UNIFORM ILLUMINATION WITH EDGE LIGHTING

• US 3,752,974 A
• Filed: 12/13/1971
• Issued: 08/14/1973
• Est. Priority Date: 12/13/1971
• Status: Expired due to Term

• Current Assignee: Coastal Genomics Inc
• Original Assignee: Lewis William Myers, Myron Lewis Baker
• Inventors: Baker, Myron Lewis, Myers, Lewis William
• Primary Examiner(s): Braun, Fred L.
• Application Number:
  US05/207,218
• Time in Patent Office: 610 Days
• Field of Search: 240/1EL,2.1,8.16,16R
• US Class Current: 362/627
• CPC Class Codes: B60K 2360/336 Light guides
• CPC Class Codes: B60Q 3/14 lighting through the surface to be illuminated
• CPC Class Codes: B60Q 3/64 for a single lighting device
• CPC Class Codes: G02B 6/0021 for housing at least a part of the light source, e.g. by forming holes or recesses
• CPC Class Codes: G02B 6/0036 2-D arrangement of prisms, protrusions, indentations or roughened surfaces
• CPC Class Codes: G02B 6/0055 Reflecting element, sheet or layer

Abstract

Uniform illumination is provided from an edge lighted optical medium of a given thickness by diffusing a surface portion normally providing internal reflection of the light radiated into the edge such that at least some of the light rays striking the diffused area are reflected through the opposite surface of the medium and some are refracted through the one surface. A cleared area about the source of light free of the diffusion is provided and treated by application of coatings on opposite surface portions of the medium defining the cleared area. These coatings have an index of refraction less than that of the medium such that light is channeled by internal reflection between the surfaces of the medium and inhibited from escaping from the medium in the vicinity of the cleared area. This cleared area has a radius of preferably three to four times the thickness of the optical medium. The resulting light emmination from the surface of the medium is substantially uniform beyond the cleared area.

Claims

1. A method of providing substantially uniform illumination from an edge lighted optical medium of thickness T, comprising the steps of:

a. diffusing one surface portion normally providing internal reflection of the light such that at least some of the light rays striking the diffused surface are reflected through the opposite surface and some are refracted through the one surface to escape out of the medium;

b. providing a cleared area about the source of light free of the diffusion; and

, c. treating the cleared area by providing an interface for the surfaces of the optical medium defining the cleared area, said interface having an index of refraction less than that of the medium to assure internal reflection of light rays in the cleared area such that light is channeled by internal reflection between the surfaces and inhibited from escaping from the medium in the vicinity of the cleared area, the channeled light rays expanding towards the diffused surface portion so that the light escaping from the medium as a consequence of the diffused surface portion is substantially uniform with increasing distance from the lighted edge as measured in a plane parallel to the plane of the medium.

2. The method of claim 1 including the step of providing a highly specular surface under the diffused portion of the optical medium to reflect light refracted through the one surface back into the medium so that the level of the uniform illumination from the opposite surface is substantially increased.

3. The method of claim 2 including the additional step of providing a highly specular surface about the edges of the optical medium except the edge portion admitting light to block light from escaping from the edges.

4. The method of claim 1, in which said cleared area has a circular end boundary defined at least in part by a circle with the source of light at the center of the circle, said circle having a radius which lies between T and 10T.

5. The method of claim 4, in which said radius is from three to four times the thickness T of the optical medium.

6. The method of claim 1, in which said interface is in the form of a coating of material having an index of refraction less than that of the medium.

7. A means for providing substantially uniform illumination over a large surface area comprising:

a. an optical medium having opposite surfaces defining a first surface and a second surface parallel to each other and separated by a distance T defining the thickness of said medium; and

, b. at least one light source at an edge of said medium for radiating light into the edge of the medium between said surfaces;

c. said first surface having a diffused surface portion over a large surface area for reflecting and refracting internally reflected light radiated between said surfaces from said source out of said medium;

d. said first surface having a cleared area about said source free of diffusion, the periphery of said cleared area being at a distance from said source greater than T and less than 10T; and

, e. a coating of material having an index of refraction less than that of said medium on the surface portions of said medium defining said cleared area to thereby assure internal reflection of light rays in said cleared area.

8. The subject matter of claim 7, in which said diffused surface portion includes total reflecting means for reflecting back into said medium any refracted light otherwise escaping out of said medium through said first surface so that light is directed out of said second surface.

9. The subject matter of claim 7, including total reflecting means about the edges of said medium except for the edge portion into which light is radiated from said source.

10. The subject matter of claim 7, in which said cleared aRea has a circular end boundary defined at least in part by a circle with the light source at the center of the circle, the radius of the circle lying between 3T and 4T and in which said optical medium has a refractive index of between 1.42 and 2.00.

11. The subject matter of claim 7, in which said medium comprises an acrylic panel, said coating of material being co-extensive with said cleared area on said first surface, said material being transparent and covering the entire second surface of said acrylic panel;

a coating of acrylic overlying said coating of material on said entire second surface;

a coating of translucent white vinyl overlying said coating of acrylic on said second surface; and

a coating of opaque vinyl overlying said coating of white vinyl, portions of said opaque vinyl being removed on said second surface to define nomenclature, the said first surface having a coating of acrylic overlying said coating of material on said cleared area and extending beyond said cleared area a first given distance;

a coating of opaque vinyl overlying a portion of said coating of acrylic on said cleared area and terminating short of said cleared area by a second given distance, said diffused surface being provided by a coating of white vinyl on said first surface outside said cleared area; and

a coating of opaque vinyl overlying the entire first surface whereby an edge lighted panel is provided in which light emitted through the openings defined by said nomenclature is substantially uniform.

12. The subject matter of claim 11, in which said cleared surface has a circular end boundary defined at least in part by a circle with said light source at the center of the circle, the circle having a radius R between 3T and 4T said first given distance being from 0.25R to 0.75R and said second given distance being from 0.1R to 0.5R.