Daylight readable liquid crystal display

• US 5,754,262 A
• Filed: 07/28/1997
• Issued: 05/19/1998
• 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 (Northrop Grumman Corporation)
• Inventors: Lengyel, J. Michael
• Primary Examiner(s): Sikes, William L.
• Assistant Examiner(s): NGUYEN, TIEP HUU
• Application Number:
  US08/901,683
• Time in Patent Office: 295 Days
• Field of Search: 359/74, 359/66, 359/68, 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 display that is daylight readable in ambient light, external to the display exceeding about 5,000 foot candles of incident illumination, including:

(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 front filter adjacent the display element and having the characteristics of;

(1) absorbing at least about 30% of incident ambient light;

(2) reflecting less than about 2% of incident ambient light;

(3) transmitting the modulated initial transmitted light as output light;

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

1.

2. The daylight readable display of claim 1, wherein the backlight source generates at least about 5,000 fL.

3. The daylight readable 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.

4. The daylight readable display of claim 3, wherein at least one exposed surface of the display element has an anti-reflection coating.

5. The daylight readable display of claim 3, wherein at least two exposed surfaces of the display element have an anti-reflection coating.

6. The daylight readable display of claim 4 or 5, wherein at least one of the polarizers is a linear polarizer.

7. The daylight readable display of claim 1, wherein at least one surface of the filter has an anti-reflection coating.

8. The daylight readable display of claim 1, wherein the filter absorbs about 30% of the incident ambient light responsible for thermal loading.

9. The daylight readable display of claim 1, wherein the filter is a triple-pass filter.

10. The daylight readable display of claim 9, wherein the filter passes about 70% of incident light at generally blue, green, and red wavelengths.

11. The daylight readable display of claim 9, wherein the filter absorbs at least about 70% of incident light having wavelengths generally between blue and green light and between green and red light.

12. The daylight readable display of claim 1, wherein the front filter has the characteristic of absorbing at least about 50% of incident ambient light.

13. The daylight readable display of claim 1, wherein the front filter has the characteristic of reflecting less than about 0.3% of incident ambient light.

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

1.

15. The daylight readable display of claim 14, wherein the ratio of output light to reflected incident ambient light is at least about 20:

1.

31. The display of claims 1, 16, 23, 27, or 28, wherein the display element is a liquid crystal display.

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

(a) a back light source for providing initial transmitted light,

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

(c) a selective-pass front filter in front of the display element having a characteristic of transmitting the modulated initial transmitted light from the display element and selectively filtering incident ambient light; and

(d) a thermal conduction medium disposed between said front filter and the display element to reduce heating of the display element by the incident ambient light

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

1.

17. The display of claim 16, wherein the backlight source generates at least about 5,000 fL.

18. The display of claim 16, wherein the selective-pass filter absorbs 20% or more of incident ambient light responsible for thermal solar loading.

19. The display of claim 16, wherein said selective-pass front filter is a triple-pass filter.

20. The display of claim 16, wherein said selective-pass front filter passes about 70% of incident light at generally blue, green, and red wavelengths.

21. The display of claim 16, wherein said selective-pass front filter absorbs at least about 70% of the incident light having wavelengths generally between blue and green light and between green and red light.

22. The display of claim 16, wherein said selective-pass front filter reflects less than about 2% of incident ambient light.

24. The daylight readable display of claim 16 or 23, wherein the thermal conduction medium is air.

25. The daylight readable display of claim 24, wherein the backlight source is spaced a minimum of about 1 mm from the display element.

26. The daylight readable display of claim 24, wherein the display element is spaced a minimum of about 1 mm from the filter.

23. 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;

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

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

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

(3) selectively filtering the incident ambient light; and

(d) a thermal conduction medium disposed between said display element and said front filter to reduce heating of the display element by the absorbed heat energy;

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

1.

27. A display that is daylight readable in ambient light, external to the display, exceeding about 5,000 foot-candles of incident illumination, including:

(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 front filter adjacent the display element and having the characteristics of;

(1) absorbing at least about 50% of incident ambient light;

(2) reflecting less than about 0.3% of incident ambient light;

(3) transmitting the modulated initial transmitted light as output light;

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

1.

28. A display that is daylight readable in ambient light external to the display exceeding about 5,000 foot-candles of incident illumination, including:

(a) a fluorescent backlight source for providing initial transmitted light of at least about 5,000 fL;

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

(1) a first polarizer for polarizing light;

(2) 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

(3) a second polarizer adjacent the liquid crystal cell for polarizing light altered by the liquid crystal cell;

(c) a homogenous composition triple-pass front filter adjacent the display element and having the characteristics of;

(1) absorbing at least about 50% of incident ambient light;

(2) reflecting less than about 0.3% of incident ambient light;

(3) transmitting the modulated initial transmitted light as output light;

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

1.

29. A method of displaying daylight readable images in ambient light, external to the display exceeding about 5,000 foot candles of incident illumination, including the steps of:

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

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

(c) providing a front filter adjacent the display element and having the characteristics of;

(1) absorbing at least about 30% of incident ambient light;

(2) reflecting less than about 2% of incident ambient light;

(3) transmitting the modulated initial transmitted light as output light;

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

1.

30. The method of claim 29, wherein the display element is a passive matrix liquid crystal display.