US3831023A

US3831023A - Illuminating device

Info

Publication number: US3831023A
Application number: US00310883A
Authority: US
Inventors: M Coffman
Original assignee: Individual
Current assignee: Individual
Priority date: 1970-08-20
Filing date: 1972-11-30
Publication date: 1974-08-20
Anticipated expiration: 1991-08-20

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 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.

Description

iinite Sttes atet n91 @oiiiman ELLNATING DEVICE Moody L. Coiiman, 1832 NW. 17th St, Oklahoma City, Okla. 73106 Filed: Nov. 30, 1972 Appl. No.: 310,883

Related US. Application Data Continuation of Ser. No. 65,473, Aug. 20, 1970, abandoned.

Inventor:

[52] US. C1. 2410/1016 R, 40/125 R, 40/130 R, 161/1, 350/104 int. Ci lFZlv 13/04, G09f 13/00 Field 01' Search. 40/136, 133 R, 130 R, 130 B, 40/125 N; 350/102404, 106, 127, 128, 129;

References Cited UNITED STATES PATENTS v17 w i /777 Fukumitsu 40/136 Morita 161/5 Primary Examiner-Joseph F. Peters Attorney, Agent, or FirmDunlap, Laney, Hessin, Dougherty & Codding 5 7] 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 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.

5 Claims, 4 Drawing Figures IILLUMKNATING DEVICE RELATED APPLICATION BRIEF DESCRIPTION OF THE PRESENT INVENTION The present invention provides a device which ef- This application is a continuation application of my 5 fects directional, substantially total reflection of light US. application Ser. No. 65,473, filed Aug. 20, 1970, now abandoned, and 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 US. 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 US. 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 US. 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 US. 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 observer of 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 US. Pat. No. 2,043,690 to Arbuckle et al. and U5. Pat. No. 1,893,024 to Gill.

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 refract 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 the surfaces 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 element 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 with the accompanying drawings which illustrate the invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I 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. I of the drawings, shown therein is a structure consisting of a curved body of glass, clear plastic or similar light transmitting material. The body I is positioned in a medium I2 which is of lesser optical density than the material of the body. Typically, the body I0 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 I0 is configured, in accordance with the present invention, to have a pair of boundary defining surfaces I4 and I6, such surfaces being non-parallel. In the specific illustrated embodiment of the invention, the surfaces I4 and I6 are arcuately shaped, being formed on different radiuses. The arcuate surfaces I4 and I6 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. I.

Given the location of the body It) in the less dense medium I2 and the geometric configuration ascribed to the medium I2 and its surfaces I and I6, reference will next be made to the behavior of a light ray impinging upon the surface I4 of the body 10. An incident light ray impinging upon this surface is designated by reference character I8a. The angle of incidence of the light ray 18a upon the surface I4 is 0 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 I4, the light ray is refracted and enters the more dense medium of the body 10. The refracted ray, designated by refer ence character 18b, extends at an angle of refraction 6 with respect to the normal line previously described.

At the surface I6 bounding the body 10 on the opposite side thereof from the surface I4, 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 I4 and I6 in relation to each other, total reflection of the light rays can be obtained at the surface I6. The reflected ray I80, as well as the refracted ray 18b 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 I passes through the medium of the body III and arrives at the surface I4, it again undergoes refraction in passing out of the body It) into the less dense medium I2. 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, sin0, n sinO 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 6 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. I, if the body I0 is glass and the medium I2 is air, both indices of refraction are known, and the angle of incidence of ray I811 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 I4 can be oriented so that a desired angle of refraction 6 obtains in the medium I0, and the path of travel of light through this medium from the surface 114 thus selectively controlled. The importance of the direction of travel of light in the body It) is based upon the importance of the angle at which the light ray impinges upon the surface I6 forming the second boundary of the more dense medium.

At this surface forming the interface between the denser medium of the body I0 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 I0 such that the angle of incidence 6;, of this ray upon the surface I6 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 the

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 It), and substantially no light has been permitted to pass through this body.

After reflection at angle of reflection from the surface 16, the light ray 1&- travels through the body 10 to the surface 114. Where the

surfaces

14 and 16 parallel, the light ray 18c would impinge upon surface 14 at the same angle of incidence (0 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, nonparallel 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 medium 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 l4 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 observer stationed along this line will perceive the body 10 as highly illuminated in contrast to other surroudning 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 illu trated 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 55 light, such as a street light 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 39. It will be noted in referring to FIG. 3 that the light rays 28 which impinge upon thehemispherical dimples 24- are totally reflected as rays 32 which travel toward the eye 30 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. l. 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 from 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. 4 of 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 sur faces, if rays are considered as impinging upon hemigood, 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 system for directing light from a light source to a desired first location, and for affording concurrent viewing from said first location of an object at a second location through a transparent physical barrier between said first location and said second location, said system comprising:

a transparent base plate adapted to be disposed be tween said first and second locations in the line of sight therebetween whereby an object at the sec ond location can be seen through the transparent base plate from the first location;

a light source; and

a body of transparent, light-transmitting medium supported on said base plate at a position to be out of the line of sight between said first location and said second location when said base plate is disposed between said first and second locations, said body of transparent, light-transmitting medium being spaced from the light source and 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 body is positioned in a second medium of lesser density than the transparent light transmitting medium of said body, and so that no light from said light source is refracted at said second uncoated surface and transmitted through said second surface into said second medium, 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 said second uncoated boundary surface are refracted to a desired path through said second medium to said desired location, said desired path being divergent from the path of light rays from said source incident upon said one portion of said first boundary surface, said first and second uncoated boundary surfaces of said body of transparent, light transmitting medium being contiguous to, and surrounded by, said transparent base plate.

2. A system as defined in claim 1 wherein said first and second boundary surfaces are hemispherical in configuration.

3. A system as defined in claim 1 wherein said first and second boundary surfaces are hemispherical in configuration and project from said base plate in the general direction of said light source.

4. A system as defined in claim 3 wherein said body is glass and is transparent.

5. A system as defined in claim 3 and further characterized as including a plurality of said bodies arranged to form numerical indicia.

Claims

1. A system for directing light from a light source to a desired first location, and for affording concurrent viewing from said first location of an object at a second location through a transparent physical barrier between said first location and said second location, said system comprising: a transparent base plate adapted to be disposed between said first and second locations in the line of sight therebetween whereby an object at the second location can be seen through the transparent base plate from the first location; a light source; and a body of transparent, light-transmitting medium supported on said base plate at a position to be out of the line of sight between said first location and said second location when said base plate is disposed between said first and second locations, said body of transparent, light-transmitting medium being spaced from the light source and 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 nonparallel 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 body is positioned in a second medium of lesser density than the transparent light transmitting medium of said body, and so that no light from said light source is refracted at said second uncoated surface and transmitted through said second surface into said second medium, 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 said second uncoated boundary surface are refracted to a desired path through said second medium to said desired location, said desired path being divergent from the path of light rays from said source incident upon said one portion of said first boundary surface, said first and second uncoated boundary surfaces of said body of transparent, light transmitting medium being contiguous to, and surrounded by, said transparent base plate.