Colour liquid crystal display devices

• US 20030011728A1
• Filed: 07/01/2002
• Published: 01/16/2003
• Est. Priority Date: 07/10/2001
• Status: Active Grant

• Current Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Original Assignee: Koninklijke Philips N.V.
• Inventors: Battersby, Stephen J.
• Granted Patent: US 7,154,574 B2
• Time in Patent Office: Days
• US Class Current: 349/106
• CPC Class Codes: G02F 1/133514 Colour filters
• CPC Class Codes: G02F 1/13475 in which at least one liquid crystal cell or layer is doped with a pleochroic dye, e.g. GH-LC cell G02F1/13476 takes precedence
• CPC Class Codes: G02F 1/1362 Active matrix addressed cells G02F1/134336, G02F1/134363 take precedence

Abstract

A colour liquid crystal display device has an array of display pixels (10) for modulating input light and an array of associated colour filter elements (40) which comprise electro-optic filtering elements switchable electrically between a colour filtering state in which a required colour output is produced and a state in which they are substantially transparent to the input light. Such switching can be used beneficially, for example to reduce power consumption by sacrificing full colour output and allowing the brightness level of a back light to be decreased in view of the increased optical efficiency of the pixels when the filter elements are in their transparent state, or to improve viewability in the case of a reflective display used in poor ambient lighting.

Claims

1. A colour liquid crystal display device comprising an array of display pixels each of which is driveable to modulate a light input and has associated therewith a respective colour filter element for colouring the modulated light, wherein the colour filter elements comprise electro-optic elements which are electrically switchable at least between a state providing colour filtering and a state in which they are substantially transparent to the input light.

2. A device according to claim 1, wherein the device includes a light source providing the light input to the display pixels whose light output level can be adjusted and wherein the light source is controlled so as to produce a lower light output level upon the colour filter elements being switched to their substantially transparent state.

3. A device according to claim 1 or claim 2, wherein the colour filter elements are switchable collectively.

4. A device according to claim 1 or claim 2, wherein the colour filter elements of one colour are switchable independently of the colour filter elements of a different colour.

5. A device according to any one of the preceding claims, wherein the colour filter elements are switchable to an intermediate state in which slight colouring of the modulated light is obtained.

6. A device according to any one of the preceding claims, wherein the colour filter elements comprise electro-optic colour filtering material disposed between facing electrodes to which switching voltages are applied, the electrodes being connected to a control circuit operable selectively to control the voltage applied to the electrodes.

7. A device according to claim 6, wherein the electro-optic colour filtering material comprises a guest-host liquid crystal material containing dye.

8. A device according to claim 7, wherein the display pixels are arranged in rows and columns and wherein the colour filter elements are provided as colour filter strips, each strip being of one colour and associated with a respective row or column of display pixels, and the strips being organised in repeating groups of different colours.

9. A device according to claim 8, wherein the display pixels are defined by opposing electrodes carried on the facing surfaces of two, spaced, substrates between which liquid crystal material is disposed, and wherein the colour filter elements are carried on the outside surface of one of the substrates.

10. A device according to claim 8, wherein the display pixels are defined by opposing electrodes carried on the facing surfaces of two, spaced, substrates between which liquid crystal material is disposed, and wherein the colour filter elements are carried on the inner surface of one of the substrates.

11. A device according to claim 10, wherein the guest-host material comprises droplets dispersed in a polymer matrix.