US1975243A - Glow lamp - Google Patents

Description

R. M. WILLIAMS GLOW LAMP Filed Dec INVENTOR Patented Oct. 2 1934 GLOW LAMIP Richard Melvin Williams, Rutherford, N. J., as-

signor to- Richard Howland Ranger, Newark,

Application December 21, 1931, Serial No. 582,199 5 Claims. (Cl. 176-122) The present invention is concerned with gas eous glow lamps, that is, with lamps wherein the source of light is a gas which v becomes luminous when an electric current passes through it. More 5 specifically, the invention deals-with gaseous glow lamps designed for use in translating variations in electric current intensity into variations in light intensity; as a recording device for television signals, for instance.

.The most important requirement for lamps of this type is that their discharge or conducting region shall be confined to assmall a space-as possible, so that a small and intense spot of light is produced. The reason for this is obviousall tele- 16 vision systems are based upon the division-of the transmitted scene by some scanning means into a plurality of elementary areas, the transmission of a plurality ofelectric'signals of intensity corresponding to the average light intensity of each 20 of these elementary areas, and the re-translation of these electric signals into light intensities in the same relative geometric location as were the original picture elements. The more concentrated the source of light at the recording end, the smaller and brighter the picture elements and the more perfect the reproduction will be. In the prior art, such concentration of the discharge region has'been accomplished by the confinement of the cathode by an insulated shell, allowing only a small free passage for the electric current. Most of the discharge then takes place at the entrance to this passage. No very high light intensities are possible by this desigmhowever, without undue heating of the cathode.

It is a primary object of this invention to develop a gaseous glow lamp capable of producing an extremely intense spot of light without overheating.

, A second requirement for this type of lamp is for it to have a most eflicient frequency'characteristic; that is, for the gas to return very quickly to its original non-conducting state after discharge has ceased. This characteristic determines the rapidity with which successive current pulses can be supplied to the lamp, and consequently is, a great factor in its eificiency as a recording or translating unit. Accordingly, the second object of my invention is to develop a gaseous glow lamp of improved frequency character-'- istic.

gaseous glow lamp whose discharge will emit a large proportion of white light. As will be explained below, certain types .of discharge emit 65 monochromatic light of various colors, while oth- The third object of my invention is to provide a er types of discharge emit white light. Both types of discharge are present in any gaseous glow lamp, but white light should predominate in a lamp to be used for picture translation, as the reproduced picture then becomes more distinct and-less fatiguing to the observer. 7

My attainment of the above objects is explainedin the succeeding paragraphs of this specification, and illustrated by the accompanying drawing, of which Fig. 1 is. a cross-sectional view of a glow lamp embodying the principles of my invention, and Figs. 2 and 3 are views of alternate arrangements of the elements of the lamp.

Referring now to Fig. 1, the gas-filled glass containing vessel 1 is formed into two presses 2 and 3 located as shown. Embedded in press 2 are two metallic members 5 and 6, and supported between these members is the cathode 8, consisting of an inner metallic shell 7 and an outer coating of highly emissive material such as the oxides of barium and strontium.

Embedded in press 3 is a supporting member 18, carrying the fine tungsten anode 16. Surrounding the anode and embedded also in the press 3 is a tubular shield 17, which may either be of insulating material or of conducting material insulated from member 18 and anode 16. The configuration of the end cap 13 of the shield 17 leaves only the small tubular passage 14 to connect the gas in the constricted anode region. 15 with the gas in the main chamber of the lamp. Members 5 and 6 terminate in leads 11 and 12, which are in turn connected to the metallic prongs 9 and 10 projecting from the base 19 of the lamp. A steady heating current is applied to the prongs 9 and 10 in order to obtain maximum electron emission from the cathode 8. We will assume that the prong 9 and the lead 11 are maintained at ground potential. 1

Now, when a signal voltage is applied across prong 9 and the anode support 18, a'potential drop is produced inside the lamp between the anode 16 and the cathode 8, and the gas in chamber 15 becomes ionized through loss of electrons .to the anode 16. Due to the potential drop existing betwen anode 16 and cathode 8, the positively charged gas ions drift from anode 16 towardscathode 8. At the same time, the free electrons emitted by cathode 8 are accelerated by the potential drop towards'theanode 16. At the entrance ,to passage 14, a highly concentrated stream of ions traveling .out meets with a stream of electrons attempting to enter, and a series of collisions take place, with a resulting emission 01' light quanta. no

The collisions between electrons and ions may be of two types. The first type, called a resonance-potential impact, occurs when an electron and an ion collide and re-separate. Monochromatic light is emitted as a result'of such s. collision. The second type of collision occurs when an electron and a positive ion recombine and form a neutral atom and from this type of collision intense and very nearly white light is emitted. The construction shown in Fig. 1 tends to increase greatly the number of collisions of the second type, as will be shown, and thus to make the light emanating from the small collision region at the entrance to passage 14 very intense *and very nearly white color.

It has been demonstrated that the potential drop through an enclosed gaseous medium is proportional to the cross-sectional area of the enclosure. Furthermore, the speed of a charged particle such as an electron or an ion is proportional to the potential drop in the region through which it is traveling. Thus, in Fig. '1, the potential drop through chamber 15 and the passage 14 is far greater than the potential drop between the entrance to passage 14 and the cathode 8, and consequently the electrons traveling between cathode 8 and passage 14 are subjected to very much smaller accelerating forces than the ions traveling from anode 16 to passage 14. Of course, since the ions are very much heavier than the electrons, the average velocity of the latter is far greater than thatrof the former even so, but-their relative velocity is much lower than would he the case were the electrons subject to a high and the ions to a low potential drop. For this reason the probability of any electron colliding with an ion and being held by the latter (second type collision) is greatly increased, as the lower the speed of the electron, the less its tendency merely to be deflected by the ion, rather than to combine with it 7 The superiority of my invention over the prior art, therefore, is inherent mainly in the confinement of the anode rather than the cathode. When the cathode is confined, precisely the reverse of the above-described ccndition-prevails the electrons are highly accelerated and are thus less likely to recombine with the ions.

The construction of my invention also improves the frequency characteristic of the lamp, since the space charge in the main region of the lamp (outside of chamber 15, that is) is negative, consisting almost entirely of electrons. These electrons are light and active and thus recombine rapidly afteT the discharge is ended, reducing the gas to its original neutral and non-conducting state in a short time. Were the space-charge positive; that is, due to a predominance of ions, on the other hand, the recombination would take place much more slowly, due to the greater weight and sluggishness of the ions. Furthermore, the rate of recombination is a function of the product of the respective concentrations of electrons and positive ions present in the gas. When the space-charge is negative, the positive ion concentration diminishes with recombination, but the electron concentration is continually replenished by the cathode, so that the rate of recombination ismuch more rapid than in the-case of a positive space-charge, when both concentrations decrease as the recombination procedes.

In Fig. 2 are shown two views of the most efficient construction for the lamp elements in an embodiment of my invention. The anode 16 and its tubular shield 1'? are exactly the same as in the form shown in Fig. 1. The cathode however, is made in the form of a circular strip .of oxide-coated metal located as shown just beyond the passage 14. With the construction shown in Fig. 2 practically the entire discharge of 'the lamp is concentrated in the space enclosed by the cathode, since very few positive ions can escape into the main chamber of the lamp to collide with the electrons emitted from the outer circumference of the ring-cathode 20. W

While the construction shown in Fig. 2 is highly efilcient, it is correspondingly diflicult and expensive to manufacture, and in a practical embodiment of my invention a compromise must accordingly be reached between the degree of eficiency necessary and the allowable unit cost of construction. In Fig. 3, for instance, is shown a design for a cathode-anode assembly which is. less expensive to build than the forms shown either in Fig. 1 or Fig. 2, since it involves only one press within the lamp. The cathode 8 is mounted as in Fig. 1 upon supports 5 and 6, and the anode 16 is supported from press 2 directly adjacent to cathode 8. The'tubular anode shield 21 is in this case extended above the top of cathode 8 and bent at a right angle as shown, so that the end cap 13 and passage 14 bear the same geometric. relation to the anode 8 as they do in the form of Fig. 1. I have found the design of Fig. 3 far easier to build than that or Fig. 1, and only slightly less eflicient.

Qbviously, many yariationstof design are pos sible in addition to those shown, while still retaining the essential principles "of my invention. It is only necessary that the anode be confined within a generally tubular chamber, that a small passageway connecting this chamber with the main body of the lamp be located in juxtaposition to the cathode, and that a cylindrical beam 7 of vision from the aforesaid passageway out of the lamp (see Fig. 1) be left clear of obstructions. Accordingly, I feel myself entitled to the exclusive use during the term of grant of Letters Patent of any and all modifications which may fall fairly within the spirit and scope of my invention, as defined by the following claims.

I claim:

1;: In a gaseous discharge lamp construction, an anode, a tubular member surrounding said anode and extending outwardly therefrom, an end piece for said tubular member pierced by a small orifice, a cathode extending toward said anode, the end of said cathode approaching closely to the said end piece but not obstructing a view of the said end piece in a line of vision paralleling the extension of said tubular member and leaves connected to the cathode for maintaining a current therethrough.

2. In a gaseous glow lamp, a press, an anode supported from said press, a second press located apart from said first press, a cathode supported from said second press, and a cylindrical shell supported from.said first press, insulated from said anode, enclosing said anode, and extending outwardly therefrom towards the said cathode, the direction of such extension being such that said extension and said. cathode have no common point.

3. A gaseous discharge lamp comprising a cathode, two terminals exterior to the lamp connected tov said cathode for establishing a circuit therethrough, an anode, a single terminal exterior to the lamp connected to said anode, a tubular shield of relatively small cross-sectional area housing said anode and having a restricted aperture at 150 5. A gaseous discharge lamp comprising a gas filled container and within the container a cathode, leaves connected to said cathode for maintaining a current therethrough, an anode, and a shield of relatively small cross-section as compared with the cross-section of said container enclosing said anode and insulated therefrom, the anode projecting into one end of said shield, the opposite end of the shield being formed with a restricted discharge aperture, substantially as and for the purposes described.

RICHARD MELVIN WILLIAMS.

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