Патент USA US2135284код для вставки
N_ov. 1, 1938. >2,135,284 c. G. l-'oUND4 CATHODIC LAMP AFiled Feb. 2e, 1938, (0000 $000 @U00 7000 âwwìy 6000 5000 4000 3000 /000 0 «2f / 2 '3 _ 4 ó‘ 6 7 8 `9 /0 o/.scHA/ïeE cU/rEE/vr//IMPERESJ TEMPERATURE Inventor: Clncto? G Found, l-Iís Attorney Patented Nov. 1, 1938 _ y2,135,234 „ UNITED STATES PATENT OFFICE 2,135,284 _ cA'rnoDro LAMP Clifton G. Found, Schenectady, N. Y., assignor to General Electric Company,` a _corporation of New York ‘ Application February 26, 1938, Serial No. 192,808 3Claims. (CL 176-122) 'I'his application is a continuation-impart of my application Serial No. 103,566, ñled October l, 1936. - , ' . My invention relates to a gas-filled or discharge 5 lamp of the so-called “cathodic” type _in which light generation is largely Aconñned to a region closely adjacent the cathode. It is an object of the invention to provide an electrode structure which will permit a greater 10 luminous output for a given size of cathodic lamp than can be obtained with the structures hereto fore employed. It is a further object to provide a high intensity cathodic lamp in which the light output is substantially insensitive to ambient tem 15 perature variations. The novel features which I desire to protect herein will be pointed out with particularity in trons of low energy content as is more fully ex plained in the following. The neon or other inert gas, on the other hand, has been found to serve a multiplicity of functions which add both to the convenience of operation and the efficiency 5 . of the lamp. Thus, besides facilitating the initia tion of a discharge between the lamp electrodes and the subsequent vaporization ofthe sodium, the neon provides atoms which serve as a deflect ing means to lengthen the total path of the mov- 10 ing electrons, which would otherwise proceed al most directly through the ñeldof sparse sodium atoms to the anode. 'I‘his increase in the aver age path of travel of an individual electron greatly enhances the -probability of vits encountering a l5 sodium atom in a light-emitting impact. In addition to the two functions just described, the appended claims. The invention itself, how- . neon is capable of a further service which makes ever, together with further objects and advan 20 tages thereof, may best be understood by refer it particularly useful in the cathodic type of lamp. It has been observed that the voltage drop in an 20 ence to the following specification taken in con >electron discharge tube having closely spaced nection with the drawing, in which Fig. 1 is a electrodes is largely concentrated in a narrow perspective view of a cathodic lamp embodying sheath around the cathode which sheath may be my invention; and Figs. 2 and 3 are graphical less than 116 of a Acentimeter in thickness. It is 25 representations illustrating the improved charac teristics which are realized by the use of the in vention. ' The lamps with which -my invention deals are of the >thermionic discharge type employing an 30 incandescible cathode and are conventionally con structed so that the distance between the cathode and the anode is comparable to the least dimen sion of the envelope. As a result of such- con struction substantially all of the utilizable light 35 energy is generated within a restricted radial dis tance of the cathode. It is, therefore, convenient to refer to such a light source as aV "cathodic” lamp. Cathodic lamps of the type with which my in 40 vention is particularly concerned comprise a sealed envelope defining a discharge space which contains suitable electrode structure, a vaporiza ble substance such as sodium and an inert or non condensable gas such as neon. It will be under 45 stood, however, that although sodium and neon are particularly'referred to-in the following speci ' within this sheath that emittedelectrons receive 25y v substantially all their energy, such energy being conveniently expressedl by giving the number of volts against which an electron of the given en ergy content is capable of moving. . If the condi tion of operation of the lamp is such that an elec- 30> tron~ passing from the sheath with an energy con tent above 16.5 volts collides with a, neon atom, lt may either ionize the same or excite it to lumi nosity, depending upon the exact energy values involved. The impinglng electron will not, of 35' course, be destroyed, but will continue its journey with its energy reduced by an amount which rep resents the ionization or excitation voltage of the neon. - i , If such an electron of diminished energy, con- 40 veniently referred to as a secondary> electron, re tains, as is very likely to be the case, an energy of Vless than 5.1 volts and encounters a sodium atom, it will not be able to ionize the latter. In stead, a transfer of energy of, another type will 45 take place which is conventionally referred to as This is- a. phenomenon which requires an electron energy of between 2.1 and 5.1 volts. _An excited sodium iication, it is possible, and my invention contem- , an excitation of the- sodium atom. plates, that equivalent materials such as I_nercury or caesium may be substituted for the former while 50 >other inert gases such as argon or krypton may be used instead ofv thelatter. ^ It is a function of the sodium or-equivalent vaporizable material to provide a source of sub stantial numbers of atoms which may be brought 55 to a state of light radiation by impact with elec atom is, generally speaking, capable of two further' 50 changes in condition; it may, if undisturbed for a brief period, return to its natural state, such return being accompanied with the production of light, or it may be converted into ‘a sodium ion by » a further impact with an electron having energy 56 2 2,135,284 coiled or straight, coated with an electron emis of 3 or more volts. 'I'his latter conversion not~ only fails to result in the production of light, but sive substance such as an alkaline earth metal Ialso eliminates' an excited sodium atom.- - This Y form ,of ionization by successive impacts with sec oxide and supplied with heating current through, suitable lead-in connections I 9 and 20. This fila ondary electrons is conventionally referred as cu mulative ionization. It tends to increase rapidly with increasing concentrations of excited atoms. In view of the above it is obviously desirable ment is supported more or less resiliently at its upper end by a bent metal ribbon I3 which in turn is mounted on a pair of vertical supports I5 for the most efiicient production of light that all _and I6. These latter elements are coated with a heat-resisting material, such as alumina, for the purpose of preventing their'destruction during used in producing from unexcited sodium atoms the operation of the device. For reasons to be a maximum .number of ' excited sodium- atoms shortly explained, I consider that the anode. and which, as before explained, are av potential source cathode should have opposed, discharge-receiving of light. Correlatively, the concentration or >surfaces of as great a longitudinal extent as the dimensions of the envelope permit. With a tubu 15 “crowding” of excited sodium atoms should be lar envelope construction such as that shown, the ' kept so low that cumulative ionization is sub electrodes should extend lengthwise of the enve stantvially avoided.A ' lope for a distance substantially greater than the , With the aboveprinciples in view it is believed that the nature of my invention now may be tube diameter and preferably commensurate with its length. For energizing the lamp, I have in 20 clearly understood. . g dicated an elementary circuit comprising a main Referring to Fig. '1, I have illustrated an elon gated sealed envelope I terminating at its base transformer 22, a filament transformer 23 and a » in a reentrant stem 2 provided with a press 3. current. limiting resistor 24. 10 available- secondary electron energy should be A filling of a ñxed gas such as neon is provided By analogy with accepted usage in other types . in the envelope I and a quantity of sodium, or other vaporizable material, is deposited on the of discharge lamps it has heretofore been deemed 25 most advantageous, both for electron generation and for conservation of heating energy, to con struct-the cathode member of a cathodic lamp in the form of a concentrated electron source, such as a closely coiled wire helix; I have found, 30 however, that by using an elongated configura wall of the tube as shown at 4. ` Observations indicate that actual generation of light in a cathodic lamp takes place within a re stricted radial distance of the cathode defined by the range within which substantially all second ary-electron energy will be absorbed. In the case v tion such as that specified above, a greater lumi of a sodium lamp, in normal operation, the entire nous output may be obtained than has hereto fore been deemed possible with lamps of the type tube may> appear to be filled with a diffused so dium glow. This is because sodium resonance _ radiation, actually generated within the re stricted region only, is continually absorbed and reemitted by. sodium atoms in the outlying space. Luminous emission from the tube is thus viewed 40 externally as though it were taking place from the outer portion of 'the lamp. The dimensions of the region of light genera tion are determined in part by the concentration of excitable atoms which in turn depends on the 45 ratio of neon pressure to sodium pressure. The optimum condition which can be obtained is that at which the light generating region is co extensive with the volume of the bulb. It is not practical to assign an exact value for the best 50 neon pressure to be employed, but this factor may ~ be determined experimentally for any given tube construction. I have obtained most satisfactory resultsvwith a pressure of neon in the neighbor hood of 400 microns of `mercury and a pressure 55 of sodium of the order -oi’ magnitude of one _micron. In order to prevent gradual condensation of the s_odiuminto the relatively cold' base of the tube a mica disk 6 is provided which effectively 60 divides the base froml the main body of the en velope. Through this disk lead-in wires are passed which at one end are sealed into the mem ber 3 and at the other end serve to support the various electrodes. The anode 5 is shown as> comprising a coiled ribbon ofsuitable metal, for example, nickel,.forming a helix which has its axis substantially coincident with the major- axis " of the envelope I.> >This anode is supported from the press 3 by a pair of conducting .rods 8 and 9, 70 of whichfthe latter is provided with van external connection to permit a suitable potential to be impressed on the anode. - _ Concentrically arranged within the anode -I provide a thermionic or incandescible cathode- II -75 comprising an elongated metal ñlament, either in question. This unexpected result I attribute 35 to the fact that a more advantageous distribu tion of emitted electrons is obtained. »In other words, while the total number of electronsmay be unchanged, any unit volume of gas adjacent the cathode is subject to relatively less-`electr„on 40 bombardment. Consequently, excitation of sodi um atoms is disposed over so great a space that cumulative ionization as above defined is sub stantially prevented up to very high discharge currents. This means, of course, that a much 45 greater amount of energy can-be utilized in light production- without cumulativeionization becom ing the predominant energy absorbing factor. When the ratio of neon to sodium pressure also is so chosen that the region of secondary energy 50 absorption extends radially as far as the wall of the envelope, optimum operating conditions exist. - In previously constructed lamps of the type in question a maximum of light output has been obtained at a sodium' pressure such that less 55 than all the secondary electron energy is ab sorbed. Any increase in pressure above the criti cal value magniñes cumulative ionization to such an extent that a net loss rather than a net gain in light output is realized. As a conse 60 quence of this enforced suboptimal mode of operation changes in sodium pressure produced by variations _in ambient temperature cause cor- ' responding ‘changes in light generation. My present invention, however, makes it possible to 65 use current densities adequate to vaporize more than enough sodium to absorb all the secondary electron energy while avoiding :excessive cumu lative ionization. As a result constant luminous output is obtained which output is independent 70 of ambient temperature variations. - Referring to Fig. 2, I have provided curves illustrating the relative importance of the vari ous factors referred to in the foregoing. The' coordinates chosen are such that .the curves 75 2,185,284 show the variation in luminous output with changes in are current for different operating conditions. 'I'he lower curve, indicated as curve A, com prises the output characteristic of a cathodic lamp of known type in which the cathodev com prises a relatively concentrated coil. It will be seen that While the luminous output increases linearly with cu'rrent up to a value of about 11/2 10 amperes, above that value -the curve iiattens out to such an extent that little or no gain is realized by increasing the current input. 'I'he curve B shows the improvement obtained' in the operation of a cathodic lamp of identical construction with that of curve A by carefully selecting an optimum ratio of neon to sodium pressure -which in the instance chosen operated at such temperature that the sodium;~ vapor pressure was approximately one micron. How 20 ever, in spite of thefact that a considerable in-` crease in luminous output is .realized by the a certain point. However, with an extended cathode such as. characterizes my invention, excessive cumula tive ionization will not set in until an amount of sodium vapor is present in excess of that re quired to utilize all available secondary electron energy in the excitation of light. ï When a com-> pletely adequate supplyl of vaporized sodium is present, a further increas'e in temperature and 10 in sodium vapor pressure obviously cannot'in crease the light generation. Consequently" Aa range of temperature exists in which constant light output will obtain at least up to the point where even the extended nature of the cathode cannot prevent excessive cumulative ionization from occurring. 'I'his range comprises, for ex ample, the yregion from y to z on curve E of Fig. `3. The point y indicates the temperature re-_ quired to vaporize the least amount of sodium sufficient to produce maximum,A light excitation, i. e., 'to permit full utilization of available elec curs at currents materially in excess of 5 am tron energy. peres. represents the temperature vat which excessive cumulative ionization begins to occur. ' whichv this curve was obtained the envelope and other structural parts were of precisely the same- 'I'he point z, on the‘other'hand, It is obvious that if the lamp can be operated so that its normal temperature of operation corre sponds to the point l0 on curve E, the light output of the lamp may be substantially insensitive lto_ dimensions as were employed in connection with curves A and B. However, as a result of the variations in ambient temperature (at least as long as such variations do not carry the oper ating temperature of the lamp above z or »below increased gaseous volume traversed by the emit ted electrons, a current intensity corresponding il). to'an ar'c current of 10 amperes was employedwithout producing any manifestation of satura tion due to cumulative ionization. A luminous tained by selectingthe proportions and heat in 35 sulation of the lamp such that at the preferred operating currents, i. e. for discharge currents _corresponding to the range of emcient operation ofthe lamp, the temperature of the lamp will output Iof approximately 10,000 lumens was ob tained in a lamp having a volumetric content of approximately 450 cubic centimeters and using a power» input of. approximately.- 200 watts. To the best of my knowledge this is the first time that an output of this magnitude has been at tained in a cathodic, lamp irrespective of the 45 than' a net, gain in light output is realized above change indicated a definite saturation eiïect oc The curve C represents the results obtained by using( an electrode arrangement such as is shown> in Fig. 1 in connection with an optimal neon pressure of about 400 microns. In the tests Irom> 40 3 input employed. ' ‘ ~ A further advantage attendant upon the use of an extended rather than a concentrated cath ode consists in the‘ possibility of making a cath odio -lamp which is substantially insensitive to 50 variations in ambient temperature. l Where a concentrated cathode is employed, a continuous variation of luminous output with temperature occurs, as is indicated, for example, by curve D in Fig. 3._ In this curve a condition 55 of constant current operation is assumed, the As a practical matter, this result can be ob be maintained at a point corresponding to the 40 point O. The determination of this point for a given lamp is a matter which will oil‘er little dith culty for one`skil1ed in the art. Ordinarily, the maintenance of the requisitev temperature will require the .use of some type of heat conservator in connection’ with thejdischarge envelope so as to achieve the proper relationship between the energy supplied to the discharge and that dissi pated fromthe envelope. Such a conservator .f may, for example, take the form of a transparent vacuum jacket such as is indicated at 25 in Fig. 1. The form of lamp which I have described is exemplary only and it will be understood that various modiñcations o_f 'structure may be used. For example, the anode may be constituted of'a 55 screen-like mesh rather than a spiral ribbon changing the proportions or insulation of the- -as illustrated and the cath°ode may lcomprise an discharge envelope. 'I'he rising portion of the, velongated helical structure rather than a straight curve to the left of the point X Vis due to the ñlament such as that shown in Fig, 1. I aim in 60 the >appended -claims to cover all such variations 60 increase with temperature of _the number ofso dium atoms .available for light excitation. 4The of form and use as fall within the> true spirit and _ , decreasing portion of the curve, on the other scope. of the foregoing disclosure._ What I claim as new and desire to secure‘by - hand, I consider to be due to the destruction Letters Patent of the United States is: _ of excited sodium atoms- by .cumulative ioniza 1. A cathodic lamp- comprising _an envelope tion. With a concentrated cathode, the concen tration of excitedsodium atoms in the vicinity of .- which encloses a discharge-Supporting gas. a temperature being varied, for’.example, by the cathode increases extremely rapidly with rising sodium pressure. Consequently cumula vaporizable light-producing substance, and a pair of cooperating electrodes having mutually facing great enough to nullify thev favorable effect of discharge-receiving surfaces of as great longi tudinal extent as the major dimension of the the increased availability of sodium atoms even before enough atoms are provided to make it lation of the envelope .'being such that at dis charge ‘currents within the range of eillcient op 70 tive ionization adjacent to the cathode becomes theoretically possible to utilize all available elec~ ' 75 tronv energy.v For this reason a net'loss rather envelope permits, the proportions and heat insu eration of the lamp the amount of said substance maintained inthe vapor phase is appreciably 4 2,185,284 place, whereby the luminous output of said lamp above the least amount suflicient for maximum light excitation at 'such currents but below the is substantially insensitive to variations in am value at which excessive cumulative ionization bient temperature. 3. A cathodic lamp comprising an elongated takes place, whereby the luminous output of the lamp is substantially insensitive to variations in tubular envelope enclosing an inert gas, a quan - tity of sodium and concentrically arranged dis ambient temperature. charge electrodes having opposed discharge-re 2.` A cathodic lamp including an elongated tu ceiving surfaces which extend longitudinally of bular envelope which encloses a discharge-sup porting gas, a vaporizable light-producing sub 10 stance, and a vpair of cooperating electrodes hav-` - ing mutually facing discharge-receiving surfaces which extend longitudinally of the envelope a distance substantially greater than the diameter thereof, the proportions and heat insulation of the' envelope being such that at discharge cur rents within the range of emcient operation of the lamp the amount of said substance main tained in the vapor phase is appreciably above the leastamount sumcient for maximum light 20 excitation at such currents but below the value at which excessive cumulative ionization takes the envelope a distance substantially greater than the diameter thereof, the proportions and heat insulation of the envelope being such as to main-v tain in the vapor phase during operation of the lamp a quantity of sodium intermediate between the least amount suflicient for maximum light ex citation at the operating current of the lamp and. 15 the amount at which cumulative ionization be comes excessive, whereby the luminous output of the lamp is substantiallyv independent of vari ations in ambient temperature. ' ' cm'roN G. FOUND.