Thin-panel illuminator for front-lit displays

• US 4,373,282 A
• Filed: 05/29/1981
• Issued: 02/15/1983
• Est. Priority Date: 12/26/1979
• Status: Expired due to Fees

• Current Assignee: Hughes Aircraft Company (Rtx Corporation)
• Original Assignee: Hughes Aircraft Company (Rtx Corporation)
• Inventors: Wragg, Robert
• Primary Examiner(s): Mancene, Gene
• Assistant Examiner(s): Foycik, Michael J.
• Application Number:
  US06/268,512
• Time in Patent Office: 627 Days
• Field of Search: 40/546, 40/547, 40/563, 362/26, 362/29, 362/30, 362/31, 427/289, 427/290, 264/2.6, 264/138, 264/139, 264/2.7, 264/162
• US Class Current: 40/546
• CPC Class Codes: G02B 6/0036 2-D arrangement of prisms, protrusions, indentations or roughened surfaces
• CPC Class Codes: G02B 6/0038 Linear indentations or grooves, e.g. arc-shaped grooves or meandering grooves, extending over the full length or width of the light guide
• CPC Class Codes: G09F 2013/1804 Achieving homogeneous illumination

Abstract

A device for illuminating a display surface. Light is introduced through an end surface of a transparent substrate having front and back plane parallel opposed surfaces and thereby directed into the interior of the substrate. The back surface is textured with a multiplicity of shallow depressions such as grooves or dimples which have shallow sloped sides. These sides are configured so that light is selectively directed from the interior of the substrate through a limited angle out of the substrate towards a display surface adjacent and coextensive with the back surface of the substrate and away from a viewer observing the display surface through the substrate. The device provides uniform, high contrast illumination of underlying large area graphic displays such as maps, photographs, charts, and the like.

Claims

1. A front-lit illumination panel for providing directional illumination to a display surface comprising:

(a) an optically transparent substrate having first and second parallel opposing major surfaces, said first major surface having a multiplicity of irregular depressions therein; and

(b) an optically transparent material having an index of refraction closely matching that of said substrate partially filling the depressions in said substrate so as to give each of said depressions a regular concave, meniscus shaped surface, each said depression thereby having gently sloping sides and a relatively shallow slope angle to said first major surface so that light from the interior of said substrate is selectively aimed through either said first or second major surface, the light exiting through said first major surface being directed toward a display surface co-extensive with and adjacent to said first major surface and the light exiting said second major surface being directed away from a viewer observing said display through said substrate.

2. The device of claim 1 wherein said light exiting through said first major surface is within the angle θ

_m -φ

_m and said light exiting said second major surface is within an angle θ

_m where;

φ

_m =maximum slope angle of said depressions, and

θ

_m =90°

-sin^-1 [n sin(ψ

-φ

_m)]

where

n=index of refraction of said substrate, and

ψ

=sin^-1 (1/n).

3. The device of claim 2 wherein said viewer observes said display at an angle V, where V is the supplement of angle θ

_m relative to said second major surface.

4. The device of claim 1 wherein said depressions in said first major surface are grooves.

5. The device of claim 4 wherein said grooves are oriented in pseudo-random directions.

6. The device of claim 4 wherein said grooves have a width W of 0.001 inch or less and an average intergroove spacing greater than five times W.

7. The device of claim 1 wherein said depressions are spaced apart by a distance which decreases with their distance from said end surface such that said display surface has substantially uniform illumination with distance from said edge.

8. The device of claim 2 wherein the maximum slope angle (φ

m) of said depressions is 3°

or less.