Liquid crystal display with holographic diffuser and prism sheet on viewer side

• US 5,629,784 A
• Filed: 04/12/1994
• Issued: 05/13/1997
• Est. Priority Date: 04/12/1994
• Status: Expired due to Term

• Current Assignee: First Chicago/NBD Bank N.A., Guardian Industries Corporation (KOCH Industries Incorporated)
• Original Assignee: OIS Optical Imaging Systems, Inc. (KOCH Industries Incorporated)
• Inventors: Vergith, Nicholas D., Abileah, Adiel
• Primary Examiner(s): NOT, DEFINED
• Assistant Examiner(s): NOT, DEFINED
• Application Number:
  US08/229,337
• Time in Patent Office: 1,127 Days
• Field of Search: 359/40, 359/41, 359/42, 359/69, 359/609, 359/599, 385/901
• US Class Current: 349/112
• CPC Class Codes: G02F 1/133504 Diffusing, scattering, diffracting elements associated to illuminating devices G02F1/133606
• CPC Class Codes: G02F 1/133615 Edge-illuminating devices, i.e. illuminating from the side

Abstract

A backlight liquid crystal display including a collimated backlight for illuminating a display panel having a liquid crystal layer sandwiched between rear and front polarizers, the panel including an optical refracting film and a diffuser laminated adjacent the front surface of the panel. The refracting film and light scattering diffuser may be either exterior or interior the front polarizer, but on the viewer side of the liquid crystal layer. The optical system of the refracting faceted film along with the diffuser maintains the resolution of the display, improves the contrast ratio over a wide range of viewing angles, reduces its ambient light reflectively, reduces color shifting, substantially eliminates inversion, and enlarges the effective viewing zone of the display.

Claims

1. In a backlit liquid crystal display which includes a backlight assembly for directing light toward a display panel, said display panel including a liquid crystal layer and being capable of providing an image to a remotely positioned viewer, the improvement comprising:

an optical system disposed on the viewer side of said liquid crystal layer, said optical system including a film means for substantially enlarging the effective viewing zone of said liquid crystal display and for providing substantial uniformity of contrast ratio and color uniformity in the viewing zone, and wherein said film means has a plurality of optical facets therein; and

wherein said optical system includes a diffuser, and wherein said diffuser and said film means are affixed to said panel and sandwiched between a first polarizer and said liquid crystal layer so as to reduce the ambient diffused reflection of said display panel.

2. A backlit normally white twisted nematic liquid crystal display capable of providing an image to a remotely positioned viewer, comprising:

a display panel including a plurality of pixels, each said pixel being comprised of a pair of driving electrodes sandwiching a twisted nematic liquid crystal layer therebetween;

a backlight for directing at least partially collimated light toward said display panel;

an optical system affixed to said panel including a holographic diffuser and a refracting means disposed on the viewer side of said twisted nematic liquid crystal layer, said optical system providing said display with a contrast ratio of at least about 70;

1 along the 0°

vertical viewing axis at horizontal viewing angles up to about ±

60°

, and whereby said refracting means maintains the resolution of the displayed image; and

wherein said display includes means for obtaining a specular 30°

reflectance of less than about 2%, and a diffused 30°

reflectance of less than about 5%.

3. The display of claim 2, wherein said optical system provides said display with a contrast ratio of at least about 90:

1 along the 0°

vertical viewing axis at horizontal viewing angles up to about ±

60°

.

4. The display of claim 2, wherein said display has a specular 30°

reflectance of less than about 0.3%, and a diffused 30°

reflectance of less than about 3%.

5. A backlit liquid crystal display comprising:

a backlight for directing rays of light toward a display panel;

said display panel including a liquid crystal layer and means for applying a voltage to said liquid crystal layer;

a holographic diffuser and a faceted film means for substantially collimating ambient light directed toward said liquid crystal layer, said diffuser and said faceted film means affixed to said display panel on the viewer side of, said liquid crystal layer, wherein said display panel when white substantially collimated light is directed toward said panel from said backlight has at least the following viewing characteristics;

a) a specular reflectance at about 0°

vertical, 30°

horizontal of less than about 2.0%;

b) a diffused reflectance at about 0°

vertical, 30°

horizontal of less than about 4%; and

c) a contrast ratio of at least about 60;

1 at viewing angles of one of;

(i) about 0°

vertical, ±

60°

horizontal; and

(ii) about 0°

horizontal, ±

40°

vertical.

6. The display of claim 5, wherein the 30°

diffused reflectance is less than about 1.2%.

7. In a backlit liquid crystal display which includes a backlight assembly for directing light toward a display panel, said display panel including a liquid crystal layer and being capable of providing an image to a remotely positioned viewer, the improvement comprising:

an optical system disposed on the viewer side of said liquid crystal layer, said optical system including a film means for substantially enlarging the effective viewing zone of said liquid crystal display and for providing substantial uniformity of illumination with respect to contrast ratio and color uniformity, and wherein said film means has a plurality of optical facets therein; and

wherein said backlight directs substantially collimated light toward said display panel, and said facets of said film means face said backlight and said light liquid crystal layer, said facets reducing the display'"'"'s ambient light reflection and improving the displayed image'"'"'s uniformity over a large range of viewing angles, and wherein said display further comprises a diffuser disposed exterior said film means, said film means thereby being disposed between said liquid crystal layer and said diffuser and wherein said diffuser is holographic and includes a roughened light scattering surface facing said viewer.

8. The display of claim 7, wherein said film means is laminated to the exterior surface of a first polarizer with said facets abutting said exterior surface of said first polarizer, and

wherein said diffuser is affixed to said film means, said film means being sandwiched between said diffuser and said first polarizer.

9. The display of claim 7, wherein said optical facets are substantially triangular in nature.

10. The display of claim 7, wherein said display is a normally white twisted nematic type display and has a contrast ratio of at least about 80:

1 at one of;

(i) along the 0°

vertical viewing axis at horizontal viewing angles of about ±

60°

; and

(ii) along the 0°

horizontal viewing axis at vertical viewing angles of about -30° and

+40°

; and

wherein said display has a specular 15°

reflectance of less than about 2.0% and a diffused 30°

reflectance of less than about 4%.

11. A backlit liquid crystal display for displaying an image having improved viewing characteristics to a viewer, the display comprising:

a collimating backlight for directing substantially collimated light toward a display panel, said display panel including;

(i) a twisted nematic liquid crystal layer sandwiched between a front polarizer and a rear polarizer, said front polarizer being located on the viewer side of said liquid crystal layer;

(ii) electrodes for applying a voltage across said liquid crystal layer;

(iii) a light redirecting or redistributing means disposed on the viewer side of said liquid crystal layer, said light redirecting or redistributing means for enabling;

(a) substantially no backscatter in both transmission directions so as to reduce reflections in both directions; and

(b) in the transmission direction from said backlight toward the viewer, said light redirecting means diffusing light emitted from said backlight over a wide range of angles toward the viewer so as to improve contrast; and

wherein as a result of said light redirecting or redistributing means, said display has a specular 30°

reflectance of less than about 0.3%, a diffused 30°

reflectance of less than about 1.2%, and a contrast ratio at viewing angles of about 0°

vertical, ±

30°

horizontal, of at least about 60;

1.

12. A method of displaying an image to a viewer using a twisted nematic liquid crystal display with reduced reflection and an enlarged viewing zone, the method comprising the steps of:

providing a collimating backlight;

emitting collimated light from the backlight toward the twisted nematic liquid crystal display;

selectively applying voltage across a liquid crystal layer in the display by way of electrodes;

redistributing the light after it exits the liquid crystal layer using a light redistributing system disposed on the viewer side of the liquid crystal layer;

substantially eliminating backscatter in both transmission directions using the redistributing system so as to reduce reflections in both directions;

diffusing light traveling from the liquid crystal layer toward the viewer over a wide range of angles using the redistributing system in order to improve contrast;

as a result of the distributing system, displaying an image to the viewer having a contrast ratio at viewing angles of about 0°

vertical, ±

30°

horizontal, of at least about 60;

1; and

.

as a result of the distributing system, reducing specular 30°

reflectance to less than about 0.3% and diffused 30°

reflectance to less than about 1.2%.