Daylight readable liquid crystal display

• US 6,172,725 B1
• Filed: 05/19/1998
• Issued: 01/09/2001
• Est. Priority Date: 04/11/1995
• Status: Expired due to Term

• Current Assignee: L-3 Communications Corporation (L3Harris Technologies, Inc.)
• Original Assignee: Litton Systems Incorporated
• Inventors: Lengyel, J. Michael
• Primary Examiner(s): Sikes, William L.
• Assistant Examiner(s): NGUYEN, DUNG T
• Application Number:
  US09/081,548
• Time in Patent Office: 966 Days
• Field of Search: 349/104, 349/137, 349/105
• US Class Current: 349/104
• CPC Class Codes: G02F 1/133385 with cooling means, e.g. fans
• CPC Class Codes: G02F 1/133509 Filters, e.g. light shielding masks

Abstract

A daylight readable LCD which may be used to communicate information as high contrast images (static or dynamic, color or monochrome) in bright ambient lighting conditions over a wide temperature range in direct sunlight. A contrast enhancement filter assembly is disposed at the interface between a backlit display and a user. The contrast enhancement filter assembly includes a triple bandpass contrast enhancement filter that preferably passes light efficiently in each of the red, green, and blue primary wavelengths and substantially absorbs all other wavelengths. Display contrast is increased because of the absorption of incident light having wavelengths that differ from the light produced by the internal backlight source within the display. This results in the display having a blacker background and enhanced purity of the color primaries. The display element is disposed generally behind the contrast enhancement filter assembly. An air gap separation is preferably provided between the contrast enhancement filter assembly and the display element to allow a heat conducting medium to flow therebetween to control thermal loading of the display. A fluorescent backlight assembly provides at least about 5,000 fL of illumination. An air gap separation is preferably provided between the display element and the backlight to allow a heat conducting medium to flow therebetween to control thermal loading of the display. The ratio of output light to reflected incident ambient light is at least about 5:1.

Claims

1. A daylight readable display for use in bright ambient light comprising:

(a) a backlight source for providing initial transmitted light;

(b) a display element adjacent the backlight source for modulating the initial transmitted light to display images; and

(c) a selective-pass front filter in front of the display element, having the characteristics;

(1) absorbing heat energy in a solar radiant spectrum of incident ambient light;

(2) transmitting the modulated initial transmitted light from the display element; and

(3) selectively filtering incident ambient light;

wherein the combination of backlight source, display element, and filter reduce heating of the display element and provide a ratio of output light to reflected incident ambient light of at least about 5;

1.

2. The display of claim 1 wherein the selective-pass filter absorbs 20% or more of incident ambient light responsible for thermal solar loading.

3. The display of claim 2 wherein at least one surface of the display element has an anti-reflective coating.

4. The display of claim 1 wherein the selective-pass filter is a triple-pass filter.

5. The display of claim 1 wherein the selective-pass filter passes about 70% or more of incident light at generally blue, green, and red wavelengths.

6. The display of claim 1 wherein the selective-pass filter absorbs at least about 70% of the incident light having wavelengths generally between blue and green light and between green and red light.

7. The display of claim 1 wherein the selective-pass filter reflects less than 2% of incident ambient light.

8. The display of claim 1, wherein the display element includes:

(a) a first polarizer for polarizing light;

(b) a liquid crystal cell adjacent the first polarizer for selectively altering the orientation of the E-field of incident light polarized by the first polarizer; and

(c) a second polarizer adjacent the liquid crystal cell for polarizing light altered by the liquid crystal cell.

9. The display of claim 1 wherein at least two surfaces of the display element have an anti-reflective coating.

10. The display of claim 1 wherein at least one surface of the selective-pass filter has an anti-reflective coating.

11. The display of claim 1 wherein the selective-pass filter absorbs about 30% of the incident ambient light responsible for thermal loading.

12. The display of claim 1 wherein the selective-pass filter absorbs at least 50% of the incident ambient light.

13. The display of claim 1 wherein the selective-pass filter reflects less than about 0.3% of incident ambient light.

14. The display of claim 1 wherein the ratio of output light to reflected incident ambient light is at least 10:

1.

15. The display of claim 1 wherein the ratio of output light to reflected incident ambient light is at least about 20:

1.