LED Street Light Glare Reduction via Spectral Tuning
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Solution Overview
Problem
Outdoor light fixtures, such as street lights, often cause glare due to unsuitable luminance distribution and extreme luminance contrast, leading to discomfort for drivers and pedestrians, and there is a need for alternatives to mercury-based light sources that reduce glare effectively.
Innovation Solution
A light emitting device with a light emission peak wavelength between 400 nm and 490 nm and a fluorescent material with a peak wavelength between 570 nm and 680 nm, achieving a correlated color temperature of 1,950 K or less, an average color rendering index of 51 or more, and glare indices Ls1/L and Ls2/L of 0.493 or less and 1.082 or less, respectively, to minimize glare and discomfort.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If high luminance LEDs are used for outdoor illumination, then illumination efficiency is improved, but glare and discomfort to drivers and pedestrians increase
Solution Approach 1:
The patent applies parameter changes by carefully selecting and controlling the spectral characteristics of the light emitting device. Specifically, it uses a light emitting element with peak wavelength 400-490 nm excited by blue LED, combined with fluorescent materials having specific peak wavelengths (570-680 nm for first fluorescent material, 460-550 nm for second fluorescent material), to achieve a correlated color temperature of 1950K or less. This spectral parameter optimization reduces the proportion of short-wavelength light that causes glare while maintaining illumination efficiency.
Solution Approach 2:
The patent employs composite materials by combining multiple fluorescent materials with the light emitting element. It uses a first fluorescent material (peak 570-680 nm) and a second fluorescent material (peak 460-550 nm) together with the blue LED-excited light emitting element, creating a composite light source with optimized spectral distribution. This composite approach enables simultaneous achievement of high illumination efficiency and reduced glare by balancing different wavelength components.
2Use of energy by moving object
If mercury-based light sources are used for outdoor lighting, then illumination performance is improved, but environmental safety deteriorates due to mercury regulation
Solution Approach 1:
The patent adopts LED-based light emitting devices that are environmentally safe and have long operational life, replacing mercury-based HID lamps. Although LED initial cost may be higher, their extended service life (25,000-50,000 hours) and lack of hazardous materials make them more economical and environmentally friendly over time, aligning with the Minamata Convention on Mercury.
Solution Approach 2:
The patent changes the fundamental illumination parameter from mercury arc discharge to LED-based electroluminescence with optimized spectral characteristics. By controlling the emission spectrum through selective fluorescent materials to achieve 1950K or less correlated color temperature, it replicates the warm white light quality of traditional outdoor lighting while eliminating mercury content entirely.
3Use of energy by moving object
If blue LED with narrow spectrum is used, then energy efficiency is improved, but color rendering index deteriorates
Solution Approach 1:
The patent uses composite fluorescent materials to broaden the emission spectrum while maintaining LED energy efficiency. By combining a first fluorescent material (peak 570-680 nm, covering red-orange region) with a second fluorescent material (peak 460-550 nm, covering cyan-blue-green region), it creates a comprehensive spectral coverage that improves color rendering index (Ra≥51) while preserving the energy efficiency of LED excitation.
Solution Approach 2:
The patent applies local quality by strategically placing fluorescent materials with specific emission characteristics to supplement the blue LED spectrum. The first fluorescent material (570-680 nm peak) targets the red-orange wavelength region, while the second fluorescent material (460-550 nm peak) fills the cyan-green gap, creating localized spectral enhancements that collectively improve overall color rendering without compromising energy efficiency.
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
The solution effectively reduces glare and discomfort by optimizing the light emission spectrum and color temperature, providing improved visibility and comfort for users of outdoor light fixtures.
Implementation Method 1
a light emitting element having a light emission peak wavelength in a range of 400 nm or more and 490 nm or less
Implementation Method 2
a first fluorescent material having a light emission peak wavelength in a range of 570 nm or more and 680 nm or less
Data Source
AI summary
A light emitting device comprises a light emitting element having a light emission peak wavelength in a range of 400 nm or more and 490 nm or less and a first fluorescent material having a light emission peak wavelength in a range of 570 nm or more and 680 nm or less, and emits light having a correlated color temperature being 1,950 K or less, an average color rendering index Ra being 51 or more, a full width at half maximum of a light emission peak having a maximum light emission intensity in a light emission spectrum of the light emitting device being 110 nm or less, and a first glare index Ls1/L that is a ratio of a first effective radiance Ls1 to a luminance L being 0.493 or less, wherein Ls1 and L are as defined in the disclosure.