Front-lit liquid crystal display having brightness enhancing film with microridges which directs light through the display to a reflector

• US 5,608,550 A
• Filed: 01/17/1996
• Issued: 03/04/1997
• Est. Priority Date: 06/24/1994
• Status: Expired due to Term

• Current Assignee: 3M Company
• Original Assignee: 3M Company
• Inventors: Epstein, Kenneth A., Wenz, Robert P.
• Primary Examiner(s): Sikes, William L.
• Assistant Examiner(s): Malinowski, Walter J.
• Application Number:
  US08/578,884
• Time in Patent Office: 412 Days
• Field of Search: 359/40, 359/42, 359/48, 359/49, 359/50, 359/69, 359/599, 359/613, 359/625, 362/26, 362/31, 385/36
• US Class Current: 349/57
• CPC Class Codes: F21V 5/02 of prismatic shape F21V5/04 takes precedence
• CPC Class Codes: G02B 5/0242 by means of dispersed particles
• CPC Class Codes: G02B 5/0284 used in reflection
• CPC Class Codes: G02B 6/0001 specially adapted for lighting devices or systems lighting or signalling on vehicles using light guides B60Q1/00; lighting devices for vehicle dashboards B60Q3/10; lighting devices for vehicle interior using light guides B60Q3/62; lighting devices mounted on the vehicle rear part using light guides F21S43/235; measuring arrangements having light conducting pointers G01D13/265; illumination of liquid crystal displays G02F1/1336; illuminated signs G09F13/00
• CPC Class Codes: G02B 6/0028 Light guide, e.g. taper
• 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: G02B 6/0048 with stepwise taper
• CPC Class Codes: G02F 1/133504 Diffusing, scattering, diffracting elements associated to illuminating devices G02F1/133606
• CPC Class Codes: G02F 1/133616 Front illuminating devices
• CPC Class Codes: G09F 13/0409 Arrangements for homogeneous illumination of the display surface, e.g. using a layer having a non-uniform transparency arrangements of reflectors G09F13/14

Abstract

A front-lit display, having a ridged transparent film thereon. The ridges on the film bend glancing light rays down into the display. The light rays are reflected by a reflector below the display, pass back through the display, and exit the film in a direction substantially normal to the display. Thus, the ridged film enhances the brightness of the display for a given light source.

Claims

1. A front-lit display system, comprising:

a display comprised of a plurality of pixels having front and back major surfaces;

a transparent film having two major opposing surfaces, one smooth and the other having a plurality of parallel ridges, wherein the smooth surface is adjacent the front surface of the display, and wherein the ridges have a pitch greater than one ridge per pixel;

a reflector provided adjacent the back surface of the display; and

a light source for directing light rays onto the film, wherein the light rays enter the film via the ridges, are reflected down through the film by total internal reflection, pass through the display, are reflected by the reflector, pass back through the display, and exit the film, whereby the film enhances the brightness of the display.

2. The system of claim 1, wherein the ridges are each comprised of a first face for accepting the light rays and a second face for reflecting the light rays down toward the display by total internal reflection, and wherein neighboring ridges are separated by a third face parallel to the smooth face of the film.

3. The system of claim 1, wherein the ridges are each comprised of a first face for accepting the light rays and a second face for reflecting the light rays down toward the display by total internal reflection, and wherein neighboring ridges are adjacent each other.

4. The system of claim 1, wherein the light source is comprised of a light tube and a reflector.

5. A front-lit liquid crystal display, comprising:

a liquid crystal display having front and back major surfaces and a plurality of pixels therebetween;

a transparent film having two major opposing surfaces, one smooth and the other having a plurality of parallel ridges, the ridges having a height within the range of from about 5 μ

m to 20 μ

m, the distance between neighboring ridge peaks being within the range of from about 10 to 20 times as great as the height of the ridges, the ridges having a pitch of at least one ridge per pixel, wherein the smooth surface is adjacent the front surface of the display;

a reflector provided adjacent the back surface of the display; and

a light source for directing light rays onto the film, wherein the light rays enter the film via the ridges, are reflected down through the film by total internal reflection, pass through the display, are reflected by the reflector, pass back through the display, and exit the film, whereby the film enhances the brightness of the display.

6. A front-lit display system, comprising:

a display having front and back major surfaces;

a transparent film having two major opposing surfaces, one smooth and the other having a plurality of parallel ridges, wherein the smooth surface is adjacent the front surface of the display;

a reflector provided adjacent the back surface of the display; and

a light source for directing light rays onto the film, wherein the light rays enter the film via the ridges, are reflected down through the film by total internal reflection, pass through the display, are reflected by the reflector, pass back through the display, and exit the film, whereby the film enhances the brightness of the display;

wherein the ridges are each comprised of a first face for accepting the light rays and a second face for reflecting the light rays down toward the display by total internal reflection, neighboring ridges being separated by a third face parallel to the smooth face of the film, and wherein the first face of each ridge forms an angle α

within the range of from about 70°

to 90°

with respect to the smooth surface of the film and the second face of each ridge forms an angle β

within the range of from about 40°

to 50°

with respect to the smooth surface of the film.

7. A front-lit display system, comprising:

a display having front and back major surfaces;

a transparent film having two major opposing surfaces, one smooth and the other having a plurality of parallel ridges, wherein the smooth surface is adjacent the front surface of the display;

a reflector provided adjacent the back surface of the display; and

a light source for directing light rays onto the film, wherein the light rays enter the film via the ridges, are reflected down through the film by total internal reflection, pass through the display, are reflected by the reflector, pass back through the display, and exit the film, whereby the film enhances the brightness of the display;

wherein the ridges are each comprised of a first face for accepting the light rays and a second face for reflecting the light rays down toward the display by total internal reflection, neighboring ridges being adjacent each other, and wherein the first face of each ridge forms an angle α

within the range of from about 5°

to 20°

with respect to the smooth surface of the film and the second face of each ridge forms an angle β

within the range of from about 60°

to 90°

with respect to the smooth surface of the film.

8. The system of claim 7, wherein the distance between adjacent peaks of the ridges is preferably within the range of from about 3 to 10 times greater than the heights of the ridges.

9. A front-lit display system, comprising:

a display having front and back major surfaces;

a transparent film having two major opposing surfaces, one smooth and the other having a plurality of parallel ridges, wherein the smooth surface is adjacent the front surface of the display;

a reflector provided adjacent the back surface of the display; and

a light source for directing light rays onto the film, wherein the light rays enter the film via the ridges, are reflected down through the film by total internal reflection, pass through the display, are reflected by the reflector, pass back through the display, and exit the film, whereby the film enhances the brightness of the display;

wherein the ridges are each comprised of a first face for accepting the light rays and a second face for reflecting the light rays by total internal reflection, and wherein neighboring ridges are separated by a third face which is inclined at an angle within the range of from about 1°

to 3°

with respect to the smooth surface of the film so that the third face is angled toward the light source.

10. The system of claim 9, wherein the first face of each ridge forms an angle α

within the range of from about 70°

to 90°

with respect to the smooth surface of the film, and wherein the second face of each ridge forms an, angle β

within the range of from about 40°

to 50°

with respect to the smooth surface of the film.

11. A front-lit display system, comprising:

a display having front and back major surfaces;

a transparent film having two major opposing surfaces, one smooth and the other having a plurality of parallel ridges, wherein the smooth surface is adjacent the front surface of the display;

a reflector provided adjacent the back surface of the display; and

a light source for directing light rays onto the film, wherein the light rays enter the film via the ridges, are reflected down through the film by total internal reflection, pass through the display, are reflected by the reflector, pass back through the display, and exit the film, whereby the film enhances the brightness of the display, wherein the film has a plurality of parallel grooves therein parallel to the ridges, wherein a groove is provided adjacent each ridge on the side of the ridge opposite the light source.

12. The system of claim 11, wherein the grooves are at least 1/5 as deep as the ridges are high.

13. A front-lit display system, comprising:

a display having front and back major surfaces;

a transparent film having two major opposing surfaces, one smooth and the other having a plurality of parallel ridges, wherein the smooth surface is adjacent the front surface of the display, wherein the ridges are within the range of from about 5 μ

m to 20 μ

m high and the distance between neighboring ridge peaks is within the range of from about 10 to 20 times as great as the heights of the ridges;

a reflector provided adjacent the back surface of the display; and

a light source for directing light rays onto the film, wherein the light rays enter the film via the ridges, are reflected down through the film by total internal reflection, pass through the display, are reflected by the reflector, pass back through the display, and exit the film, whereby the film enhances the brightness of the display.

14. A front-lit display system, comprising:

a display having front and back major surfaces;

a transparent film having two major opposing surfaces, one smooth and the other having a plurality of parallel ridges, wherein the smooth surface is adjacent the front surface of the display;

a reflector provided adjacent the back surface of the display; and

a light source for directing light rays onto the film, the light source comprising a point light source and a light pipe, parallel to the ridges, having a plurality of notches on the side of the pipe opposite the display, wherein light rays enter the film via the ridges, are reflected down through the film by total internal reflection, pass through the display, are reflected by the reflector, pass back through the display, and exit the film, whereby the film enhances the brightness of the display.

15. The system of claim 14, wherein the point light source is a light emitting diode.

16. The system of claim 14, wherein the light pipe has a rectangular cross-section.

17. A front-lit display system, comprising:

a display having front and back major surfaces;

a transparent film having two major opposing surfaces, one smooth and the other having a plurality of parallel ridges, wherein the smooth surface is adjacent the front surface of the display;

a reflector provided adjacent the back surface of the display; and

a light source for directing light rays onto the film, the light source comprising a point light source and a light pipe, parallel to the ridges, the light pipe decreasing in thickness along its length from the end nearer the point light source, the thickness being decreased by a plurality of steps provided in the side of the pipe opposite the display, wherein the light rays enter the film via the ridges, are reflected down through the film by total internal reflection, pass through the display, are reflected by the reflector, pass back through the display, and exit the film, whereby the film enhances the brightness of the display.

18. A front-lit display system, comprising:

a display having front and back major surfaces;

a transparent film having two major opposing surfaces, one smooth and the other having a plurality of parallel ridges, wherein the smooth surface is adjacent the front surface of the display;

a reflector provided adjacent the back surface of the display; and

a light source for directing light rays onto the film at an angle γ

of less than 5°

with respect to the smooth surface of the film, wherein the light rays enter the film via the ridges, are reflected down through the film by total internal reflection, pass through the display, are reflected by the reflector, pass back through the display, and exit the film, whereby the film enhances the brightness of the display.

19. The system of claim 18, wherein the angle γ

is about 2°

.

20. A front-lit display system, comprising:

a display having front and back major surfaces;

a transparent film having two major opposing surfaces, one smooth and the other having a plurality of parallel ridges, wherein the smooth surface is adjacent the front surface of the display;

a reflector provided adjacent the back surface of the display;

a first light source for directing light rays onto the film, wherein the light rays enter the film via the ridges, are reflected down through the film by total internal reflection, pass through the display, are reflected by the reflector, pass back through the display, and exit the film, whereby the film enhances the brightness of the display; and

a second light source, similar to the first light source, provided on an end of the display opposite from the first light source, for directing light rays onto the film, wherein a first face of each ridge forms an angle α

with respect to the smooth surface of the film and second face of each ridge forms an angle β

with respect to the smooth surface of the film, wherein α

=β

.