Redundant backlight for liquid crystal displays

Abstract

A redundant LED backlight and method for controlling the same. At least two plurality of LEDs are used to create a backlight where any individual set of LEDs may be driven at power level P to provide the desired overall luminance for the backlight. If two plurality of LEDs are used, then the LEDs may be driven simultaneously at one-half P during normal operations until a failure has been detected in one of the plurality of LEDs. In alternate embodiments, four plurality of LEDs may be used and driven simultaneously at one-fourth P during normal operations until a failure has been detected in one of the plurality of LEDs. The LEDs may be in edge-lit, direct-lit, or any combination of these two orientations. Upon failures, only one plurality of LEDs may be used to provide operation of the LED backlight and any associated LCD device.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application claims priority to U.S. Application No. 61 / 353,986, filed Jun. 11, 2010, titled Redundant Backlight for Liquid Crystal Displays, which is incorporated herein by reference.TECHNICAL FIELD[0002]Disclosed embodiments relate generally to an LED backlight system for a liquid crystal display device.BACKGROUND OF THE ART[0003]Liquid Crystal Displays (LCDs) contain several layers which work in combination to create a viewable image. A backlight is used to generate the rays of light that pass through what is commonly referred to as the LCD stack, which typically contains several layers that perform either basic or enhanced functions. The most fundamental layer within the LCD stack is the liquid crystal material, which may be actively configured in response to an applied voltage in order to pass or block a certain amount of light which is originating from the backlight. The layer of liquid crystal material is divided into many smal...

AI Technical Summary

Benefits of technology

[0010]Exemplary embodiments provide a light source for a display device having prominent color reproducibility. Exemplary embodiments also provide a light source for a display device enabling thin and compact display production continuously over extended use periods. In order to ensure color reproducibility and performance, the backlight of an electronic display should preferably perform satisfactorily at all times.

[0013]The system may include a device for monitoring the luminance produced by the first and / or second array of LEDs. The monitoring device may include predetermined operational standards for the display. When the monitoring device detects that the display has fallen below the predetermined standard for luminance, the monitoring system may send a signal to one or both control modules. If the first array of LEDs were the only source of illumination, the control modules can then switch to the second array of LEDs as there may have been a failure in the first array. The second or redundant set of LEDs can be utilized seamlessly, thus ensuring continuous operation of the LCD without the need for costly and time consuming repairs of the backlight system.

[0014]Alternatively, the first and second array of LEDs may be powered concurrently. Operating the LCD in this manner allows the two LED arrays to operate at ½ the wattage while supplying the same amount of illumination. This is noteworthy as LED efficiency (sometimes measured as lumens per watt) is inversely related to temperature and by powering each LED at a lower wattage less heat is generated and the LEDs function at higher efficiency. If one array were to fail, the other array could adequately illuminate the LCD.

Problems solved by technology

The light which is passing through each subpixel typically originates as “white” (or broadband) light from the backlight, although in general this light is far from being uniform across the visible spectrum.

When used for extended periods of time and / or outdoors, durability of the components especially the illumination sources such as LEDs can become an issue.

If the backlight system should fail completely or operate at a less than optimal level, then the LCD will not perform satisfactorily.

While this may be a simple inconvenience when LCDs are used for entertainment purposes, when used for information or data displays this can be very costly.

In these applications, when there is a failure of the backlight, the LCD may no longer display the important information for the vehicle / aircraft and controls may cease to operate.

These situations can be undesirable not only to the passengers of the vehicle / aircraft, but also other soldiers who are counting on this part of the mission.

LEDs, however, have a limited life span, and eventually their luminance will degrade until little or no luminance is generated.

Some LEDs may quickly fail simply due to a manufacturing defect or may fail due to shock / forces applied to the aircraft or ground vehicle.

This is expensive, and is often time consuming.

This is typically even more costly, and involves extensive manual labor.

This complete disassembly is not only labor intensive, but must be performed in a clean room environment and involves the handling of expensive, delicate, and fragile components that can be easily damager or destroyed, even with the use of expensive specialized tools, equipment, fixtures, and facilities.

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