Thermochromic Capping Layer for LED Color Neutrality
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Solution Overview
Problem
Converting elements used in light-emitting diodes (LEDs) often exhibit a non-neutral color when switched off due to the inherent color of phosphors, leading to light losses and reduced luminous efficiency when switched on, as conventional scattering layers fail to provide a satisfactory solution for neutralizing the color impression without compromising light emission.
Innovation Solution
Incorporating a thermochromic dye or phase change medium as an additional component in the converting element, which changes its optical properties in response to temperature, allowing the element to appear neutral when the LED is off and transparent/colorless when on, thereby minimizing light interference and enhancing luminous efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a scattering capping layer is applied to mask the inherent color of the converting element, then the color neutrality when the LED is off is improved, but light losses occur when the LED is on
Solution Approach 1:
The patent applies a dynamic approach by using a thermochromic capping layer that changes its optical properties (transparency/scattering) in response to temperature changes. When the LED is off and the converting element is cool, the layer scatters light to mask the yellowish phosphor color. When the LED is on and heats up, the thermochromic layer becomes transparent, allowing full light transmission and eliminating light losses.
Solution Approach 2:
The invention changes the optical parameters (transparency, scattering coefficient) of the capping layer by utilizing thermochromic materials whose properties vary with temperature. This allows the same layer to provide different optical functions under different operating conditions, resolving the contradiction between color masking and light transmission.
2Illumination intensity
If a translucent but not completely transparent capping layer is used to reduce visibility of the phosphor color, then the color impression is improved, but light transmission is reduced
Solution Approach 1:
The capping layer dynamically adjusts its transparency based on temperature. In the cold state (LED off), it is translucent to mask the phosphor color. In the hot state (LED on), it becomes completely transparent to maximize light transmission and luminous efficiency, thus resolving the contradiction between color masking and energy efficiency.
Solution Approach 2:
The optical parameters of the capping layer are changed by temperature variation through thermochromic effects, allowing the layer to transition between translucent and transparent states, thereby optimizing both color impression and luminous efficiency under different operating conditions.
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 use of thermochromic dyes or phase change media allows for a neutral color impression when the LED is off and improved light transmission when on, balancing the color appearance and luminous efficiency without the disadvantages of conventional scattering layers.
Implementation Method 1
a (at least one) further component, wherein the further component is either a thermochromic dye or a phase change medium
Implementation Method 2
a (at least one) further component, wherein the further component is either a thermochromic dye or a phase change medium
Implementation Method 3
Many light-emitting diodes emit a blue or bluish light, which has to be converted into a more or less color-neutral light by suitable phosphors
Data Source
AI summary
An LED illumination device includes a wavelength converting element having a matrix material, at least one phosphor, and a thermochromic dye component or a phase change medium component.