US2196567A - Lamp - Google Patents

Description

April 9, 1.940. 1 5, mm. 2,196,567

F1166. July 27, 1937 2 Sheets-Sheet 1 Patented Apr-.9, 1940 UNITED STATES;

PATENT OFFICE LAMP George Sperti, Cincinnati, Ohio, assignor to Sperti Lamp Corporation, New York, N. Y., a a corporation of Delaware Application July 27, 1937, Serial No. 156,025

24' Claims...

This invention relates to electric light sources of the type embodying an arc, for example, an arc in mercury vapor which provides a source of ultra-violet radiation. This application is a continuation in part of my prior application,

- 0 in low regions, particularly where the atmos- 30 2,046,096, there are disclosed lamps adapted for general use under the same conditions as the ordinary incandescent lamp and' reprodwcing substantially the solar spectrum. These lamps embody an'incandescent elementas a source of 35 visible radiation and an are as a source of ultraviolet radiation, the radiation from these two sources being combined and filtered so that it .about 2950 Angstrom units. The light from 40 these sources is or white color and closely readapted for use in such alamp but also suitable for use per se when the radiation of the incandescent filament is not needed. In accordance with the present practice of making incandescent 55 lamp the incandescent filament is of tungsten (01.1'16-1) andis preferably operated at high temperature plications, and to a novel are unit particularly in a high pressure atmosphere to increase the efllciency of the lamp. In a low pressure ata gaseous discharge, however; such a filament tends to evaporate quickly, causing premature mosphere such as is desirable for the starting of destruction of the filament and blackening of the lamp bulb. By enclosing the filament and the arc in .separate chambers within the lamp, the filament chambermay have a relatively high pressure gas filling such as to prevent evaporation of the filament while the arc chamber may be adjusted to the optimum pressure for starting the gaseous discharge. j

Another reason for operating the incandescent filament at high temperature is that a filament of this kind emits more shortwave energy as its temperature increases. A tungsten filament at the temperatures found in the ordinary incandescent lamp emits in a substantially continuous spectrum down to about 3000- Angstrom units, and although the amount of energy at the extreme short end of the spectrum is small, it is desirable to'preserve these short wave radiations in the light emitted by the lamp because of their therapeutic value. In the ordinary incandescent lamp, these short wave radiations are largely absorbed by the glass bulb, but by the use of an ultra-violet transmitting glass they can be emitted with beneficial results. Preferably, however, the short wave energy of the tungsten filament should be-supplemented by short waves from some ultra-violet source such as an are in a suitable atmosphere such as mercury.

Since such an arc emits radiations of wave.

'lengths below 2950 Angstrom units and hence objectionable, itbecomes desirable to filter the does not contain wave lengths shorter than arc radiation in order to prevent the emission of harmful short waves. transmit freely to the desired short wave length "limit and would be entirely opaque beyond this limit, but the available filter materials do not cut oil sharply so that in order to prevent the transmission of undesirable wave lengths it is necessary to sacrifice a part of the desirable wave lengths. For example, when a mercury arc is used, the filter must absorb substantially all radiations shorter than about 2950 Angstrom units and filter materialsjwhich positively absorb all energy below this point will also absorb a material portion ofthe desirable energy above this point. This'means that the energy both of the are and of the incandescent fila- An ideal filter would ment is partially absorbed in the region immediately above 2950 Angstrom units, or in other the radiation from the are without afiecting the radiation from the filament. In this way all of the beneficial radiation from the filament is preserved and emitted without filtering, while the desired portion of the arc radiation is transmitted. through the filter and superposed on the filament radiation and the undesirable portion of the arc radiation is absorbed by the filter.

Another object is to provide a lamp of the type described embodying an are enclosed in an inner chamber within the lamp bulb and surrounded bya. filtering medium together with a. filament in the outer chamber surrounding the are.

.A further object is to provide an improved lamp of novel construction which operates efficiently and may be constructed cheaply and economically and which is well-adapted for quantity production methods of manufacture.

In connection with alamp of the type characterized above, as well as when the arc only is desired without an incandescent filament, it is desirable to'provide an arc unit such that the are always strikes ator below approximately volts. Glow discharge lamps wherein the discharge is established and maintained by electronic emission from a heated cathode will operate at less than 110 volts. However, such glow discharge devices are not suited for the purposes ofv the present invention because in a small enclosure the walls of the container rapidly' blacken and also because the energy is concentrated in the less desirable short wave radiation.

Accordingly, another object of the invention is to provide a novel are unit wherein the gaseous discharge is not dependent on electronic emission from a cathode but takes place by ionic conduction in a gaseous atmosphere.

Another object is to provide an arc unit'of the above type wherein novel means are provided to insure reliable starting of the arc.

A further object is to provide a novel are unit wherein the operating pressure is high enough that the discharge has the characteristics of a constricted are as distinguished from a glow discharge.

A further object is to provide a novel arc unit wherein no blackening takes place.

A still further object is to provide a lamp embodying a filament and are wherein the arc is embodied in a self-contained unit which can be manufactured and tested separately before being placed in the lamp, or used separately in combination with any suitable current limiting means, for example, a separate incandescent filament lamp.

Another object is to provide a lamp having an arc and an incandescent filament enclosed in separate chambers and so constructed that the heat from the incandescent filament tends to keep the arc chamber at the proper temperature for efiicient arc operation.

Still another object is to keep the arc chamher at a relatively.high temperature by subjecting it to external heatfrom the incandescent filament and insulating the arc chamber to prevent conduction of heat therefrom, whereby uniform heating of the entire arc chamber is obtained to produce the desired vapor pressure.

Several embodiments of the invention have been illustrated diagrammatically in the accompanying drawings, wherein Figs. 1 and 2 are respectively a perspective view and a sectional view of a lamp embodying the invention; Figs. 3 and 4 are respectively similar views of another lamp embodying the invention; Fig. 5 is a detail view of a modification of the lamp shown in Figs. 3 and 4; and Fig. 6 is a diagrammatic view of another embodiment of the invention; but it is to be expressly understood that said drawings are for purposes of illustration only and are not to be construed as a definition of the limits of the invention; reference being had to the appended claims for this purpose.

Referring first to Figs. 1 and 2, the lamp bulb i may be of any suitable size or shape and may be mounted in any suitable base 2 which as shown is of the conventional screw type adapted to be screwed into the ordinary lamp socket 3. The bulb I may be of any suitable material provided only that it transmits the desired ultraviolet radiation. Various ultra-violet transmit-- ting glasses are known. Quartz glass transmits.

freely down to below 2000 Angstrom units, and other glasses are known which transmit freely to points well below 2950 Angstrom units. A special glass known as corex transmits freely down to about 2800 or 2900 Angstrom units and absorbs strongly in the shorter wave lengths. Where a glass such as corex is used for the bulb, it constitutes an additional filter which absorbs the undesirable. short wave lengths, but it is not essential that the material of the bulb have filtering characteristics. The bulb may also be frosted or not as desired.

Fused in the neck of the bulb l is the usual standard or stem 4 which serves as a support for the various elements within the lamp and as a means for introducing the conductors into the' lamp. In the form shown, in accordance with the usual practice, the stem is fused integrally at 5 with the neck of the bulb l and conductors, 6 and I, connected respectively with the screw shell 2 and with the contact 8, extend through the standard and are fused therein. Within the bulb I is a filament 9 of any suitable type, size and shape. For example, a tungsten filament having the form of a ring is supported at its opposite ends by the conductor 6 and by a wire H) the end of which is fused in the stem 4. Filament 9 may also be supported by a plurality of wires l l centrally supported at II on a member to be described hereinafter which, as respects the supporting of the filament, is the counterpart of the glass rod that is secured to the stem'4 in the ordinary incandescent lamp. Preferably the bulb l is evacuated and filled with an inert gassuch as nitrogen, argon, etc., at a relatively high pressure sufficient to prevent substantial evaporation of the filament, which pressure may for example be near atmospheric. This permits operation of the filament at high temperature without excesdescent filament 8 and likewise topermit the If 2,190,507 maintenance independently or a pressure suitable ent of one another the filament chamber pressure may be low if desired and the arc chamber pres sure may have any desired value; The are enclosing bulb or chamber may be of any suitable type, size and shape and may be mounted within the lamp in any suitable manner. In the form shown, the glass rod that is employed as a filament support in the usual incandescent lamp is replaced by an assembly comprising a bulb l3 and a supporting stem l4 secured to the standard I, the upper end of the bulb i3 constituting the filament support i2 referred to above.

The bulb i3 may be of any suitable material which transmits the desired ultra-violet radiations, such as any known ultra-violet transmitting glass, in which case the bulb is provided with an external filter l5 which absorbs substantially all wave lengths shorter than 2950 to 3000 Angstrom units. As filter materials, a thin sheet of mica gives good results,or the bulb it may be coated with various suitable transparent varnishes, preferably of cellulosic base, impregnated or not with a suitable salt which provides the desired absorption. The mica (or varnish, etc.) may be on the inside of the bulb i3 instead of on the outside if desired, as described hereafter in connection with the lamp shown in Fig; 4. If the bulb l3 4 is formed of a material having filtering characteristics, as for example corex, it may not be necessary to add the filtering shield i5 particularly if the thickness of the bulb is increased. Where thin corex is employed, however, it is preferable to use the filter l5 because the thin corex does not positively absorb all of the objectionable short wave energy. The supporting stem ll may be of the same material as the bulb l3 and may be fused to the bulb and to the standard 4, but it will be understood that metallic or other supports may be employed for the bulb.

As indicated above, it is desirable to provide an arc unit wherein the discharge has the characteristics of a constricted arc as distinguished from a glow discharge and wherein the discharge takes place by ionic conduction so that electronic emissi'oii from a heated cathode'is not necessary. In such a lamp the electrodes may have any suitable form and may suitably comprise coils or grids of wire such as tungsten or the like which are proportionedto operate cold or at least at a suifl ciently low temperature that there is no evaporation of the electrode material. To secure starting of the min such a device, however, it is necessary to provide for activation of the electrodes and to this end the electrodes are located in proximity to a quantity of thermionically active oxide and provision is made for heating this oxide @to a relatively high temperature during an initial processing or activating operation. It has been found that after such activating operation, the.

arc will start between the electrodes as soon as the current is turned onv without any heating of 1 trodes, and the filaments 22 and 23 remaining '10.

the oxide, i

In the construction shown in Figs. 1 and 2, provision is made for heating the thermionically active oxide by a heater circuit in series with the incandescent filament 9 to accomplish the desired activation of the electrodes during the filament circuit and an' arc isestablished at relatively high voltage until activation takes place. i

'is increased the are concentrates between sleeves l6 and i1 areheated by internal filaments 22 and 23, filament-23 being connected at one end by means of a conductor 2| with the end of the filament 9 and at the other end by a conductor 25 with one end of the filament 22 and the opposite end of filament 22 being connected by a conduc tor 26 with the conductor 1. It will accordingly be seen that filaments 9, 23 and 22 are in series and that when current passes through this circuit, filaments 22 and 23 become hot and heat thetubes l6 and IT. The sleeveiG is connected by a cond tor 21 with the conductor 26, while the sleeve i is connected by a conductor 28 with the conductor 24, these connections being arranged so that the potential drop through the filaments 22 and 23 is impressed across the sleeves and the electrodes hereinafter'described. To increase the potential drop a resistance 29 may be inserted in the lead 25, whereby any desired drop may be provided while at the same time the heating filaments 22 and 23 may be properly proportioned according to thescharacteristics of the sleeves to give the proper heating effect.

The are chamber i3 is preferably evacuated to a point suitable for eflicient arc operation and contains a quantity of'ionizable material which radiates in the ultra-violet region of the spectrum. A convenient material for this purpose is is notoperating. Should the quantity of mercury vapor exceed somewhat the amount which can be maintained in the arc chamber in the form of vapor at ordinary temperatures, itwill be ad-' sorbed by the elements in the bulb and will condense on the walls of the bulb and then will be vaporized on heating.

In the-form shown in Figs. land 2, the electrodes have the form of fiat coils or grids 3i and '32 which are supported from the tubes i6 and I1 and are electrically connected therewith and with the filament circuit by suitable wires 33 and '34. y

In the initial activating operation, the oxide coatings on the tubes i8 and Il' are heated by. the

Thereafter the arc bulb isfurther evacuated and the mercury and neon or argon introduced,

whereupon the bulbis sealed. After this initial activating operation, the arc strikes quickly between the electrodes 3i and 32 as soon as potential is applied and without allowing time for any, heating of the tubes Iiiand ii, the current passing through the gaseous path between the eleccool. The arc starts-first in the neon or other gas, but as the vapor pressure of the mercury the electrodes as a mercury discharge.

The normal operation of a completed lamp may be summarized as follows, When the lamp is screwed into the socket 3 and current is turned on, potential is impressed across the leads 6 and I causing a potential to be applied across the electrodes 3| and 32, the amount of which depends on the relative proportions of the filament 8 on the one hand and the circuit 22, 29, 23 on the other hand. Preferably, these elements "are proportioned so that the potential across the electrodes is about 60 volts or greater. The neon arc strikes immediately without any preliminary heating of the sleeves l6 and I1. As the filament 9 is heated to incandescence, it imparts heat to the arc chamber I3 which, together with'the heat generated in the arc chamber itself by the discharge current, causes the mercury vapor pres-.

sure to increase so that the arc is converted into a mercury discharge.

Figs. 3 and 4 illustrate a somewhat different construction for a lamp embodying the invention. This lamp embodies a suitable base 2 and outer bulb I in which is enclosed an incandescent filament 35 of tungsten or the like, said-filament ,being supported by wires 36 mounted on an inner bulb 31 and also by supporting wires 38 and 39. It will be understood that these elements preferably are the same as'those described above in connection with Figs. 1 and 2. The are chamber or bulb 31 is in this instance supported by means of a band 40 of suitable metal which surrounds the base of the bulb and has .welded thereto supporting wires 4| and 42 which are fused in the standard or stem 43 of the lamp.

Within the'arc bulb 31 is a pair of electrodes together with a quantity of mercury or other suitable material indicated graphically at 44 whereby an arc is formed between'the electrodes. Adjacent the electrodes are sleeves or tubes 45 of suitable insulating material such as quartz glass, said tubes being surrounded by sleeves 46 of nickel or other suitable material and said sleeves being preferably coated with an oxide or mixture of oxides such as strontium, thorium and barium as described above. Each tube 45 and its sleeve 46 are supported by means-of a pair of metal bands" suitably connected as by welding to a supportingwire 48 that is fused in the usual standard or stem 49 of the inner bulb.- The electrodes themselves comprise grids 50 which in this case take the form of coils of wire such as tungsten surrounding the oxide sleeves and secured to the supports 48 in any suitable manner as by welding. One end of the incandescent filament 35 is connected by a wire with the outer end of one of the supports 48, and the other support 48 is connected by a wire 52 with the lamp base 2. In this way potential is applied to the electrodes to start an arc in the bulb 31, the potential drop between the electrodes being established by a circuit within the bulb 31 which is in parallel with the arc path and which comprises filaments for heating the oxide sleeves during the activation period. As shown, a wire 53 connected to one of the supports 48 leads to a filament 54 positioned within one of the tubes 45. A conductor including a resistance 55 connects the other end of filament 54 with a similar filament 56 positioned within the other quartz tube 45, and the other end of filament 581s connected by a wire 51 with the support 48.

The resistance 55 is the counterpart of the resistance 29 shown in Figs. 1 and 2, except that it is within the inner bulb 31 for' the purpose of reducing the number of leads into the inner bulb and making it an entirely enclosed unit. However, if the arc strikes to the resistance itself it will probably be burnt out very quickly. Hence the exposed resistance 55 is protected as by coating it with a cement such as that known as alundum which is insulating. and does not evaporate. Another means of protecting the resistance 55 is shown in Fig. 5, wherein the quartz glass tubes 45 are connected by a tube 58 of any suitable material, the tubes 45 and 59 being preferably formed by tubing bent into the form of a U.

The bulb 31 is preferably provided with afllter 58 which in this instance is within the bulb 31 .instead of outside it as described above in connection with Figs. 1 and 2. The filter 58 therefore not only. assists in absorbing the short waves so that they are not emitted by the lamp but also protects the material of the bulb 31 from injurious short waves. It is well known that many ultra-violet transmitting glasses when exposed for long periods to ultra-violet radiation undergo changes known as solarization where by the transmission characteristics of the glass are altered. By placing the filter inside the bulb, solarization can be substantially prevented.

Fig. 6 shows another embodiment of the invention wherein the arc element is not contained within an outer bulb as in the embodiments previously described. As .shown in Fig. 6- the arc unit comprises an elongated bulb 60 having an electrode at each of its ends. In the form shown .the electrodes comprise wire coils 6| similar to the electrodes of Figs. 3 and 4, said wire coils 6| being mounted by welding or otherwise on supports 62 that are fused in the ends of the bulb 60 and constitute leads for applying potential to the electrodes. Within each electrode is an oxide coated sleeve or tube 63 containing a heater filament similar to those previously de- -'scribed. These sleevesi or tubes 63 are also carried by the supporting} wires 62 one end of each filament being connected to the support 82 and the other end of each filament to a lead 64 passing through the end of the bulb. The filaments are connected in series with one another by an external connecting wire 65 which may contain a resistance 66 to adjust the potential applied across the electrodes. This are unit is operated in series with a suitable external current limiting device such as an incandescent lamp 61. The operation ofthe arc is the same as described above in connection with preceding embodiments, except that in this case the operating temperature of the arc is maintained only by the energy dissipated within the arc bulb.

The starting voltage for the arc is the sum of the voltage drops in the heating filaments and resistances therebetween and in a device designed to operate on house lighting circuits should be about 60 volts or greater. It will beunderstood that the distribution of energy between the incandescent filament and the arc may vary widely. For a '75 watt lamp, for example, the energy dissipated in the arc may be in the neighborhood of to 20 watts and the remainder may be dissipated in the filament. v In an arc unitsuch as shown in Fig. 6, however, it may be desired to dissipate much greater energy, for example, several hundred watts. During operation of the lamp the arc chamber is maintained at a temperature high enough for eflicient arc operation since it is surrounded by the main filament and enclosed within the outer bulb whereby there is substantial insulation against conduction away of heat. The heat provided in this way causes the are chamber to heat uniiormly throughout so that the desired vapor 'pressurecan be maintained with a very small amount oi mercury and whereby the usual large pool of unvaporized mercury is eliminated The radiation from the main tungsten filament maybe emitted by the lamp without filtering and hence without absorption of any of the available ultra-violet energytherefrom. This preserves in the emitted radiation the small amount of energy at the ultra-violet end of the spectrum of the incandescent tungsten. The radiation from the arc chamber, supposing mercury to be used, is filtered through the walls of the arc'chamber and/or through the filter shield IE or 58 which effectively absorb all of the energy ofobjectionable. short wave lengths. The are energy of longer wave lengths, however, both in the invisible ultra-violet portion of the spectrum and in the blue end of the visible spectrum, passes freely through the walls of the arc chamber and the filter I! or then through the outer bulb l.' x

The resultant spectrum of the lamp is the substantially continuous spectrum of incandescent tungsten having superimposed thereonthe arc energy in the short wave length ultra-violet region and in the blue part of the visible spectrum so that the light from the lamp approachesnatural sunlight very closely in quality. The entire lamp is of simple construction and economical in manufacture. The ultra-violet element can be manufactured separately from the incandescent element and tested separately before being incorporated in the lamp. The manufacture of the complete lamp is thereafter similar to the 58 and are activated so that the arc strikes between them without allowing time for the heater filaments to heat the sleeves. This prevents disintegration and destruction of the sleeves and provides long life. In view of this operation of the arc unit, it will be seen that the heater filaments are not necessary except as a means or activating the sleeves or the electrodes during the manufacture oi the lamp. This also makes for longer life in that the lamp will continue to operate in the same manner if the'heater filament circuit should be burnt out or destroyed during activa tion or thereafter. Since the oxide sleeves carry no arc current, it will also be seen that theyneed not be connected to the circuit.

While only three embodiments of the invention have been described and illustrated in the drawings it will be understood that the invention is capable of a variety of physical expressions. The shape and size or the lamp and of the inner arc chamber and the materials used may be varied as desired. The shape and size of the incandescent filament, and the size, type and form of the arc electrodes can also be varied as desired. The ionlzable material. within the arc chamber may be other than mercury, and the type and characteristics of the filters l6 and 58 will depend upon' the characteristics of the arc, and also on the efiect to be produced. For instance, slight changes in the shortest transmitted wave length will cause varying degrees of tanning and erythema, and such efl'ects can be controlled by the characteristics of the filter. Themost desirable short wave length limit for general purposes is probably between 2950 and 3000 Angmethods now used for constructing the ordinary strom units, but for some purposes it may be deincandescent lamp. Owing to the relatively high sired to emit waves as short as 2800 or 2850 Anggas pressure within the filament chamber, the stromfunits. These and other changes, many of filament can be operated at high temperatures which will now occur to those skilled in the art,

without danger of blackening of the lamp chamher or of premature destruction oi the filament, thus providing greater operating emciency and greater .emission of the short wave length energy.

At the same time conditions within the arc chamber are such as to provide for efliclent operation and there isno possibility of contact of the ionlzable material with thernain filament nor of arcing to or from the main filament. Due to these features, the lamp may be operated disealed inner bulb, an incandescent filament in said outer'bulb, a pair of arc electrodes in said inner bulb, said inner bulb also containing a pair of, thermionically active elements and heatin rectly from 110 volts and hence can be used in filaments therefor, a resistance outside said inthe ordinary damp socket without damage. ner bulb and connected between said heatin Since the light in the lamp is of white color, and filaments in series, the circuit comprising said since the outer bulb may if desired be frosted, the heating filaments and resistance being connected illuminating eflect is the same as that produced in series with said incandescent filament between .by the modern incandescent lamp except that the light shades more toward white than the light from a tungsten filament due to the additional energy in the blue portion of the visible spectrum. If desired, the outer bulb may be left transparent while the inner bulb is frosted preferably on its outside. This procedure hides from view the elements within'the inner bulb and difiuses the illumination from the arc, giving the lamp a the terminals of the lamp, said electrodes being connected to said heating filaments whereby the potential drop through said heating filaments and resistance is impressed across said electrodes.

2. A lamp comprising a closed outer bulb containing an incandescent filament, a closed-inner bulb, means in said inner bulb for establishing an arc comprising a pair oi-electrodes, a pair of thermionically active elements and heating filaments therefor, and a resistance connected in series between said heating filaments, said electrodes being connected to said heating filaments whereby the potential drop through said heating filaments and resistance is impressed across said electrodes, the circuit comprising said heating filaments and resistance being connected in series with said incandescent filament between the 3- A lamp comprising a closed outer bulb containing an incandescent filament, a closed inner bulb, means in said inner bulb for establishing an arc comprising a pair of electrodes, a pair of thermionically active elements and heating filaments therefor, and a resistance connected in series between said heating filaments, said electrodes being connected to said heating filaments whereby the potential drop through said heating filaments and resistance is impressed across said electrodes, the circuit comprising said heating filaments and resistance being connected in series heating filaments and resistance is impressed' across said electrodes, and means for connecting said filaments to a source of electrical energy.

5. An electric arc lamp for emitting ultraviolet and visible light comprising in combination two bulbs of refractory material adapted to transmit ultra-violet and visible light and positioned one within the other, the outer bulb being provided with a base for insertion into a socket,

said outer bulb containing in addition to the inner bulb a filament of substantial resistance and the inner bulb containing mercury, a pair of electrodes each comprising a grid electrically connected to and surrounding a sleeve coated with material adapted to emit-electrons when heated, and a heating filament enclosed within each of said sleeves, said filament in vsaid outer bulb and the filaments in the inner bulb-being all connected in series across the terminals of said base and said electrodes being connected between the points of greatest potential differences of said filaments within the inner bulb whereby the filament in the outer bulb serves as a ballast resistance 'for the arc and as a source of visible light. i

6. A lamp comprising two sealed bulbs one within the other, an incandescent filament in .one bulb, the other bulb containing a pair of -metal takes place, and a quantity of thermionically active material disposed adjacent eachelectrode and separated from the arc path thereby.

7. A lamp comprising two sealed bulbs one within the other, an incandescent filament in one bulb, the other bulb containing a pair of spaced unheated electrodes each comprising a coil of without being heated to a temperature at which evaporation of said metal takes place, and a member having a thermionically active surface disposed adjacent each electrode and surrounded thereby.

8. A lamp comprising two sealed bulbs one within the other, an incandescent filament in one bulb, the other bulb containing a pair of spaced unheated electrodes each comprising a coil of refractory metal wire and an'ionizable medium having a suflicient operating pressure to support a constricted arc discharge between said electrodes, said filament and electrodes being so connected that the lampQzur'rent passes in series through the filament and are path and said elec- 'trodes being proportioned to carry said current without being heated to a temperature at which evaporation of said metal takes place, a member comprising a sleeve having a thermionically active surface disposed adjacent each electrode and screened from the arc path thereby, and a filament enclosed in each sleeve and insulated therefrom, said enclosed filaments being connected in parallel with the arc path.

9. A lamp comprising two sealed bulbs one within the other, an incandescent filament in one bulb, the other bulb containing a pair of spaced unheated electrodes each comprising a coil of refractory metal wire and an ionizable medium having a sufficient operating pressure to support a constricted arc discharge between said electrodes, said filament and electrodes being connected so that the lamp current passes in series through the filament and are path and said electrodes being p oportioned to carry said current without being heated to a temperature at which evaporation of said metal takes place, a

' member comprising a sleeve having a thermionically active surface disposed adjacent each electrode and screened from the arc path thereby, and a filament enclosed in each sleeve and insulated therefrom, said enclosed filaments being connected in parallel with the arc path and each i V sleeve being electrically connected with its adjacent electrode.

10. A lamp comprising two sealed bulbs one within the other, an incandescent filament in one bulb, the other bulb containing a pair of spaced unheated electrodes each comprising a helix of refractory metal, said electrodes and filament being connected so that the lamp current passes in series through the filament and arc path and said electrodes being proportioned to carry said current without being heated to a temperature at which evaporation of said metal takes place, an ionizable medium in said are bulb having a suflicient operating pressure to support a constricted arc discharge between said electrodes, a

sleeve within eachhelix having a thermionically active surface, and a filament enclosed within each sleeve and insulated therefrom, said filamerits being connected-in parallel with the arc path.

within the other, an incandescent filament in one bulb, the'otherbulb containing a pair of spaced unheated electrodes each comprising a helix of refractory metal, said electrodes and filament being connected so that the lamp current passes in series through the filament and are path and said electrodes being proportioned to carry said current without being heated to a temperature at which evaporation or said metal takes place, an ionizable medium in said arc bulb having a suflicient operating pressure to support a con- 11. A lamp comprising two sealed bulbs one,

' ments being connected in parallel with the arc path and each sleeve being electrically connected with its adjacent electrode.

12. A lamp comprising two sealed bulbs one within the other, an incandescent filament in one bulb, the-other bulb containing a pair of spaced unheated electrodes of refractory metal and a quantity of thermionically active material disposed adjacent each electrode and screened thereby from the arc path between said electrodes, means connecting said electrodes and filament so-that the lamp current passes in series through the filament and are path, and an ioniz able medium in said bulb comprising a rare gas and a vaporizable material in an amount less than that required to saturate the space in said are bulb at normal operating temperature of the device but suflicient to support aficonstricted arc discharge between said electrodes.

13. A lamp comprising two sealed bulbs one within the other, an incandescent filament in one bulb, the other bulb containing a pair of spaced unheated electrodes of refractory metal and a pair of elements comprising a thermionically active material, one of said elements being adjacent each electrode and screened thereby from the arc path "between said electrodes, each element being electrically connected to its adjacent electrode and said electrodes and filament being connected so that the lamp current passes in' series through said filament and the arc path between said electrodes, -an ionizable medium in said bulb comprising a rare gas and a vaporizable material in an amount suflicient to support a constricted arc discharge between said electrodes at normal operating temperature.

14. A lamp comprising two sealed bulbs one within the other, an incandescent filament in ,one

bulb, the other bulb containing a pair of spaced unheated electrodes of refractory metal and a pair of elements comprising a thermionically active material, one of said elements being adjacent each electrode and screened thereby from the arc path between said electrodes, each-element being electrically connected to its adjacent electrode and said electrodes and filament being connected so that the lamp current passes in series through said filament and the arc path between said electrodes, an ionizable medium in said bulb comprising a rare gas and a vaporizable material in an amount suiiicient to support a constricted arc discharge between said electrodes at normal opera-ting temperature, said electrodes being proportioned to carry the lamp current without bein heated to a temperature at which evaporation of said refractory metal takes place.

15. An arc lamp comprising a bulb, a pair of spaced unheated arc electrodes therein each comprising a coil of refractory metal wire, each coil surrounding an element comprising a thermionspaced unheated arc electrodes therein each comprising a coil of refractory metal wire, each coil surrounding an element comprising a thermionically active oxide, an ionizable medium in said bulb having a suflicient operatingopressure to support a constricted arc discharge between said electrodes, said electrodesbeing proportioned to carry the arc current without being heated to a temperature at which substantial evaporation of said refractory metal takes place, said bulb being enclosed in an outer bulb to. prevent conduction of heat awayfrom said inner bulb.

17. An arc lamp comprising -a bulb, a pair of spaced unheated arc electrodes therein comprisingcoils of refractory metal wire, an element adjacent each electrode comprising a thermionically activeoxide, said electrodes being proportioned to carry the arc current without being heated to a temperature at which substantial evaporation of said refractory metal takes place, and a vaporizable material within said envelope inan amount which is less than that necessarytto saturate the space within said bulb at' the normal operating temperature of said device but which and a vaporizable material said envelope in an amount which is less .than that necessary to saturate the space within said bulb at the normal. operating temperature of said device but which is sufiicient to support a constricted arc discharge between said electrodes, said bulb being enclosed within an outer bulb to prevent conduction of heat away from said inner bulb.

19. An arc lamp comprisingabulb, a pair of fl? spaced arc electrodes therein each comprising a helix of refractory metal wire, an element coated with a, thermionically active omde within-each helix, said element and helix being electrically connected and at the same potential, and an ionizable medium in said envelope comprising a. vaporizable material in an amount which is less than that necessary to saturatethe space within said bulb at the normal operating temperature of said device but which is suflicient to support a constricted arc discharge between said electrodes.

20. An arc lamp comprising a. bulb, a pair of spaced arc electrodes therein each comprising a helix of refractory metal wire, an element coated with a thermionically active oxide within each helix, said element and helix being electrically connected and at the same potential, and an ionizable medium in said envelope comprising a vaporizable material in an amount which is less than that necessary to saturate the space within said bulb at the normal operating temperature of said. device .but which is suflicient to support a constricted arc discharge between said electrodes, said bulb being enclosed within an outer bulb to prevent conduction of heataway from said inner bulb. f

21. An arc lamp comprising a. bulb, a pair of spaced unheated electrodes therein of refractory metal, a thermionically active element adjacent each electrode and with the adjacent electrode interposed between said element and the arc path, each of said elements comprising a sleeve coated with refractory oxide and a filament within and insulated from said sleeve, a pair of leads,

.to one of said leads, and an ionizable medium in said envelope comprising a vaporizable material and having an operating pressure sufilcient to support a constricted arc discharge between said electrodes.

22. An arc lamp comprising a bulb, a pair of spaced unheated electrodes therein of refractory metal, a thermionically active element adjacent each electrode and with the. adjacent electrode interposed between said element and the arc path, each of said elements comprising a sleeve coated with refractory oxide and a filament with? in and insulated from said sleeve, each sleeve being electrically connected directly to its adjacent electrode, a pair of leads, said filaments being connected in series across said leads and each electrode being connected to one of said leads, and an ionizable medium in said envelope comprising a vaporizable material and having an operating pressure sufiicient to support a constricted arc discharge between said electrodes.

23. An arc lamp comprising a bulb, a pair of spaced unheated electrodes therein each comprising a helix of refractory metal, a thermion ically active element disposed within each helix and comprising a sleeve coated with refractory oxide and a filament within and insulated from said sleeve, a pair of leads, said filaments being connected in series across said leads and each helix being connected to its adjacent lead, and an ionizable medium in said envelope comprising a vaporizable material and having an operating pressure suflicient to support a constricted arc discharge between said electrodes.

24. An arc lamp comprising a bulb, a pair of spaced unheated electrodes therein each comprising a helix of refractory metal, a thermionically active element disposed within each helix and comprising a sleeve coated with refractory oxide and a filament within and insulated from said sleeve,jeach sleeve being electrically connected directly to the surrounding helix, a pair of leads, said filaments being connected in series across said leads and each helix being connected to its adjacent lead, and an ionizable medium in said envelope comprising a vaporizable material and having an operating pressure sufllcient to support a constricted arc discharge between said electrodes.

GEORGE SPERI'I.

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