US3292029A - Sealed beam headlight with glassbeaded light reflecting shield - Google Patents

Description

Dec. 1966 P. v. PALMQUIST ETAL 3,292,029

SEALED BEAM HEADLIGHT WITH GLASS-BEADED LIGHT REFLECTING SHIELD Filed Aug. 7, 1963 I I III/1111111112 r 5 5 v/ m E mww W N U w WM? 7 m 4 Ma. P a #C P w United States Fatent Gfltice 3,292,029 Patented Dec. 13, 1966 3,292,029 SEALED BEAM HEADLIGHT WITH GLASS- BEADED LIGHT REFLECTING SHIELD Philip V. Palmquist, Maplewood, and Chi Fang Tung,

Lincoln Township, Washington County, Minn, assignors to Minnesota Mining and Manufacturing Company, St. Paul, Minn, a corporation of Delaware Filed Aug. 7, 1963, Ser. No. 300,475 Claims. (Cl. 313113) This invention relates to improvements in sealed-beam light fixtures, particularly for the headlights of automobiles. The improvement of this invention imparts to the fixtures an apparent illumination as observed by the driver of an approaching automobile (having operating headlamps) even when the resistance lighting elements of the fixtures are inoperable.

The invention also relates to new shield elements for interposition between a resistance lighting element and the lens face for a sealed-beam headlamp as well as methods for making the same. Further, the invention relates to and provides new sheet structures from which shields for such use may rapidly be punched or stamped and shaped.

Much attention has heretofore been given toward improving the safety features of primary illuminationsources by adding to them various reflex-reflecting structures capable of operating even after the primary source fails. Specifically, reflex-reflecting plastic cube-corner elements have been added to otherwise complete lighting fixtures, but such elements are of such nature that they have not been possible to use in combination with an existing light source except in locations either entirely separate from the source (which is ineffective to impart an apparent luminous characteristic to an inoperable source), or in locations which interfere with the pattern of primary light emission by the source. In short, they have been generally unsatisfactory for use in headlight devices for automobiles, since the primary light emission from the headlamp must be of established intensity and exhibit an established pattern.

Reflex reflectorization of portions of the parabolic concave reflector of sealed-beam light fixtures has also been proposed. It, however, also reduces the light emission of the beam under ordinary operation conditions, and is relatively ineffective for light-return under reflexreflecting conditions. Part of the problem in this connection has been caused by the particular pattern of light distribution which must be created by the lens and arrangement of elements in a sealed-beam light fixture.

This invention solves such problems as aforenoted by providing a composite sealed-beam light fixture having a special beaded reflex-reflecting shield as an integral part thereof. The sealed structural devices of this invention are capable of emitting primary light of equal or higher intensity than otherwise comparable sealedbeam fixtures lacking the specialized reflex-reflectorization of the shield as taught herein, yet they are entirely effective to serve as reflectors of incident light and thereby alert the night-tirne driver of an approaching automobile (having at least one operating primary source headlamp) as to the relative position of an automobile having headlamps of the invention with defective resistance elements.

A significant benefit accruing by use of the structure of this invention is that of retention of the light pattern of a sealed-beam under normal operation when the resistance lighting element of the beam is functioning without interference with effective reflex-reflective incident light return by the sealedbeam fixture after failure of the lighting element.

Another benefit provided by the invention is that of convenient reflex-reflecting shields having specialized design and operating characteristics, suitably made by simply stamping the same and shaping the same from a sheet material inherently possessing the required properties for withstanding the intense temperatures of exposed resistance lighting elements within a sealed-beam headlamp as well as free of ingredients which, under the environmental conditions within a sealed-beam lamp during operation, would significantly alter the lamp life of a sealedbeam unit.

The invention will be described by reference to a drawing, made a part hereof, wherein:

FIGURE 1 is a sectional schematic view through a sealed-beam lamp of the invention;

FIGURE 2 is a schematic front elevation taken on line 2-2 in FIGURE 1;

FIGURES 3 and 4 are a sectional schematic view and a front schematic view, respectively, of a slotted shield in accordance with the invention;

FIGURES 5 and 6 are a sectional schematic view and a front schematic view, respectively, of a further embodiment for a shield in accordance with the invention; and

FIGURES 7 and 8 are schematic cross sections through two different types of sheet structures for shields of the invention.

Referring now to FIGURES 1 and 2, the lamp structure of the invention comprises at least one electrical resistance lighting element (e.g., a tungsten filament) and preferably two such elements 10 and 11 (for high and low beam) within a substantially parabolic concave specularreflecting housing 12 having a transparent lens plate 13 over the open face of the housing. The lens 13 is hermetically sealed in a known manner to the housing 12 about the perimeter portions 14 thereof. The resistance lighting elements are located in a conventional manner near the axis of the substantially parabolic concave reflector housing, and in closer proximity to the inside surface of the reflector housing 12 than the inside surface of lens 13. Electrodes 15 connected to and supporting resistance lighting elements 10 and 11 extend through the parabolic concave specular-reflecting housing and are provided at their exterior terminals with any suitable connectors 16 for attachment to a source of electricity. The electrodes are hermetically sealed in the parabolic housing in a known manner. Within the hermetically sealed envelope of the lamp (i.e., within the lamp interior defined by the parabolic concave housing 12 and lens 13) is located a special shield 17, suitably essentially circular in shape (i.e., disc shaped) and suitably concave with its concave portion facing toward at least one (and preferably all) resistance lighting elements in the parabolic housing. The shield is supported by any suitable means such as a rod 18 hermetically mounted in the parabolic housing. Preferably, the location of the shield is such that the axis of the parabolic housing passes through the area of the shield defined by the outer periphery thereof. Also, the outer periphery of the shield properly should define an area sufficiently large to mask out at least one resistance lighting element from head-on view through the lens plate; but that area should be less than about one-half the total area of a plane perpendicular to the axis of the lamp structure and passing through the shield. Direct exposure of the shield to the resistance lighting elements within the hermetically sealed envelope of the lamp is encountered; and the atmosphere surrounding both is the same. An appropriate atmosphere widely used .is an inert one consisting of approximately 12% nitrogen and 88% argon. For convenience of manufacture, rod 13 and lighting elements and 11 (preferably also shield 17) should lie Within the concave space defined by the parabolic reflector, not projecting out of that space beyond a plane through the peripheral portion 14 of the reflector.

Shield 17 may take many different forms. It may be essentially a solid disc-like structure. It may further be concave, and preferably oriented with its concave surface facing the resistance lighting elements, which inci-dentally also causes it to face the parabolic reflector housing of the lamp structure. If desired, the shield may be provided with a central opening of varied shape, including a bow tie shape as illustrated in FIGURES 3 and 4. Of special interest is a concentric concaveconvex dish shape as illustrated in FIGURES 5 and 6. Tests of composite sealed-beam structures of the invention having reflex-reflecting shields shaped in the form of a concentric concave-convex dish (with the central concavity oriented toward the light filaments) have shown a light return under reflex-reflecting conditions approximately ten times greater than that of an otherwise identical headlamp (including a non-refiex-refiectorized concentric concave-convex dish shield) not provided with the special reflex reflectorization as taught herein.

As schematically illustrated in FIGURES 7 and 8, the reflex-reflecting shield structures for the invention include a monolayer of small transparent glass beads having underlying reflective means in optical connection therewith. The glass beads are present in a compact monolayer, which is difficult to illustrate in a drawing. Their refractive index must lie within the range of approximately 1.8 to 2.0, with approximately 1.9 being preferred.

While the diameter of the beads may vary, it usually will lie within the range of about 20 microns up to about 200 microns, with beads or transparent microspheres within the range of about 25 to 75 microns, or possibly as high as 100 microns, preferred. They are provided with underlying approximately hemispherical specular-reflecting metallic caps or surfaces which serve in combination with the lens properties of the beads or microspheres to effect reflex-reflection of light.

Further, the reflex-reflecting structures for the shields must be capable of withstanding significantly high tem peratures such as approximately 1000 F. without any substantial deterioration and without significant alteration of the lamp life of a sealed-beam unit. While tungsten filaments may reach even higher temperatures (e.g., 4500 F. or even 5000" F.), the temperatures reached byshields are significantly lower than that reached by resistance lighting elements in the structure due to the fact that the transmission of intense heat from the lighting element is largely by way of radiation and the shields as taught herein largely serve to reflex-reflect infrared or heat radiation as well as light rays, thereby remaining considerably lower in temperature than the resistance lighting elements. Further, the metal base for shields according to the invention serves as a conductor of heat in combination with the metal post or support rod 18 for the shield, whereby excessive heat build-up in the shield is avoided. And in practice the shield is mounted in spaced relation from filaments such that the shield temperature does not exceed about 1000 F. in operation of the lamp. Of course, the temperature reached by the shield is greatly in excess of that at which decomposition of known organic materials occurs. Thus, the temperature resistance requirement for the shield precludes the use of organic binder materials as customarily used in reflex-reflecting structures.

Shields according to the invention must not only he formed of inorganic materials but must be essentially free of ingredients which volatilize under the operating conditions for a sealed-beam unit inasmuch as the atmosphere within the unit cannot be substantially altered without adversely affecting the lamp life of the unit. It is when the lamp life of the unit has expired, and prior to replacement of the unit with a new one, as well as under parking conditions and the like, that the improved sealed-beam lighting units of the invention inherently possess the long-desired characteristic of returning incident light striking the headlamp back toward its source, thereby alerting the driver of any oncoming properly lighted vehicle of the presence of a vehicle possessing either defective headlamps or headlamps not in operation at the moment. Such critical requirements as aforenoted for beaded reflex-reflecting sheeting have not heretofore been met by any earlier known reflex-reflecting structure with which we are familiar.

A special beaded reflex-reflector for use in accordance with the invention will now be described. As illustrated in FIGURE 7, a suitable embodiment of a refiex-reflecting shield for the sealed-beam assembly of the invention comprises a compact monolayer of small glass beads provided with underlying approximately hemispherical specular-reflecting metallic caps 71 partially embedded in an approximately hemispherical manner within a glass enamel 72 supported on a metal sheet or base substrate 73.

The glass enamel bond for this structure characteristically has a coefficient of thermal expansion at least equal to, up to about twice (preferably between about 5 and 50% greater than) the coefficient of thermal expansion exhibited by the glass beads in the structure, thereby tending to pinch the glass beads and hold them under compression within the structure. Well known dialatometer tests may be used to determine the coefiicient of thermal expansion of materials used.

In addition, the glass enamel bond is substantially free of ingredients in a condition which permits them to volatilize at temperatures up to about 1000" F. under a pressure of about 700 millimeters of mercury. Preferably the glass enamel bond is substantially free of volatile ingredients under such severe test conditions as 1000 F. at a pressure of about 40 millimeters of mercury. The important consideration is that of maintaining the glass enamel bond (even if it may become slightly softened under the temperature conditions of lamp operation) substantially free of ingredients which volatilize at the temperatures to which the bond is subjected in a sealed-beam lamp under the pressure conditions chosen for the lamp operation. Since such pressure conditions may vary, most reliable performance is assured by maintaining the bond substantially free of ingredients which are volatile under the most severe conditions. However, while the inert gas environment within a sealed-beam lamp is generally maintained at a reduced pressure as compared to atmospheric pressure, and the reduced pressure maintained within the lamp is such that it does not increase beyond atmospheric pressure even under the temperature conditions reached by the sealed atmosphere during operation of the lamp, few lamps attain operating temperatures without a noticeable increase in the pressure of their gases. Thus operable structures of the invention are possible when the properties of shield elements and the gas pressure conditions are so balanced that the shield elements may possess reduced requirements (e.g., free of volatile formation at 1000 F. and 700 mm. of Hg). Of course, lamps formed with shield elements satisfying the more rigid requirements may exhibit a greater length of life as a primary light source.

To reduce volatile ingredients in a glass enamel bond, overfiring of the bond has been found to be effective. In other words, if the glass enamel chosen for the bond is ordinarily considered to be matu-rable within two minutes at 600 C., a substantially longer firing (e.g., five to ten minutes at 600 C.) has been found effective to drive off essentially all volatile ingredients. Preferably firing is conducted in an inert atmosphere. Generally the time of overfire will range from about twice the minimum normal maturation firing period to approximately five times that period.

Shields having glass bonds and the structural features illustrated in FIGURE 7 were prepared using an aluminum base sheet approximately 32 mils thick previously shaped in the form of concave discs of approximately 1% inches in diameter, to which was coated an enamel slip composition capable of being fired to form a glass enamel which adheres to aluminum and has a suitable coefficient of thermal expansion, as compared to the base metal, such that the glass enamel remains adherent to the metal under the variable temperature conditions to which the resulting structure is subjected in headlamp operation. A suitable slip for use on aluminum metal substrate consists of about 4.56 parts by weight calcium silicate, 3.44 parts by weight boric acid, 1 part by weight pigment grade titanium dioxide, and 100 parts by weight glass frit dispersed in about 45 parts water. The glass frit chosen for this slip was a known one, and consisted of 15.6 mol percent TiO 38.1 mol percent SiO 1.1 mol percent P 0 0.6 mol percent Sb O 4.7 mol percent B 0 1.9 mol percent ZnO, 3.1 mol percent CdO, 0.6 mol percent SrO, 9.5 mol percent K 0, 17.1 mol percent Na O, and 7.7 mol percent Li O. After grinding in the usual manner, the slip was adjusted by the addition of Water to a specific gravity of about 1.70 to 1.75 and. then sprayed upon the shield to form a film having a weight of about 0.027 gram per square inch after firing. The film is preferably extraordinarily thin; but useful results are gained at greater thicknesses up to approximately 0.2 gram per square inch. (Sufiicient skill in applying the film is gained after .a few test experiments to determine what thicknesses are formed during a limited spray period.) While the slip is still wet, glass beads specially treated in the following manner were sprinkled thereover.

The beads selected had a refractive index of 1.92 and a size range of approximately 40 to 75 microns. The composition of the glass beads or microspheres consisted of 43.5% TiO 29.3% BaO, 14.3% SiO 8.38% Na O, 3.06% B 0 and 1.44% K 0. The glass of the beads started to soften at about 610 C. They are capable of withstanding a 600 C. curing for the enamel without significant alteration. The beads were silvered (i.e., provided with continuous coatings of silver metal) using now conventional techniques for chemically depositing silver as a film. They were then coated with a refractory film by mixing them as a slurry in a water solution of 2% by weight hydrated alumina (a micro-fibrillar form of hydrated alumina). They were filtered from the bath after a couple minutes and then dried at 350 C. to convert the fibrils of hydrated alumina on the surface of the silvered beads to a non-dispersible condition. The filmtype coating of hydrated alumina was converted into a highly porous solid composed of interlocking fibrils of gamma alumina by heating at 450 C. to 500 C. for a few minutes. It is believed that this coating forms a thermal barrier to insulate the silver coating on the beads and inhibit the tendency it may have to diffuse into an inorganic bond. Other refractory film-forming powdery materials may alternatively be used.

For convenience of embedding the treated beads at approximately their equators in a slip coating, they then may be, and preferably are, passed through a water dispersion containing about 6% by weight of .a fluorocarbon compound solution (e.g., 28% solids of a chromium com- 6 plex of a perfluorocarbon compound dissolved in isopropanol), filtered and dried at about 300 F. Alternatively, other surfactant treatments (e. g., silicone treatments) may be used, if desired.

After the thus treated beads were sprinkled (preferably in excess to form a monolayer) on the slip coated metal base cap of the shield, the slip was dried at about 250 C. for about 15 minutes, and any excess beads then brushed off. The coated cap or shield was fired at about 600 C. for approximately 5 minutes (which is about 2 to 3 times the normal maturation time for the enamel).

After firing, silver and any residual refractory filmforming material on the exposed. portion of the hemispherically embedded beads were etched off in a now conventional manner using, for example, an acid treatment (an. 10% nitric acid solution for about 20 seconds). The etched shield was then thoroughly washed, dried and then mounted in a headlamp as aforediscussed.

In this structure, the coefficient of thermal expansion of the enamel bond (room temperature to start of softening which is about 460 C.) is approximately 15.8 10- cm./crn./C. as compared to approximately 13 'l0- cm./crn./ C. for the glass beads (room temperature to start of softening which is about 610 C.). During cooling of the matured enamel bond, the greater shrinkage of the enamel layer tends to grip or hold under compression the individual bead elements partially embedded in that layer.

An alternative beaded reflex-reflector especially desirable for use in making the shield element of the invention is illustrated in FIGURE 8, and consists of a compact monolayer of small transparent glass beads having the refractive index aforedescribed partially embedded in an approximately hemispherical manner into a ductile and malleable metal base sheet 81. The deformation strength of the metal base sheet must be less than the crushing strength of the glass beads selected for the structure. Stated another way, the Knoop hardness of the metal substrate must be less than (preferably no more than 30% of) the Knoop hardness of the glass beads for the structure. Known glass beads of practical use in reflex-refleeting applications all have a crushing strength and Knoop hardness significantly higher than aluminum, which is a preferred metal for use in such structures as here discussed.

A preferred metal bonded structure is one consisting of a compact monolayer of glass beads having a refractive index of approximately 1.9 partially embedded into an aluminum base sheet having a Knoop hardness of approximately 23.81. Glass beads for partial embedding in metal should have a diameter such that at least fall Within a limited size range having an upper size limit no larger than 30% greater than the lower size limit. Illustratively, glass beads varying from 60 to 75 microns in diameter give excellent results in this structure.

While reflex-reflecting structures consisting of glass beads and metal may be formed at normal room temperature conditions using pressure, it is much preferred to form the structure by pressing the glass beads partially into the metal at slightly elevated temperatures up to approximately 20 C. below the melting point of the metal. Processing under elevated temperature conditions advantageously imparts to the final sheet product an improved bonding or gripping of beads by the metal. In fact, even when the sheet product is maintained in fiat stock form, beads in it are under some compression when the product is formed using heat and pressure to partially embed the beads in the metal. Regardless of whether or not the flat sheet stock is formed using heat with pressure, subsequent stamping of a shield to form a concave structure will cause partially embedded beads to be under compression in the concave side of the structure.

A specific illustration of a procedure suitable for use in forming this preferred sheet structure for shields now follows. For illustration purposes both sides of the sheet structure will be coated with beads and rendered reflex-reflecting. The base metal sheet selected was malleable and ductile aluminum consisting essentially of 99.5% aluminum with about 0.5% impurities. The sheet was approximately 32 mils thick and had a Knoop hardness of about 23.81. It was cleaned in a conventional manner so as to be free from dirt and grease. Two other metal sheets, hereinafter called cushion sheets, were also cleaned. For reasons as will become evident, the hardness of the cushion sheets must be in excess of that of the malleable and ductile sheet which becomes part of the reflex-reflecting composite. The cushion sheets selected were aluminum alloy having a Knoop hardness of 43.34. On one side of each of the cushion sheets was then coated a thin film (e.g., no greater in thickness than about one-half the diameter of beads selected for the final structure, preferably between about 0.5 and 10 microns thick) of temporary binder material; and for this purpose oil has been found entirely effective. A monolayer of transparent glass beads of the type discussed in the previous specific example, but lying in the range of 60 to 75 microns in diameter, was then formed over each oilcoated surface of the cushion sheets by sprinkling the beads thereover and dumping off any excess. The cleaned malleable and ductile sheet was then placed between the cushion sheets (with the monolayer of beads on each cushion sheet facing toward the malleable and ductile sheet and in contact therewith), and the assembly passed between coacting cylinders which served to subject the assembly to pressure. A pressure of about 3200 p.s.i. at a temperature of about 550 F. was sufficient to press the heads into the malleable and ductile sheet and partially embed them with good adhesion. Slight deformation pockets may be noted in the cushion sheets upon removal from the assembly, but they are not objectionable and may aid in achieving desired bonding into the central ductile sheet. The monolayers of glass beads partially embedded and bonded in the ductile sheet were then cleaned with solvent for the temporary binder (so as to remove any which may have transferred). The sheet then may be die cut into shield shapes as desired, and pressed or die shaped into concave or other forms useful for shield purposes.

The metal selected for use in forming metal bonded structures will usually be selected for its specular-reflecting properties in addition to its ductility. An excellent material to use in this respect is aluminum substantially free of other metals. However, where a ductile base metal is considered suitable for use but lacks the particular specular-reflecting properties or color desired, it is convenient to apply a thin layer of specular-reflecting metal (e.g., a layer of vapor deposited aluminum) over the base metal selected for use and rely upon the specular reflectance properties exhibited by the veneered metal which deforms and caps itself about beads partially embedded into the veneered side of the base structure. Also, if desired, pre-silvered beads may be used in forming a metal bonded structure; but greater simplicity is possible by use of a base metal possessing both thespe-cular-reflectance properties and softness required for pressing beads therein. If desired, metal bonded bead structures may be formed using powdered metallurgical techniques, usually with some sacrifice of brilliance of retro-reflection and sacrifice of the simplicity of formation gained by pressure bonding.

Preferably the thickness of metal base for shields according to the invention will lie between about 10 mils and 40 mils; but structures of the invention having metal bases of even greater thickness may be useful in specialized applications.

Either or both sides of any shield according to the invention may be reflex-reflectorized. Where only one side is reflex-reflectorized, it is preferable to so mount the shield that light rays incident to a headlight pass through the lens thereof, strike the parabolic concave specular reflector of the headlight, reflect toward the face of the shield directed toward the resistance lighting elements, are retrodirected (from that reflex-reflectorized face) in a reflex-reflecting manner back to the parabolic concave specular reflector near the point of initial incidence, and are then returned out of the headlight in a beam substantially parallel (but with some divergence up to a few degrees) to the original incident rays. Reflexreflectorization of the side of the shield facing outwardly of the headlamp is also desirable in practice; and it contributes toward the total reflex-reflective light return by the assembly.

It will be understood that the refractive index for the glass beads of reflex-reflecting sheet structures of the invention may vary in a known manner from the range of 1.8-2.0 where the resulting structure is to be used in ap plications requiring a different refractive index for the glass beads. Thus beads having a refractive index (12 as low as about 1.7 and as high as about 2.5 or even 2.9 may be useful in the sheet structures herein described.

That which is claimed is:

1. In a sealed-beam light fixture of the type having a. substantially parabolic concave specular-reflecting housing, a transparent lens plate over the visuallyexposed face of the housing and hermetically sealed to the housing about the perimeter thereof, and at least one resistance lighting element within the housing and surrounded by an essentially-inert atmosphere confined within the envelope defined by the housing and lens plate, the improvement comprising a reflex-reflecting all-inorganic shield located within the envelope defined by the housing and lens plate between the resistance lighting element of said fixture and said lens plate, said shield being surrounded by said inert atmosphere and consisting essentially of glass beads of refractive index between 1.8 and 2.0 firmly bonded in partially embedded condition in an inorganic material with hemispherical specular reflecting means about the underlying bonded hemispherical portions of said beads, said shield being essentially free of ingredients volatilizable therefrom at temperatures up to 1000 F. at 700 mm. of Hg and being positioned with its surface of partially embedded glass beads facing toward said resistance lighting element.

2. A sealed-beam light fixture of the type set forth in claim 1 wherein the improvement additionally resides in the fact that the location of the reflex-reflecting all-inorganic shield is such that the axis of the parabolic housing passes through the area of the shield defined by the outer periphery thereof, which outer periphery defines an area at least sufficiently large to mask out said one resistance lighting element from head-on view through said lens plate, said area being less than one-half the total area of a plane perpendicular to the parabolic axis of said light fixture passing through said shield.

3. A reflex-reflecting shield especially adapted for use as a light-returning element within a sealed beam light fixture, comprising a monolayer of reflex-reflecting com plexes, each said complex consisting of a glass bead of refractive index between about 1.8 and 2.0 and an underlying hemispherical speculanreflecting cap, and a glassy bond material in which said reflex-reflecting complexes are firmly hemispherically bonded, said glassy bond material being substantially free of ingredients volatilizable therefrom at temperatures up to about 1000 F. under a pressure of about 700 mm. of mercury and exhibiting a coeflicient of thermal expansion at least equal to, and no greater than twice than, the coefficient of thermal expansion exhibited by the glass beads in said shield structure.

4. A reflex-reflecting sheet structure comprising a monolayer of reflex-reflecting complexes, each consisting of a glass bead between 20 and 200 microns in diameter and an underlying hemispherical specular-reflecting cap, and a glassy bond material in which said reflex-reflecting complexes are firmly hemispherically bonded, the coeflicient 9 19 of thermal expansion of said glassy bond material being References Cited by the Examiner at least equal to, and no greater than twice than, the co- UNITED STATES PATENTS efficient of thermal expansion exhibited by the glass beads 2,379,702 7/1945 Gebhard in said structure, and the melting temperature of said glass 5 2 379 741 7 1945 palmquist g 32 beads 'being in excess of said glassy bond material. 2,876,375 3/ 1959 Marsh 313--117 5. A unified reflex-reflecting sheet structure comprising the reflex-reflecting sheet structure of claim 4 and a JAMES LAWRENCE Pnmary Exammer' metal sheet base to which the glassy bond material of the GEQRGE WESTBY Examiner reflex-reflecting structure of claim 4 is firmly adhered. 10 F. ADAMS, V. LAFRANCHI, Assistant Examiners.

Claims (1)

1. IN A SEALED-BEAM LIGHT FIXED OF THE TYPE HAVING A SUBSTANTIALLY PARABOLIC CONCAVE SPECULAR-REFLECTING HOUSING, A TRANSPARENT LENS PLATE OVER THE VISUALLY-EXPOSED FACE OF THE HOUSING AND HERMETICALLY SEALED TO THE HOUSING ABOUT THE PERIMETER THEREOF, AND AT LEAST ONE RESISTANCE LIGHTING ELEMENT WITHIN THE HOUSING AND SURROUNDED BY AN ESSENTIALLY-INERT ATMOSPHERE CONFINED WITHIN THE ENVELOPE DEFINED BY THE HOUSING AND LENS PLATE, THE IMPROVEMENT COMPRISING A REFLEX-REFLECTING ALL-INORGANIC SHIELD LOCATED WITHIN THE ENVELOPE DEFINED BY THE HOUSING AND LENS PLATE BETWEEN THE RESISTANCE LIGHTING ELEMENT OF SAID FIXTURE AND SAID LENS PLATE, SAID SHIELD BEING SURROUNDED BY SAID INERT ATMOSPHERE AND CONSISTING ESSENTIALLY OF GLASS BEADS OF REFRACTIVE INDEX BETWEEN 1.8 AND 2.0 FIRMLY BONDED IN PARTIALLY EMBEDDED CONDITION IN AN INORGANIC MATERIAL WITH HEMISPHERICAL SPECULAR REFECTING MEANS ABOUT THE UNDERLYING BONDED HEMISPHERICAL PORTIONS OF SAID BEADS, SAID SHIELD BEING ESSENTIALLY FREE OF INGREDIENTS VOLATIZABLE THEREFROM AT TEMPERATURES UP TO 1000* F. AT 700 MM. OF HG AND BEING POSITIONED WITH ITS SURFACE OF PARTIALLY EMBEDDED GLASS BEADS FACING TOWARD SAID RESISTANCE LIGHTING ELEMENT.

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