US2018620A - Positive column lamp - Google Patents

Description

0a. 22, 1935. L. BECK I 2,018,620,

POS ITIVE COLUMN LAMP Original Filed May 31, 1932 9 INVENTOR M-ULBEC/f BY ATTORNEYJ Patented Oct. 22, 1935 PATENT OFFICE POSITIVE COLUMN LAMP Leo L. Beck, Westfield, N. J., assignor to Claude Neon Lights, Inc., New York, N. Y., a corporation of New York Application May 31, 1932, Serial No. 614.403 Renewed March 16, 1935 6 Claims.

The present invention relates to gas discharge positive column luminous tubes.

It is a continuation in. part of applications Ser. No. 373,922 filed June 26, 1929 and Ser. No. 432,024 filed February 28, 1930.

The luminous rare gas tube signs now commonly employed for display and advertising purposes have largely displaced the older electric signs employing incandescent bulbs. Nevertheless such tubes are subject to limitations that have greatly restricted their sphere of usefulness. The voltage necessary to operate such tubes is high, e. g. 2,000 to 20,000 volts. At such high voltages only very small currents can be used. Consequently, the brilliancy of such tubes,

i. e., the light energy emitted per unit area of the tube surface, is very low, so low that the daylight advertising value is poor. By this is meant the fact that such tubes are relatively inconspicuous in sunlight or daylight. Darkness is required to make such tubes effective and'therefore they possess their chief. attracting value only at night or on dark days or in dark places.

Moreover, for general illuminating purposes, such tubes have not proven successful owing to a large extent to the fact that it is difficult to concentrate the light thereof in to a small space, that is, on account of the small amount of light energy emitted per unit area of tube surface, it is extremely diff cult to concentrate into a convenient volume enough energy to render such tubes available for general illuminating purposes, e. g., the illumination of oillces, factories, homes, etc.

The present invention marks a long step for ward in the luminous tube art.

It provides a luminous tube which can be operated at ordinary supply or line potential of the order of 110-220 volts, and at high current densities for example 0.1 to 1.25 amperes per square centimeter of positive colunm cross section.

It provides a luminous tube having a high.

brilliancy, for example a brilliancy of the order of 1.5 Lamberts. (The Lambert is a practical unit of intensity and is edual to one lumen emitted per square centimeter of. the diffusing surface.) This brilliancy is many times greater than that characterizing the older tubes and as a result, the advertising value of the tubes of the a present invention is about as much greater than that of the older tubes as that of those tubes was, in turn, greater than the advertising value of the incandescent bulbs which were largely replaced by the former.

It provides a luminous tube by m ans of which a large quantity of light may be concentrated into a relatively small space. For example, in the older tubes, taking as an example a length of tubing about 3 feet long and millimeters in diameter, it was customary to have a current of 5 about 0.030 ampere at a potential fall of about 300 volts in a filling of neon gas, said gas having a potential drop of about 100 volts per foot. The energy consumed was therefore about 300x .030: 9 watts. The potential fall of a tube of the present invention having the same diameter may be only about 100 volts, but the current may be as much as 0.5 ampere or more, with a corresponding energy consumption of 50 or more watts. The amount of light emitted is roughly proportional to the energy input and therefore the light of the present invention is much more intense than that of the older tubes. Consequently, it is available for general illuminatingpurposes, indoors and outdoors, and is not restricted to the field of advertising and display. In fact, the present invention inaugurates a new era in illumination. I

One of the problems solved by the present invention was the problem of illuminating a considerable length of tubing when only a low potential of 110-220 volts was available. With the older tubes which operated at extremely high voltages this problem was not presented and it was customary to operate lengths of tubing as much as ten feet in length. The details of the solution of the problem will be more fully described hereinafter, but it may be said that the solution of the problem opened the door to the solution of the problem of increasing efliciency in general, that is, the success achieved in operating considerable lengths of tubing at low voltage turned out to be only one phase of the problem of increasing efliciency so that whether the length of tubing be short or long, it may, according to the present invention, be operated at a greatly improved efllciency. For the preparation of many types of tubing for sign and display purposes, it is necessary that a certain minimum length of tubing be successfully illuminated, this for the reason that such tubing has to be bent into various shapes and for the bending operation there is always a certain minimum length that cannot be reduced. The present invention provides a tube long enough to be bent into the shape of a letter or other desired design, even though the-available voltage may be as low as 110 volts. In other. words, the length of tubing or what amounts to the same thing, the "quantity of light obtainablefrom a source of predetermined potential has been greatly increased. The invention, having increased eiliciency on long tubes, is however applicable toa tube irrespective of the length.

The overall efllciency 01- a tube or lamp or the present invention may be as high as 18 lumens per watt electrical energy consumed. Moreover, such light may be substantially of one color, for example the characteristic orange red color of neon. The possibility of obtaining so much light of a given color from a unit quantity oi electrical energy, i. e., the "color efllciency",is incomparably, greater than that obtainable with the older incandescent lamps.

- tures thereof to obtain light having a wide range oi color characteristics and by a suitable blending, light having substantially the same composition as daylight may be produced. Thus-the interior or exterior of buildings may be illuminated either by artificial daylight or by light having any desired color. The decorative and utilitarian possibilities of the lamps of the present invention are almost infinite.

The present invention relates particularly to tubes employing neon as the principal gas filling,

in which the source of light is that radiated by a positive column of. the rare gas. Such lamps are distinguished from those in which the light emanates largely from a film or luminous gas cover-v ing a cold cathode, known as negative glow lamps.

In lamps of this class, the electrodes are so close together that no positive column exists. The

luminosity of such lamps is very low and the source of light is very different from that radiated by the positive column light of the present invention. In negative glow lamps most of the potential fall occurs at the cathode, resulting in great inemciency, whereas in the lamps of the present invention by far the greatest potential drop occurs through the relatively long column of gas which constitutes the positive column, the

cathode drop being a very minoriraction o! the overall voltage.

. The group of rare gases, argon, krypton and xenon have collectively and individually a much lower potential gradient than neon. The potential gradient is a measure of the resistance of the gas to the discharge or electricity through it by ionization and may be expressed as the minimum potential fall or drop, which occurs through a unit column of gas, 1. e., a unit length of gas column in a tube having a given diameter, when that column or gas is ionized and illuminated by an electrical discharge. 1

I have found that the potential drop through a positive column of neon can be greatly decreased by incorporating with the neon small proportions, e. g., 0.05 to 1.0 per cent of a gas selected from the group composed of argon,krypton and xenon. For example I have incorporated with neon, in a tube having a length of about forty inches between the electrodes, and an inside diameter of about 14.5 millimeters and provided with a thermionic cathode, about-0.5 per cent-oi argon, and have found that the potential drop between the cathode and anode is'greatly educed.- This discovery is a considerable advance in the art because it permits a much longer tube to be operated from a source of current of fixed or predetermined potential. I found, however, that the luminosity oi the positive column or neon tends to be decreased by the incorporation 5 of the low potential gradient gas, whether the latterbe argon, krypton or xenon, that is, the characteristic orange red neon color tends to be impaired. However, I then discovered that, without sacrificing the potential-reducing property of the low potential gas, I could restore the brilliant intense neon color by increasing the current density. This result was unexpected but very gratifying because by the combination of increased current density and use of argon, krypton or xenon (in conjunction with a principal filling or neon) I was able to obtain a high lumi nosity oi neon at a greatly increased efliciency, that is, at a greatly decreased potential drop or gradient through the column of mixed gases.

This new result was quite unexpected because it was thought that by increasing the current density I would merely increase or accentuate the pale, insipid light radiated by the argon, krypton or xenon. Instead however. upon reaching a certain minimum current density, the neon suddenly shone forth in all its brilliance.

By experiment I round that a relation exists between the per cent of low potential gradient gas and the minimum current density necessary to use in order to offset the dimming effect of the low potential gradient gasand restore the brilliant neon light; or to put it another way,

a relation exists between the current density and the maximum permissible percent 01' low potential gradient gas, (i. e., argon, krypton or xenon). For example, taking argon as an example ot a low potential gradient gas, it the current density is about .0.1 ampere per square centimeter 01' positive column cross section, then the maximum permissible per cent of argon is about 0.1 per cent (the remainder being neon). As the current density increases, more and. more I argon may be employed, so that if a current density as high as 2.5 amperes per square centimeter of positive column cross section be employed, as much as about 1.25 per cent of argon can be used, and as the proportion of argon is increased, the emciency oi the tube increases. For manypurposes however, it sufllces to use about 0.20 per cent of argon and a current density of about 02 to 0.25 ampere per square centimeter of cross section. With extremely high current densities such as 2.0 to 2.5 amperes per square centimeter considerable energy is lost in the form of heat so that it is generally desirable to .use just as little .low potential gradient gas as possible. Krypton is more efllcient than ar-- gon, that is.'it requires much less krypton than argon to produce the same increase in lighting efliciency. For example, about 0.15 per cent of krypton will accomplish the same result'as about 0.30 per cent of argon. v

I recommend for ordinary purposes, that is, 35 for ordinary illuminating lamps and display tubes, a range of proportion of low potential gradient gas of 0.05 to 0.50 per cent and a corresponding range of current density of 0.05 to 1.0 amperes per square centimeter of cross section of the positive column. Where it is necessary to have a higher current density in order sity of the order of 2.5 amperes per square centimeter of positive column cross section.

In addition to providing the tube with a gas.

filling which operates at high efficiency, I also provide it with suitable electrodes, one or both of which is a thermo-emissive or thermionic electrode depending on whether direct or alternating current is used. I make the cathode sumciently emissive so that at the cathode the fall of potential is very low as compared with cold cathodes. This is done by coating a metalLc grid with a suitable salt or oxide of barium (or a mixture of salts or oxides of barium and strontium) and then activating the cathode i. e., heating the cathode, decomposing the. salt or oxide and bombarding the residual decomposition product to develop oractivate the residue and render it capable of emitting electrons when heated to a high temperature. When an electrode so constructed acts as cathode, the oathode fall of potential is low and only a small amount of energy is lost in the form of work ,done in the transmission of energy from the emissive electrode .to the gaseous ions. Therefore the low cathode fall of potential coacts wiih the low potential drop through the positive column of gasto provide an overall or total potential fall through the tube which is lowenough to be operable from a predetermined source of low voltage of the order of 110-220 volts, even when a ballast resistance is in series with the tube.

The fall of potential through a column of rare gas in a tube is a function of the diameter of the tube and pressure of the gas and according to the present invention the pressure of gas for a given gas, and for a tube of given diameter is so chosen that the pressure is an optimum one, i. e., a pressure corresponding to a minimum potential gradient. For example, if the tube has an inside diameter of about 15 millimeters thepressure of gas is preferably about 7 'to 8 mini-'- meters and if the tube has an inside diameter of 30 millimeters the optimum pressure is less, e. g., I to 3 millimeters from which information it will be observed that the optimum pressure decreases as the diameter of the tube increases.

The invention will be described in greater detail by reference to the accompanying drawing which shows one of the many forms of luminous tubes that may be employed to embody the manufacture of the present invention and means for practicing the art or process thereof. v Figure 1 shows a luminous tube with thermion'ic cathodes and a diagrammatic representation of the external electric circuits for operating the tube, parts being broken away to more clearly show the constructionof the tube.

Figure 2 is an enlarged section on the line 2--2 of Figure 1 showing a plan. view of the grid cathode.

Figure 3 shows a strip of metal used in the construction of the cathode shown in Figures 1 and 2.;

Figure 3 shows a strip of metal l6 four inches in length and increasing in width from the ends toward the center thereof. The width of vthe strip at the ends is 2 millimeters and at the center is 3 /2 millimeters. It is mad'e'of a nickel silicon alloy and has a thickness of about 0.002 inch. This strip of metal is then bent and shaped into the form of a grid, as shown clearly in Figure 2. The ends of this grid are then joined with supportingp'osts or wires II and connected respzciively with lead wires 2 and 5 for one electrode and 9 and ill for the other electrode. Prior to asrembling the tube with its grid electrodes, the latter are degasified by heating at a high temperature in an atmosphere of hydrogen. They are then cooled, and coated with a coating comprising barium carbonate or other suitable substance and are subsequently mounted in the tube and heated to a high temperature such as 1000 C. or 1200 C. in vacuo. Decomposition of the coating takes place in the presence of the nickel silicon alloy and the latter becomes coated with a firmly adherent and highly emissive coating. Aft:r assembling the tube, evacuating it and activating the coating on the electrodes by heating, and as hereinafter described, the tube is charged with a filling which in a typical case is a mixture of neon with about 0.25 per cent of argcnat a pressure of 7 millimeters (at 25 C.). The inside diameter of the tube in this typical case is 14.5 millimeters and the distance between the electrodes is 40 inches. The discharge current supplied to the tube through the lead.

is a reatively high current density as compared' with currents of 25 to 30 milliamperes employed in high voltage cold cathode tubes. Typical range; ofcurrent densities which may be employed are from 0.05 to 2.5 amperes per square centimeter of cross section ot the gas column corresponding to a range'of proportion of low a potential gradient'gas-from 005 to 1.25 per cent.

As a guidein selecting the proper current density for a given per cent of low potential gradient ga: the followingtable is submitted:

Percent Percent density neon argon l per centimeter) (Approximate) 99- 90 0. l0 0. l 99. 75 0. 25 v O. 3 99. 0. 50 0. 9 99. 25 0. 75 1. 3 99. ()0 l. 00 l. 8 98- 75 .1. 25 2. 4

of the cathode near the supporting wires l8 have a tendency to be cooler than the other portions of the cathode with the result that the emission at those points is lowered, and there is thus a tendency for emission to be concentrated in the said other portions. It has, however, been found possible to compensate for this lack of uniformity by increasing the surface of the cathode progressively towards the center portions thereof, as shown clearly in Figures 1 and 3, and by this means it has been found possible to provide a cathode having .an improved emission from the print of view of uniformity and uniform distribution of the emission over the entire surface theremethod of accomplishing this is to employ the ring members 32. Each of these is supported by a wire 34 passing through the press andis in spaced relation to the corresponding electrode, so that it is possible to pass a discharge current between the electrode and its ring during manufacture of the C. is reached, exhaustion being; continued during the baking operation. By means of circuits not shown in the drawing a heavy current (e. g. 11.5

'amperes) is sent through each electrode to heat it by resistance and decompose the coating there- .on, (which may be a mixture of the carbonates of strontium and barium). when the vacuum gauge shows that no more gas is evolved from the decomposition in this manner, the mode of heating Just described is terminated and a direct discharge current passed between each cathode and its corresponding ring I! by connecting the wires 34 to the positive pole of a source of current and the electrodes l to'the negative pole and passing a discharge current between the respective rihgs as anodes and the respective. grids i as cathodes. Ionization or are current now flows from ring to grid as shown by the appearance of a blue glow in the intervening space. v Pumpin is continued until the blue glow disappearaand the rings 32 become red hot due tobombardment by electrons.

At this point, a' pure electron discharge occurs from cathodes i to their corresponding activating rings or anodes I2 and the. vacuum in'the tube should be very high (e g. II- mm. of mercury) exhaustion having been continued during the activation. The getter is now flashed, the tube is allowed to cool to room temperature and a mixture of neon with a proper proportion of low potential gradient gas is then introduced into the envelope 8 whereupon the latter is sealed off from the pump (not shown in drawing).

These details of construction of the electrodes or their equivalents are desirable to provide electrodes which will, during a period of useful commercial life, ully withstand the action of 'currentsofhighdensityandatthesametime function-at a low cathode'drop. During operation of the tube when in commercial me, more or less t thereof by positive ions may ocour and the electrodes must stand up \mder this bombardment in order to be. .The-inventionalsoincludesasapartofthe combination thereof an improved electrical circult for supplying heating current to the thermo emissivecathodeorelectrodesandforsupplying discharge current. .As shown in Figure L'the coils II and 22 receive current from a commonprimaryooilflandthiscurrentpassea through-theleadwireslandlandilandiree spectivelyandthroughthegridsofthe'electrodes to heat the same to an emissivetemperature.

'Inthetypicalcaseieferredbabovethehuting current'necessary to secure satisfactory operationoftheelecirodesmaybelamperes'ineachof theheatingcircuitsthesaid 'coilsllandll. Thedischargecurrentatm voltsistappedoifatthepointsflandliandthe discharge circuit comprises an inductance II,

This inductance or its equivalent is included in the discharge'circuit asanelementthereofpartlytocausethecurrenttolagbehindthevoltlgeso astoobviatethetendenoyofthetubetobeexns i-s attheendofeachhalf-cycleandto P de for asteadrlight. Thesaid may consist of a coil wound upon a closed core and may be provided with an adjustable airgap so as to be variable. The inductance also acts as a ballast or choke and acurrent limiting device. Wide ranges of current density may be applied'to the 5 tube by adjusting the values of the inductance. As shown, the inductance, the secondary coil, and the primary coils are enclosed in a box and there is thus provided a very simple and emcient current supplying means for the discharge 10 tube in which are combined the means not only for supplying discharge current but also heating current for, the electrodes.

The rings 32 perform a very helpful function not only during manufacture of the tube but also l when it is in use commercially. After the manufacture of the tube is finished, the wires 34 are respectively joined to the wires 6 and Ill and the rings 32 thus become a part of the discharge circuit. During each half cycle of the discharge 2 which occurs with alternating current, through the circuit 3, 5, ".10, II, II and I, the ring 32 at one end of the tube acts as anode while the grid l attheother end ofthe tube actsascathode. Thus; the ring carries the anode current and the grid carries the cathode current. It appears that the electron or anode current passes more easily from the gas to the metallic ring 32 than it would pass into the coated grid. In any event, the use of the ring in this way aids in preventing flickering and in increasing the life of the cathode, whatever may be the theory to account for it.

' When it is desired to operate the tube, discharge potentialis applied to terminals .3 and l. The current induced in coils 2. and 35 22 beats the respective electrodes I! at each end of the tube 8 to an emissive temperature. Thereupon, ionizing means not shown in the drawing is applied to the tube to'initiate the discharge. 8uch ionizing means may comprise a high fre- 40 quency, field which is brought into proximity to the tube so as to initiate ionization of thegas within the envelope l,or it may comprise an'inductive kick coil which may form a subsidiary partof the dischargecircuitinsucha manner that the currentflowing through the said. coil issuddenlycollapsedtogenerateahighpotential discharge or kick in serieswith the-positive column between the electrodes i. Other means of creating initial ionization of the gas withinthe 'envelopemay also be employed and-as soon as.

such initial ionisationoccurs the'potential appliedtotheelectrodesifromtheter'minalsland 4, causes the tube to "strike or become illuminated and thetubeofthepresentinventionthere-' after may be illuminated continuouslyor intermittentlythroughoutalongperiodofusefulcommerciallife. Itisalsotobeobservedthatthe. tubeshowninngurehinsteadofhavi'ngthestraight form of positive column therein delineated may be bent'into any desired design according to the teachings of the present invention.

The'principles of the invention and certain illustrative embodiments thereof have been completely described and disclosed herein and this description and disclosure will enable all those centimeter of positive column cross section, a gas selected from the group consisting of argon, krypton and xenon, the proportion of said gas being the maximum that can be employed with respect to the current density without impairing the characteristic color of the neon, the range of this proportion being from 0.05 to 1.25 per cent, and means to discharge through the tube currents having a density' of 0.05 to 2.50 amperes per square centimeter of positive column cross section.

2. A positive column gaseous discharge tube containing a principal filling of neon, a thermionic cathode capable of transferring to the gas filling electrical energy having a density of the order of 0.05 to 1.0 ampere per square centimeter of positive column cross section, a gas selected from the group consisting of argon, krypton and xenon, the proportion of said gas being the maximum that can be employed with respect to the current density without impairing the characteristic color of the neon, the range of this proportion being from 0.05 to 0.50 per cent, and

means to discharge through the tube currents hkvinga density of 0.05 to 1.0 amperes per square centimeter of positive column cross section.

3. The method of producing a positive column gaseous discharge light in anenvelope containing a principal filling of neon and a thermionic cathode capable of transferring to the gas filling electrical energy having a density of the order of 0.05 to 2.50 amperes per square centimeterof positive column cross section which comprises mounting the said cathode in the envelope,

charging the envelope with neon and a gas se-- lected from the group consisting of argon, krypton and xenon, the proportion of said gas being the maximum that can be employed with respect to the current density without impairing the characteristic color of the neon, the range of this proportion being from 0.05 to 1.25 per cent, heating the thermionic cathode to an emissive temperature and discharging through the positive column a current having a minimum density which is within the'range of 0.05 to 2.50 amperes per square centimeter of cross section of the positive column.

4. The method of producing a positive column gaseous discharge light in an envelopecontaining the principal filling of neon and a thermionic cathode capable of transferring to the gas filling electrical energy having a density of the order of 0.05 to 1.0 ampere per square centimeter of positive columncross section which comprises mountdensity without impairing the characteristic color of the neon, the range of this proportion being from 0.05 to 0.50 per cent, heating the thermionic cathode to an emissive temperature'lo and discharging through the positive column a current having a minimum density which is within the range of 0.05 to 1.0 ampere per square centimeter of cross section of the positive column. 15 .5. A positive column gaseous discharge tube containing a principal filling of neon, a thermionic cathode capable of transferring to the gas filling electrical energy having a density of v the order of 0.10 to 1.0 ampere per square 20 centimeter of positive column cross section, a gas selected from the group'consisting of argon, krypton and xenon, the proportion of said gas being the maximum that can be employed with respect; to. the current density without impairing the characteristic color of the neon, the range of this proportion being from 0.10 to 0.50 per cent, and means to discharge through the tube currents havinga density of 0.10 to 1.0 ampere per square centimeter of positive column cross section.

6. Themethod of producing a positive column gaseous discharge light in anenvelope containing a principal fillirg of neon and a thermionic cathode capable-of transferring to the gas filling electrical energy having a density of the order 3 of 0.10 to 1.0 ampere per square centimeter of positive column cross section which comprises mounting the said cathode in the envelope, charging the envelope with neon and a gas selected fronnthe group consisting of argon, krypton and xenon, the proportion of said gas being the maximum that can be employed with respect to the current density without impairing the characteristic color of the neon, the range of this proportion being from 0.10 to 1.50-per cent, heating the thermionic cathode to an emissivetemperature and discharging through the positive column a current having a minimum density which is within the range of 0.10 to 1.0 ampere per square centimeter of cross section of the positive column.

' LEO L. BECK.

v being the maximum 5 that can be employed with respect to the current

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