Backlight Chromaticity Stabilization via Opposite White LEDs

Solution Overview

Problem

Liquid crystal display devices with LED backlights face issues with luminance and chromaticity changes over time, which are unacceptable in medical and broadcast equipment, as existing solutions do not effectively stabilize chromaticity despite increasing current or duty ratio to maintain luminance.

Innovation Solution

A liquid crystal display panel with a backlight unit comprising two white LEDs, where the chromaticity of each LED is positioned oppositely across a blackbody locus on an xy chromaticity diagram, allowing the drive units to adjust currents to maintain a constant intersection point, thereby stabilizing synthetic chromaticity despite temporal changes.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Illumination intensity

If the supply current to the LED is increased to stabilize luminance, then the luminance is maintained, but the chromaticity changes due to temporal variation

Engineering Contradiction:

ImproveluminanceVSAvoidchromaticity

Core Design Contradiction:

Illumination intensityVSStability of the object's composition

Solution Approach 1:

The backlight unit is divided into multiple independent LED channels (first LED and second LED) with separate drive circuits. This segmentation allows independent control of each LED's current, enabling separate optimization of luminance and chromaticity for each channel while maintaining overall color stability.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The drive circuits dynamically adjust the supply current parameters for each LED based on detected chromaticity values. By changing the current parameters adaptively, the system compensates for temporal variations in LED characteristics and maintains stable chromaticity while preserving luminance.

Inventive Principle:

Principle #35Parameter changes

2Illumination intensity

If the lighting duty ratio is increased to stabilize luminance, then the luminance is maintained, but the chromaticity changes due to temporal variation

Engineering Contradiction:

ImproveluminanceVSAvoidchromaticity

Core Design Contradiction:

Illumination intensityVSStability of the object's composition

Solution Approach 1:

The backlight unit is divided into multiple independent LED channels (first LED and second LED) with separate drive circuits. This segmentation allows independent control of each LED's current, enabling separate optimization of luminance and chromaticity for each channel while maintaining overall color stability.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The drive circuits dynamically adjust the supply current parameters for each LED based on detected chromaticity values. By changing the current parameters adaptively, the system compensates for temporal variations in LED characteristics and maintains stable chromaticity while preserving luminance.

Inventive Principle:

Principle #35Parameter changes

3Device complexity

If a single LED is used for backlight illumination, then the device complexity is low, but the chromaticity changes over time making it unsuitable for medical and broadcast equipment

Engineering Contradiction:

Improvebacklight structureVSAvoidchromaticity stability

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The backlight unit is divided into multiple independent LED channels (first LED and second LED) with separate drive circuits. This segmentation allows independent control of each LED's current, enabling separate optimization of luminance and chromaticity for each channel while maintaining overall color stability.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The control circuit detects the chromaticity values of the light emitted by each LED and uses this feedback information to adjust the supply currents. This closed-loop feedback mechanism ensures that chromaticity variations are compensated in real-time, maintaining stable color reproduction.

Inventive Principle:

Principle #23Feedback

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This configuration prevents changes in synthetic chromaticity of the light emitted from the backlight unit, ensuring consistent display quality even as the LEDs deteriorate, making it suitable for critical applications like medical and broadcast equipment.

Implementation Method 1

a first white light-emitting diode and a second white light-emitting diode that respectively emit white light

Methodology Applied

Scientific EffectLight-emitting diode: Light Emitting Diode

Data Source

PatentUS9024923B2Liquid crystal display panel and liquid crystal display device with backlight chromaticity balance

Publication Date: 2015.05.05 PANASONIC INTELLECTUAL PROPERTY CORP OF AMERICA

AI summary

The liquid crystal display panel includes a liquid crystal display unit, and a backlight unit illuminating the liquid crystal display unit. The backlight unit includes first and second white light-emitting diodes that respectively emit white light, and first and second drive units that respectively supply a current to the first and second white light-emitting diodes. The first and second drive units are respectively configured to be able to adjust supply current to the first and second white light-emitting diodes. Chromaticities of the first and second white light-emitting diodes are of a relationship of being positioned opposite each other across a blackbody locus on an xy chromaticity diagram. The first and second white light-emitting diodes change over time so that, on the xy chromaticity diagram, an intersection point of the blackbody locus and a line that passes through the chromaticities of the first and second white light-emitting diodes becomes constant.