US 3906650 A
A device for directing light in a predetermined pattern, and including a light conductive medium bounded by two non-parallel surfaces arranged with respect to a light source and with respect to each other so that light rays impinging upon the medium from a less optically dense medium are at least partially refracted at the first of the surfaces, and the refracted rays are then totally reflected at the second surface, and pass back through the surface-bounded medium to be partially refracted at the second surface and directed thereby toward an object to be illuminated. In one form of the invention, a plurality of regions of the surface-bounded, light conductive media are provided in a predetermined geometrical arrangement to provide a sign or indicia carrying device in which letters or characters appear to glow or shine in contrast to surrounding portions of the sign or indicia carrying device.
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Description (OCR text may contain errors)
United States Patent [191 Coffman Sept. 23, 1975 1 1 ILLUMINATING DEVICE 3,616,100 10/1971 Morita 161/5  Inventor: Moody L. Coffman, 1832 NW. 17th St Oklahoma City, Ok1a73102 Primary ExammerRobert W. Michell Assistant Examiner lohn F. Pitrelli  Filed: Aug. 19, I974 Appl. No.: 498,292
Related U.S. Application Data U.S. Cl 40/130 B; 40/136; 350/104 Int. C1. G09F 13/00 Field of Search. 40/136, 125 N, 130 R, 130 B,
40/133 R; 240/93, 106 R; 350/102l04, 106, 127-129; 161/1, 2, 4, 5
 References Cited UNITED STATES PATENTS 1,263,065 4/1918 .lohanson 350/129 X 1,485,445 3/1924 Van Bloem... 40/136 1,990,223 2/1935 Cochran 40/136 2,043,193 6/1936 Dunn et a1. 240/106 R X 2,180,093 11/1939 Persons 40/136 X 2,275,824 3/1942 Kirkpatrick... 350/104 X 3,012,477 12/1961 Lodge.... 161/2 X 3,312,006 4/1967 Rowland... 40/136 X 3,590,509 7/1971 Fukumitsu 40/136 Attorney, Agent, or Firm-Laney, Dougherty. Hessin & Fish 57 ABSTRACT A device for directing light in a predetermined pattern, and including a light conductive medium bounded by two non-parallel surfaces arranged with respect to a light source and with respect to each other so that light rays impinging upon the medium from a less optically dense medium are at least par tially refracted at the first of the surfaces, and the refracted rays are then totally reflected at the second surface, and pass back through. the surface-bounded medium to be partially refracted at the second surface and directed thereby toward an object to be illuminated. In one form of the invention, a plurality of regions of the surface-bounded, light conductive media are provided in a predetermined geometrical arrangement to provide a sign or indicia carrying device in which letters or characters appear to glow or shine in contrast to surrounding portions of the sign or indicia carrying device.
1 Claim, 4 Drawing Figures ILLUMINATING DEVICE RELATED APPLICATIONS This application is a divisional application of my U.S. application Ser. No. 310,883 filed Nov. 30, 1972, now U.S. Pat. No. 3,831,023 and entitled Illuminating Device, which application is a continuation application of my U.S. application Ser. No. 65,473 filed Aug. 20, 1970, and also entitled Illuminating Device.
BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to light transmissive devices which direct light by refraction and reflection to achieve a desired effect. More particularly, the invention relates to devices in which transparent or translucent media denser than air are geometrically configured to directionally reflect a maximum amount of light.
2. Brief Description of the Prior Art A variety of proposals have previously been advanced for constructing signs of glass, plastic or other transparent or translucent material arranged so as to reflect or refract light directionally and from localized areas, which areas collectively form the indicia making up the sign. For example, in U.S. Pat. No. 2,610,603, prism forming nubs of glass are arranged over an area on a supporting surface in such a way that light rays from a source impinge upon one surface of each nub, enter the glass body of the nub, and are partially reflected from a second surface of the nub toward a person located at a distance from the nubs. This results in high intensity illumination of the second nubs so that they collectively form a visual signal perceptible to the person toward whom the rays are partially reflected.
In U.S. Pat. No. 3,223,833, a dial is illuminated by placing over it a light transmitting material (which may be formed of synthetic resin) which has serrations formed therein in such a way that light entering the body of light transmitting material is reflected toward the viewer of the dial by the curved surfaces which define the serrations. A single light source can be used to produce shadow free illumination of the entire dial face.
In U.S. Pat. No. 2,477,022, a number of small glass projections constituting individual prisms, and in some cases reflectors, are collectively arranged to form indicia making up a sign. By the use of these glass projections, light from one or more sources may be directed by refraction and/or reflection from one or more surfaces of each projection to form a brightly illuminated sign.
Light reflectance and refraction characteristics are utilized in the construction of signs as disclosed in U.S. Pat. No. 1,858,975 to TaBois. One or more pieces or sheets of glass may be shaped to form the letters of the sign and the boundary surfaces of the glass are arranged so that refraction of light rays into the body of the glass occurs at first surfaces exposed to the light source. Then, at second rear or unexposed surfaces of the glass, reflection back through the glass occurs, and the final refraction of the reflected rays at the first surface directs the light rays toward an observerof the sign. To assure a sufficient degree of reflection of light from the back or second surfaces, these surfaces are silvered.
Other patents which have proposed generally similar concepts for the purpose of illuminating certain areas are U.S. Pat. No. 2,043,690 to Arbuckle et al.; U.S. Pat. No. 1,893,024 to Gill; U.S. Pat. No. 1,990,223 to Cochran and U.S. Pat. No. 3,590,509 to Fukumitsu.
BRIEF DESCRIPTION OF THE PRESENT INVENTION The present invention provides a device which effects directional, substantially total reflection of light from a predetermined area so that an intensely illuminated sign may be developed from a light transmitting medium through which little or no light will pass due to the total reflectance achieved. No silvering or special treatment of surfaces is required to obtain the described high reflectance. The principles of the invention may also be utilized to construct a light diffuser capable of providing uniform, shadow free indirect illumination.
Broadly described, this invention comprises a light transmitting medium bounded by two non-parallel surfaces and located in a less optically dense medium and spaced from a light source. The non-parallel surfaces are arranged with respect to each other and the light source so that rays from the source strike one of the surfaces, and are there partially refracted through the medium at an angle to the second surface such that total reflection of the refracted rays occurs at the second surface. The described refractance and total reflectance is achieved by utilizing Snells law of refraction to calculate the angle at which the first surface should be oriented with respect to impinging rays to re fract the rays toward the second surface in a direction suitable to obtain total reflectance at the second surface. The second surface is then oriented at a suitable angle with respect to the thus refracted rays to give the desired total reflectance. The angle can be any angle greater than the critical angle. The reflected light then passes back through the medium and is refracted once again in passing through the first surface.
By proper orientation of thesurfaces of the light transmitting medium with respect to each other and with respect to the light source, substantially all of the light may be reflected in a desired direction without the requirement of silvering any surface. The light transmitting medium may be provided as one unitary ele* ment for a few usages, but more frequently will be utilized in the form of a plurality of discrete nubs, or prismatic elements of relatively small size which are grouped and arranged to collectively form indicia which are intensely illuminated as a result of the occurrence of the described refractance and reflectance phenomena.
An important object of the invention is to provide an improved directional light reflector which reflects a higher percentage of impinging light than prior directional light reflectors, and accomplishes such reflection without the inclusion of silvered or'other treated surfaces.
A more specific object of the invention is to provide an unsilvered glass or plastic sign in which the indicia thereof are visible by illumination due to highly reflected light from a remote source.
Another object of the invention is to provide a light transmitting medium in a geometric configuration such that no light will pass therethrough from a remote source, but will instead be substantially entirely reflected in a predetermined direction.
A further object of the invention is to provide a device for providing indirect, shadow-free illumination by diffusion of reflected light over a substantial area.
Additional objects and advantages will become apparent as the following detailed description of the invention is read in conjunction the accompanying drawings which illustrate the invention.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram illustrating certain fundamental principles of the invention.
FIG. 2 is a view in elevation of a sign constructed in accordance with the invention.
FIG. 3 is a sectional view taken along line 3-3 of FIG. 2.
FIG. 4 is a diagram illustrating another application of the invention in which the principles of the invention are utilized in constructing a light diffuser device.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION Referring initially to FIG. 1 of the drawings, shown therein is a structure consisting of a curved body of glass, clear plastic or similar light transmitting material. The body 10 is positioned in a medium 12 which is of lesser optical densitiythan the material of the body. Typically, the body 10 may be constructed of glass and the medium is air. It may here be pointed out that when the word density is used herein and in the appended claims, the term means optical density.
The body 10 is configured, in accordance with the present invention, to have a pair of boundary defining surfaces 14 and 16, such surfaces being non-parallel. In the specific illustrated embodiment of the invention, the surfaces 14 and 16 are arcuately shaped, being formed on different radiuses. The arcuate surfaces 14 and 16 may or may not be concentric with respect to each other, and, moreover, need not be segments of circles (that is, formed with a constant radius of curvature). Non-parallelism in the sense of the present invention is intended to comprehend and include curved concentric surfaces of the general type illustrated in FIG. 1.
Given the location of the body 10 in the less dense medium 12 and the geometric configuration ascribed to the medium 12 and its surfaces 14 and 16, reference will next be made to the behavior of a light ray impinging upon the surface 14 of the body 10. An incident light ray impinging upon this surface is designated by reference character 18a. The angle of incidence of the light ray 18a upon the surface 14 is and is measured between the incoming ray and a line extending normal to a tangent line passing through the point of impingement of the ray on this surface. At the surface 14, the light ray is refracted and enters the more dense medium of the body 10. The refracted ray, designated by reference character 18b, extends at an angle of refraction 6 with respect to the normal line previously described.
At the surface 16 bounding the body on the opposite side thereof from the surface 14, the ray 18b is at least partially reflected, and the reflected ray is designated by reference character 18c. As will be hereinafter shown, by properly orienting the surfaces 14 and 16 in relation to each other, total reflection of the light rays can be obtained at the surface 16. The reflected ray 18c, as well as the refracted ray 18]) extend at identical angles 0 with respect to a line normal to a tangent to their point of impingement upon the surface 16, these angles being the angle of incidence and the angle of reflection upon this surface.
When the light ray 18c passes through the medium of the body 10 and arrives at the surface 14, it again undergoes refraction in passing out of the body 10 into the less dense medium 12. The refracted light ray traversing medium 12 is then designated by reference character 18d. The angle of refraction formed with a line normal to a line tangent to the surface 14 at the point of exit of the ray 18d is denominated 0 The operation of, and advantages derived from, the present invention are dependent upon the proper utilization of certain physical laws and optical principles. Snells law of refraction of light passing from one medium into another is expressed by the equation n sin 6, =11 sin 6 where n, the index of refraction in the first medium in which the ray originates;
r1 the index of refraction in the second medium into which the ray passes;
0 the angle of incidence of the ray upon the interface between the two media;
6 the angle of refraction of the ray passing through the second medium.
Given a fixed position light source from which light rays emanate and travel in one or more directions, Snells law can be utilized to determine the direction of propagation of a light ray from this source through a medium positioned to intercept such ray at one surface of the medium, provided the angle of incidence of the ray as it impinges on this surface is known, and provided further that the indices of refraction of this medium and of the medium (such as air) between the surface and the light source are known. Applying this to the diagram of FIG. 1, if the body 10 is glass and the medium 12 is air, both indices of refraction are known, and the angle of incidence of ray 18a can be measured. With these values, the angle of refraction 6 can be calculated using Snells law.
Considered in another way, given a fixed light source from which the ray 18a originates, the surface 14 can be oriented so that a desired angle of refraction 6 obtains in the medium 10, and the path of travel of light through this medium from the surface 14 thus selectively controlled. The importance of the direction of travel of light in the body 10 is based upon the importance of the angle at which the light ray impinges upon the surface 16 forming the second boundary of the more dense medium.
At this surface forming the interface between the denser medium of the body 10 and air, Snells law again applies, and, in addition, the law of reflection is of significance. This law merely states that the angle of incidence of the ray upon the reflecting surface is equal to the angle of reflection of the ray from the reflecting surface. Refraction of light passing from a relatively denser medium to a relatively less dense medium is always away from-the normal, and at some angle of incidence termed the critical angle, refraction of light at to the normal will occur. At all angles of incidence larger than the critical angle, total reflection will occur, and no refraction occurs. Thus, by making the path of light ray 18b through the body 10 such that the angle of incidence 6 of this ray upon the surface 16 is greater than the critical angle, total reflection of this ray will occur at this surface.
It will now be seen that by properly orienting surfaces 14 and 16 with respect to each other, and with respect to the source of the light ray 18a, the incoming light can be totally reflected from the two surfaces 14 and 16 considered conjunctively, even though neither surface is silvered or otherwise enhanced in reflectivity. It may be pointed out that the basic utility of the invention is based upon the obtainment of this effect. Thus, light from a remote source has been totally reflected by the body 10, and substantially no light has been permitted to pass through this body,
After reflection at angle of reflection 6 from the surface 16, the light ray 18c travels through the body 10 to the surface 14. Were the surfaces 14 and 16 parallel, the light ray 18c would impinge upon surface 14 at the same angle of incidence (6 as the ray 18b impinges upon surface 16, and due to recurring total reflection at these surfaces, the light would be trapped within the body 10. The surfaces are, however, non-parallel and therefore the light ray 180 is at least partially refracted as it passes through the surface 14 into the air. Upon refraction at the surface 14, the light emerges in me dium 12 as ray 18d extending at angle of refraction 0 with respect to the normal. It will be perceived that by proper orientation of the surfaces 14 and 16 relative to each other and to the source of light, relatively high intensity illumination can be made to occur at points along the line of travel of the ray 18d. Thus, an ob server stationed along this line will perceive the body 10 as highly illuminated in contrast to other surrounding areas where total reflection of the light does not occur.
To further illustrate one of many practical applications of the principles of the invention, reference is made to FIGS. 2 and 3 of the drawings. The device here illustrated is a sign 20 which includes a base plate 22 which may be made of transparent, translucent or opaque material. The base plate 22 is a flat member having a pair of parallel, substantially monoplanar surfaces, referred to as a front surface 22a and a back surface 22b. Formed in the base plate 20 are a plurality of substantially hemispherical dimples 24. The dimples 24 are a light transmitting material, and in a preferred embodiment of the invention, the base plate 20 and dimples 24 are integrally formed of clear plastic or glass.
It will be noted in referring to FIG. 2 that the dimples 24 are arranged on the surface 22a to constitute indicia 26 in the form of numbers. The type of sign here illustrated is a house number sign of the type used to permit the number of a residence or the like to be identified from the street in front of the residence.
The sign 20 is positioned on the step or other appropriate location in front of the residence. A source of light, such as a street light 27 or the headlights of vehicles, results in light rays 28 impinging upon the base plate 22 and dimples 24. The eye of an observer of the sign is indicated at 30. It will be noted in referring to FIG. 3 that the light rays 28 which impinge upon the hemispherical dimples 24 are totally reflected as rays 32 which travel toward the eye of the observer. This total reflection is attained by proper formation and relative orientation of the opposed surfaces of the dimples 24 to achieve the effect illustrated in FIG. 1 and hereinbefore described.
The rays 28 which impinge upon the planar front surface 22a of the base plate 22 are refracted and pass through the back surface 22b,"and the phenomena of total reflection of these rays does not occur (here 6 is smaller than the critical angle). Thus, the amount of light reflected from the dimple-free areas of the base plate 22 is less than that reflected froin the dimples. This results in the number indicia appearing to be more brightly illuminated than the remainder of the sign, and the house number stands out and is easily discernible at considerable distances.
Another application of the principles of the invention is illustrated in FIG. 40f the drawings. Here, a light diffuser device is illustrated. The device comprises a body of light transmissive material 34 having a plurality of closely placed dimples 36 or bubbles formed thereon. Each of these dimples 36 is bounded by non-parallel surfaces arranged to yield total reflection. Although the preceding discussion has, for simplicity, been concerned with the refraction and reflection of single light rays from bodies having non-parallel bounding surfaces, if rays are considered as impinging upon hemispherical dimples from several directions, then it will be seen that total reflection of these rays in multiple directions occurs. The result is diffusion of the light with resulting overlap of the reflected rays 38. Thus, fairly good, shadow free indirect illumination of a surface 40 can be obtained.
Although certain preferred embodiments of the invention have been herein described, various changes and innovations can be effected in the described illustrative structures without departure from the basic principles of the invention. Changes and modifications of this type are therefore deemed to be circumscribed by the spirit and scope of the invention except as the same may be necessarily limited by the appended claims or reasonable equivalents thereof.
What is claimed is:
1. A sign for communicating a message to a desired location by reflection of a light from a light source comprising:
a base plate having a substantially monoplanar surface;
a light source; and
a plurality of bodies each of transparent, light transmitting medium denserthan air supported on said base plate, said bodies being spaced from the light source and collectivelyarranged to form the indicia constituting the message, each of said bodies of transparent, light transmitting medium including a first uncoated boundary surface having one portion facing the light source and positioned in the path of light rays therefrom, whereby light rays from the source impinge upon said one portion, and further including a second, uncoated boundary surface on the opposite side of said body from said first boundary surface and non-parallel with respect to said one portion of said first uncoated boundary surface, said one portion of said first boundary surface being angled with respect to the path of travel of light rays from said light source, and with respect to said second uncoated surface, so that light from said light source is totally reflected from said second uncoated surface after passing into said transparent, light transmitting medium when said bodies and base are positioned in air, and so that no light from said light source is refracted at said second uncoated surface and transmitted through said second surface into the air, said first uncoated boundary surface further having a second portion thereof which is angled with respect to said second uncoated boundary surface so that the light rays totally reflected from the second uncoatcd boundary surface are refracted to a desired path through the boundary surface, said first and second uncoated boundary surfaces of each of said bodies of transparent, light transmitting medium being contiguous to, and surrounded by, said base plate.