LED Package Yellow Ring Reduction via Intermediary Layer
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Solution Overview
Problem
Conventional LED package structures suffer from the yellow ring phenomenon due to total reflection of blue light at the phosphor sheet's side region, leading to non-uniform color emission.
Innovation Solution
The introduction of a first translucent layer with a refractive index between 1 and that of the phosphor sheet, positioned on the ring-shaped region of the phosphor sheet, reduces total reflection and enhances color uniformity by using an auxiliary phosphor sheet in conjunction with the primary phosphor sheet.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If blue light passes through the side region of the phosphor sheet, then the light emitting function is achieved, but total reflection occurs causing the yellow ring problem
Solution Approach 1:
The patent introduces a first translucent layer with refractive index n1 where 1 < n1 < n2 (n2 being the refractive index of the phosphor sheet) as an intermediary between the phosphor sheet and air. This intermediate refractive index gradient reduces the abrupt refractive index difference, thereby minimizing total internal reflection of blue light at the phosphor sheet's side region and eliminating the yellow ring effect while preserving light emission.
Solution Approach 2:
The patent modifies the refractive index parameter by introducing a translucent layer with a specific refractive index range (between 1 and the phosphor sheet's refractive index). This parameter change creates a gradual transition in optical properties, reducing total internal reflection and improving color uniformity without compromising the LED's light emitting function.
2Device complexity
If the phosphor sheet is used alone, then the structure is simple, but color uniformity is poor due to the yellow ring phenomenon
Solution Approach 1:
The first translucent layer serves as an intermediary optical element that improves color uniformity by reducing total internal reflection. Although it adds a layer to the structure, the patent demonstrates that this single intermediate layer effectively eliminates the yellow ring problem while maintaining relatively simple overall device complexity.
3Illumination intensity
If the refractive index difference between phosphor sheet and air is large, then the optical contrast is high, but total reflection increases causing yellow ring
Solution Approach 1:
The first translucent layer with intermediate refractive index acts as an optical mediator that reduces the abrupt refractive index step between the high-index phosphor sheet and air. This gradual transition minimizes total internal reflection losses while preserving the necessary optical contrast for effective light emission.
Solution Approach 2:
The patent changes the refractive index parameter profile by introducing a translucent layer with refractive index n1 where 1 < n1 < n2. This creates a stepped refractive index gradient that reduces total reflection losses at the phosphor sheet interface while maintaining adequate optical contrast for light emission.
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 configuration effectively minimizes the yellow ring issue and improves the color uniformity of the LED package structure, increasing luminous flux by up to 16.67%.
Implementation Method 1
the blue light emitted from the LED chip and passing through the side region of the phosphor sheet has a large incident angle with respect to the light emitting surface of the phosphor sheet. Furthermore, the difference of refractive index between the phosphor sheet and air is large, thereby resulting in the blue light being totally reflected from the light emitting surface of the phosphor sheet
Implementation Method 2
The phenomenon of the yellow ring is usually appeared as the light emitted from the LED chip and passing through a center region of the phosphor sheet and a side region of the phosphor sheet
Data Source
AI summary
An LED package structure includes a substrate, an electrode layer and an insulating layer in a coplanar arrangement and disposed on the substrate, an LED chip mounted on the electrode layer and the insulating layer, a phosphor sheet covering entirely a top surface of the LED chip, a first translucent layer disposed on a light emitting surface of the phosphor sheet, and a reflective housing covering the side surfaces of the LED chip and the side surfaces of the phosphor sheet. The light emitting surface has a central region and a ring-shaped region surrounding the central region. The first translucent layer covers at least 60% of an area of the ring-shaped region. A refractive index of the first translucent layer is larger than one and is smaller than that of the phosphor sheet. A top surface of the reflective housing is substantially flush with the light emitting surface.