Uniform emission backlight

• US 4,714,983 A
• Filed: 06/10/1985
• Issued: 12/22/1987
• Est. Priority Date: 06/10/1985
• Status: Expired due to Term

• Current Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Lang, Warren R.
• Primary Examiner(s): Cuchlinski, Jr., William A.
• Assistant Examiner(s): NOT, DEFINED
• Application Number:
  US06/743,226
• Time in Patent Office: 925 Days
• Field of Search: 362/26, 362/27, 362/30, 362/31, 362/310, 362/246, 362/329, 362/800, 350/338, 350/339, 350/345
• US Class Current: 362/27
• 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 6/0055 Reflecting element, sheet or layer
• CPC Class Codes: G02B 6/0088 of the light guide or other optical sheets in the package
• CPC Class Codes: G02F 1/133615 Edge-illuminating devices, i.e. illuminating from the side

Abstract

A backlight having lamps inserted into ends of a transparent member is disclosed. A top surface of the member is polished and contains an opaque section opposing the lamps. A bottom surface of the member is uniformly frosted so that variations in the average depth of surface irregularities are minimized.

Claims

1. An apparatus for providing a source of light emitted throughout a predetermined area, said apparatus comprising:

a first lamp having a light source therein;

a transparent member exhibiting a critical angle (θ

_c with respect to air and having a polished top surface relative to an opposing frosted bottom surface, the bottom surface having a boundary substantially with air, said member having a first cavity therein located proximate a first end of said member, said first lamp being inserted into said first cavity so that said first lamp light source resides inside said member at a distance D₁ from the top surface; and

a first opaque section located on said member top surface opposing said member first cavity so that said first opaque section extends toward the central area of said member top surface for a distance greater than D₁ X TAN (θ

_c from a point opposing the light source.

2. An apparatus as claimed in claim 1 wherein said member additionally has a second cavity therein located proximate a second end of said member, the apparatus additionally comprising:

a second lamp having a light source therein, said second lamp being inserted into said second cavity so that said second lamp light source resides inside said member at a distance D₂ from the top surface; and

a second opaque section located on said member top surface opposing said second cavity so that said second opaque section extends toward the central area of said member top surface for at least a distance equivalent to D₂ X TAN (θ

_c from a point opposing the second lamp light source.

3. An apparatus as claimed in claim 2 wherein:

said member has first and second sides substantially parallel to each other and substantially perpendicular to the top and bottom surfaces; and

said member first and second sides and first and second ends are frosted relative said member top surface and said member sides and ends having a boundary substantially with air.

4. An apparatus as claimed in claim 2 wherein:

said member has first and second sides substantially parallel each other and substantially perpendicular to the top and bottom surfaces;

each of said member first and second sides has first and second end sections relative to a central section; and

said member first and second ends and the central sections of said first and second sides are frosted relative to said member top surface and end sections of said first and second sides.

5. An apparatus as claimed in claim 1 wherein:

the bottom surface of said member comprises surface irregularities; and

the depth of surface irregularities of the bottom surface of said member varies less than 35 microinches.

6. An apparatus as claimed in claim 1 wherein said first opaque section comprises paint, said paint being substantially black in color.

7. An apparatus as claimed in claim 1 wherein the first cavity in said member represents a slot having a long diameter substantially parallel the first end of said member.

8. An apparatus as claimed in claim 1 wherein said member has cavity walls surrounding the first cavity, and the cavity walls are frosted relative to said member top surface.

9. An apparatus as claimed in claim 1 additionally comprising a diffuse reflector having a reflective surface facing and adjacent said member bottom surface, the reflective surface being substantially white in color.

10. A method of uniformly backlighting a display, said method comprising the steps of:

providing a point light source, a transparent member having opposing top and bottom surfaces and exhibiting a critical angle (θ

_c) relative to air, and a display;

inserting the point light source of said providing step within the transparent member of said providing step;

frosting the bottom surface of the transparent member so that the depth of surface irregularities of the bottom surface varies less than 35 microinches;

blocking passage of light at surface points on the top surface where angles formed between lines perpendicular to the top surface at the surface points and lines through the respective surface points and the point light source are less than the critical angle (θ

_c);

installing the display substantially parallel to the top surface and spaced apart from the top surface by a predetermined distance; and

providing a boundary with a bottom surface comprised substantially of air.

11. A method as claimed in claim 10 wherein the member of said providing step has ends and sides connecting the top and bottom surfaces, and the method additionally comprises the step of frosting the ends and sides of the member.

12. A method as claimed in claim 10 additionally comprising the steps of:

providing a second point light source;

inserting the second point light source within the transparent member of said providing step; and

blocking passage of light at second surface points on the top surface where angles formed between lines perpendicular to the top surface at the second surface points and lines through the respective second surface points and the second point light source are less than the critical angle (θ

_c).

13. A method as claimed in claim 10 wherein the member of said providing step has sides and ends connecting the top and bottom surfaces and the method additionally comprises the step of frosting a central section of the sides relative to sections of the sides which are proximate the ends.

14. A method as claimed in claim 10 additionally comprising the step of installing a diffuse reflector facing the bottom surface.

15. A display apparatus having a backlight, said apparatus comprising:

a transparent plastic member exhibiting a critical angle (θ

_c) with respect to air, having opposing and substantially parallel top and bottom surfaces, having opposing and substantially parallel ends, and having first and second cavities through the bottom surface thereof, said member bottom surface, ends, and sides being frosted relative to the top surface, and said member bottom surface being frosted so that surface depth irregularities vary less than 35 microinches;

a liquid crystal display located substantially parallel to and facing said member top surface and spaced apart from said top surface by a distance of at least 0.050 inch;

first and second lamps having first and second light sources, respectively, said first and second lamps being located within the first and second cavities of said member so that the light sources of said first and second lamps are each located approximately a distance D away from said member top surface;

a circuit board located substantially parallel to and facing said member bottom surface;

first and second reflective strips located substantially parallel to and facing said member first and second sides respectively; and

first and second opaque sections located on said member top surface extending perpendicularly away from points opposing said first and second lamp light sources, respectively, for distances greater than D X TAN (θ

_c).

16. An apparatus as claimed in claim 15 additionally comprising a diffuse reflector having a substantially white surface located between said member bottom surface and said circuit board so that said reflector white surface is facing said member bottom surface.

17. An apparatus for providing a source of light emmitted throughout a predetermined area, said apparatus comprising:

a first lamp having a light source therein;

a transparent member exhibiting a critical angle (θ

_c) with respect to air and having a polished top surface relative to an opposing frosted bottom surface, first and second sides substantially parallel to each other and substantially perpendicular to the top and bottom surfaces wherein each of said member first and second sides has first and second end sections relative to a central section and the central sections of the first and second sides are frosted relative to said member top surface and the end sections of said first and second sides, said member having a first cavity therein located proximate a first end of said member, said first lamp being inserted into said first cavity so that said first lamp light source resides inside said member at a distance D₁ from the top surface; and

a first opaque section located on said member top surface opposing said member first cavity so that said opaque section extends toward the central area of said member top surface for a distance greater than D₁ X TAN (θ

_c) from a point opposing the light source.