US2374677A - Glow discharge lamp - Google Patents

Description

y L. GQLDSTEIN ETAL 2,374,677

' GLOW DISCHARGE LAMP Filed Sept. 20, 1943 MMM ATTORNEY$ Patented May 1, 1 945 GLOW DISCHARGE LAMP Ladislas Goldstein and Francis Perrin, New York, N. Y., assignors to Canadian Radium &

Uranium Corporation poration oi New York New York, N. Y., a cor- Application September 20,1943, Serial No. 503,046 W '3 Claims. (Cl. 176-122) Our invention relates to a new and improved gas-containing discharge lamp, of the'type which is designated as a glow lamp or a glow tube. Such lamps are also designated as cold electrode lamps, because the electrodes of such lamps remain unheated save by the very moderate heat which is developed by the discharge itself.

Such lamps are intended for operation under a predetermined operating voltage. In order to start or to strikesuch a lamp, it is necessary to apply a striking voltage which exceeds said operating voltage; In the circuit in which such a lamp is located, it is necessary to apply an overvoltage, which exceeds the striking voltage. This is done in order to suppress or minimize the delay in starting the lamp.

For example, inthe type of lamp which is specifically described herein, as. one example of our invention, the striking voltage can vary from 70 volts to 90 volts and the operating voltage is about 15 volts less than the striking voltage. The over-voltage which is applied to the lamp in order to start the same promptly. exceeds the striking voltage by about 5 volts.

Experience has shown that the striking voltage can vary greatly, depending upon the length of time in which the lamp has been shielded from.

light. For many uses, it is necessary to locate the lamp in a hood or casing which shields the lamp from externallight, so that the lamp canremain unexposed to light for long and varying periods of time. The period during which the lamp remains inoperative is designated as the idle period." The striking voltage varies greatly with the length of said idle period, when the lamp is struck for the first time after such idle period, if the lamp is shielded from external light during such idle period. Such idle period is designated as a shielded idle perid,.during which the lamp is shielded from external light.

In certain uses, the idle period can'beas long as one or two days, during which period the lamp is shielded from light. Under such circumstances, there can be a variation in the striking voltage of as much as 50%, in the first striking after such shielded. idle period. ,Hence, ii'the circuit is designed so as to supply a'normal overvoltage which exceeds the striking voltage by only volts,'the starting ot-the lamp can be greatly delayed, and such starting may not take place. in the first attempted striking after such shielded idle period, thus producing great unce'r-' tainty in operation, because the necessary strikin: voltage itself may greatlyexceed even the over-voltage which is applied to the lamp by the circuit, when it is desired to start the lamp after such shielded idle period.

According to our invention, we continuously irradiate the interior of the lamp, including its internal electrodes as well as its internal wall, by

means of a source of light which is independent of the circuit of the lamp. For example, this independent irradiation can be produced by means of a. phosphorescent or fluorescent mate,-

rial, such as phosphorescent zinc sulfide, intermixed with radium bromide or other radioactive material which emits alpha rays. Such mixture continuously produces light which sufliciently irradiates the glow lamp, so that the variation of the striking voltage in the first striking after a shielded idle period islimited to less than as compared with the present usual variation of about 50% or more.

radiation, we can reduce the variation in the.

By supplying sufflcient irrequired striking voltage after such shielded idle period to much less'than 10%, to as low as 5% or even less.

Another object of our invention is to provide an irradiation, wholly or mainly in those wave lengths to which the electrodes are sensitive. These wavelengths will depend upon the material of the electrodes, and it will also depend upon whether the electrodes are coatedpr uncoated. In many cases, the cold electrodes are coated with a material which emits electrons readily, and under the application of low energy. These materials aredesignated as "low work-function sub- I stances. Examples of such low work-function substances are caesium oxide, barium oxide and other materials-which are well known for this -bodiment. of our invention.

Our invention is described with reference to 'a If the lamp has such coated electrodes, visible light may be used to irradiate the bulb. However, even in this case, the violet and ultra-violet light will be more eflicient. By selecting from the well-known luminescent materials, which include phosphorescent andfluorescent materials, we can secure radiated light of various colors, thusselecting a range of wave length which ,willhave the maximum photoelectric eil'ect.

Other important objects of our invention will be stated in the'annexed description and single diagrammatic drawing, which illustrate an emstandard commercial lamp, which has a g ass bulb or envelope I, whose height is about 20 millimeters. This is provided with spaced cold electrodes 2 and 3 which are made of nickel. Said envelope l'has a gaseous filling whose pressure at V normal temperature of about 20 #c.-25 C. is about 20 millimeters of mercury. This filling consists of 99% of neon and 1% of argon. Each Of the electrodes 2 and 3 is a solid metal cylinder.

' The height of each cylinder is 12 millimeters, and its diameter is l millimeter. stated herein as an illustration, the electrodes 2 .and 3 are equal and parallel to each other. The

In the example width of the space between said electrodesis about 2-3 millimeters. The internal wall of the envelope is substantially cylindrical and the diameter of such internal wall is about millimeters.

Since commercial lamps of this type willvary from lamp to lamp, due to inaccuracies in commercial manufacture, the striking voltage can vary from lamp to lamp from about 70 volts to 90 volts, and possibly more. One th'eaverage, the operating voltage is 15 volts less than the striking voltage. The over-voltage which is applied in order tostrike the'lamp without undue delay, exceeds the striking voltage by about 5 volts. This is stated by way of illustration, because the important factor herein is to provide a uniform' striking voltage so that said striking voltage is stabilized, with a variation which is insignificant for practical purposes.

The improved lamps can be used in switches, relays, transmitting pictures by wire or radio, and for many other purposes, inwhich a stable striking-voltage is required.

After a lamp of this type has had an idle period of one or two days, during which idle period the lamp is shielded from light, the striking voltage for the particular lamp may increase by as much as 50%. After the lamp has been struck for the first time after a lon shielded idle period, its striking voltage during subsequent strikings will have-only a much smaller value, if the intermediateshielded idle.

period is very short. Therefore, an important feature of our invention is to stabilize thestriking voltage, even if the lamp has been shielded from light during a-long idle period. A long idle period can vary from ten minutes to one or two days, or even more.

A suitable self-luminescent composition can be made, for example, by intermixing with 1 gram of fluorescent zinc sulfide, 100-130 micromide or other suitable radium salt. v

When we refer'to this masS l00-l30 micrograms of radium, we refer to the mass of the radium in the radium bromide, so that the massof the radium bromide itself will exceed 100-130 micrograms. A self-luminescent composition of this type will produce a luminescense. of approximately 100 micro-lamberts.

- luminescent material can be applied to the inis therefore unnecessary to describe the specific mode of applying the self-luminescent composition, either'to the interior or exterior wall of the bulb L; The composition is preferably applied over the entire internal wall, or over the entire external wall of the bulb I, but our invention is not limited thereto. Said composition may be applied to one or more spots, either to said. internalwall or to saidexternal wall. The composition is preferably not applied to the electrodes 2 and 3.

The photoelectric eflect of an illumination of about 100 micro-lamberts is sumcient to supply enough photons, so that according'to our theory, there will also be sufilcient free electrons in the gaseous filling of the lampin order to stabilize the striking voltage. Likewise, some ionization may be',produced by the alpha'and beta, rays which are emitted by the radium, but I our invention is particularly directed to the photoelectric eilfect.

On the other hand, if the coating would consist of zinc sulfide or other phosphorescent material alone, such coating would not stabilize .the striking voltage after a substantial shielded idle period.

In additionto making the walls of such tubes of glass or. i otlier light-permeable material, it is well known;- make such walls of metal or other material whichvis impermeable to light. In. such case, we locate the self-luminescent ma terial in'the interior of the bulb. The selfner surface of the glass or metal bulb, or to the material, or to any suitable carrier which is located within the bulb. Said carrier may be fixed to the interior wall of the'bulb. For example, such carrier may be a rod of glass or 40 the like, which is fixed to the interior wall of p the bulb. In eifect, such a carrier would be an, extension of the interior wall of the bulb.

Likewise, if the self-luminescent material is external to the wall of the bulb, such selfluminescent material may be mounted upon a Such a composition canbe applied either to I the internal wall or to-the external wall of the envelope I. The wall of the'envelope I can be made of material which is permeable to ultra violet rays. There are wllknown types of glass which are permeable to ultra-violet rays, and we can use such wellknown glass compositions.

'However, the invention is not limited topthe use of ultra-violet rays, and it may be that ultra-violet rays are not emitted by theacti-- vated fluorescent zinc sulfide.

It is well known to apply such compositions to a glass wall. or the like, by incorporating such compositions in suitable transparent varnishes or lacquers which are optionally but not necessarily, permeable tothe ultra-violet rays, as

well'as to the rays in the visible spectrum. It

' grams of radium, in the formpf radium brocent material does not affect this normal discharge current under the same conditions of voltage and external resistance.

The weight of the radium which is.utilized in I the self-luminescent material for. the specific lamp described herein, may vary from about 2 micrograms to 20 micrograms. When'we refer to a "glow discharge, we refer to a discharge in which-the discharge current is less than in the arc discharge or in the spark discharge. In order to maintain the glow discharge between cold electrodes, and in order to prevent such discharge from becoming an arc discharge or a spark discharge, we limit the discharge cur- ,rent by suitable external resistances. The cold electrodes 2 and 3 have substantially'no disinte- 7 gration in the glow discharge. Such electrodes inner surface of a bulb made of any suitable herein, having a, striking voltage which varies more than 10% for striking said lamp initiallyhave a high rate of disintegration in a sustaining arc discharge or spark discharge, v

' We are concerned primarily with the starting of the lamp. After the lamp has' been started by the discharge between cold electrodes, the intensity of the discharge current may exceedthe intensity of the glow discharge, so that the lamp may operate, after starting, at glow discharge or arc discharge or spark discharge. For some uses,

able gaseous filling and spaced cold electrodes,

said lamp, when not irradiated as later specified discharge,

after a light-shielded idle period of m'ore'than ten minutes, said lamp having a source of light 'rays associated therewith, said surce delivering light rays to the interior of said lamp, said source comprising radioactive material and additional material which is activated by said radioactive material to emit said light rays, said source delivering a substantially'uniform supply of light rays, said supply being sufllcient to make said striking voltagein said initial striking uniform within a range of less than 10%.

2.,A glow discharge lamp according to claim'l, in which said source is fixed to said lamp.

. '3. A glow discharge lamp according to claim 1, in which said. source is fixed to said'lamp, and said source is spaced from said electrodes.

LADIsLAs GOLDSTEIN. FRANCIS PERRIN.

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