Backlight Support Posts and Optical Sensors for Uniform Illumination
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Solution Overview
Problem
Direct-lit backlights in electronic devices often suffer from non-uniform light distribution due to variations in the distance between light-emitting diodes and the diffuser layer, leading to unwanted intensity variations across the display.
Innovation Solution
The implementation of an array of backlight cells with light sources and cavity reflectors, supported by transparent or white polymer support posts that maintain a fixed distance between the diffuser and the printed circuit, along with optical sensors to measure and adjust pixel gain profiles for uniform illumination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If direct-lit backlight units are used with locally dimmable LEDs, then dynamic range is enhanced, but light uniformity deteriorates due to variations in distance between LEDs and diffuser layer
Solution Approach 1:
Support posts are introduced as intermediary elements between the printed circuit board and the diffuser layer. These posts maintain a precise, fixed separation distance that ensures uniform light distribution while preserving the local dimming capability of individual LED zones.
Solution Approach 2:
The separation distance between the LED array on the printed circuit board and the diffuser layer is controlled as a critical parameter. By maintaining this distance within a specific range through support posts, the patent achieves uniform light output while preserving local dimming functionality.
2Illumination intensity
If support posts are used to maintain fixed distance between diffuser and printed circuit, then light uniformity is improved, but device complexity increases
Solution Approach 1:
The patent employs support posts that can be easily integrated into the manufacturing process. The posts are positioned, adhesive is applied, and the diffuser is attached - a simple sequence that adds minimal complexity while achieving the desired uniformity.
Solution Approach 2:
The support posts are simple, inexpensive polymer structures that serve their function of maintaining separation distance. Their simplicity and low cost make them an economical solution despite adding structural elements to the assembly.
3Illumination intensity
If optical sensors are added to measure and adjust pixel gain profiles, then light uniformity is improved through dynamic compensation, but device complexity increases
Solution Approach 1:
Optical sensors are positioned to detect the actual light output from each backlight cell. This feedback information is used to dynamically adjust pixel gain profiles, compensating for any remaining non-uniformities and ensuring consistent illumination across the display.
Solution Approach 2:
The system dynamically adjusts pixel gain parameters based on optical sensor measurements. By modifying the gain profile of individual pixels in response to measured light intensity variations, the system achieves uniform illumination while maintaining the ability to adapt to manufacturing tolerances and aging effects.
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 ensures consistent backlight intensity across the display, reducing hotspots and dark areas by dynamically compensating for variations in the separation distance between the diffuser and the printed circuit, thereby enhancing image quality.
Implementation Method 1
Direct-lit backlight units have arrays of light-emitting diodes that emit light vertically through the display
Implementation Method 2
a cavity reflector that reflects light from the light source outwardly through a diffuser
Implementation Method 3
The optical sensors may each include a light-emitting device such as a light-emitting diode and a light detector. The optical sensors can measure light from the light-emitting diode that has reflected from the diffuser
Data Source
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AI summary
An electronic device may have a display with a backlight (42). The backlight provides backlight illumination for an array of pixels (24) that is displaying images. The backlight includes an array of cells (38C). Each cell contains a light source (38) with one or more light-emitting diodes (38D) and a cavity reflector (68) that reflects light from the light source outwardly through a diffuser (34) for use in forming the backlight illumination. The light sources are mounted to a printed circuit (60). Support posts (90) on the printed circuit are used to maintain the diffuser at a fixed distance (H) from the printed circuit. Sensors (104) on the printed circuit are used to measure separation distances between the printed circuit and diffuser. Adjustments to pixel gain profiles can be made based on the measured separation distances to maintain uniform illumination.