodes and operable as pilot electrodes to keep the lamp ignited and ready for instantaneous full operation, each pair of are maintaining main electrodes being electrically and independently connectable in parallel to a source of current, switch means for each of said parallel connections.

7. A high pressure electrical discharge lamp comprising in combination a quartz glass envelope having substantially short opened axial necks, a molded quartz glass seal member in welded engagement with each of said necks to provide a sealed envelope, an ionizable gas filling within said envelope, said seal member having secured and sealed therethrough a plurality of substantially elongated quartz glass seal elements, each containing axially thereof an electrically conductive metallic strip leading to the discharge chamber of said envelope, a plurality of pairs of spaced electrodes within said envelope for maintaining a plurality of discharge arcs, each of said electrodes being electrically connected to one of said metallic strips of said seal elements, a pair of said electrodes being solid incandescible activated pilot electrodes arranged in the axis of the envelope with each of said pair of pilot electrodes being substantially close to a seal member and operable to keep the lamp ignited and ready for instantaneous full operation of said lamp, at least another pair of electrodes being main electrodes arranged near the central portion of said envelope, each pair of arc maintaining main electrodes being electrically and independently connectable in parallel to a source of current by means of a switch in each of the said parallel connections.

HERMANN EDUARD KREFFI.

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

UNITED STATES PATENTS Number Name Date 2,020,731 Lederer Nov. 12, 1935 2,097,261 Spanner Oct. 26, 1937 2,177,685 301 Oct. 31, 1939 2,241,968 Suits May 13, 1941 2,265,323 Spanner Dec. 9, 1941 2,349,360 Marden May 23, 1944 2,364,889 Blair Dec. 12, 1944 2,459,516 Francis Jan. 18, 1949 2,535,773 Yoder Dec. 26, 1950 FOREIGN PATENTS Number Country Date 573,141 Great Britain Oct. 8, 1945 589,240 Great Britain June 16, 1947

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