Illumination Reflector for Area Projection

The present invention relates to an illumination reflector and more particularly to a reflector that projects a flood light pattern from a filament source.

While a portable lighting apparatus such as a flashlight having a small filament light source is generally constructed with a reflector shaped to produce a narrowly focused spot beam for illumination of a distant object, it is often desired to produce a broader flood beam to illuminate a close-by extended area using the filament light source. U.S. Pat. No. 5,424,927 issued to David R. Schaller et al. Jun. 13, 1996 discloses a flashlight having a parabolic reflector that terminates in a rectangular opening. The parabolic reflector collimates light emitted from a filament positioned at the reflector focal point. A rectangular electro-optic device driven by electronic circuitry covers the rectangular opening and operates in a first state to pass the collimated light to form a spot beam. In order to produce a flood beam, the state of the electro-optic device is switched to refract the collimated beam produced by the parabolic reflector. The use of both an electro-optic device and the required electronic drive circuitry, however, is costly and the electro-optic device reduces the amount of light directed from the reflector.

Reflectors for rectangular openings are known which have a pair of opposing parabolic or elliptic reflecting portions that are joined by planar reflective portions. The reflections from the planar reflective portions, however, often result in a non-uniform flood beam. U.S. Pat. No. 4,386,824 issued to Geoffrey R. Draper Jun. 7, 1983 discloses a motor vehicle rectangular lamp reflector which has parabolic lateral reflective portions and upper and lower reflective portions shaped to provide an infinite number of parabolic or elliptical curves. The parabolic or elliptical curves extend forwardly of the reflector body and terminate at the rectangular front opening thereof. The upper and lower reflective portions have foci (focal points) and focal axes that are coincident and increase progressively in focal length from the center of the reflector to the lateral reflective portions. As a result, a relatively complex arrangement of curves on upper and lower reflective portions is required in order to produce a flood beam. Further, the use of concave parabolic lateral reflectors results in non-uniformities in the produced flood beam.

The invention is directed to a light reflector having a cupped body with a rectangular opening at a predetermined distance from a center of the cupped body. A first pair of opposing walls and a second pair of opposing walls extend outward from the cupped body center to the rectangular opening. Each wall has a reflective internal surface which is curved to direct light from a filament source near the body center.

According to one aspect of the invention, each reflective surface of the first pair of opposing walls is curved concave to the cupped body interior and each reflective surface of the second pair of opposing walls is curved convex to the cupped body interior to form a predetermined flood beam light originating at the filament source positioned near the cupped body center and emerging from the rectangular opening, including light reflected from the reflective surfaces of the first and second pairs of opposing walls.

According to another aspect of the invention, each reflective surface of the first pair of opposing walls has a focus point in the interior of the cupped body and the filament source is positioned at the focus point.

According to yet another aspect of the invention, each reflective surface of the second pair of opposing walls has a focus point exterior to the cupped body.

According to yet another aspect of the invention, each reflective surface has a fine matte finish to increase the uniformity of the light pattern from the rectangular opening.

According to yet another aspect of the invention, the cupped body is formed by molding a plastic material such as acrylonitrile-butadiene-stryene (ABS), polycarbonate or styrene-acrylonitrile (SANS), and the reflective surfaces are formed by vacuum depositing aluminum on the plastic material.

In an embodiment of the invention, a reflector for a flashlight has a rectangular front opening and an internal reflective surface with upper and lower reflective surface sections and lateral reflective surface sections extending from a rear opening into which a lamp is inserted. Each of the upper and lower reflective surfaces has its focus point positioned in front of the lamp filament in the cupped body interior and each of the lateral reflective surfaces has its focus point exterior to the cupped body. The upper, lower and lateral sections are shaped to convert light radiated from the lamp filament into a limited size flood beam by breaking up the filament image and reflecting the resulting light.

FIG. 1 is a perspective view of a reflector illustrative of the invention;

FIG. 2 is a front plan view of the reflector shown in FIG. 1;

FIG. 3 is a cross-sectional view taken along line 3-3' of FIG. 2;

FIG. 4 is a cross-sectional view taken along line 4-4' of FIG. 2;

FIG. 5 illustrates a lamp positioned in the reflector depicted in the cross-sectional view of FIG. 3 and sample light ray paths; and

FIG. 6 illustrates a lamp positioned in the reflector depicted in the cross-sectional view of FIG. 4 and sample light ray paths emanating from the lamp.

FIGS. 1 and 2 depict a perspective view and a front plan view, respectively, of a reflector illustrative of the invention and generally denoted as 1. As shown in FIG. 1, the reflector 1 has a generally cupped shaped body with a center aperture 15 into which a lamp (not shown) is inserted and a rectangular opening 30 through which light passes to project a flood beam. The cupped body has upper and lower walls 5 and 20 and lateral walls 10 and 25 between the aperture 15 and the rectangular opening 30. The upper wall 5 is shaped as a curve downwardly concave with respect to the cupped shaped body interior that extends between the aperture 15 and the rectangular opening 30. The lower wall 20 is shaped as a curve downwardly concave with respect to the cupped shaped body interior that extends between the aperture 15 and the rectangular opening 30. Left lateral wall 10 is shaped as a curve outwardly convex to the interior of the cupped shaped body between the aperture 15 and the rectangular opening 30 and right lateral wall 25 is shaped as a curve outwardly convex to the interior of the cupped shaped body between the aperture 15 and the rectangular opening 30.

FIG. 3 shows a cross-sectional view taken along line 3-3' of FIG. 2 that illustrates the shape of the upper and lower walls 5 and 20. Referring to FIG. 3, the upper wall 5 and the lower wall 20 are symmetrical with respect to the central axis of the cupped shaped body. The interior reflective surfaces of the upper and lower walls form curves concave with respect to the central axis of the cupped body. These interior reflective surfaces are shaped to direct light impinging thereon from a focus point in front of the light source toward the rectangular opening 30 so that a substantially uniform beam pattern of predetermined vertical extent is formed.

The reflecting surfaces of upper wall 5 and lower wall 20 are curved to redirect light rays impinging thereon from the light source so that the light rays emerging from the rectangular opening form a uniform beam over a predetermined vertical range. The curve of upper wall 5 generally has a form that satisfies the following relationship: ##EQU1## where

D is the depth of the reflector and W is the width of the rectangular opening 30 shown in FIG. 3.

The curve formed by the reflecting surface of the lower wall 20 is symmetrical to that of the wall 5. The precise shape of the curves for the upper wall 5 and the lower wall 20 of the reflector may be determined by computer modeling techniques well known in the art.

FIG. 4 shows a cross-sectional view taken along line 4-4' of FIG. 2 that illustrates the shape of the lateral walls 10 and 25. Referring to FIG. 4, the left lateral wall 10 and the right lateral wall 25 are symmetrical with respect to a central axis of the cup-shaped body. The interior reflective surfaces of the lateral walls form outwardly convex curves arranged to direct light impinging thereon toward the rectangular opening 30 so that a beam pattern of predetermined horizontal extent is formed. The reflecting surfaces of lateral walls 10 and 25 are curved to direct light rays impinging thereon from the light source so that the light rays emerging from the rectangular opening form a uniform beam over a predetermined horizontal range. The curve of lateral wall 10 generally has a form that satisfies the following relationship: ##EQU2## and D is the depth of the reflector and H is the height of the rectangular opening as shown in FIG. 4.

The focus points of this curve are exterior to the cupped body and behind the cupped body. The curve formed by the reflecting surface of the lateral wall 25 is symmetrical to that of the wall 10. The precise shape of the curve for the lateral walls 10 and 25 of the reflector may be determined by computer modeling.

The combination of the concave curved upper and lower walls 5 and 20 and the outwardly convex lateral walls 10 and 25 limit the extent of the beam in both the vertical and horizontal directions to provide a uniform flood beam.

For a flashlight reflector that has a rectangular opening of 2.5".times.3.5" and is 2.5" deep to produce a 3'.times.4' rectangular light pattern at a distance of 3 feet from the rectangular opening, a curve defined by the following equation (3) may be used for the upper wall 5.

Lower wall 20 follows a curve that is symmetrical with respect to equation (3). A curve defined by the following equation (4) may be used for the shape of the left lateral wall 10.

Left lateral wall 25 is shaped according to a curve that is symmetrical to that of equation 4.

For a flashlight reflector that for that has a rectangular opening of 2.0".times.2.75" and is 2.25" deep to produce a 2.5'.times.3.5' rectangular light pattern at a distance of 3 feet from the rectangular opening, a curve defined by the following equation (5) may be used for the upper wall 5.

Lower wall 20 follows a curve that is symmetrical with respect to equation 1. A curve defined by the following equation 6 may be used for the shape of the left lateral wall 10.

The other lateral wall 25 is shaped according to a curve that is symmetrical to that of equation 6.

FIG. 5 shows a cross-sectional view corresponding to line 3-3' in FIG. 2 with a filament 55 in a lamp 50 that is inserted in the aperture 15 to illustrate light rays being reflected by the reflecting layers of the lower wall 20. A light ray 60 from the filament 55 is reflected from the lower wall 20 in close proximity to the rectangular opening 30 and emerges from the rectangular opening 30 as light ray 61. In similar manner, a light ray 64 impinges on the lower wall reflector 20 to reflect as a light ray 65, and light ray 67 is not reflected by lower wall 20. As can be readily seen, the light rays reflected from upper wall 5 are symmetrical to those reflected from lower wall 20. The light rays from upper wall 5 and lower wall 20 all emerge from the rectangular opening 30 having different directions within a predetermined vertical range in accordance with the restrictions imposed by equation 1.

FIG. 6 shows a cross-sectional view corresponding to line 4-4' in FIG. 2 with the lamp 50 inserted in the aperture 15 to illustrate light rays obtained from the reflecting layers of the lateral walls 10 and 25. A light ray 71 from the filament 55 is reflected from the lateral wall 10 in close proximity to the lamp 50 as light ray 72. The light ray 72 is further reflected from lateral wall 25 as light ray 73. Light ray 82 emerges directly from rectangular opening 30. Light ray 85 is reflected from a black reflective wall as light ray 86 and is further reflected by lateral wall 10 to emerge as light ray 87. As can be readily seen, the light rays reflected from lateral wall 10 are symmetrical to those reflecting from lateral wall 25. The light rays reflecting from lateral walls 10 and 25 all emerge from the rectangular opening 30 having different directions within a predetermined horizontal range in accordance with the restrictions imposed by equation 2.

The reflector cupped body may be formed by molding a plastic material such as acrylonitrile-butadiene-stryene (ABS), polycarbonate, or styrene-acrylonitrile (SANS). Polycarbonate is preferred because of its strength and resistance to heat. The reflective surfaces may be formed by vacuum depositing aluminum on the interior of the walls 5, 10, 20 and 25 obtained by the molding of the plastic material. The reflective surfaces may preferably be matte finished to increase the uniformity of the flood beam pattern.

It is to be understood that the specific embodiments described herein are merely illustrative of the spirit and scope of the invention. Modifications can readily be made by those skilled in the art in accordance with the principles of the invention.