LED Backlight Color Control Using Integrated Photodetectors
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Solution Overview
Problem
LED-based backlight systems for LCDs face challenges in maintaining precise color and intensity uniformity due to variations in light output among individual LEDs, leading to color shifts and reduced performance over time, especially in applications like FSC LCDs where precise color control is critical.
Innovation Solution
Incorporating a photo detector, such as a photodiode or LED, to monitor the intensity of each color LED and using a controller to adjust the drive current based on measured ratios of photo currents, ensuring precise color and intensity control, even in the presence of ambient light, without requiring costly waveguides or optics that reduce display brightness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If LED arrays are calibrated during manufacturing to produce uniform brightness and color, then illumination uniformity is improved, but the system degrades with use as LEDs age at different rates
Solution Approach 1:
The patent incorporates photodetectors that continuously monitor the light output from individual LEDs and provide feedback signals to a control system. This feedback mechanism enables real-time detection of LED output variations and aging characteristics, allowing the system to dynamically adjust drive currents to maintain uniform illumination and color stability throughout the operational lifetime of the display.
Solution Approach 2:
The system transitions from static calibration performed once during manufacturing to dynamic adjustment during operation. The control system continuously modifies drive currents based on real-time photodetector measurements, adapting to aging LEDs and maintaining uniformity without requiring manual recalibration or replacement of components.
2Measurement precision
If photo detectors are added to monitor LED intensity, then color and intensity control precision is improved, but device complexity increases
Solution Approach 1:
The patent integrates photodetectors and control circuitry directly into the display structure, merging multiple functions into unified components. The photodetectors are positioned to monitor LED output within the existing display architecture, and the control system consolidates calibration and operational control functions, reducing the need for separate external monitoring and control devices.
Solution Approach 2:
The control system performs multiple functions including calibrating individual LED brightness during manufacturing, monitoring real-time light output through photodetectors, adjusting drive currents to compensate for aging, and maintaining color uniformity across the display. This multi-functional approach eliminates the need for separate dedicated systems for each function.
3Illumination intensity
If LED arrays use local dimming to improve contrast ratio, then image quality is improved, but illumination uniformity becomes more difficult to maintain
Solution Approach 1:
The patent divides the LED array into multiple independently controllable zones or regions, each with its own photodetector and control circuitry. This segmentation enables local dimming operations on specific display regions while maintaining uniformity control within each zone, allowing the system to achieve high contrast ratios through selective dimming without sacrificing overall illumination uniformity.
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 solution allows for continuous monitoring and adjustment of LED light output, maintaining uniform color and intensity across the display, enhancing performance and reducing the need for special optics, while being applicable to various LED-based lighting systems, including FSC LCDs and solid-state lamps.
Implementation Method 1
Each LED driver IC includes a photodiode, or other light detecting device, integrated into the driver IC to measure the intensity of light produced by each LED
Implementation Method 2
LEDs provide a number of advantages over traditional light sources
Data Source
AI summary
Illumination devices and related systems and methods are disclosed that can be used for LCD (Liquid Crystal Display) backlights, LED lamps, or other applications. The illumination devices can include a photo detector, such as a photodiode or an LED or other light detecting device, and one or more LEDs of different colors. A related method can be implemented using these illumination devices to maintain precise color produced by the blended emissions from such LEDs. One application for the illumination devices is backlighting for FSC (Field Sequential Color) LCDs (Liquid Crystal Displays). FSC LCDs temporally mix the colors in an image by sequentially loading the red, green, and blue pixel data of an image in the panel and flashing the different colors of an RGB backlight. Precise and uniform color temperature across such a display can be advantageously maintained by continually monitoring ratios of photodiode currents induced by the different colored LEDs in each illumination device as each color is flashed.