LED Filament Phosphor Layering for Lower Cost and White Off-State
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Solution Overview
Problem
LED-filaments using manganese-activated fluoride phosphors face high manufacturing costs due to the high usage amount required and the phosphors' high expense, and they exhibit an undesirable yellowish appearance in the off-state, deterring potential customers.
Innovation Solution
Configure the LED-filaments with a partially light-transmissive substrate to direct more blue excitation light to the front face, allowing for a higher brightness narrowband red phosphor on the front and a less expensive broadband red phosphor on the back, reducing the overall phosphor usage and incorporating a light scattering layer to improve the off-state 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 quality is improved, but the manufacturing cost increases significantly due to higher phosphor usage amount and higher phosphor material expense
Solution Approach 1:
The patent divides the phosphor application into two separate layers: a first photoluminescence layer containing narrowband red phosphor applied directly to the LED chip, and a second photoluminescence layer containing broadband red phosphor applied over the first layer. This segmentation allows the expensive narrowband phosphor to be used only where it is most needed (directly absorbing blue light from the LED), while the cheaper broadband phosphor handles the remaining wavelength conversion, thereby reducing overall manufacturing cost while maintaining high brightness and CRI Ra performance.
Solution Approach 2:
The patent applies different phosphor materials with different properties to different locations and functions within the LED structure. The narrowband red phosphor is specifically positioned where it can most effectively convert blue light to red light (directly on the LED chip), while the broadband phosphor is applied in the outer layer for additional wavelength conversion. This local optimization of phosphor placement and selection reduces the total amount of expensive narrowband phosphor needed while maintaining the desired optical performance.
2Stability of the object's composition
If equal amounts of phosphor are applied to both faces of the substrate to ensure uniform color emission, then the color consistency is improved, but the usage amount of expensive manganese-activated fluoride phosphor doubles
Solution Approach 1:
The patent segments the phosphor application into functional layers rather than applying equal amounts uniformly to both faces. The first photoluminescence layer with narrowband red phosphor is applied directly to the LED chip where it provides the primary wavelength conversion, while the second photoluminescence layer with broadband phosphor is applied over it. This layered segmentation allows for optimized phosphor distribution that maintains color consistency through the combined effect of both layers rather than requiring equal phosphor amounts on both substrate faces.
Solution Approach 2:
The patent uses a composite photoluminescence structure combining two different phosphor materials (narrowband red phosphor and broadband red phosphor) in separate layers. This composite approach allows the narrowband phosphor to provide precise red emission for high CRI Ra while the broadband phosphor supplements the wavelength conversion, achieving color consistency through the synergistic combination of materials rather than through symmetric phosphor distribution.
3Ease of manufacture
If a light scattering layer is incorporated to improve the off-state appearance to white color, then the visual appearance is improved, but the device structure becomes more complex
Solution Approach 1:
The patent merges the light scattering function with the existing photoluminescence layers by incorporating a light scattering material directly into the second photoluminescence layer that already contains the broadband red phosphor. This integration combines multiple functions (wavelength conversion and light scattering for improved off-state appearance) into a single layer, avoiding the need for separate additional structural components and thereby minimizing the increase in device complexity while achieving the desired visual improvement.
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 a more desirable white color, enhancing market appeal and reducing production costs.
Implementation Method 1
incorporating a light scattering layer to improve the off-state appearance
Implementation Method 2
LED-filaments whose visual appearance resemble the filament of a traditional incandescent lamp... comprise COG (Chip-On-Glass) devices having a plurality of low-power LED chips mounted on one face of a light-transmissive glass/ceramic substrate. Front and back faces of the light-transmissive substrate are coated with a phosphor-impregnated encapsulant
Data Source
AI summary
An LED-filament comprising: a substrate; a plurality of LED chips on a front face of the substrate; a photoluminescence material layer comprising at least one 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 a light scattering material that is in contact with and covers the photoluminescence material layer and covers at least a part of a back face of the substrate; wherein, when the LED-filament is in an off-state, the color of the light scattering layer resembles the color of the light scattering material.