Overcoated LED Filament White Appearance Scattering Layer
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Solution Overview
Problem
Conventional LED filaments appear colored in the unlit state, which is aesthetically undesirable, especially in decorative and general-purpose lamps.
Innovation Solution
An overcoated LED filament design featuring an underlying layer of phosphor material with a colored appearance and an over-coated layer comprising a resinous material loaded with a scattering agent, which appears white when unpowered, minimizing spectral power and luminous flux losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If an LED filament is coated with phosphor material to convert blue light to other wavelengths, then the light conversion efficiency is improved, but the filament appears colored in the unlit state which is aesthetically undesirable
Solution Approach 1:
The coating is divided into two separate layers: an underlying phosphor layer for light conversion and an overcoated scattering layer for aesthetic appearance. This segmentation allows each layer to perform its specific function independently, resolving the contradiction between efficiency and appearance.
Solution Approach 2:
The scattering layer acts as an intermediary between the phosphor layer and the external environment. It mediates the visual appearance by scattering light to create a white appearance while allowing the phosphor layer to maintain its light-converting function underneath.
2Ease of manufacture
If an overcoated layer with scattering agent is added to achieve white appearance, then the aesthetic appearance is improved, but the device complexity increases
Solution Approach 1:
The scattering layer uses standard materials (resinous material with scattering agents like TiO2 or SiO2) where the key parameter is the concentration of scattering agent (5-50 wt%). By controlling this parameter rather than creating entirely new material systems, the complexity is managed while achieving the desired white appearance.
3Ease of manufacture
If the scattering layer is made thicker to enhance white appearance, then the aesthetic appearance is improved, but the lumen loss and radiated power loss increase
Solution Approach 1:
The scattering layer is designed with optimal thickness and scattering agent concentration (5-50 wt%) that provides sufficient white appearance without excessive scattering. This partial action approach achieves the necessary aesthetic effect while minimizing light loss, avoiding the diminishing returns of overly thick coatings.
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 changes the appearance of LED filaments from colored to white while maintaining acceptable performance levels, with minimal lumen and radiated power losses, typically less than 5%, and providing a uniform white appearance across the visible range.
Implementation Method 1
an over-coated layer comprising a resinous material loaded with a scattering agent that causes the LED filament to appear white
Implementation Method 2
one or more LED dies coated with an underlying layer of a phosphor material exhibiting a colored appearance
Data Source
AI summary
An overcoated LED filament includes an LED filament comprising one or more LED dies coated with an underlying layer of a phosphor material exhibiting a colored appearance, and an over-coated layer comprising a resinous material loaded with a scattering agent that causes the LED filament to appear white.