Patterned Reflectors for Uniform Backlight Brightness
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Solution Overview
Problem
Direct-lit backlights for LCDs face challenges in achieving uniform brightness and minimizing display thickness due to optical losses and 'hot spots' caused by the distance between LEDs and diffuser plates, leading to increased overall thickness and undesirable optical losses.
Innovation Solution
The implementation of a backlight design featuring a substrate with light sources, a reflective layer, and patterned reflectors with specific thickness profiles and geometries, along with a diffusive layer containing hollow glass beads, which enhances light distribution and hides light sources, thereby reducing thickness and improving brightness uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a diffuser plate or film is positioned at a distance from the LEDs to achieve desired light uniformity and avoid hot spots, then brightness uniformity is improved, but the overall display thickness increases
Solution Approach 1:
The patent transitions from a conventional planar diffuser plate to a three-dimensional microlens array structure. Each microlens is positioned at a specific height above the LED, creating a vertical dimension for light manipulation. This 3D configuration allows the optical components to be closer to the LED while still achieving effective light diffusion and uniformity, thereby reducing the overall display thickness compared to traditional 2D diffuser plate arrangements.
Solution Approach 2:
Instead of using a single uniform diffuser plate, the patent employs an array of individual microlenses, each tailored to the specific light emission characteristics of its corresponding LED. Each microlens can be independently optimized for its local region, allowing precise control over light distribution patterns. This localized optimization enables effective hot spot elimination and brightness uniformity achievement with reduced optical distance, thus minimizing display thickness.
2Length of stationary object
If the optical distance between LEDs and diffuser plate is decreased to reduce display thickness, then display thickness is reduced, but optical losses increase
Solution Approach 1:
The patent replaces the traditional mechanical/optical system of a large-distance diffuser plate with a micro-scale lens array system. The microlenses, being much smaller and positioned closer to the LEDs, can effectively collect and redirect light with minimal optical path length. This substitution of the optical configuration reduces the optical distance while maintaining or improving light utilization efficiency, thereby reducing both display thickness and optical losses simultaneously.
Solution Approach 2:
The patent changes key optical parameters including the focal length, diameter, and spacing of the microlenses to optimize performance at reduced distances. By carefully selecting these parameters, the microlens array can achieve effective light diffusion and uniformity distribution even when positioned very close to the LED sources. This parameter optimization enables the system to maintain low optical losses while minimizing the optical distance and overall display thickness.
3Reliability
If individual LEDs are turned off to improve dynamic contrast ratio, then dynamic contrast is improved, but light uniformity deteriorates due to minimal impact from LED light spread
Solution Approach 1:
The patent segments the light diffusion function into multiple independent microlenses, each associated with a specific LED. When an LED is turned off for local dimming, its corresponding microlens stops contributing light to that region, creating a sharper light cutoff. This segmentation allows individual LED control to have a more pronounced effect on local light distribution, enabling dynamic contrast improvement while maintaining better light uniformity compared to conventional backlights where LED light spread causes uniformity degradation when LEDs are individually controlled.
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 design results in thinner, more efficient direct-lit backlights with improved light recycling and reduced 'hot spots, achieving uniform brightness across the display while minimizing overall thickness.
Implementation Method 1
a first reflective layer on the substrate
Implementation Method 2
a plurality of patterned reflectors over the plurality of light sources. Each patterned reflector is aligned with a corresponding light source and includes a thickness profile
Implementation Method 3
a diffusive layer on the light guide plate. The diffusive layer includes hollow glass beads
Data Source
AI summary
A backlight includes a substrate, a plurality of light sources proximate the substrate, a first reflective layer on the substrate, and a plurality of patterned reflectors over the plurality of light sources. Each light source includes a size measured in a plane parallel to the substrate. Each patterned reflector is aligned with a corresponding light source and includes a thickness profile. The thickness profile includes a substantially flat section and a curved section extending from and surrounding the substantially flat section. The substantially flat section varies in thickness by no more than plus or minus 20 percent of an average thickness of the substantially flat section. The substantially flat section includes a size in a plane parallel to the substrate equal to or greater than the size of each light source.