Directional LED Display Emission With Uniform White Color
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Solution Overview
Problem
Conventional LEDs emit light in a wide range of angles, which can lead to directional emission challenges and color uniformity issues over angle in display applications.
Innovation Solution
The development of nanowire LEDs with specific optical structures and geometries that facilitate directional far-field patterns while maintaining good color uniformity, achieved by configuring red, green, and blue LEDs to emit light within a specific solid angle with minimal chromaticity difference from a white point.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If conventional LEDs are used with wide angle emission, then light output is high, but directional emission is poor and color uniformity deteriorates
Solution Approach 1:
The patent modifies the physical parameters of the LED structure, specifically the cavity depth and reflective layer positioning, to transform the emission pattern from wide-angle Lambertian to directional. By adjusting the optical path length and reflectivity parameters, the LED achieves concentrated light output in a specific direction while maintaining high overall luminosity.
Solution Approach 2:
The invention introduces a vertical cavity dimension beneath the light-emitting region, creating a controlled optical path through the third dimension. This vertical dimension allows for precise manipulation of light directionality by positioning reflective layers at specific depths, thereby controlling the angular distribution of emitted light.
2Ease of operation
If directional emission is achieved, then light directionality is improved, but color uniformity over angle deteriorates
Solution Approach 1:
The patent optimizes the cavity depth parameter to be approximately one-quarter of the emission wavelength, creating a resonant condition that enhances directional emission while maintaining consistent color characteristics. This specific parameter tuning ensures that the optical path difference does not cause wavelength-dependent phase shifts that would degrade color uniformity.
Solution Approach 2:
The invention employs a uniform reflective layer with consistent optical properties throughout the cavity structure. This homogeneity in the reflective characteristics ensures that all wavelengths are treated equally, preventing color separation and maintaining uniform color output across the directional emission pattern.
3Ease of operation
If additional optics are used for directional emission, then directionality is improved, but device complexity increases
Solution Approach 1:
The patent integrates the directional emission function directly into the LED structure by merging the light-emitting region with an underlying optical cavity and reflective layer. This consolidation eliminates the need for separate external optical components such as lenses or reflectors, achieving directional control while minimizing device complexity.
Solution Approach 2:
The optical cavity structure serves multiple functions simultaneously: it provides mechanical support, defines the emission direction, and maintains color uniformity. This multi-functionality reduces the need for additional specialized components, thereby simplifying the overall device architecture while achieving the desired directional emission performance.
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 approach enables directional light emission with improved color uniformity, ensuring that white light emitted by the display has a chromaticity difference less than 0.01 from the white point in any direction within the solid angle of emission.
Implementation Method 1
optical interference within each LED causes light to be emitted in a preferential direction
Implementation Method 2
a reflective region located an optical distance less than 1 μm from the light emitting region
Data Source
Figure 1A~1D
Figure 2A~2C
Figure 3A~3C
AI summary
A full color display includes multiple pixels and has a white point, a direction of emission and a solid angle of emission around the direction of emission characterized by a half-cone angle θ. Each pixel includes: a sub-pixel including a red LED having a first geometry emitting red light into a range of emission angles, such that a fraction of the power emitted within the solid angle of emission is at least 1.2 * (1-cos(θ) 2); a sub-pixel including a green LED having a second geometry emitting green light into a range of emission angles, such that a fraction of the power emitted within the solid angle of emission is at least 1.2 * (1-cos(θ) 2); and a sub-pixel including a blue LED emitting blue light into a range of emission angles, such that a fraction of the power emitted within the solid angle of emission is at least 1.2 * (1-cos(θ) 2). The LEDs are configured such that, in any direction within the solid angle of emission, white light emitted by the display has a chromaticity difference Du'v' from the white point of the display which is less than 0.01.