US2068287A - Electric lamp - Google Patents

Description

Jan. 19, 1937.

D. GABOR ELECTRIC LAMP Filed oct. 9, 1954 2 sheets-sheet 1 pNveNToRza QE NES GABOR H15 ATTORNEY. 7

Jan. 19, 1937. D. GABOR ELECTRIC LAMP Filed Oct. 9, 1954 2 Sheets-'Sheet 2 ffy. /a

INVENTOR f yDENES SABOR HIS ATTO? UNITED "STATES,

ELECTRIC LAMP Denes Gabonudapest, Hungary Application October 9, 1934, Serial No. 747,593 In Hungary October 14, 1933 13 Claims.

The luminescence of gases and vapours has been utilized for the production of light or ultraviolet radiation in electric lamps of various de- Alamps hitherto realized or suggested is, however, signs. A common and essential feature of all that by means of electrodes or by induction, electric elds are produced in 'a discharge space.A This eld produces an electric stream of ions and electrons and by this stream the input of the electric field is transformed in the same discharge space, partly in heat and partly in radiation. All discharge lamps such as arc lamps, glow lamps, spark gaps or electrodeless induction lamps of all designs, work on this principle.

This invention relates to a lamp or light source in which the transformation of the electric energy into radiation is performed in a manner employing a different principle. The essential part of -the new lamp is a device which shall be called electron beam source, in which the electric input of the lamp is first transformed into kinetic energy of electrons. The velocities of these electrons correspond to the voltage applied to the lamp, which is preferably in the range of 50-300 Y,

volts. Beams of these electrons enter a lighting space, containing gases or vapours or a mixture thereof. The total intensity of these electron beams corresponds to the main current flowing through the lamp. Under working conditions the gases and vapours in the lighting space are ionized and form a plasma, an electrically neutral medium, appreciably free from electric fields. The plasma contains positive ions and electrons in very nearly equal concentrations. The latter, which under working conditions have average energies of the order of a few volts shall be called plasma-electrons, to distinguish them from the beam-electrons, or primaries, which have initial energies of 50-300 volts.

It has' been discovered that a new process for the transformation of the kinetic energy of the primary electrons cornes into action if the intensity of the electron beams and the pressure in the lighting space is properly chosen, resulting in a high lighting efliciency. This process is the transfer of the kinetic energy of the primary electrons to plasma electrons by means of the electrostatic forces acting between these charged particles. The plasma electrons in turn utilize this energy by collision with gas molecules exciting these to radiation. This process has proved more efficient than the direct utilization of the primary energy by collision with molecules. The conditions necessary for the carrying out'of the new process are: a high concentration of plasma-eleotrons, therefore a high primary intensity, and an appropriate choice of the pressure. At too llow a pressure the primary electrons` strike the walls, without having delivered their energy within the lighting space. of the primaries is mainly lost by collisions with molecules and the efliciency decreases again.

Thus for instance in ya lamp filled with neon and working at '70 volts, the eiiiciency was 10 lumens per watt at a pressure of 0.4 mm. neon 10 and a current of 0.6 amp. At 0.3 mm. neon and 0.25 amp. the efliciency was only 5 lumens per watt and at 0.6 mm. and 1.2 amps. only 'l lumens per watt.

Although the optimal pressure varies accord- 15 ing to the nature of the llinggas or mixture, it can be stated as a rough rule that the pressure ls best chosen in such a way that the linear dimensions of the vessel shall be from 5 to 50 times the mean free path of the primaries. This gives for the inert gases helium and neon a few tenths, or argon and the metals of the second column of the periodic system a few hundredths, and for the alkaline metals a few thousandths mm. Hg-pressure.

In the accompanying drawings which illustrate 25 this invention Fig. 1 is a drawing of the lamp, showing only the main parts, I being the vemel containing the lighting space, with walls transparent to the radiation desired. In this example the vessel has the form of a pear-shaped bulb containing near its neck the electron source 2, the design of which is explained later. This source emits electron beams of high intensity, starting for example parallel to the lamp axis, but diffusing 35 soon after leaving the sourceand filling the whole lighting space with a radiating plasma.

The electron beam source in the lamp according to this invention has to emit electron beams with velocities corresponding to 50-300 volts and o intensities of several hundred milliamperes or several amperes into a space filled with 'a highly ionized gas, in a perfectly controlled way. Moreover, the electrons must be produced economically, with as small power consumption as possible.

In the electron beam source according to the invention the strong electron beam required is emitted by one or more electron guns of special design and dimensions by which a perfect control of the beam production is obtained and uncon- 50 trolled gas discharges, especially arcing safely avoided.

According to one method of carrying out the invention a large number of small electron-guns vare chosen. 1t has been found that each of the 55 At too high a pressure the energy 5 weak beams which together constitute the primary beam of the lamp can be produced with a positive characteristic, i. e. with a current rising with increased voltage. This may be effected according to this invention, by a prevailing electronic space charge inside the electron guns. Since each unit possesses a positive characteristie, they can safely work in parallel, and the whole source can even be put on the mains with-v out stabilizing elements such as resistances, chokes and the like, as required by ordinary gas discharge devices.

An example of an electron beam source according to this invention is shown in Figs. 2 and 3. This is constructed essentially of conducting and insulating discs piled together so as to form a solid body. The cathode 3 is a disc of metal, e. g. nickel, having formed in it a. great number of concave dimples 4, which are distributed according to some regular pattern. These dimples form the cathodes of the electron guns. They are coated with electron-emitting materials of low work function, e. g. baryta. The cathodic body is indirectly heated by a heating body 5, a spirally wound wire, e. g. of tungsten, embedded in the groove between two insulating discs B and 'I of refractory ceramic material.

Three discs are placed over the cathode, 8, 9 and I0, all three having corresponding perforations, which together with the dimples in the cathode form the accurately adjusted small electron guns. Of these 8 and I0 are of insulating material, while 9 is conducting and shall be called the accelerating electrode. Disc I0 will be referred to as the plasmaillter, for reasons to be explained below. The whole source is put in a case II, of metal or preferably of ceramic insulating material, to prevent heat losses. 'I'his is fitted with a conducting sleeve I2, representing the anode. This is the electrode through which the current which enters the lighting space in the form of the primary electron beams returns into the system mains. It is almost exclusively carried into the anode by slow plasma electrons. If the anode has a sumcient area there is no anodedrop' on it, nor even a negative drop, and the loss is practically negligibl t Fig. 3 is a view of th so rce from the plasma side, showing the orifices I the electron guns.

Fig. 4 is a section of one o `-the electron guns, on which the working principle can be demonstrated, I4 is the cathode. The concave, that is the oxide coated surface emits electrons which start perpendicularly to it thereby avoiding,y hitting the accelerating electrode I5. Another ini.- portant function of the eoncavity is that it creates an increased negative space charge before the cathode, thus contributing to the current limitation. After passing through the accelerator, the electrons fly across the plasma-filter I6, the most essential part of the device, into the lighting space.

The space I1 between cathode and accelerator will be referred to as the accelerating space. The accelerator may be connected with the anode, in which casethe electrons obtain their full velocity within this space. It may however be maintained at a lower potential. This can be realized, for example by connecting the accelerator with the anode across a high resistance or by putting it on apotentiometer. In this case the electrons are further accelerated between I'I and the plasma, reaching the orice with full velocity.

The plasma-filter I6 of insulating material has the important function of preventing the highly ionized plasma from intruding into the accelerating space, which would lead to a breakdown of the negative space charge and result in an arc, destroying the cathode or the whole source. 'I'his is effected by the filter in `the following way: The walls of the filter collect a number of stray electrons and assume a negative charge. By this they repel the rest of the electrons and therefore the beam is concentrated essentially about the axis of the holes, thus creating a negative space charge. By this a eld is produced along the axis which accelerates slightly the electrons coming from the cathode and repels the electrons coming from the plasma side. The positive ions on the contrary are drawn inwards, but because of the strong radial field most of them are thrown upon the walls, where they are neutralized. Thus only a slight fraction reaches the accelerating space, insumcient to neutralize the space charge or to disintegrate the cathode. On account of its filtering action on the constituents of the plasma, ions and electrons, the member is given the name of plasma-filter.

The electron and heat losses in the filter can be reduced to a few percent of the whole input by correct dimensioning. 'I'he losses are mainly determined by the number of ions formed by the primary beam within the lter, as every positive ion formed attracts one electron to the wall. These losses are also reduced by the circumstance, that the filter holes are heated by the hot cathode. therefore the gas is diluted in them and the mean free path is increased.

An electron gun of the kind described has a positive characteristic which is only a function of the geometrical dimensions and of the gas pressure, but independent of the heating and emissivity of the cathode. Thus the input of such a source can be exactly predetermined and remains constant even if there is an eventual partial wear of the cathode. Beam sources of this kind rcan be put on the mains of lighting systems with 1 the usual voltages of 110-250 volts.

It has been found, that if the plasmalter is properly dimensioned, the accelerating electrode and the concavity of the cathode can be dispensed with, thus allowing an important simplification of the whole device. Fig. 5 shows a section of the simplified electron source, which contains only the plane, preferably oxide coated cathode I8 and the plasmaflter I9. In this case the electrons are accelerated between cathode and plasma.- The action of the negative charge on the walls ensures as described above a positive characteristic. NoA arcing occurs, which would be inevitable if an oxide coated cathode was exposed directly to a plasma. Such a source will start automatically after heating the cathode and applying the voltage, no special starting device being required.

This device will .only work correctly if properly dimensioned, the characteristics being very sensitive to the length and cross dimensions of the holes. For round holes the diameter is the most important dimension, for slits the width. 'I'he importance of the diameter is illustrated by the following example: Let the voltage be volts, the lling gas neon, and the pressure 0.25 mm. For obtaining a current of 40 milliamperes out of one hole the following lengths are required: with 0.89 mm. diameter, 1.3 mm.; with 0.93 mm., 1.8 mm.; with 0.97 mm., 2.5 mm. 'Ihus a. change of 4% in the diameter requires for its compensation a change of about 40% in length.

The importance of the length is shown by the following example: at 100 volts and 0.25 mm. neon a hole of 0.93 mm. diameter yields 40 ma. at 1.8 mm. length, while at 2.3 mm. length it yields only 15 ma.

By varying the diameter and the length of the holes within rather narrow limits it is possible to develop sources for every required voltage and current. As we can still choose the number of the holes freely, there is even an infinite variety of sources possible for one given lamp. Experiments have shown that with a filter having small holes it is possible to keep the length down, and by this the losses, and to have at the same time a low current density, thus preventing excessive wear on the cathode. Excessively small holes however require filters too thin to be easily manufactured and require sources which are too big. On the other hand holes of large diameter require small sources, having few holes or even only one hole. As however the current density in thiscase is high, filters with only one or a few holes are preferably used in conjunction with plasma-cathodes such as are described below. rlhus 1.1 mm. can be considered as a practical upper limit for the hole diameter whereas 0.8 mm. is a practical lower limit.

In another construction of the beam source a plasma may be employed as electron source. This plasma can be produced by an auxiliary discharge, preferably an aro. Fig. 6 is a section of suclr` ay source. 'I'he source contains a cathode 20, which is coated with substances of low work function and is preferably of the type used for arc discharge lamps or rectifiers. The sleeve 2| is the anode of the auxiliary arc. Both cathode and anode of the arc are enclosed in a box 22 of ceramic insulating material. One face of this box is the plasmalter 23. The sleeve 24 on the outside of the box is the anode, as in the previous patterns.

The auxiliary arc, which is operated at low voltage, (l0-25 volts) fills the whole of the inside of the box 22 with its plasma. As soon as the accelerating voltage is applied to the anode 24, electron beams pass 1through the holes. The characteristics of the filter are but little different from what they were with plane cathodes underneath them. With this device filters are practicable having only a few holes or even only one.

Experiments have proved that it is possible to draw almost the whole current of the arc through the holes of the plasmafilter. It is even possible to switch oi the anode 2| after having started the electron beams, the ,whole current flowing now from the cathode 20 to the filter through the plasma corresponding to the negative glow in arcs. The current flows in the form of space charge limited electron beams through the filter 23 i. e. in a way that is essentially different from the electricity transport obtaining in all known gaseous discharge devices. The current returns to the mains through 24 in the form of slow plasma-electrons.

It is however possible to start the phenomenon described not by an arc but by a glow. For this purpose the auxiliary anode 2| is connected with the positive main across a resistance, too high to allow an arc.

In a further development of this invention, the heating of the cathode may be dispensed with, by using a special type of cathode. It is known that on certain cathode materials, which generallyl have low heat conductivity with a high power for electron emission, arcs can be struck on cold cathodes. Fig. 'i illustrates an electron source fitted with a cathode 25 of this kind. A faint glow is started by means of theauxiliary electrode 26, connected across the high resistance 21 to the positive main. The electron beams start instantaneously from the holes of the filter 28 and in a very short tirne'the current increases to its final intensity. For lamps of this kindthe current must not be less than a certain minimum of the order of 1 ampere to secure the self-maintenance of the cathode spot. 23 is the anode. Although the phenomena at the cathode are in this case the same as in an arc, the production of the electron beams by the plasmafilter occurs in essentially the same way. Therefore the current-voltage characteristic is very nearly the same as for the arrangement shown in Fig. 5, the only difference being, that a few volts are added to the voltage for supplying the cathode drop and the heating of the cathode.

Beam sources with plasma electron sources have the great Vadvantage that filters of any shape can be used, the plasma fitting exactly to any surface. Thus for example, a convergent bundle of beams can be produced as shown in Fig. 8. Here the plasmafilter 30 is spherically bent and emits electron beams converging in one point 0. This point is surrounded by a nearly globularly shaped very intense glow. In certain gases and vapours such as helium, mercury and cadmium the colour emitted by this concentrated glow has a different colour from and a higher efficiency than the more diffuse glow surrounding it. In other gases as e. g. neon and sodium the efficiency decreases at too high current densities. die may be used advantageously, as shown in Fig. '9, where the plasmaflter 3| has a convex shape.

An advantage common to the lamps with plasina-source as compared with the other constructions is that the number of fast positive ions striking the cathode can be reduced to almost zero. Thus the cathodes in these sources are working under the same conditions as in low voltage arc lamps permitting of very long lives. Another very important feature of these sources is that cathodes of the self-heating type can be employed, which strike immediately after switching in the lamp. Thus in lamps with permanent gases the lamp gives full light intensity from the start.` In lamps which also contain metal vax pours, the intensity rises further and reaches its final value after a few minutes. It has been found, however, that already the initial efficiency can equal the efficiency of incandescent lamps if neon is used as a starting-gas. Neon gives in the new lamps a soft orange-yellow colour, less glaringly red than in neon discharge tubes.

Theory and experiments have shown that for higher voltages, such as 220-250 volts a better efficiency can be obtained for a given input if two lanmps of half this input and half the voltage are connected in series, than if the whole input is consumed in one lamp. Fig. 10 shows how two lamps can be connected in series in one bulb, using a common electron source. In Fig. 10 the essential parts are:-The cathode l32 and the plasma filter 33. The bulb is divided into two parts by means of a diaphragm 34, a central hole in which is covered by a second plasma-filter 35, of the same dimensions as 33. The anode 36 is flush with the diaphragm and its lead 31 is insulated. Here the plasma of the first chamber 38 serves as electron source to the second cham- With such gases a divergent bun- 1 ber 3S. The two equal plasmaiilters and Il divide the voltage in two equal halves.

So far only direct current constructions have been described. Constructions suitable for alternating current lamps may be made by doubling the essential parts. Fig. l1 shows an alternating current electron beam source, corresponding in design to the direct current source illustrated in Fig.5. Il is the heating body of rei'ra'ctory ceramic material. 'I'his body is fitted with a spiral groove containing the heating coil 4|, which is connected with the system mains parallel to the main lamp circuit. The heating body is iitted with two metallic sheets l2 and which constitute the two cathodes. Instead of sheets a metallic coating such as nickel may be used, for the same purpose. The cathodes are coated with electron-emitting material, such as baryta. 'Ihe cathodes are covered by the plasmafllter M and all parts are enclosed by the ceramic case l5. This is fitted on the outside with two sheets and l1, constituting the anodes. These can be also metallic coatings or preferably carbonized parts of the surface.` The latter is more advantageous, as in alternating current lamps'the anodes have the potential of the cathode in every second half-period and sputtering as well as the danger of arcing is reduced by carbonizing. The whole source-is held together by a rivet 48.

Fig. 12 illustrates a plan view ofthe source with the plasma-filler removed, showing exposed the cathod I2 and I3 on lthe heating body 40. 4B and 41 are the two anodes.

It is also possiblein the .case of alternating current to dispense with the outer anodes and use the cathodes alternatinglyas anodes and cathodes. To avoid however a potential drop between the momentaryanode and the plasma, which would result in haiving the voltage and the input, the number of the holes working as anodes must be chosen greater than the number of holes working as cathodes, e. g. only a part of the holes must be coated with electron emitting material. It is still better to give th'e anodeholesq-greater diameters than the cathode-holes. 'Ihe ariintage of this arrangement is, besides its simplicity, that the sputtered material penetrates very slowly in the lighting space and that the anode loss is utilized in heating the cathodes.

Figs. 13 and 14 show a section and plan respectively of an alternating current beam sourceV with a plasma as electron source. The case 4I is divided in two sections. Each cathode I! and 5l is tted with a shield 5I, 52 opposite the holes of larger diameter 5I of the plasmalter 53. The electron beamspas through the smaller holes 55. Each section of the case contains striking electrodes 56, 51, connected with the mains across high resistances 5I, 59. In Fig. 14 a part of the plasmaillter has been removed.

Fig. l5 is another pattern of the electron beam source according to the invention for alternating current. In this construction the electron beams start through slits radially in all horizontal directions. 6I and 6I are the two cathodes, both heated by the heating body 62 which is connected immediately with the mains. 63 is a at disc. 64 and 65 two cups, all three of refractory ceramic material which constitute together the case of the beam source, leaving appropriately adjusted slits 6i and 61 on both sides of 63 for the passage of the electron beams. 'I'he current returns from the plasma through holes il to the anodes 69, which are shaped as ilares preferably oi.' one A piece with the cathodes. 1l and 'Il are the two striking electrodes, connected with the oppodte cathodes by means of high resistances 12, 13 which can 'easily be manufactured in the form of' thin strips of coating with graphite or some other suitable material on the insulating disc 4.

Fig. 16 illustrates a complete lamp made according to this invention; the bulb 'Il has an approximately spherical shape. The electron beam source 15 projects a little from the neck 1i, which can be long in the case of permanent gases but must be kept short if metal vapours are employed, to avoid condensation of the-metals on cold spots. The seals are preferably beads. sealed in the neck. The lamp may be tted with a screw socket 11 or with any other standard lamp socket. Such a lamp may be secured in any lampholder instead of an incandescent lamp and be operated immediately on the mains of lighting systems with the usual voltage of 1D0-250 volts. 'Ihe current required by the new lamp is of the order of magnitude of the currents of incandescent lamps. Units of any usual or convenient-size can be manufactured.

All gases and vapours can be used in the lamp according to the invention. The eiilciency obtained with these equals the best eiiicienciesl obtained in gas discharge lamps, and even surpasses it in many cases. A particular advantage of the new lamp is, however, that a mixed light can be obtained by using two or more different fllling gases or vapours, which do 'not emit light simultaneously in the known gaseous discharge lamps.

Thus for instance it is possible in the new lamp to have a simultaneous strong emission of neon Vand sodium, while in sodium discharge tubes containing neon hitherto made the light emission of neon is almost totally suppressed by sodium.

For general lighting purposes white light is generally required and this has not yet been realized in a satisfactory way in any gas discharge lamp. In the'new lamp, however, it is possible to obtain a white light of good quality by mixing neon with mercury vapour. A still better quality with a high eiliciency, surpassing considerably the efficiency of incandescent lamps, has

been obtained by maxture of neon, sodium and cadmium. In this mixturej the neon yields the best part of the red and a smaller part of the green, while cadmium yields the blue and violet and a part of the green and red and sodium contributes the yellow line.

'I'hus the new light source possesses a number of advantages, hitherto only obtained with incandescent lamps, but not with gas discharge lamps, such as: white light, broad range of rating, operating on the usual lighting systems without special auxiliary devices as transformers, chokes or the like. automatic starting after switching in, and a handy form, suitableformass production. In addition, however, it has advantages peculiar to luminescent gases or vapours, that is a broad range of colours and high lighting eiiiciency.

I claim:

1. An electric lamp comprising an envelope enclosing a lighting space containing rariiied gases, an anode, an electron beam source which in turn comprises a hot cathode and a body or plasmalter provided with openings for the passage of the electron beams, said body or plasmalter separating the cathode from the lighting space and from the anode, and having insulating material on its surface exposed to the electron beams and to the lighting space, the openings having lateral 76 dimensions so'restricted that the voltage-current characteristic oi' the lamp is positive and independent of excess electron emission by said cathode.

2. An electric lamp for use on alternating current comprising an envelope enclosing alighting space containing raried gases two anodes an electron beam source for emitting electron beams in both half cycles of said alternating current which in turn comprises two hot cathodes and a plurality of bodies or plasmafllters provided with openings for the passage of the electron beams said bodies or plasmaillters separating the cathodes from the lighting space and from the anodes and having insulating material on their surfaces exposed to the electron beams and to the lighting space the openings having lateral dimensions so restricted that the voltage-current characteristic of the lamp is positive and independent of excess electron emission by said cathodes.-

3. An electric lamp comprising an envelope enj closing a lighting space containing rarified gases,l an anode, an electron beam source which yin turn comprises a hot cathode and a body or plasmaiilter provided with openings for the passage of the electron beams, said body or plasmafilter separating the cathode from the lighting space and from the anode, and having insulating material on its surface exposed to the electron beams and to the lighting space, the openings having lateral dimensions so restricted that the voltage-current characteristic of the lamp is positive andv independent of excess electron emission by said cathode, the depth of any one of said openings being not more than three times the smallest lateral dimension thereof.

4. An electric lamp for use on alternating current comprising an envelope enclosing a lighting space containing raried gases, two anodes, an electron beam source for emitting electron beams in both half cycles of said alternating current, which in turn comprises two hot cathodes and a plurality of bodies or plasmalters provided with openings for the passage of the electron beams, said bodies or plasmalters separating the cathodes from the lighting space and from the anodes, and having insulating material on their surfaces exposed to the electron beamsand to the lighting space, the openings having lateral dimensions so restricted that the voltage-current characteristic oi' the lamp is positive and independent of excess electron emission by said cathodes, the depth of any one of said openings being not more than three times the smallest lateral dimension'thereof.

5. An electric lamp comprising an envelope enclosing a lighting space containing raried gases, an anode, an electron beam source which in turn comprises a hot cathode and a body or plasmalter provided with openings for the passage'of the electron beams, said body or plasmafilter separating the cathode from the lighting space and from the anode, said cathode backing said body or plasmalter, said body or plasmaiilter having insulating material on its surface exposed to the electron beams and to the lighting space, the openings having lateral dimensions so restricted that the voltage-current characteristic of the lamp is positive and lindependent of excess electron emission by said cathode.

6. An electric lamp for use on alternating current comprising an envelope enclosing a lighting space containing rariiied gases, tw`o anodes', an electron beam source for emitting electron beams in both half-cycles of said alternating current, which in turn comprises two hot cathodes and a plurality of bodies or plasmaiilters provided with openings for the passage of the electron beams, said bodies or plasmaiilters separating the cathodes from the lighting space and from the anodes, said"cathodes backing said bodies or plasmafllters, said bodies or plasmalters having insulating material on their surfaces exposed to the electron beams and to the lighting space, the openings having lateral dimensions so restricted that the voltage-current characteristic of the lamp is positive and independent of excess electron emission by said cathodes.

7. An electric lamp comprising an envelope enclosing a lighting spacecontaining rarifled gases, an anode, an electron beam source which in turn comprises a hot cathode enclosed in a case and communicating with the lighting space and the anode-only through openings provided in a body or plasmafllter, said cathode being separated `from Vthe body or plasmaiilter by a distance exceeding substantially the length of the mean free path through the gases, said body or plasmafilter having insulating material on its surface exposed to the electron beams andto the lighting space, the openings having lateral dimensions so restricted that the voltage-current characteristic of the lamp is positive and independent of excess electron emission by said cathode.

8. An electric lamp for use on alternating current comprising an envelope enclosing a lighting space containing raried gases, two anodes, an electronbeam source for emitting electron beams in b'oth half-cycles of said alternating current, which in turn comprises two hot cathodes each enclosed in adjacent recesses of a case, and com- .municating with the lighting space and the anodes only through openings provided in a body or plasmalter, said cathodes being separated from the body or plasmalter by a distance exceeding substantially the length of the mean free path through the gases, said body or plasmalter having insulating material on its surface exposed to the electron beams and to the lighting space, the `openings having lateral dimensions so restricted thatthe voltage-current characteristic body or plasmalter provided with openings for the'passage of the electron beams, said body or plasmafilter separating the cathode from the lighting space and from the anode and having insulating material on its surface exposed to the electron beams and to the lighting space, the openings having lateral dimensions so restricted that the voltage-current characteristic of the lamp is positive and independent of excess electron emission by said cathode.

l0. An electric lamp for use on alternating current comprising an envelope enclosing alighting space containing raried gases, two anodes, an electron beam source for emitting electron beams in both half-cycles of said alternating current which in turn comprises two indirectly heated hot cathodes heated by heating bodies connected in `series with each other and to the terminals of the lamp, said heating bodies being parallel to the path oi' the discharge current, a

plurality oi.' bodies or plasmalters provided with openings for the passage of the electron beams,

said bodies or plasmalters separating "the cathodes iromthe lighting space and'from the anodes and having insulatingmaterial on their surfaces exposed to the electron beams and to the lighting space, the openings having lateral dimensions so restricted that the voltage-current 10 characteristic of the lamp is positive and independent oi excess electron emission by said cathodes. v

11. An electric lamp .for use on alternating curt rent comprising an envelope enclosing a lighting space containing rariiied gases, two anodes, an

electron beam source for emitting electron beams in both halt-cycles oi.' said alternating current w,cgmprising a casing having therein two hot cathodes each enclosed in adjacent .recessesof said casing, and communicating with the lighting space only through openings provided in a plurality of bodies or plasmaiilters, said bodies or plasmalters having insulating material on their surfaces exposed to the electron beams and to the lighting space,'the openings having lateral dimensions so restricted that the voltage-current characteristic of the lamp is positive and independent of excess electron emission by said cathodes, said anodes communicating with the 3() lighting space through openings rin .said casing enclosing said cathodes.

12. An electric lamp comprising an envelope enclosing a lighting space containing rariiied gases, an anode, an electron beam source which 35 in turn comprises a hot cathode enclosed in a case and communicating with the lighting space and the anode only through 'openings provided in a body or plasmanlter, auxiliary means inside said case for starting a discharge, said cathode being separated from the body or plasmaiilter by 5 a distance exceeding substantially the length of the mean free path through. the gases; said body or plasmafilter having insulating material on its surface exposed to the electron beams and to the lighting space; the openings having lateral dimen- 10 rent comprising an envelope enclosing a lighting 15 lspace containing raried gases, two anodes, an

electron beam source for emitting electron beams in both half cycles of said alternatingv current comprising a casing having therein two hot cathodes each enclosed in adjacent recesses of 20 said casing, and communicating with the lighting space only through openings provided in a plurality of bodies or plasmalters, said bodice or plasmalters having insulating material or their surfaces exposed to the electron beams and to the 25 lighting space, said recesses` also containing means for starting the discharge, the cathodes being separated from the body or'plasmatllter by a distance exceeding substantially the length of the mean free path through the gases, the openings having lateral dimensions so restricted that the lamp is positive and independentA of excess electron emission by said cathodes.

DENES GABOR.

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