US3005102A - Self luminous lamps - Google Patents

Description

Oct. 17, 1961 J, MacHUTCHlN ETAL 3,005,102

SELF LUMINOUS LAMPS Original Filed April 2, 1957 INVENTORS JOHN G. MAC HUTCHIN DAVID L. PROSSER CHARLES H.WRIGHT ATTOR Y United States Patent 3,005,102 SELF LUMINOUS LAMPS John G. MaeHutchin and David L. Presser, Berwicir,

Pa and Charles H. Wright, Overland Park, Kane,

assrgnors to United States Radium Corporation, Morrrstown, N.J., a corporation of Delaware Continuation of application Ser. No. 650,247, Apr. 2, 1957. This application Dec. 4, 1958, Scr. No. 778,202

Claims. (Cl. 250-77) This invention relates to lamps of the self-luminous type in which the light source comprises a phosphor excited by radioactive material.

This application is a continuation of copending application Serial No. 650,247, filed April 2, 1957, now aban doned.

Heretofore it has been customary to employ selfluminous phosphors to produce visible light only of low intensity. These have been employed chiefly in luminescent paints and the like. They have not beeen useful in lamps to illuminate other objects because their light output is so low. Although there has been widespread use for such self-luminous phosphors, there has also been an unsatisfied demand for lamps capable of providing light of considerable intensity and in which the light source comprises a phosphor excited by a radioactive material. The present invention provides such a lamp and includes a novel light-giving element of inherent brightness heretofore unattainable. This element is mounted in a structure which includes a suitable light reflector, shielding members and other components which cooperate to provide many new characteristics and advantages.

An understanding of the invention will be had from the following description considered in connection with the accompanying drawing in which:

FIG. 1 illustrates the invention applied to a lamp of the portable or hand type shown partially in cross-section;

FIG. 2 shows a modificationof the lamp of FIG. 1 which differs therefrom primarily in that the reflector is spherical instead of parabolic, and the shape of the light element is modified accordingly;

FIG. 3 illustrates a modified form of light element which has an increased and more eflicient light output;

FIG. 4 is a front elevational view of a modification as embodied in a sign-type lamp structure;

FIG. 5 is a cross-sectional end view line 5-5 of FIG. 4; and

FIG. 6 is a cross-sectional. view taken along the line 66 of FIG. 4, of the tubular light element.

The lamp structure illustrated'in FIG. 1 comprises a cylindrical casing 1, preferably a tube of metal such as brass, to which is attached a shell 2, also of metal such as aluminum, for example. The casing is closed at the bottom, as shown. In the upper end of easing 1 a saddle cup 3 is secured by brazing. This cup may be of brass, if desired. A hole 4 at the center of the cup is large enough to receive the or light element 5 described below. A polished reflector 6 of aluminum or chrome-plated brass is secured at its lower extremity to a supporting ring member 7 which rests in the cup 3 and, at its upper periphery, is shaped to support the lamp element. The two are preferably cemented together by an annular seal 8 of suitable material such as epoxy resin below described.

Between reflector 6 and shell 2 a layer of radiationabsorbing material 9 is interposed. This shield should be of material of a nature and thickness sufflcient to absorb all or substantially all of the dangerous radiation emitted from the sides of the light element 5. In the particular embodiment here illustrated this shield comprises a continuous sheet of taken along the lead approximately /s inch 3,505,102 Patented Get. 17, 1961 2 thick. This shield is not required when relatively low radiation energies are involved, e.g., those of tritium.

The reflector 6 is bent outwardly at its upper edge to form a flange 10 which rests against the upper edge of the shoulder 9, as shown. The periphery of flange 10 is of a diameter which makes a good fit within the straight rim portion 11 of shell 2.

Across the top of reflector 6 a transparent cover 12 is placed so as to rest on flange 10. This cover may be of a suitable plastic material such as methyl methacrylate, but preferably is of glass of suflicient density and thickness to absorb radiocative cmanations from the front of the lamp. It may be flat as shown, or in the form of a lens. Occasionally it is desirable to employ a cover comprising a glass layer superimposed by a layer of plastic material. The usual commercial glass, especially lead glass, would be suitable for a short time, but experience has proved that thereafter such glass becomes darkened by the radioactive emanations. Therefore, it is important that a material be employed for this light-transmit-. ting cover which will not darken appreciably under the conditions of use. A material especially successful for this purpose is cerium-bearing glass. In that. type of glass cerium is usually present as a salt or an oxide, and cornmerical forms presently available include Corning #8362, Pittsburgh #6740 and Penberthy Med-D. The density of the first-mentioned glass is approximately 3.2, of the second 2.7 and of the third 4.0.

The glass cover above described is held in place by a retaining ring 13, here of aluminum, which is secured to the casing rim 11 by screws 14. In order to make a tight seal between the reflector and the cover 12, and

bottom of the self-luminous lamp 1 also toavoid breakage of the glass, gaskets 15 are interposed above and below the cover 13 as shown. These gaskets should be of material which is not only resilient but which will maintain this and its other desired characteristics when subjected to radioactive emanations. A cork-like material known as Wisoid has been found to be suitable.

The light element 5 which incorporates several novel features, comprises a hollow'capsule or bulb of transparent material. It has been found that glass of a ceriumbearing type, as above described in connection with cover 12, is suitable for this purpose. It should be of material which does not darken appreciably under the conditions of use and which also can be maintained completely gastight under reasonable pressure. As shown, the element 5 comprises an upper bulbous portion 16 and a lower stem portion 17. The lower portion passes through hole 4 in the saddle cup 3. and is retained in place by cementing material 18 which should be of a type substantially unaffected by radioactive emanations. Epoxy resin is suitable for this purpose. Two suitable epoxy resins are Araldite #502 manufactured by Ciba, and Epon #6 'manufactured by Shell Chemical Corporation. Beneath the cement material 18 is a thick plug 19 of plastic material, such as methyl methacrylate. If additional shielding is required to the rear of the structure, this plug may be of lead, or a disc or cup-shaped piece of lead may be placed immediately above it.

The self-luminouslight element 5 comprises the bulb 16, 17 as above described. In the particular embodiment here illustrated, the bulbous portion 16 was approximately /8 inch high and A inch maxi-mum diameter, inside dimensions. The inner surface is coated with a layer of phosphor crystals of thickness corresponding to approximately 50 to milligrams of phosphor per square cm. The art has developed a large variety of phosphors, certain of which provide a substantially colorless light, and others of which produce light of various For many by zinc-cadmium-sulfide phosphor is satisfactory. This type is copper activated and" includes only a small proportion of cadmium. Other well-known types of phosphors which are also suitable are zinc sulfide, zinc silicate, cadmium tungstate and cadmium sulfide.

The phosphor layer may be bound to the surface of the glass by various adhesives, including organic, inorganic and semi-organic types. Sodium silicate is an example of an inorganic adhesive suitable for the purpose. Organic adhesives include Du Pont butyl methacrylate, and certain colorless epoxy resins such as the mentioned Araldite #502. Inorganic types such as sodium or potassium silicate are preferred for their stable properties.

' After the phosphor coating has been applied and properly dried, the bulb is evacuated and filled with radioactive gas, preferably krypton85. This can conveniently be done through the stem 17 before it is sealed off. The quantity of gas injected into the bulb will determine the brightness to a large degree. Since krypton gas, as presently available from the U.S. Atomic Energy Commission, contains a comparatively small percentage (about 5%) of active Kr-8'5, a larger quantity of the gas must be used than would be the case were this proportion greater. In the light bulbs here discussed krypton gas pressures ranging from 150 to 400 millimeters of mercury are suitable. In a typical example this would represent approximately 150 millicuries of Kr85. This combination is capable of producing brightness levels of from 500 to 1500 microlamberts. Provided higher surface radiation (radioactive) levels are tolerable, the brightness level can be increased substantially through use of bulbs designed for, and filled to, high internal gas pressures, i.e., in excess of one atmosphere. For reasons of safety it is desirable to maintain the pressure within the bulb less than that outside it, but this is not always possible especially for lamps which are to be employed at high altitudes or where brightness levels of several thousand microlamberts are required.

For many purposes a radioactive gas of energy lower than krypton-85 is suitable. For example, if it is sufficient that the light emitted from the lamp be of somewhat lower intensity, a radioactive gas such as tritium may be employed. Since tritium emits no gamma radiation and only low-energy beta, the shielding problems are less severe. An embodiment of the invention also suitable for tritium as the activating substance is described below in connection with FIGS. 4-6. Since tritium gas is presently available in purer form than is the krypton, it may sometimes be employed at a lower pressure than in the case of krypton, for example, 50 to 400 mm. of mercury. The trajectory range of beta particles emitted by tritium is of the order of 2.5 to 3.0 millimeters, so this fact should be considered in proportioning the cavity within the bulb which encloses the gas. In other words, if the inside radius of a given bulb is, say 5 mm., the gas in the central portion will have substantially no exciting elfect on the phosphor material on the inner surface of the bulb, because it is too far away. This elfect is less at lower internal gas pressures. In the case of krypton-85 the radiated particles, having more energy, are effective at a greater distance from their :point of origin.

In the case of 99% pure tritium gas, several curies of tritium could be utilized while still maintaining the internal pressure at less than atmospheric. On this basis it is feasible to use up to approximately 30 times as many curies of tritium as Kr-SS, within the same pressure range. Under these conditions brightness levels of from 300 to 1000 microlamberts can be readily achieved. Higher brightness levels are possible through use of tritium at pressures in excess of one atmosphere.

It the radiation-absorbing characteristic of the cover 12 is inadequate to shield sufiicient'of thethe radioactive emanations, especially the more dangerous gamma and high energy beta radiations, it is advisable to employ an additional screen such as cap 21 which is affixed to the top of the bulb. A sheet of lead is suitable -for this purpose. It is preferable to include a light-reflecting surface or material (not shown) between this cap and the exterior surface of the bulb portion 16. The dimensions and location of cap 21 are important in connection with the invention because they should be such as to intercept deleterious or dangerous radioactive emanations from the bulb, while intercepting to a minimum the light output from the lamp. For example, most of the radioactive emanations escaping from element 5 which are not intercepted by shield 9 will be intercepted by shield 21. It is intended that the remaining few which escape will be absorbed by cover :12. In the rearward direction cement l8 and plug 19 provide radiation shielding but, as above stated, additional lead shielding can be inserted here, if necessary. Although cap 21, opaque to light, will prevent direct light radiation forwardly from the light element, it does not appreciably interfere with the forward emission of light after reflection from parabolic reflector 6. By proportioning light-enntting bulb 5 and reflector 6 in accordance with well known optical principles the light emitted from the lamp as illustrated can in fact be of quite uniform intensity over the area to be illuminated.

The self-luminous lamp illustrated in FIG. 2 is fundamentally the same as that of FIG. 1. Consequently many of the details shown in FIG. 1 are omitted from FIG. 2. The principal differences between the two embodiments are primarily of an optical nature. Reflector 22 is here represented as being of spherical curvature. Consequently, the cross-sectional area of the emitted light beam and the light-intensity distribution will be difierent as compared with the beam of FIG. 1. The use of a spherical reflector in the lamp of FIG. 2 necessitates for best efliciency a modification in the shape of the light-emitting bulb which in this case is more nearly spherical 1n form. This is apparent from the drawing in which the bulbous portion 23 and the phosphor coating 24 on the be, the same as those described in connection with FIG. 1.

FIG. 3 illustrates a modified form of a self-luminous element suitable for use in the lamp of FIG. 1 or of FIG. 2. For several reasons the form of light element here shown is preferable to the simpler form illustrated in the prior figures. Although the structure of the ele ment of FIG. 3 may be slightly more expensive to manufacture, it is more efiicient and will produce greater light intensity than the examples previously described. By forming the light element with a double wall, two notable improvements are introduced. First, the quantity of radioactive gas may be decreased because itis employed more e'fliciently, and this may reduce the cost for gas more than the structural cost is increased. Second, the total area of the luminescent phosphor surface is considerably increased and this increases the light output without materially increasing the overall size of the element. FIG. 3 is not drawn to scale with respect to the other figures, and the element may actually be no larger than the elements shown in the other figures.

As will be seen from FIG. 3, this light element comprises a core body '26 and an envelope 27 which completely surrounds the upper bulbous portion 28 of the core body. The two are sealed together near the bottom of the bulbous portion at which the neck 30 begins. If both the core body and the envelope are of glass as is presently preferred, they can readily be fused together to form an annular joint 29. In this embodiment the inner .cavity 31 .of body 26 need not be evacuated, a d may contain air. Before assembly a phosphor coating 32 is appliedto the exterior surface of the bulbous portion 28. Also before assembly the inner surface of envelope 27 is coated with a phosphor layer 33. The gas may be introduced through a glass tube at point 35, after evacuation. This tube is then sealed off in the usual manner. The lead shielding cap 36 corresponds to caps 21 and 25 of the preceding figures and is employed for the same reason. The thickness of coating 32 can be greater than that of coating 33 because most of the light from the inner coating must pass through the outer coating. Under any given conditions there is usually an optimum coating thickness, which will fall .within the following preferred ranges: For the inner coating 32 the thickness may correspond to approximately 150 or more milligrams of phosphor per square cm. of surface. For the outer coating 33 the thickness should correspond to approximately 50 to 150 milligrams of phosphor per square cm. of surface. Ideally, the

coating layer 33 would be one phosphor crystal thick with no voids between crystals. The phosphor crystals of preferred type are of approximately 8 to 10 microns in thickness. However, the crystals employed are sufliciently translucent to absorb very little of the light which is intended to pass through them, if the layer is within the range specified.

The distanceseparating the inner surface of envelope 27 and the outer surface of body 28 parallel thereto should be as small as possible'in view of certain factors: The cubical dimension of the resulting chamber 34 should be sufiicient to accommodate the required quantity of radioactive gas with a given maximum permissible working pressure. 1 As above indicated, the distance can be greater when algas is employed which emits radioactive particles of higher energy and therefore of longer trajectory.

The embodiment of the invention illustrated in FIGS. 4, and 6 is of the same fundamental type as that above described, but is adapted to a specifically different purpose. [AS before, it comprises a self-luminous light element secured approximately at the focus of an optical reflector, but in this instance it is of the box or sign type. It is important that the light be of uniform intensity over the illuminated area, but not necessarily of great brightness, if it is intended only to trans-illuminate a sign panel or the like. On the other hand, if the mentioned sign panel is replaced by a panel of clear glass, for example, and a light element of high intrinsic intensity is employed, the lamp will comprise a floodlight having a variety of advantages.

Accordingly, the lamp structure as illustrated in FIGS. 4 and 5 comprises a casing or box 54 which may be formed of any suitable sheet metal. In the example shown, the box was approximately 11 /2 inches long, 6 inches high and 5 inches deep. If shielding against radioactive emanations is required, this may readily be inserted within the box. At the front of the box, angles 37 are secured, as shown, so as to support a sign panel 38 which can be slipped in against them from the side. This would be the right side, or end, of the box as it appears in FIG. 4. This panel may be retained in place by bending over tab 51 which is integral with the frame 40. In the embodiment shown, the sign panel comprises a sheet of translucent glass which is covered with opaque paint except for the unpainted letters Exit through which the light passes. In front of the sign panel a cover glass 39 is inserted to protect the sign and retain it in place. This glass is preferably of the ceriumbearing type above described. Alternatively, it may comprise a thick sheet of suitable plastic material. This cover is retained in place by the metal frame 40.

Reflector 44 comprises the surface generated by translating a parabolic curve along a straight line. Therefore, any section taken through the reflector in a plane perpendicular to the mentioned line would show a parabola as represented in FIG. 5. Brackets 41a, 41b and 410 equally spaced along the back of box 54 support the reflector; These brackets,. whichfit the reflector contour, are secured to the back of the box by flanges 43a, 43b and 430, respectively, and by bolts 42 passing through them. The reflector is locked in the brackets by means of claws 45 which are bent over the front edges of the reflector. The lamp as a unit may be attached to a wall or other support 47 by means of plates 46.

The light element shown in FIGS. 4, 5 and 6 comprises a straight tube 48 which, in the particular embodiment here illustrated, was approximately 10" long and E6" in diameter. Tubes of smaller diameter, for instance A", are preferable in some cases. Ihe tube is preferably of non-darkening glass, such as that previously described, coated on the inside with a suitable phosphor layer 49 of the nature above specified, and sealed gas-tight at both ends after evacuating and filling with radioactive gas. A lead shield 50 extending the length of the tube 48 along the front thereof may be added, if desired, to increase the shielding of radioactive emanations. However, if tritium is employed as the exciting material this shield would be unnecessary, because the beta particles will notpenetrate the glass wall of the self-luminous tube. Also, as aboveipointed out, the glass cover 39, as well as the sign panel 38 will provide shielding.

The tube 48 is retained in position in reflector 44 by means of clamps 52 and 53 secured at opposite ends, as illustrated. By suitably proportioning'these clamps, the tubular light element may be positioned, as desired, with respect to the focal axisof the reflector. Thus the distnibution of light from the reflector may be adjusted to provide light uniformly or non uniformly distributed over the illuminated area. To provide uniform distribution, thelight element should be symmetrically disposed with respect to the focal line.

The principles of construction, including the use of suitable materials as described in connection with the preceding figures, apply similarly to the embodiment of FIGS. 4, 5 and 6. For example, this light element could, as in FIG. 3, comprise a double-walled structure, such as would result from inserting a glass rod or closed glass tube in tube 48 and centrally locating it, leaving a cylindrical space between the resulting parallel walls which would comprise a gas chamber corresponding to chamber 34 of FIG. 3. From the description of that figure it will be evident that if the two opposing surfaces of this chamber are coated with phosphor layers and the chamber filled with krypton-8S, as before, the light output of the element will be considerably increased. Useful brightness levels are also obtained in such an arrangement using tritium gas. Such a light element is especially adapted for use in the lamp structure of FIGS. 4 and 5 when employed as a flood lamp. In this case the sign panel 38 would be omitted.

The foregoing descriptions of specific embodiments of the invention are given merely by way of example, it being understood that no limitations are intended thereby.

We claim:

1. In a self-luminous light emitting unit, a casing, a light source in the casing, a reflector mounted within the casing and about the light source to direct from the casing the light emitted from said source, said light source comprising a sealed bulb of transparent material resistant to darkening under beta-ray bombardment, a phosphor coating on the inside surface of the said bulb, a radioactive beta-ray emitting gas within said bulb at subatmospheric pressure, all points in said bulb being within average beta-trajectory distance of the nearest portion of phosphor, and a beta-ray absorbing shield seated over the bulb substantially transverse to the path of light directed out of the casing, said shield being light reflective on the surface thereof seated against said outer bulb.

2. A unit according to claim 1 which includes a window of transparent non-darkening material spanning said re- 7 fi'ector and covering the light source therewithin, and a beta-ray absorbing shield surrounding said reflector within said casing. v V t V 3. In a self-luminous light emitting unit, a casing, a reflector mounted Within the casing and having an optical center, a light source comprising a hollow gas-tight bulb of non-darkening glass including a bulbous portion and a relatively slender stem" portion, means securing said stein portion in said casing sotha't said bulbous portion is substantially syrrnne'trically positioned about theoptical center of said reflector, a phosphor coating on the inner surface of said bulbous portion, a radioactive gas selected from the group krypton-85 and tritium within said bulbous portion, all points within said bulbous portion being Within average beta-trajectory distance of the nearest portion of phosphor, a. first cover of transparent non-darkening glass disposed across the top of said reflector within said casing, a second cover of transparent plastic disposed over said first cover, means securing both covers to said casing, gas-tight sealing means interposed between at least one of said covers and said casing, adjoining first shields of beta and gamma ray absorbing material between said 7 reflector and said casing and in said casing behind said bulb, and a second shield of beta and gamma ray absorbing material seated on the front of said bulb to intercept radioactive radiations forwardly emitted from said bulb without substantially intercepting light reflected from said reflector, said second shield being light-reflective on the surface thereof seated against said bulb.

I 4. In a self-luminous light emitting unit, a casing, a light source in the casing, a reflector mounted within the casing and about the light source to direct light emitted from the source out of the casing, said light source being a self-luminous sealed bulb, a phosphor and a radio- 8 active beta-ray emitting gas at sub-atmosphericp'ressure "contained within said bulb, allpoints within said bulb being within average beta-trajectory distance of the nearest portion of phosphor, and a beta-ray absorbing shield seated on said bulb substantial-1y transverse to the path of light directed out of the casing, said shield being lightreflective on the surface therof seated against said bulb. S. 'In a. self-luminous light emitting unit,- a casing, a light source in the casing, a reflector mounted within the casing and about the light source to direct from said casing the light emitted from the source, said light source comprising a self-lurninous sealed bulb, a phosphor coating on the inner surface of said bulb, a radioactive betaray emitting gas contained within said bulb at sub-atmos phericv pressure, all points within said bulb being within average beta-trajectory distance of the nearest portion of phosphor, and a beta-ray absorbing shield s'eated on said bulb substantially transverse to the path of light di-, meted out of the casing, said shield being light-reflective on the surface thereof seated against said bulb.

References Cited in the file of this patent UNITED STATES PATENTS 1,275,890 Flannery na Aug'. 13, 1918 1,534,937 Foley Apr. 21, 1925 1,630,171 Coram May 24, 1927 2,910,593 Laing et a1 Oct. 27, 1959 OTHER REFERENCES Wallhausen: Use of Radioisotopes in the Production of Self-Luminous Compounds, article in Peaceful Uses of Atomic Energy; Aug. 20, 1955; vol. 15', pp. 307 to 309.

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