Backlighting of nematic curvilinear aligned phase liquid crystal display panels

• US 5,283,563 A
• Filed: 03/20/1990
• Issued: 02/01/1994
• Est. Priority Date: 03/20/1990
• Status: Expired due to Fees

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Finch, William W., Miller, Stuart C., Davenport, John M., Allen, Gary R., Hansler, Richard L.
• Primary Examiner(s): Oberley, Alvin E.
• Assistant Examiner(s): Mengistu, Amare
• Application Number:
  US07/496,395
• Time in Patent Office: 1,414 Days
• Field of Search: 340/784, 340/716, 350/345, 359/53, 359/71, 359/88, 359/98
• US Class Current: 349/77
• CPC Class Codes: G02F 1/133615 Edge-illuminating devices, i.e. illuminating from the side
• CPC Class Codes: G02F 1/13476 in which at least one liquid crystal cell or layer assumes a scattering state

Abstract

A liquid crystal display (LCD) is provided with a source of backlighting which augments reflected incident light to provide increased contrast. A liquid crystal cell which does not contain dye, but becomes clear when a field is applied, is sandwiched in back of a liquid crystal cell with a dye and electrically connected so that when the front liquid crystal cell is turned ON to make selected portions of it transparent, the back liquid crystal cell is OFF so that corresponding portions of it are highly reflecting. No voltage is allowed to be applied across nonselected portions of the front liquid crystal and a voltage is applied across corresponding nonselected portions of the back liquid crystal making the nonselected portions of the back liquid crystal clear, producing a display of high contrast. Sandwiched to the rear of the back liquid crystal cell is a clear plastic wedge which is edge lighted. The edge lighted wedge only appears bright in the areas where the voltage on the back liquid crystal cell is OFF or not applied thereto.

Claims

1. A backlighted liquid crystal display comprising:

a first liquid crystal cell and a second liquid crystal cell disposed in a substantially aligned position relative to one another, said first liquid crystal cell having a first transparent substrate coincident with a front surface of said liquid crystal display and sealed with a second transparent substrate to form a first chamber containing a first liquid crystal, and said second liquid crystal cell being integral with said second transparent substrate and containing an encapsulated second liquid crystal, said first and second liquid crystal cells each including electrodes deposited on said first and second transparent substrates and connected to a source of voltage for applying a voltage across selected portions of said first and second liquid crystals;

switching means connecting said electrodes to said source of voltage so that when a voltage is applied across a selected portion of said first liquid crystal causing the selected portion to become transparent, voltage is prevented from being applied across a corresponding portion of said second liquid crystal so that the corresponding portion is diffusely reflecting, said switching means further preventing voltage from being applied across nonselected portions of said first liquid crystal and applying a voltage across corresponding nonselected portions of said second liquid crystal, said switching means control of said nonselected portions associated with said first liquid crystal making the nonselected portions of said second liquid crystal clear; and

an edge lighted clear wedge in optical contact with said second liquid crystal cell, light propagated within said wedge being internally reflected except where said second liquid crystal is diffusely reflecting, whereby incident light which is transmitted through said first liquid crystal cell and reflected by said second liquid crystal is augmented by light from said edge lighted plastic wedge.

2. A liquid crystal display recited in claim 1 wherein said third transparent substrate and said wedge are integrally formed of a moldable thermoplastic.

3. A liquid crystal display recited in claim 1 wherein said edge lighted wedge comprises:

a transparent wedge having back and front surfaces, at least one of which is converging, and a generally rectangular shaped edge between said surfaces, said front surface being co-extensive with an area of said second liquid crystal cell to be illuminated;

a high efficiency light source; and

at least one light guide optically coupling light from said light source to said rectangular shaped edge so that light entering the wedge is internally reflected from the back surface and emitted from said front surface where said second liquid crystal cell is diffusely reflecting.

4. A liquid crystal display recited in claim 3 wherein said wedge is formed of a plastic material.

5. A backlighted liquid crystal display as recited in claim 3 further comprising a diffuse reflective coating applied to said back surface.

7. A liquid crystal display as recited in claim 1 wherein said second transparent substrate and said wedge are integrally formed of a moldable thermoplastic, said plastic wedge having back and front surfaces, at least one of which is converging, and a generally rectangular shaped edge between said surfaces.

8. A liquid crystal display as recited in claim 7 further comprising;

a high efficiency light source; and

at least one light guide optically coupling light from said light source to said rectangular shaped edge so that light entering the plastic wedge is internally reflected from the back surface and emitted from said front surface where said second liquid crystal cell is diffusely reflecting.

6. A backlighted liquid crystal display comprising:

a first liquid crystal cell and a second liquid crystal cell, said first liquid crystal cell containing a first liquid crystal with a dye, and said second liquid crystal cell containing a second liquid crystal with no dye, said first and second liquid crystal cells each including electrodes connected to a source of voltage for applying a voltage across selected portions of said first and second liquid crystals;

switching means connecting said electrodes to said source of voltage so that when a voltage is applied across a selected portion of said first liquid crystal causing the selected portion to become transparent, voltage is prevented from being applied across a corresponding portion of said second liquid crystal so that the corresponding portion is diffusely reflecting, said switching means further being effective for preventing voltage from being applied across nonselected portions of said first liquid crystal and applying a voltage across corresponding nonselected portions of said second liquid crystal, said switching means control of said nonselected portions associated with said first liquid crystal making the nonselected portions of said second liquid crystal clear; and

an edge lighted clear plastic wedge in optical contact with said second liquid crystal cell, light propagated within said wedge being internally reflected except where said second liquid crystal is diffusely reflecting, whereby incident light which is transmitted through said first liquid crystal cell and reflected by said second liquid crystal is augmented by light from said edge lighted plastic wedge.

9. A backlighted liquid crystal display, comprising:

a first liquid crystal cell and a second liquid crystal cell disposed in an essentially aligned manner relative to one another, said first liquid crystal cell having a first transparent substrate coincident with a front surface of said liquid crystal display and sealed with a second transparent substrate to form a first chamber containing a first liquid crystal, and said second liquid crystal cell having a second chamber containing a second liquid crystal associated therewith, said second chamber being formed between a second pair of transparent substrates, said transparent substrates having electrodes disposed thereon such that voltage can be selectively applied across portions of said first and second liquid crystals;

switching means connecting said electrodes to a source of said voltage, said switching means being effective so that, when voltage is applied across a selected portion of said first liquid crystal rendering said selected portion transparent, voltage is prevented from being applied to a corresponding adjacent portion of said second liquid crystal thereby rendering said corresponding adjacent portion to be diffusely reflective, said switching means further being effective such that, when said selected portion is energized, voltage is prevented from being applied across non-selected portions of said first liquid crystal and coincident therewith, voltage is applied to corresponding non-selected adjacent portions of said second liquid crystal thereby rendering said non-selected adjacent portions transparent; and

a source of backlight disposed in optical contact with said second liquid crystal, said backlight source capable of providing a substantially uniform light across said second liquid crystal such that light propagated within said backlight source is internally reflected except where said second liquid crystal is diffusely reflective and whereby, incident light which is transmitted through said first liquid crystal cell and reflected by said second liquid crystal, is augmented by light from said backlight source.

10. A backlighted liquid crystal display as set forth in claim 9 wherein said second pair of transparent substrates is comprised of said second transparent substrate associated with said first liquid crystal cell and a third transparent substrate.

11. A backlighted liquid crystal display as set forth in claim 9 wherein said backlight source is an edge lighted wedge in optical contact with said second liquid crystal.