US2135715A - Electric lamp - Google Patents

Description

Nov. 8, 1938.

G. E. INMAN ELECTRIC LAMP 5 Sheets-sheet 1 Filed Aug. 50, 1.93/1

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Inventor: George Blnman,

H@ Attfmwey- G. E. INMAN ELECTRIC LAMP Filed Aug. 30, l1925-1 3 Sheets-Sheet 2 Inventor: George E. by

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G. E. INMAN ELECTRI C LAMP Nov. 8, 1938.

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Inventor:

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Patented Nov. 8, 1938 PATENT, OFFICE ELECTRIC LAMP George E. Inman, East Cleveland, Ohio, assignor to General Electric Company, a corporation of New York Application August 30,

6 Claims.

This invention relatesto electric lamps and the like, and particularly to vapor lamps such as the so-called low-pressure positive column" type or the cathodic glow type, lgiving diiIuse rather than sharply localized or intense concentrated luminosity. Theinvention is concerned with lamps that contain a. vaporizable working substance, e. g., sodium and some other metals, and operate with very small v'aporV pressure of such` substance. In such lamps, the absolute vapor pressure of the working substance is usually about l or 2 microns for sodium.l Vapor pressures of low order are characteristic `of the typical diiuse glow discharge, that generally appears to ll the whole lamp bulb.

Very usually, vapor lamps contain a small amount of easily ionized gas like neon, argon, etc., whose (partial) pressure in the lamp is around 1 or 2 to 7 mm.,'to assist'in starting the sodium or other vapor discharge. This is the more desirable in lamps using a difllcultly Vaporizablel working substance like sodium, ascontrasted with one that is much more easily vaporized like mercury.

Commercial sodium vapor lamps aim at operating temperatures around 250 C. for maximum 'eiciencyi while the actual temperatures of their 'envelope or bulb walls range from about 220 C.-

or less to about 275 C. or more. The boiling point of sodium being about 877 C., the sodium vapor in the commercial lamp bulb is continually condensing on its inner surface and Vaporizing again, .with a tendency toy accumulate and remain in'any region or area that is relatively cool, because of the slower vaporization from the cooler region. This means that the sodium vapor pressure in the envelope will tend to fall below that corresponding to the general lamp temperature, and to approach thatcorrespond- 40 ing to the lowest temperature: i. e., that the'lamp will virtually lack sodium, and its light output and efficiency suier correspondingly. Or if the attempt is made to remedy this by forcing the lamp to operate at a higher current density in the glow discharge, and thus heat up its coolest region(s) to 250 C. or thereabout, then the general lamp temperature will be forced still higher,

and the efciency will also suffer.

Practically, it is very difficult to designa commercial lamp of the diiuse arcl discharge type containing' dificultly vaporizing metal so as to be evenly heated by its arc discharge; and the variation in wallftemperature is apt to be even less favorable than the above-suggested 1934, serial No. 742,126

range of 220 C. to '275 C. in the sodium vapor lamp.

While an adequate though small vapor pressure of sodium or the like is essential to the operation of an arc discharge vapor lamp, and while the most favorable sodium pressure for eiliciency is that corresponding` to a (uniform) temperature of about 250 C., the current density in the discharge is also very important to the eiiiciency, and in a contrary sense: i. e., the lower the current density, the greater the luminous efciency of the discharge. However, discharge currents that would be highly favorable `from this point of view are insumcient to heat the lamp to the temperature that is most favorable as regards vapor pressure of a working substance suchA as sodium. This is so even when the sodium vapor lamp is operated in a double-walled vacuum jacket in orderto` conserve heat, as is customary.

Other limitations and drawbacks of such vapor lamps have lain in the necessity of a ballast resistance in series with the lamp, to control and limit rise of current through the lamp as it heats up; and of either providing compensating resistances, reactors, or transformers to allow such lamps to operate in parallel on ordinary (alternating current) lighting circuits of -120 volts, or else operating a plurality of the lamps in series.

I have found that these difliculties can be overcome, and a very high' operating eillciency realized in a lamp of vthis general type, by supplying additional heat as uniformly as possible ahd as nearly according to the deficiency in the various parts of the lamp as possible, so as to maintain a proper uniform lamp temperature with a relatively low discharge current, or current density. Preferably, and as hereinafter described, the lamp is heated internally. Suitable electrical heating means for this purpose may be operated independently, from a separate heating circuit, or may be adapted and used to ballast the lamp, or' may be used.to compensate for its low operating voltage. Useful light may be obtained f rom an incandescent body or filament thus employed, as well as heat; and the enhanced luminous Veillciency ofA the glow discharge will make up for relatively poor luminous eiilciency of such a, filament. With the improvement in eiiiciency, I may combine improvement in quality of the light, compensating for color deciency in the glow discharge, and even approximating a white light.

I also aim to make the v'apor lamp a complete operating unit in itself, without need of extrinsic accessories, such as external ballast, or resistance's, reactors, or transformers. I have here particularly-illustrated and described my invention as applied to lamps of cylindrical or tubular form; but while the cylindrical or 'tubular shape lends itself very advantageously to my purpose, it is not essential, and the invention in its broader aspects can be adapted to other shapes.

Various other features `and advantages of the invention will appear from the following description of species thereof, and from the drawings.

In the drawings, Fig. -1 is a side view of one form of lamp embodying my invention, particularly adapted for operation on alternating current.

Fig. 2 shows a vertical section through one of the electrodes shown in Fig. 1, on a larger scale.

Fig. 3 shows a vertical section through the electrodes and a refractory insulative tube on which they are mounted-certain parts being broken out--and illustrates a modification.

Fig. 4 is a side view of another form of lamp embodying the invention.

Fig. 5 is a diagram of the electric circuits and connections of the lampshown in Fig. 4.

Fig. 6 shows a vertical section through one of the electrodes shown in Fig. 4.

Fig. 'I is a side view of still another form of lamp embodying the invention.

Fig. 8 is a plan view of a spider at the top of the lamp mountv of Fig. 7.

Fig. 9 is a fragmentary side view of the lower portion'of the lamp mount of F1227, taken at right angles to Fig. 7.

Fig. l0 is a diagram of the electric circuits and connections of the lamp shown in Fig. '7.

The lamp shown in Fig. 1 comprises an envelope or bulb I0 of elongated cylindrical or tubular form, with spherically rounded end(s), and a mount II sealed into the lower end of the envelope. Being equipped with an Edison screw base I2, this particular lamp has a reduced neck I3 on which the base is secured, and its mount I I includes a tubular stem I4 sealed into the neck I3 within the base I2. Current leads I5, I6 are connected to the shell and center contacts of the base I2 and extend in through the stem I4, and are sealed in the press I1 at the inner (upper) end of the stem. In the stem I4 is also shown an exhaust tube I8 that opens into the bulb neck through the stem press I1 and is sealed oil.' at its lower end, which is hidden by the base I2. Besides stem I4 and leads I5, I 6 the mount II may include electrodes 20, 20 for the luminous glow discharge, and means for independently heating the envelope I0, as already mentioned.

The electrodes 20, '20 may be centrally arranged in the envelope vor bulb I0, so that the discharge shall tend to heat, the envelope. I0 as evenly as possible. As shown, the upper electrode 20 is almost or entirely in the upper spherical end portion of the bulb I0, while the lower electrode 2li is partly in the lower spherical end portion and partly above it. These electrodes 20, 20 may be of either indirectly heated or directly heated electron-emissive types, such as known in the art.

The independent 'heating means for the envelope I0 should be symmetrically arranged therein as regards itsV heating eilect, which generally means at as uniform distance as may be from the nearest 4envelope wall everywhere. In a tubular envelope'l, these` principles are Perhaps best satisfied by a cylindrical or linear (electrical) heater extending coaxially with the envelope III between the electrodes 20, 20, as in Fig. 1. The actual heating device here shown is a resistance wire or filament 22 (of tungsten or other material of positive temperature-resistance coeiiicient) wound in a fine helix, and heated to bright incandescence by the current through it. This heating resistance 2'.' isl preferaby enclosed in an insuiative refractory radiat ng tube 24v, of beryllia or other suitable oxide (such as thoria, alumina, or magnesia), which may be heated to a low incandescence of visible redness by the filament, thus transforming the (brighter) radiation oi' the filament to red. .The tube 24 is also adapted to prevent a discharge between'the filament 22 and one of the electrodes 20, 20 wheny there is considerable difference of potential between them, thus allowing the device to operate under a higher voltage than might be practicable without it. The electrodes 20, 20 are mounted directly on the ends of the tube 24, preferably beyond the ends of the iilament 22. The tube 24, which thus serves as a principal supporting member for various operating parts, may be mounted on the stem I4 in any suitable way, as by inserting the upturned end of the irregularly Z-bent stem lead I5 in the lower end of the tube 24, `and cementing it there, if desired. .The upper end of the tubular member 24 may be steadied -by attachment or engagement at this end of the bulb III, as around` a (molybdenum) wire 25 fused into the bulb 'wall at 26, and cemented into the tube 24 if desired. The heating filament 22 may be (electrically) connected and stretched between the end of lead I5 inside the tubular member 24 and the lower end of wire 25, which thus serves as a lead for the filament. In the present instance, the leads I5 and 25 extend into the tube 24 substantially all the way through the electrodes 20, 2l), and the filament resistanceV 22 only occupies the portion of the tube 24 between the electrodes; but in the aggregate, this heating resistance' with the electrodes extend axially lsubstantially or approximately from end to end of the main vapor space of the envelope III, above the neck I3. The like is true of the "heater broadly if regarded as coextensive with the tube 24, which diffuses the heat of the iilament lengthwise and radially throughout its own length.

The construction and mounting of the electrodes 20, 20 on the member 24 may be identically the same, and is shown for the upper electrode in Fig. 2. This upper electrode 20 includes a heating resistance coil 30 wound helically on the member 24, and consisting o! a (tungsten) filament itself coiled in a fine helix. To the ends of the heating resistance 30 are connected (molybdenum)l current leads li and 32, which also make a couple of turns around the member 24. These resistance and lead coils are enclosed or embedded in a refractory insulative covering 33, which may be formed of a beryllia paste applied as suchand then baked on. Around the covering 33 is fixed a (nickel) tube 34, which is in turn coated with electron-emissive material 35, such as barium oxide. From their coils, the current leads 3I, 32 extend lengthwise oi' the member 24 out from under the beryllia covering 33, andl just outside it each of them is anchored to the member 24-as by a lashing of a couple of turns of (molybdenum) wire 36 with its ends twisted together-to prevent any slight pull on the lead from disturbing the covering 30. The upper electrode lead 3l is welded to another (molybdenum) lead wire 31, to which is also welded another lead 38 itself (electrically) connected to the emissive-coated tube 34 of the upper electrode 20. 'I'he lower electrode 20 has current leads 32, 39, likewise-lashed and anchored to the member 24. The lower lead 32 of the upper electrode 20 and the upper lead 32 of the lower electrode 20 are directly connected, preferably by being in one continuous length, which is here shown as making about one and a half turns around the member 24 between the' two electrodes.. The lower lead 39 of the lower electrode 2U is welded to the stem lead I6, which extends `up into the bulb l to one side of the member 20. The emissive-coated tube 34 of the lower electrode- 20 is also connected to the stern lead I6 by a lead 4I welded to the latter.

While the resistance 22 and the discharge gap between the electrodes 20, 20 might be connected. in parallel so far as the heating function of resistance 22 is concerned, there are important ad- Subject to this last limitation, it need not, of I vantages in connecting them in series, which is accomplished by welding the lead wire 31 to the wire 25 already mentioned, as shown in Figs'. 1

and 2. Thus the (tungsten) filament 22 ballasts the lamp, and may also increase the over-all resistance of the lamp so as to enable the lamp to be operated onv standard lighting circuits of around 110 to 120 volts. Assembly of the lamp as-hereinafter described is easier if the wire 31 is somewhat iiexible or even resilient between its connections to wires 3l and 25, which is facili-` tated by coiling this portion of wire 31 in a few large turns encircling wire 25.

In a lamp bulb of the type here shown, with a reduced' neck I3 and a stem I4, it is difdcult or impossible to bring the neck to the same temperature as the bulb proper, since the contracted space or recess in the neck tends (for various reasons) to run cool. is a loose-fitting glass shield 42, of inverted cup form, occluding the neck I 3 about where it merges or joins with the bulb proper, with a narrow but extended clearance or crack 43 around the shield, that will be closed by the (liquid) sodium or other working substance condensing in the clearance when the lamp is first operated for any length of time. Thus the crack or joint at 43 is sealed and the neck recess is eiectually shut off from the vapor space of the bulbl I0, so that lit cannot gradually entrap nearly all the metal in the lamp and leave the'latter with an inadequate atmosphere of metal vapor, as explained above. When this type of shut-oil' is used, the lamp y should be charged with an excess of sodium or other metal as compared with ordinary practice, so that after formation of the seal at 43, there may still be plenty of metal left for the normal operation of the lamp. The width of the clearance or crack at 43 should be great enough to insure against its being all taken up by temperature changes, so as to grip the shield 42 tight in the neck I3 and perhaps burst the latter; and it should be small enough all around the shield to be in a practical way capillary;.so that a film of (liquid) metal cannot exist indefinitely on one or `both walls of the clearance (the adjacent shield and neck surfaces) without eventually touching the opposite wall all the way around.

course be uniform all around the shield, and the latter may even touch the surrounding wall atone side. In general, a clearance of about 0.01.

As shown in Fig. 1, there inch radial width, more or less, will be found member 24, which may be tignuy cemented' l therein as indicatedat 45. The lead wire I6 extends through a` small hole in the shield 42 and is cemented tightly therein as indicated at 46. On the lead wire I6 is shown (insulatively) mounted 4a hermetically sealed glass capsule 41 for containing a charge of vaporizable working substance. 'I'his capsule 41 may be encased in a short length of thin-walled (nickel) tubing 48 crimped in at the ends to retain the capsule.

In the manufacture of the lamp, the mount Il with `all the partsand their connections above describedincluding stem I4, leads I5, I6, capsule 41 (if used), members 24, shield 42, electrodes 20, and wire 25is completed as shown in Fig. 1 before insertion in the lamp bulb I0, which at this time has a hollow tabulature 49 (like an exhaust tubulature) on its upper end, as indicated in dot and `dash lines in Fig. 1. After inserting the mount II in the bulb lll with the upper end of wire 25 in the tubulature 49, the latter may be fused oif and sealed around the Wire 25 as shown in full lines; and then the stem I4 may be sealed into the neck i3 with the usual pull-down? fused seal used in incandescent lamp manufacture. The pull-down thus given the mount 'II in sealing-in draws the finely-coiled heating resistance filament 22 taut inside the tubular member 24, its coils stretching apart to permitany amount of pull-down required. 'I'he wire 3,1 will yield either to allow wire 25 to push into member 24 when the mount Il is inserted inv bulb i0, or to permit the lsubsequent pull-down or both.

If the wire 25 is cemented or otherwise fixed tight in the upper end of the tubular member 24,-

with the filament 22 properly stretched therein, the operation of fusing the wire 25 into the hollow (dot-and-dash) tabulature 49 will most naturally be deferred until after the stem I4 has been sealed into the neck I3 (with the usual pulldown seal). The fusing ofwire 25 into tubulature 49 may also be thus postponed, if preferred, even when Wire 25 is not cemented or otherwise fixed in the upper end of member 24.'

After the lamp has been exhausted, it may bev rounding the lamp Ill and the capsule is thusheated until the pressure of its contentsdue to the heat generated in the metal casing 48 explodes or ruptures-the capsule, which is softened by the heat. If the energy of the high frequency coil is powerful enough, the metal casing 48 may be dispensed with; although it is useful to re-4 tain the pieces of the ruptured capsule.

Fig. 3 illustrates a modified construction in which the heating resistance 22 extends through the electrodes 20, 20, and may assist in heating them. In this case also, therefore, the resistance 22 may extend with the electrodes 20, 20 substantially or approximately from end to end of the bulb (not shown), as pointed out in connection with Fig. 1.

In the operation of thedevice, starting cold;

the current flows at first through the electrodeheating resistances 30, 3|) and their interconnecting lead 32 and the envelope-heating resistance 22, in series; but as the electrodes 20, 20 heat up, more and more currentis carried by ions of the neon or other gas inthe gap between them. As the whole lamp heats up and vaporizes some sodium or other metal, the metal ions `participate in the luminous discharge-in shunt with the resistances 3i),` 30 and lead 32. The lamp is internally heated by the lament resistance 22 as well as by the heat incident to the arc discharge (including that of the electrode-heaters 30, 30),

vand the member 24 absorbs heat from all these sources and equalizes its distribution lengthwise of the envelope I0. There is also an automatic equalization due to the shunting of current away from the electrode heaters 30, 30 by the discharge as it increases. space are heated to substantially uniform temperature throughout their extent by coaction of the heater 22 with the discharge, assuring an adequate supply of metallic vapor for carrying the current of the luminous discharge, and giving very much greater luminous emciency than if the lamp had to be forced in order to vaporize the sodium entirely by the heat of the glow discharge.

As already stated.' a sodium vapor lamp operates mos't eiiiciently at a temperature of about 250 C.; so that the less current has to be used in the glow discharge to maintain this tempera- .ture of the envelope, the better the lamp eiliciency. Lamps constructed in accordance with my invention operate at about 250 C. with a discharge energy consumption as low as about 0.1 or even 0.05 watt per square centimeter of envelope surface. While this gain in glow discharge eiiiciency is partly oiset by the energy used in the (tungsten filament) heating resistances 22, which (especially with their coverings 24) are less efiicient light producers than the discharge, the

overall luminous elciency is still very much improved by the heater.

While combination of the red-deficient yellow light from sodium vapor with that of a tungsten lament 22 would give a combined light of improved quality even with the lament bare because of the compensatory red-emitted by the tungsten, the greater quantity of red emitted by the ceramic (beryllia) tube 24 when heated by the filament sufllces (when the parts are properly proportioned) to compensate substantially quantitatively for the red deficiency of the sodium glow, or, in other words, balances the yellow. By including a small compensatory amount of mercury with the sodium in the lamp, the yellow of the sodium can be balanced with the bluegreen from the mercury, as Well as with the red from the tube 24, and a substantially or approximately white light thus produced. Whether this is done or not, more complete mixture of the different qualities or color tones of light from the glow discharge and from the heater (22, 24) can be obtained by enclosing the device in a lightdiffusing globe, or by frosting the envelope i0, or by a combination of such measures. When the lamp is enclosed in a glass vacuum jacket to reduce the loss of heat, as is commonly done with sodium vapor lamps, one or both walls of such jacket may be frosted or otherwise made diffusing.

The independent envelope-heating means need not necessarily be concentrated in a single axial heater as in Fig. l, but may be divided into a plu- Thus the walls of the vapor extend in the direction of the electrodeaxls asl in Fig. l.' `The electrodes 20a, 20a iiccupyl the same positions (axial and longitudinal) inthe bulb as in Fig. 1, and are interconnected by an axial (molybdenum) current lead 32a. 'I'his lead 32a may be supported at midlength from the members 24, 24 by a bridge support comprising (molybdenum) wires 50, 50 wrapped around the members 24, 24 and fused into an insulative refractory (alumina) part 5I through'which the lead 32a extends. 'The lowermelectrode v20a is connected to the upper end of th stem lead I6, which extends up through a" refractoryinsulating (alumina) tube or sleeve 24a in which it may be tightly cemented. The upper electrode 20a is connected vto the wire 25a sealed into the upper end of bulb metal condensation as in the clearance 4l, and

While various connections of the heating illa.- y

ments 22, 22 with reference to the electrode discharge gap are possible-e. g., all in parallel or all in seriesL-I prefer to connect the filaments in parallel with one another and in series with the discharge gap. This is accomplished by welding both leads |5a, i5a to the stem lead I5 and welding both leads 25h, 25h, to the wire-25a. As shown, the leads 25h, 25b are vreally legs of one U-bent wire whose mid-portion is weldedto the wire 25a at the upper end. of the upper electrode 20a.

In Fig. 4, the shield 42a not only forms part of the mount i2, as in Fig. 1, but also serves as a means of holding the tubular supporting members 24, 24 in position relative to one another, and of mounting the lower electrode 20a in mid-position relative to them. This purpose, indeed,V the shield 42a answers even more effectively and directly than does the union of the leads i5a, I5a, I6 and I5 by welding and bythe stem i4. Projecting inward from the shield 42a, the long, slender, members 24, 24 have their opposite ends heldin proper relation by the spider formed by the united wires 25h and 25a, which also serves as a means of mounting the upper electrode 20a in mid-position relative to the members 24, 24. The supporting members 24, 24 and theirV associated parts are steadied in the envelope I0 by the attachment of the wire 25a to theenvelope at 2B, as in Fig. l.

'I'he construction of the electrodes 2Ua, 20a may has an external coating 35 of electron-emissive material.

In the central holes in the plugs 33a, 33a are (nickel) current leads-3io, 32h for the upper electrode 20a; and 32h, 39a for the lower electrode 20a-and between these leads are connected a heating resistance 30a such as a finely coiled tungsten ilament. The tube 34a is (electrically) connected to the lead 3 Ia (or 39a) by a conductive (nickel) strip 38a. The lead 31a is'welded to the wire 25a, the lead 39a to the stem lead I6 and the leads 32h to opposite ends of the lead 32a. In operation, the glow discharge between the electrodes 20a, 20a is in parallel with the electrodeheating resistances 30a, 30a.

The electric circuits and connections of the lamp shown in Fig. 4 are diagrammatically illusytrated in Fig. 5, and marked with the same reference characters as in the foregoing description.

Various parts and featuresy shown in Figs. 4, 5,

and 6 are marked with the same reference numerals as the corresponding ones in Figs. 1, 2,

and 3 (with a subscript letter where distinction appears desirable), as a means of dispensing with repetitive description; and it will be understood that the same materials may be used with corresponding parts in Figs. 4, 5, and 6 as in Figs. 1,'2, and 3, except as otherwise indicated above. The operation of the lamp shown in Figs. 4, 5, and 6 is similar to the lamp of Figs. 1, 2, and 3, and the same remarks apply as regards balance of color vtones of light from the arc discharge and the heater, use of mercury with sodium, use of frosting or other light-diffusing means and of a vacuum jacket, etc.

Figs. 7, 8, 9, and 10 illustrate particular advantages of multiplying the heaters or ballasts, and of using an odd number--three inthe present instance-grouped around the electrodes 20a, 20a in their midst, each consisting of an insulative refractory tubular member 24 and a (tungsten) heating and ballast filament22 within it.' The particular advantage of the odd number of 'ballasts 22 is that all can be connected inseries with the electrode gap, thus allowing a heavier and more durable wire tobe used for the resistance elements 22 because of the increased length which is permitted. As the number of heaters is increased, also, the uniformity of envelope heating given by a single axial heater (Fig. 1) is more and more nearly approximated.

Dispensing with repetitive description by the use of the same reference characters vas in Figs. .1, 4, 5, and 6 to indicate corresponding parts and features-with distinctive le'tters where distinction appears necessary-it may be noted that in The button 55 insulates the wires 25c, 25d and 25e,

from one another. The arms of the -wire 25c are covered with insulating sleeves 56, to prevent any electrical discharge betweenA them and the upper electrode. 20a; and the ends of these sleeves are cemented to those of tubes 24, 24 and to button 55` with insulative cement 51, for the same purpose. The upper electrode 20a is connected to wire 25e,

which is in turn connected to wire 25d by a wire 31h welded to wires25d and 25e. The upper end of the mount may be steadied by attaching the wire 25e to the bulb Il) at 26 as in Figs. 1 and 4. 'I'he electrical connection of the three laments 22 in series with one another and with the electrodes 20a, 20a by the wires I5, 25c, I6b, 25e, 3'lb, 25d, and I6 and the connections of the electrodeheating resistances 30, 30, will all be readily understood from the wiring diagram in Fig. `when examined in connection with Fig. 5. It is to be noted that the electrode gap (and the lead 32a) are interposed between two directly interconnected resistances 22 and the third resistance 22, so that the diierence of potential between each electrodeI and the resistances 22 is less than if the three string, and this string as a unit were connected in series with the electrode gap.

What I claim as new and desire to secure by Letters Patent' of the United States, is:

l. A 'vapor lamp vcomprising an envelope with electron-emissive electrodes therein; a charge of vaporizable working substance in said envelope producing only a small vapor pressure therein during operation of the lamp;l and a single Walled luminous tube enclosing a heating resistance and ballast means in the vapor space of said envelope, a heating resistance surrounded by one of said electrodes, a current lead external to said tube and connecting said heating resistance in shunt with the discharge path between said electrodes, said resistance and ballast. means being connected in series with said heating resistance and the electrode gap and heating said tube to luminosity, said tube being directly 'exposed to the luminous vapor space and being adapted and arranged to heat the walls of said space to substantially uniform temperature sufficient to maintain an adequate atmosphere of the metal vapor throughout said space, and emitting lightl tube enclosing a heating resistance and ballast means in the vapor space of said envelope, a heating resistance surrounded by one of said electrodes, current lead external to said,tube and connecting said heating resistance in shunt with the discharge path between said electrodes, said resistance and ballast means being connected in series with said heating resistance and the electrode gap and heating said tube to luminosity, said tube being directly exposed to the luminous vapor space and beingy adapted and arranged to be luminous when said lamp is at equilibrium and to heat the walls of said space to substantially uniform temperature suiilclent to maintain an adequate atmosphere of the metal vapor throughout said space,v and having such resistance, relative to the operating resistance across the elec- 4trode gap, that the device can operate on ordisaid envelope, a heating resistance surrounded by one of said electrodes, a current lead external to said tube and connecting said heating resistance in shunt with the discharge path besaid lamp is at equilibrium and being directly exposed to the luminous vapor space.

4. An operating assembly for a device oi' th character described comprising cooperating coaxial diiuse-discharge electrodes; means for mounting said electrodes with a discharge gap between them consisting of a single walled-refractory insulative tubular supporting means extending in the direction of the electrode axes; a heating resistance wrapped around said tubular support means and interposed between said support means and one of said electrodes, a current lead outside of said tubular support means and connecting said resistance in shunt with the discharge path between said electrodes; and resistance means in said tubular means connected in series with said heating resistance and with the electrode gap.

5. An operating assembly tor a device oi' the character described comprising cooperating coaxial diuse-discharge electrodes; means for mounting said electrodes in a bulb, with a discharge gap between them, including a shield for 5 occluding the base end or neck of the bulb. re fractory insulative tubular supporting means affixed to and projecting from said shield and supporting means affixed to' said tubular supporting means and fused into said bulb; a current lead lo interconnecting said electrodes; and resistance means in said tubular means connected -in series with the electrode gap.

6. An operating assembly for a device of the character described lconsisting of a group of sym- 15 metrically arranged substantially parallel refractory insulative tubes; one of said tubes being lin contact with two of the other tubes, means at opposite ends of said tubes for holding them in position relative to one another; cooperating dif- 20 fuse-:discharge electrodes mounted on said means in the midst of the group oi' tubes, at opposite ends thereof, a heating resistance mounted in said electrodes and a current lead outside of said tub'es and connecting said heating resistances in shunt 25 to the discharge path between said electrodes; and resistances in said tubes connected in series with said heating resistances and the electrode gap. v

GEORGE E. INMAN. E

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