LED Filament Scattering Layer for Lower Phosphor Use
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Solution Overview
Problem
The high cost and undesirable yellowish appearance of LED-filaments in the 'off-state due to the use of expensive manganese-activated fluoride phosphors, which are required in large quantities to achieve desired brightness and color rendering index (CRI Ra), and the challenge of achieving uniform color emission in both forward and backward directions.
Innovation Solution
Configuring LED-filaments with a partially light-transmissive substrate and LED chips that emit more light in the forward direction, using a higher brightness narrowband red phosphor on the front face and a less expensive broadband red phosphor on the back face, and optionally incorporating a light scattering layer to reduce phosphor usage and improve appearance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If manganese-activated fluoride phosphors are used to achieve high brightness and high CRI Ra, then the color rendering index and brightness are improved, but the manufacturing cost increases significantly
Solution Approach 1:
The patent applies different phosphor materials to different locations: narrowband red phosphors (manganese-activated fluoride) are applied only to the front face where they are most needed for high CRI Ra, while broadband red phosphors are used on the back face and in combination with green phosphors. This localized application of high-performance materials reduces overall phosphor usage and cost while maintaining the required optical performance.
Solution Approach 2:
The patent segments the phosphor application into distinct layers and locations: a first photoluminescence layer with narrowband red phosphor on the front face, a second photoluminescence layer with broadband red and green phosphors, and optional third and fourth layers on the back face. This segmentation allows optimization of material usage in different regions, reducing the total amount of expensive narrowband red phosphor needed.
2Illumination intensity
If large quantities of manganese-activated fluoride phosphors are used to achieve desired brightness, then the brightness is improved, but the manufacturing cost increases significantly
Solution Approach 1:
The patent concentrates narrowband red phosphor application to specific locations (front face) where it provides maximum benefit for CRI Ra, rather than uniformly applying it throughout. This localized concentration reduces the total quantity of expensive phosphor material needed while maintaining brightness and color rendering performance.
Solution Approach 2:
The patent uses composite phosphor systems combining narrowband red phosphors with broadband red and green phosphors in different layers and locations. This composite approach allows the system to achieve high brightness and CRI Ra using smaller quantities of expensive narrowband materials supplemented by more economical broadband materials.
3Stability of the object's composition
If the same phosphor-impregnated encapsulant is applied to both faces of the substrate, then uniform color emission is achieved in forward and backward directions, but the cost of manufacture increases
Solution Approach 1:
The patent applies different phosphor compositions to different faces: the front face receives narrowband red phosphors for optimal CRI Ra performance, while the back face uses broadband red and green phosphors. This differentiated approach maintains sufficient color uniformity between faces while reducing the quantity of expensive narrowband phosphor needed.
Solution Approach 2:
The patent modifies the phosphor composition parameters between front and back faces, using different phosphor types and ratios optimized for each location's specific optical requirements. This parameter differentiation allows cost reduction through selective material usage while maintaining overall color consistency.
4Illumination intensity
If narrowband red phosphors are used to achieve high CRI Ra, then the color rendering index is improved, but the absorption capability is substantially lower requiring 5 to 20 times greater usage amount
Solution Approach 1:
The patent strategically places narrowband red phosphors only where they are most effective (front face near the LED chip) rather than distributing them uniformly. This localized placement maximizes their impact on CRI Ra while minimizing the total quantity required, overcoming their low absorption capability limitation.
Solution Approach 2:
The patent segments the red phosphor function between narrowband and broadband types, with narrowband phosphors handling the critical CRI Ra contribution on the front face and broadband phosphors providing supplementary red emission on the back face and in combination layers, reducing overall narrowband phosphor usage.
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
Reduces phosphor usage by up to 90% while maintaining brightness and CRI Ra, and improves the 'off-state' appearance to white, enhancing consumer appeal and reducing manufacturing costs.
Implementation Method 1
a light scattering layer that is in direct contact with and covers at least the photoluminescence material, wherein the light scattering layer comprises particles of light scattering material
Implementation Method 2
one or more photoluminescence materials (typically inorganic phosphor materials), which absorb a portion of the blue light emitted by the LED and re-emit light of a different color (wavelength)
Data Source
AI summary
A light emitting device comprising: a substrate; a plurality of LED chips on a front face of the substrate; a photoluminescence material layer comprising broadband green to red photoluminescence material that is in contact with and covers each of the plurality of LED chips; and a light scattering layer comprising particles of light scattering material that is in contact with and covers the photoluminescence material layer; wherein there is no photoluminescence material layer on a back face of the substrate; and wherein, when the device is in an off-state, the color of the light scattering layer resembles the color of the light scattering material.