US2246486A - High intensity stroboscofic lamp - Google Patents

Description

l,June 17,Al 1941. P. w. BLACKBURN HIGH INTNSITY STROBOSCOPIC LAMP Filed Jan. 21, 1937 `2 Sheets-Sheet 1 ATTORNEY June 17, 1941. P. w. BLACKBURN 2,246,486

HIGH NTENSITY STROBOSCOPIC LAMP Filed Jan. 21, 1957 2 Sheets-Sheet 2 j 5% Y lNvENToR 3 mu Mr/www.

34 b 2am/ www ATTORNEY Patented June 17, 1941 man mrENslrY s'rnonoscorrc mur Philip W. Blackburn. East Orange, N. J., signor to Westinghouse Electric Manuf actnring Company, East Pittsburgh, Pa., a corporation of Pennsylvania.

Application January 21, 1937, Serial No. 121,383

invention relates to discharge lamps and 4Claims.

more particularly to such furnishing instantaneous flashes of light of high intensita/which may be synchronized with the movement of an object to be photographed or inspected.

In my application Serial No. vf133,156. filed June 30, 1934, now patent No. 2,168,861, dated August 8`, 1939, I disclosed a stroboscopic lamp` comprising an elongated envelope 'with an electrode at each end and the portion between said ends elongated and reduced in section, the anode being so formed that the light output from said lamp could be directed therethrough and the lamp used like an ordinary ilashlight. The present.` invention relates to an improvement in a lamp of that general type.

An object of my invention is to provide a.

fstroboscopic lamp comprising an envelope with a neon filling at such a high pressure that it will not operate on an applied direct current voltage, a grid being employed to act as a trigger and allow a discharge through said lamp of very high intensity for the production of very strong ashes of light.

Another object of my invention is to provide a lamp supplied from a source of direct current and including a condenser operating in parallel therewith, whereby, when an associated grid is energized for ionizing the contained gas, said lamp is operated by discharging the condenser with the instantaneous development of a veryv strong flash of light of exceedingly short duration.

A further object of my invention is the operation of a lamp containing a rare gas at such a high intensity that the light obtained therefrom is changed from that having a line spectrum characteristic of the gasto that having a band spectrum, resulting in the production of substantially 'achromatic light.

`A still further object of my invention is the production of a lampsuitable for motion picture work in which a relatively high potential is re'- quired forstarting, but in which the drop-out potential is low so that an associated condenser is well discharged and short, intense :dashes obtainable, the frequency o! said ilashes being limited bythe charging of the condenser, said lamp having a relatively long life when only a moderate number of flashes per second, as would be suitable for` motion-picture work, are required. v

Other objects and advantages of the invention relating to the particular arrangement and construction of various parts will become apparent as` the description proceeds.

v Referring to the drawings illustrating my invention, the scope whereof is deilned by the appended claims:

Fig. 1 is an elevational view oi one embodiment of my lampassociated with means for taking motion pictures.

Fig. 2 is a detailed sectional view on the line II-II of Fig. l, looking in the direction of the arrows.

Fig. 3 is a diagram illustrating the character of the light ilashes which may be obtained from my lamp.

Fig. 4 is a transverse sectional view on` the line IV--IV in Fig. 1, looking in the direction of. the arrows.

Fig. 5 is a longitudinal sectional view on the line V-V of Fig. 4, looking in the direction of the arrows.

Fig. 6 is a transverse sectional view on the line VI-VI of Fig. 1, looking in the direction of the arrows.

Fig. 7 is a transverse sectional view on the line VII--VII oi Fig. 1, looking in the direction of the arrows.

Fig. a is a iongituamn Semoun view on the i line VIII-VIII of Fig. 7, looking in the direction of the arrows.

`is shown a stroboscopic lamp Il) provided with a sealed envelope Il of glass or other suitable vitreous material. `If it is desired to use the lamp for supplying actinic light, as for taking motion pictures, said vitreous material is preferably quartz or glass pervious to ultra-violet light.

The envelope l I is preferably filled with a rare inert monatomic gas, such as neon, at a pressure or about 32 millimeters of mercury, some variation, however, being permissible, say from 25 to 3 2 millimeters. In the present embodiment, it is intended that no mercury shall be included in the envelope, in order to provide for a more uniform operation oi! the lamp.

The envelope Il is elongated and its end portions formed of sufficient size to contain a voltage activated cathode I2 and an anode I3, that portion of the envelope or tube II between said electrode-containing end portions being pref- -erably so elongated and reduced in diameter,

as shown, that the ratio between the internal diameter of the attenuated portion of the envelope and the length of said portion is within the' range between 1/30 and l/50. In one em- -bodiment of my invention, I have secured good results in making the overall length' of the envelope 4 feet 4 inches, the length of the restricted portion 3 feet, and the outside diameter of said restricted portion approximately 1 inch, thereby giving an inside diameter to said restricted portion of approximately inch. I do not, however, wish to be limited to these specific dimensions.

The cathode of the tube is desirably cup-shaped as shown in detail in Figs. 7 and 8. It may be of nickel about .01" in thickness, generally cylindrical, and about 7" long and 2" in diameter. The sides of the cylindrical portion I4 of the cathode I2 are desirably reinforced, and the eiective electron emission area increased, by longitudinally ei'rtending angular members I5 of nickel having their short legs welded in place, as illustrated, and their about l/ legs extending inwardly. The outer end of the cathode is desirably closed by the plate I6 from which extend one or more conductors I1 connecting with the medium 4bi-post base I6 which may be employed.

The cathode is desirably centered and braced with respect to end portions of the tube by straights pieces of nickel I9, the intermediate portions of which are welded to the outer surface of the cylindrical portion of the cathode. and the ends of which engage the inner surface of the end portion of the envelope II which receives the cathode. In order to facilitate starting and operation of the tube, the interior of the cylindrical portion I6 of the cathode is desirably coated with electron emission material 22. composed of material such as the carbonatos of barium and strontium. 'I'he inner end oi' the cylindrical portion I4 of the cathode is desirably partly closed by a nickel .plate 28 provided with a central aperture 2I, desirablyabout 1'.' in diameter, which restricts the discharge in cross section near the cathode and avoids a tendency to sputter said electron-emission material 22.

'I'he anode I8 may be of similar construction, but about 3" shorter than the cathode I2, and on account of being shorter, no bracing means at its inner end is required, nor any electron emission material need be applied to the inner surface of the cylindrical portion 23 of the anode I3 or the reinforcing angles 24 thereof. The outer end of the cylindrical portion 23 is closed -by means of a plate 25, from which extend conducting means 26 to the medium :bi-post -base 21, which is desirably employed. The inner end need not be partly closed.

In order to operate such a lamp as just described for the production of intense flashes of light of very short duration, a grid 28 is employed. Said grid may :be either internal or external and serves as a trigger for initiating the discharge. The construction of the illustrated yform of grid 28 is shown in detail in Fig. 6. Said grid 28 comprises merely a pair of relatively short plates 29 and 30 secured together by bolts 3|, and each provided with lingers 32 and 33 bent to partially surround a short length of the attenuated portion of the envelope II. The trigger is actuated by supplying current, from a source of high voltage or frequency, to ionize the gas filling in the envelope I I.

A direct current potential relatively high, 'but not high enough to cause a discharge, is applied to the terminals I8 and 21 by means of conductors 34 and 35 from a suitable source of direct current. With`a lamp such as specifically described, the potential may be about 1,000 volts, but, inasmuch as the average power supplied to the tube is small, on account of the shortness of the flashes, it would -be lpossible to employ storiage batteries for this purpose if desired, as only about 21/2 amperes are drawn on the average. With a. lamp in which the attenuated portion is 1A in diameter and 1' long, I may use the same voltage, but only drawing from 70 to 75 milliamperes, with good results.

Inasmuchasl the instantaneous flashes oi.' high intensity desired coul-d not be secured from the prime source of power without unnecessarily increasing the capacity of said source, as well as the size of the conductors for supplying the mo mentary relatively enormous flow oi' current when the lamp flashes, I employ a condenser 36 in .parallel with the lampl as Shown most clearly in Fig. 1. The capacity of the condenser determines the amount of energy in each ilash of light and because of this, it is necessary that the capacity of said condenser be proportionate to the size of the lam-p. For a lamp as specifically described in which the overall length is 4 4, I have found that a condenser of about 90 microfarads capacity should be employed. With a smaller lamp, that is. one in which the attenuated lportion is only 1 long and 1A" in diameter, it is only necessary to use a 5 mi-crofarad condenser. The life of such a lamp is as long as 200 hours when ashed not often'er than twenty-four times a second. The high current density in the lamp during ilashes changes the spectrum of the gas so that a band spectrum results, superimposed on the line spectrum of the gas. With neon a pinkish-white light is obtained.

I will now describe a preferred manner of operating my lamp for taking motion pictures:

Associated with my lamp I0 is means for taking motion pictures comprising a sprocket drum 31, over which a motion-picture llm 38 passes. Said drum is carried on a shaft 39, provided with an interrupter 40, formed as an insulating cylinder 4I with metal contact strips 42 inserted therein, and serving to periodically connect and disconnect the brushes 43 and 44, for making and breaking the circuit from the battery, or other source of direct current 45, through the primary 46 of high voltage coil 41 and condenser 48. The shaft 39 and associated interrupter and sprocket drum may be ldriven from van electric motor 49 supplied from a suitable source of power 50, through switch 5I, starter 52, and speed regulator 53, Iby means ofthe gearing 54, 55, and 56. As an alternative, a suitable source of alternating current may be employed for actuating the trigger 28, instead of the battery 45, if desired.

In operation, the rel-ation between the optical center of each separately cuitto be broken through the coil 41, thereby resulting 1n a flash in the lamp I0 just when the particular section of lm is in position With reling the instantaneous development c! a flash oi' light of high intensity in said tube or envelope I I. lIi' the lamp l0 is the sole source ot light in taking the motion pictures, it is clear that there is no necessity for any shutter, as the positioning oi the iilm sections may be accurately synchronized with the ilashing oi' the lamp III, so

'that each time a illm section comes into place it is exposed to the scene illuminated by an instantaneous ilash of light iromi the lamp Il.

This does not mean, however, that a motion picture camera with a shutter may not be employed, as it can be so synchronized with the arrangement disclosed that when the shutter is open and the illm indexed and atrest, the lamp will be iiashed and the' picture taken. However, because of the extremely short duration of each flash, the iilm may be in motion continuously, as it will not travel an appreciable distance during. a flash.

The manner in which the light ilashes are delivered from the lamp ,|0, is clearly shown in Fig. 3 which indicates that high intensity light flashes 58 are developed which rise to a maxialmost perpendihularly, and fade away nearly as rapidly, in accordance with the current flow through the lamp. In other words, as soon as the discharge of the lamp is initiated by the actuation of the trigger 28, the condenser 36 is immediately discharged with the development of an instantaneous current of very high intensity, which dies down almost as quickly as it rises, while the condenser is being discharged.

It will be understood that the effective portions of the current, for purposes of photography, are those above a certain value represented by the horizontal dotted line, and the current below that portion does not give an eilective light. It will therefore be seen that the flashes, insofar as effectiveness is concerned, are very sharply deiined and especially suitable for motion-picture work.

Referring now to the embodiment of my in vention illlustrated in Fig. 9, there is shown a stroboscopic lamp Ill* embodying my invention, connected to a source of power by means of conductors 34 and 35 in parallel with a condenser 36", as in the previous embodiment. In the present embodiment the lamp is connected for taking an ordinary still" photofiash picture by means of a camera 59. For that purpose, a grid 28 is employed on the lamp lll"l connected to one terminal of the secondary 51 of a high-voltage coil Il, the other terminal of said secondary being grounded as indicated at 60, as in the previous embodiment. In the present embodiment,

the primary 46 of the high-voltage coil Il is connected to a battery, or other source of direct current 45, and a condenser 48*ab through a key or switch 40' operable simultaneously with the shutter of the camera 59, so that, when the key isdepressed, the condenser and high-voltage coil are charged, and, when released, the shutter is opened to expose the sensitized medium, such as a film or plate, and the lamlp flashed for llluminating the object to be photographed. It will be understood that the connection between the shutter and the lamp shouldbe such that era. Alternating the nach is exactly timed to correspond with the exposure of the sensitive medium in the camcurrent trigger actuating means may be substituted. for the battery IBI, as in the previous embodiment.

Fig. 10 shows a circuit in which there is no trigger for operating my lamp ill". In this case,

the direct current supply, to which the lamp is eonnected by means of conductors 34h and lib, the condenser Il being in parallel as heretofore, is sumciently high so that a constant breakdown of the tube would occur if there were no condenser `or resistance in the circuit. However, since a condenser discharge is required for satisfactory operation of the lamp, the rate of charging the condenser can be tinted, by a proper i value lof the resistance 8|, so that a ash will occur immediately after the condenser is fully charged. It willthereiore be seen that by varying the resistance 6I, we can time the flashes as desired, as ii a trigger were employed, with the exception that the timing is not quite as easily controlled.

Fig. 11 illustrates two spectra obtainable when using a lamp embodying my invention. The lower spectrum 62 is of .the kind of light obtainable when operating my lamp continuously without a condenser, or other means for producing spaced ilashes. In this event the lamp may be operated with a voltage of 1500 and an input current oi 2 amperes, the spectrum of the light produced corresponding with that of the illling gas. Inasmuch as I prefer to employ neon, the spectrum is characteristic of that gas.

The upper spectrum 63, illustrated in Fig. 11, is that produced when using a condenser, as previously described, for obtaining intense ashes of substantially achromatic light. This shows that the character of the light is changed as compared with the lower spectrum. Instead oi having the lines substantially restricted to the red end of the spectrumfwe obtain a considerable number of lines toward the violet end, so that substantially achromatic light is produced, which is suitable for photographic and other work requiring light having strong actinic properties.

In explanation of this unusual result, I might say that on account of discharging at enormous current through the enclosed neon gas, said current during a flash being of the order of thousands of amperes rather than units, the electrons of the gas atoms, through which the current passes, are displaced to a much greater extent than when only a small current is passed through the tube, so that momentarily the gas can be considered as dissociated or transmuted, resulting in the development of light vibrations having frequencies not normally attributable to the light developed from neon gas. The result is that a light having a broad band spectrum with superimposed lines is secured, as distinguished' from the line or narrow band spectrum of the gas utilized.

In view of the foregoing it will be seen that I have devised a stroboscopic lamp which delivers instantaneous :dashes of high intensity of very short duration, which flashes may be accurately spaced andsynchronized with movements of associated parts, such as the exposable portions of the iilm of a motion picture camera, so that use is made of the ashes exactly when they are needed. It will be understood, however, that my lamp is also suitable for other purposes, such, for example, as a constant light source and as a ilasher in a lighthouse or beacon.

'I'he carbonate coating on the cathode is, of course, decomposed by heat after sealing-in and exhaust to develop the desired electron emisslvity.

It Will also be seen that by the employment of an excessively intense discharge through the the tube containing neon or other suitable gas, a continuous spectrum of substantially monochromatic light is obtained, rather than the line spectrum of the gas, whereby such ilashes have the desired actinic value for motion-picture and any other work.

Although preferred embodiments of my invention have been illustrated and described, it will be understood that modiilcations may be made within the spirit and scope of the appended claims.

I claim:

1. A discharge lamp normally energizable by about one thousand volts direct current and comprising a hollow elongated gas-filled vitreous envelope consisting of a pair of end chambers connected by an intermediate portion about three feet long and seven-eighths of an inch in diameter, an electrode in each end chamber, one of said electrodes being hollow cylindrical about seven inches long, two inches in diameter, and adapted to act as a cathode, and the other being hollow cylindrical about four inches long, two inches in diameter, and adapted to act as an anode, and a grid comprising conductive plate means provided with fingers at least partially surrounding said intermediate envelope portion and adapted to be energized from a source of high voltage or frequency, to cause it to act as a trigger by ionizing said gas lling to initiate a discharge between said cylindrical electrodes.

2. A discharge lamp normally energizable by about one thousand volts direct current, comprising a hollow elongated vitreous envelope containing an inert monatomic gas free from mercury, and consisting of a pair of end chambers connected by an intermediate portion about three feet long and seven-eighths of an inch in diameter, an electrode in each end chamber, one of said electrodes being hollow cylindrical, about seven inches long, two inches in diameter, closed at one end, partially closed at the other end by an inwardly extending annular ange, adapted to act as a cathode, and reenforced by members angular in section, one leg of each member being connected to the inner surface of said cylinder and the other A leg extending radially inward, said inner surface and legs being coated with electron-emission material, and the other electrode being hollow cylindrical, about four inches long, two inches in diameter, adapted to act as an anode, and similarly reenforced, the pressure of the contained gas being about thirty-two millimeters, and a grid comprising a pair of plates secured together and each provided with fingers bent to at least partially surround said intermediate envelope portion and adapted to be energized to ionize the gas filling in said envelope and initiate a discharge between said cylindrical electrodes.

3. A discharge lamp comprising a hollow elongated vitreous envelope, containing an inert monatomic gas free from mercury and at a pressure of about 32 millimeters, and consisting of`a pair of end chambers connected by a relatively long attenuated intermediate tube, an electrode in each end chamber, one oi said electrodes being a hollow cylindrical shell, closed at one end, partially closed at the other by an inwardly extending annular ange, reinforced by members, angular in section, one leg of each member being connected to the inner surface of said shell, and the other leg extending radially inward, said inner surface and legs being coated with electron-emission material, and said electrode, as a whole being adapted to act as a cathode and nearly twice as big as the other electrode, said other electrode being similarly constructed and adapted to act as an anode, a grid comprising short plate means provided with ngers bent to at least partially surround said tube, and adapted to be energized to ionize the gas illing and initiate a discharge between said electrodes.

4. A discharge lamp comprising a hollow elongated vitreous envelope, containing an inert rare monatomic gaseous lling free from mercury and at -a pressure of about 32 millimeters, and consisting of a pair of end chambers connected by a relatively long attenuated intermediate tube, Ian electrode in each end chamber, one of said electrodes being a hollow cylindrical shell, closed at one end, and with its inner surface coated with electron-emission material, and said electrode, as a whole being adapted to act as a cathode and much larger than the other electrode, said other electr-ode being adapted to act as an anode, a grid comprising short ngcr means engaging the exterior of said tube, and adapted to be energized to ionize the gas lling and initiate a discharge between said electrodes when energized by not more than about one thousand volts direct current.

PHILIP W. BLACKBURN.

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