US 2877342 A
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March 10, 1959 w. H. BEACH 2,877,342
DIFFUSING LENS FOR SPOT LIGHT REFLECTOR Filed Oct. 4. 1952 ay/i/m NTOR- ATTORN EYS;
United States Patent DIFFUSING LENS FOR SPOT LIGHT REFLECTOR William H. Beach, Fairfield, Conn., assignor to The Bridgeport Metal Goods Manufacturing Company, Bridgeport, Conn., a corporation of 'Connecticut Application October 4, 1952, Serial No. 313,178
4 Claims. (Cl. 240-41.4)
This invention relates to diffusing lenses, particularly a diffusing lens for spotlight reflectors for use in flashlights and similar devices. There are two kinds of hand flashlights in general use. One is the spotlight producing a narrow concentrated beam for long range work. The other is a flood light useful for short distances and closeup work. Both are suitable for their purposes, but they cannot be used interchangeably with entirely satisfactory results. When used at close range the light concentration of the spot is normally bright enough to make eye adjustment diflicult, and when the eye adapts itself to the spot pattern it loses much of its ability to see in the area outside the spot. This makes it somewhat unsatisfactory for repair work or reading, and so forth. The flood light, on the other hand, normally illuminates a large area at low intensity, consequently it is useless at longer distances.
It is therefore an object of the present invention to produce a lens which will provide convenient means for converting a spotlight into an instrument suitable for close range work, by changing the small spot pattern to a larger circle of even intensity and free from rings, shadows and other blemishes.
It is also an object to produce a combination lens which forms a circular light pattern of convenient size, substantially even, and of useful intensity.
With the foregoing and other objects in view, I have devised the construction illustrated in the accompanying drawing forming a part of this specification. It is, however, to be understood the invention is not limited to the specific details of construction and arrangement shown, but may embody various changes and modifications within the scope of the invention.
In this drawing:
Fig. 1 is a longitudinal section of the light end of a hand flashlight or spotlight, with this improved lens applied;
Fig. 2 is a plan view of the surface of one side of the lens;
Fig. 3 is a plan view of the surface on the opposite side of the lens, the showing of both surfaces being exaggerated;
Fig. 4 is a section through the lens and greatly enlarged;
Fig. 5 is a section of a portion of one end of a flashlight and a portion of the lens still further enlarged, and
Fig. 6 is a similar section of the lens taken at right angles to Fig. 5.
It is an object of the invention to produce a lens primarily for hand flashlights, although it could be used for other adaptations, which will evenly diffuse the light in a certain size area, say, for example, one or two feet in diameter, or even larger, so that when used for repairing or the like there is no glare like that of a concentrated spot beam, but the lighted area is uniformly illuminated without shadows or areas of varying intensity. The lens in the drawing is shown greatly enlarged and the details greatly exaggerated. For a hand flashlight it is normally about one and three-quarters inches in diameter ice and about one-sixteenth inch thick, although of course the size may be varied as found desirable. In the flashlight shown in Fig. 1, there is the usual open-ended casing 10 in which is the dry cell battery 11 and the usual parabolic reflector 12 about the lamp bulb 13 provided with the usual incandescent filament 14 supported by the conductor wires 15 and 16, one of which, as for example the wire 16, is also secured to the glass bulb as shown at 17. Across the open side of this reflector is usually a plain glass disc 18, although this may be omitted if desired, and outside and over this disc is the improved lens 19 of this invention. The reflector usually has an outwardly extending flange seated over the end of the casing 10 and the parts are held together by a cap 20 threaded onto the casing and having a flange 21 overlying the lenses to re tain them in place. The relative position of the parabolic reflector and light bulb is normally adjustable, or may be pre-focused, to give the concentrated or focused light beam, but such adjusting means is not shown in the drawing. The plain glass disc 18 is to close the open side of the reflector and protect the reflector and the light bulb.
The improved lens 19 comprises a disc of transparent material such as glass, or a suitable plastic, and one side surface of this lens is composed of a series of concentric ridges or rings 22 separated by concentric annular grooves or channels 23. That is, the transverse surface of this side of the lens is composed of alternate convex and concave ridges 22 and grooves 23 which are tangent to each other at the intermediate points 24 where these curves join. In effect, this surface forms a series of alternate convex and concave annular lenses, each of which concentrates or spreads the substantially parallel or other light beams passing through the lens. These ridges and grooves are preferably reversed arcs of circles tangent at their joining point 24 so they make a continuous uniform reverse curve in the cross section. In the form shown they are of substantially the same radius, although for the purpose involved they are not necessarily so. As the light beams from the reflector, either the parallel or other beams indicated at 25, Fig. 5, go through these surfaces, they are deflected and diffused in all directions and cross each other, as indicated at 26 and 27. As above indicated, the size of these ridges and grooves is greatly exaggerated on the drawing, and since the focal length of each is a fraction of an inch the effect in a practical range is to spread and diffuse the light. Moreover, each ring and groove spreads the light over the whole beam pattern, and, owing to defects in the lamp and reflector which are normally not made to optical tolerances, this surface does not produce a beam pattern of uniform intensity or free from blemishes. Also the filament support wire, such as the wires 15 and 16, used in prefocused or adjustable focus flashlight lenses, casts a wedge-shaped shadow which is quite noticeable.
To achieve the necessary degree of diffusion, the other or opposite surface of the lens is composed of a series of contiguous, concave, radially extending grooves or channels 28. These in effect form negative lenses which spread the light rays passing through them, and as these concave grooves or channels extend radially of the lens they therefore are arranged at right angles to the ridges and grooves 22 and 23 on the first side of the lens at any point on this lens, and therefore they spread the light at right angles to the action of the ridges and grooves 22 and 23. In other words, the light rays, either the substantially parallel or other rays 29 from the parabolic reflector or lamp, are deflected and diffused in all directions and cross each other as shown at 30. They do not have any material effect on the size of the beam pattern, but they do diffuse the pattern very well, and the shadow of the filament support wire is not noticeable in the resultant beam or on the illuminated surface. surfaces produces a circular light pattern of convenient size, substantially even, and of useful intensity.
In the reversely curved surface the more of these surfaces the better the diffusion of the light, but for manufacturing purposes they have to be made of radii of sufficient length to be practical for the manufacturing operation. For a flashlifiht lens of the size indicated, the distance between the centers of the alternate ridges 22 is about .08, with, of course, the same distance between the centers of the grooves, "and the radii of the curves 22 and 23 are about .10. For the grooves or channels 28 on the opposite side of the lens for the size indicated, about sixty of these grooves are provided and drawn on the arc of a circle of about .375 in diameter, with their centers spaced about 6 at the periphery of the disc, as shown at 32, Fig. 3. The radius could, however, vary continuously throughout the length of the grooves, and such shape might be more accurate optically. The thickness of the lens is also preferably gradually reduced or tapered from the center toward the rim, such, for example, as shown in Fig. 4, by tapering the surface with the grooves 28 about 2, as indicated at 31, Fig. 4.
It will thus be seen that this lens in effect has a surface on one side composed of a series of concentric: annular or circular, contiguous, alternate positive and negative lenses for both spreading and concentrating the light passing through the lens, and on the other side the surface is composed of a series of contiguous radially extending negative lenses, which, because of their radial position, are at substantially right angles to the alternate annular positive and negative lenses on the other surface. Neither one alone would give sufiicient diffusion of the light desired, but the combination of the two together thoroughly and uniformly diffuses and provides a uniform illumination for the surface illuminated by the resultant beam, eliminating shadows of such members as the filament wire support and also rings and other areas of varying intensity. It has been found the same effect is secured whichever way the lens is used, that is, whether it is used as shown with the annular ridges and grooves on the outside, or reversed with the radial grooves on the outside.
The lens may be made of transparent plastic, glass or other material of suitable optical properties and. capable of withstanding shock or fracture to a reasonable extent. Its thin, in effect fiat, overall dimension permits storage of the lens when not in use in, for example, the end cap of a casing of a container. When it is desired to have a diffused light or beam the cap 20 is unscrewed and one of these disc lenses 19 is placed on top of the plain glass disc 18, or the disc 18 could be removed and disc 19 mounted in its place. As a result the device provides a focused light combined with a thin lens. The design of the lens surface is such that the lens is not subject to damage from abrasion encountered in normal use.
Its use is not necessarily confined to flashlights, but may be extended to lanterns or other lighting devices where the same or similar problems are encountered.
Having thus set forth the nature of my invention, I claim:
The combination of the two 1. In a spotlight and the like including a substantially parabolic reflector and a lamp bulb at substantially the focal point of the reflector, a light diffusing lens over the open side of the reflector to diffuse the light from the bulb and the reflector, said lens comprising a transparent disc the surface on one side consisting of a series of circular, annular, concentric, alternate transversely convex ridges and concave grooves, and the surface on the other side consisting of a series of contiguous, concave radially extending grooves.
2. In a spotlight and the like including a substantially parabolic reflector and a lamp bulb at substantially the focal point of the reflector, a light diffusing lens over the open side of the reflector to diffuse the light from the bulb and the reflector, said lens comprising a transparent disc the surface on one side being composed of concentric, annular, alternately arranged ridges and grooves, the ridges being convexly curved transversely and the grooves being concavely curved with the meeting edges of adjacent ridges and grooves substantially tangent to each other, and the surface on the other side of the disc composed of adjacent radially extending concave grooves.
3. In a spotlight and the like including a substantially parabolic reflector and a lamp bulb at substantially the focal point of the reflector, a light diffusing lens over the open side of the reflector to ditfuse the light from the bulb and the reflector, said lens comprising a transparent disc the surface on one side consisting of alternate concentric circular ridges and grooves, these ridges and grooves being reversed arcs of circles with those of adjacent ridges and grooves tangent to each other at their joining point forming a continuous alternately curved surface, and the surface on the other side of the disc consisting of a series of adjacent radially extending transversely concavely curved grooves.
4. In a spotlight and the like including a substantially parabolic reflector and a lamp bulb at substantially the focal point of the reflector, a light diffusing lens over the open side of the reflector to diffuse the light from the bulb and the reflector, said lens comprising a transparent disc the surface on one side of which is composed of concentric circular rings the cross sections of which are alternate concave and convex adjacent arcs tangent to each other forming a series of alternately arranged concave and convex concentric annular lenses to alternately spread and concentrate substantially parallel light beams passing through the lens from the reflector, and the other surface of the disc being composed of a series of radially extending contiguous transversely concave channels forming a series of radial concave lenses at substantially right angles to the lenses on the first side of the disc.
References Cited in the file of this patent UNITED STATES PATENTS 1,261,375 Foster Apr. 2, 1918 1,370,885 Frederick et al Mar. 8, 1921 2,551,954 Lehman May 8, 1951