US2788462A - Stroboscopic light source - Google Patents

Description

April 9, 1957 R. B. MaCFARLANE 2,788,462

STROBOSCOPIC LIGHT SOURCE Filed June '7, 1954 INVENTOR.

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STROBOSCGPIC LIGHT SOURCE Richard B. MacFarlane, Oakland, Calif. Application June 7, 1954, Serial No. 434,816

3 Claims. (Cl. 313-205) pressure, the preferred content being sometimes nitrogen but more usually one of the monatornic gases such as helium, neon, or argon, or mercury vapor. Mounted within the envelop and sealed at one end to the wall thereof, is an elongated discharge tube which is usually more or less convoluted. The end of the tube which is not sealed to the wall is open and communicates directly with the rarified gas in the body of the envelop. Within that end of the tube which is sealed to the envelop wall there is mounted an electrode (the cathode) which has a terminal projecting outwardly through the wall of the envelop. Within the body and external to the tube, the anode st ucture is mounted, such anode structure some times comprising a sin le electrode, sometimes a pair. Terminals for the anode or anodes are brought out through the wall of the tube.

The light source of the present invention is very similar in appearance to that just described. There are, however, highly important structural diflferences which lead to ditlerences in operation of an important nature which, for certain purposes at least, give the device of this invention increased value. Like the prior art devices, the present invention comprises a partial evacuated envelop containing a gas or vapor at low pressure. Within the envelop is an elongated, light-permeable discharge tube, preferably of convoluted form, but in contrast with the prior art structures both ends of this elongated tube are sealed to the wall of the envelop, and electrodes are sealed through the envelop wall so as to project into both ends of the tube instead of one end only; unless the device is to be combined with other apparatus not directly related to the present invention, no electrode is used in the body of the envelop, external to the discharge tube itself. At some location along the course of the discharge tube, and preferably at a location within the envelop which is most remote from the electrodes sealed therethrough, there is formed an aperture connecting the bore of the discharge tube with the body of the envelop.

Among the objects of the invention as embodied in the construction thus described, is to provide a source of higher luminosity for a given power input than has heretofore been available; to provide a device of more rigid construction and less liable to breakage; to provide a light source of the positive-column type having a lower deionization time than prior art devices of the same general character and hence able to resolve into separate light flashes pulses recurring at a more rapid rate; to provide a light source of the general character described wherein the clean up effect or reduction of gas pressure within the envelop due to adsorption by the walls is reduced, so that the pressure in the envelop remains within the working range for a longer period and the source therefore has a longer life; to provide a light source wherein no deposit a volatilized material from the electrodesupon the envelop wall can occur and wherein any such deposit occurring upon the walls of the discharge tube itself'is limitedto the area immediatelysurrounding the electrodes and does not extend to portions of the device where it can intercept and absorb any material portion of the emitted light energy, thus, again, increasing the effective life of the device; to provide a light source which does not have to be poled in a particular direction with respect to the exciting pulses applied thereto, so that it may be used in standard types of sockets, either of its electrodes being equally effective as either anode or cathode; to provide a light source of the type described wherein only that portion of the contained gas which is activated to emit light is ionized, the remaining gas being relatively cool and providing a large reservoir to'maintain the life of the device as clean-up does occur; and, broadly, to provide a light source of unusually high intensity which is, at the time, resistant to breakage and uniform in characteristics over long effective life.

The nature of the invention will be best understood by the following detailed description of a specific embodiment of the invention taken in connection with the accompanying drawing.

The single figure of the drawing is an elevation, partly in section, of one embodiment of the invention as specifically described herein, portions of the envelop and the discharge tube being broken away in order to show more clearly the construction.

As shown in the figure, the body of the lamp comprises a completely sealed envelop 1, formed preferably of glass, although for special purposes it could be of fused quartz or of other vitreous, light permeable material, including in the latter term both completely transparent and translucent materials. In general, the completely transparent types of envelop are to be preferred, since maximum illumination is ordinarily desired. The shape of the envelop is of very minor importance; a cylindrical envelop with domed ends such as is illustrated is convenient, but pear-shaped, substantially globular, or other shaped enelopes may be used if desired.

Mounted within the envelop and sealed to the walls thereof is the discharge tube 3. The discharge tube is preferably of the same material as .the envelop itself. In the lamp shown, the discharge tube is shown as convoluted so as to concentrate a relatively long length in a relatively confined space, but it will be recognized that if desired both envelop and discharge tube could be r linear, so as to give a line source of light instead of a concentrated one.

In the present instance both ends of the convoluted discharge tube are sealed into the end of the envelop to which a base 5 of the tube (indicated in dotted lines) is eventually attached. It is also convenient to locate the exhaust tip I through which the lamp is-evacuated at this same end of the lamp, where it will be concealed and protected by the base.

Althoughthe dimensions of the lamp are not critical, or, in fact, actually germane to the invention as such, it may be notedthat the particular lamp here described en1 ploys an envelop 1% inches inoutside diameter and approximately 2%. inches in total length. The discharge tube within this envelop has a total length of approxi' mately one foot, with a bore or lumen of 4 millimeters, although discharge-tubes varying from 3 millimeters up ward to 20 millimeters in bore may be used, common practice being usually within the range of 3 to 7 millimeters.

The particular feature to be noted about this discharge tube is the aperture 9 in its wall, which communicates from the discharge tube bore into the body of the envelop. While the location of the aperture 9 is not critical, best results are obtained if its location is spaced physically as far from the ends of the tube as space will permit.

Electrodes 11 and 11 are sealed through the wall of the envelop at the point where the discharge tube joins the latter, so that the electrodes project into the discharge tube. The material of the electrodes is notimportant; they may be of iron, or of nickel steel having a composition which will provide substantially the same coefficient of the glass used, in accordance with well known practice. The electrodes are provided with terminals 13, 13', for connection with pins 15, 15 secured to the base 5.

In manufacture the envelope is first thoroughly evacuated through the tip 7, before the latter is sealed off. In the course of the evacuation the envelop and the discharge tube within it are thoroughly out-gased in accordance with well known practice, so as to prevent contamination of the gas filling of the tube by undesired impurities, released from the walls of the tube when the latter heat in operation. After evacuation and out-gasing whatever gas is to be used as the light source is introduced at proper pressure and the tip 7 is sealed off.

It may be noted that if desired the final clean-up of the envelop, before the admission of the active gas, may be facilitated-by the use of one of the well known getter materials. Because such materials usually leave an opaque coating on at least a portion of the envelope, however, it is preferred to accomplish the evavuation by a straight pumping and baking technique. This is a matter of detail, however, and either technique falls within the scope of the present invention.

A wide variety of gases may be used within the lamp. The rare, monatomic gases may be employed, with or without the addition of a small amount of mercury, the latter, of course, providing a mercury vapor which contributes to and usually dominates the spectrum of the light emitted. Of the rare gases xenon gives the most effective light for photographic purposes if used alone. The mercury spectrum is, of course, highly effective photographically, particularly if an envelop or discharge tube transparent to the ultraviolet is used. Xenon, however, is relatively expensive. A light which is very brilliant and quite comparable both visually and photographically to that emitted by xenon is provided by a mixture of 15% neon and 85% of carbon dioxide. This mixture emits a light having a color temperature of from 6500 to 7000 K. Nitrogen is also a possible gas for use in tubes of this character, although for most purposes its spectrum is not as desirable as some of the other materials mentioned.

With any of the gases mentioned, the amount admitted is preferably such as to provide a pressure within the envelop from 1 /2 to 6 millimeters of mercury. For discharge tubes of internal diameters within the range here described pressures of from 4 to 6 millimeters of mercury are to be preferred, but it should be noted that with discharge tubes of larger bore it is possible upon occasion to use pressures as high as 20 millimeters of mercury. Since, as in all devices of this character, clean-up does occur to some extent, it is desirable that the pressure used be toward the upper limit of the range appropriate to the discharge tube of a given bore, this being conducive to a longer life lamp. The 1.5 millimeter figure first given marks approximately the lower limit of the practical range, although with suitable exciting voltages it is not necessarily an absolute limit.

In operation lamps built and described as illustrated have been found to emit approximately 3 times the light, for a given power input, of lamps having the same length and caliber of discharge tube and the same gas content,

' adsorption is small.

but of the open-end discharge tube construction which is described in the prior art. The lamps of this invention have no rectifying characteristics, the two electrodes being substantially identic'aL-and operating equally Well as either cathode or anode. The structure wherein both ends of the discharge tube are sealed to the envelop is somewhat more difiicult to construct than the single sealed-end end type. The structure is, obviously, more rigid; where a lamp of the usual open end construction is rapidly pulsed it is possible for the free end to set up a suflicient vibratory motion so that it actually can be heard. The double sealed end is much more rigid and resistant to shocks which can ocur both in shipment and in operation.

When the tube is excited the entire discharge path lies within the discharge tube itself; even at the orifice 9 into the main reservoir there is no apparent luminosity which escapes. The gas which remains in the envelop, un-

ionized and unatfected by the discharge, is available to cool the discharge tube and this tends to speed up deionization.

Electrode sputter is limited to the area immediately surrounding the electrodes and does not discolor the discharge tube to cause absorption of the emitted light. Absorption of gas by the walls of the discharge tube is also limited very largely to this area, and since this is also the highest temperature portion of the tube there is also some reliberation of the absorbed gases, so that the total Outside of the discharge tube, in the body of the envelop, there is available a relatively large volume of gas which tends to maintain the pressure within the discharge tube and prolong the life of the device. In combination with the rigid construction which tends to prevent accidental termination of the life of the lamp the over-all result is a device of high efficiency, high constancy of performance characteristics, ruggedness and long life.

What is claimed is as follows:

1. A gaseous discharge lamp comprising a partially evacuated envelop, a continuous elongated light-permeable tube within said envelop and sealed thereto at both ends, a pair of electrodes, sealed respectively into the ends of said tube and connections sealed outwardly through said envelop each consisting of a single conductor connected to one of said electrodes, said tube having an aperture formed therein connecting the bore thereof with the body of gas within said envelop.

2. A gaseous discharge lamp comprising a partially evacuated envelop, a continuous elongated light-permeable tube within said envelop and sealed thereto at both ends, a pair of electrodes, sealed respectively into the ends of said tube and connections sealed outwardly through said envelop each consisting of a single conductor connected to one of said electrodes, said tube having an aperture formed therein at a location spaced from both of said electrodes.

3. A stroboscopic light source comprising a partially evacuated envelop, a continuous convoluted elongated transparent tube within said envelop and having its ends sealed to the wall thereof, a pair of similar electrodes projecting into the ends of said tube and connections sealed through the wall of said envelop each consisting of a single conductor connected to one of said electrodes, said tube having an aperture formed therein connecting the bore thereof with the body of gas within said envelop at substantially the location most remote from said electrodes.

References Cited in the file of this patent 2,273,520 Henninger et al. u,- Feb, 17,

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