Phosphor Layer Colored Beads Off-State Color
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Solution Overview
Problem
The off-state color of phosphor layers, such as YAG phosphor layers used in conjunction with blue LEDs, appears yellow or yellow-green when exposed to ambient white light, which is not aesthetically pleasing, especially in applications like overhead lighting where the front surface is visible.
Innovation Solution
Incorporating glass beads with diameters slightly larger than the phosphor layer thickness, where some beads contain magenta or cyan pigments or quantum dots, into a transparent binder with YAG phosphor, allowing these beads to protrude and change the off-state color when exposed to white light, while maintaining the on-state white light emission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a YAG phosphor layer is applied over blue LED dies to create white light, then the on-state white light emission is achieved, but the off-state color appears yellow or yellow-green which is not aesthetically pleasing
Solution Approach 1:
The patent applies composite materials by combining YAG phosphor particles with colored glass beads (containing pigments or quantum dots) and transparent binder to form a multi-component phosphor layer. This composite structure allows the layer to maintain its white light emission function while adding color control capability through the colored beads that reflect or emit specific wavelengths under ambient light, thereby resolving the aesthetic issue of yellow off-state appearance without fundamentally changing the manufacturing process
Solution Approach 2:
The patent applies local quality by incorporating colored glass beads with specific optical properties into the phosphor layer to selectively modify the off-state color appearance. The colored beads are distributed within the phosphor layer to locally add color characteristics (magenta, cyan, or other hues) that counteract the yellow appearance under ambient light, while maintaining the overall white light emission function when LEDs are active
2Illumination intensity
If colored beads with magenta or cyan pigments are added to the phosphor layer to adjust off-state color, then a wide range of off-state colors including neutral shades can be achieved, but there is a potential 20% reduction in efficiency due to light blockage
Solution Approach 1:
The patent applies parameter changes by adjusting the concentration, size, and color composition of glass beads in the phosphor layer to optimize the balance between off-state color appearance and on-state light transmission efficiency. By controlling the bead parameters (such as using smaller beads or optimizing their distribution), the design achieves diverse off-state colors while minimizing the 20% efficiency loss through careful parameter selection
3Loss of energy
If transparent beads are added to allow blue light to pass through and maintain efficiency, then light transmission is improved, but the off-state color control capability is reduced
Solution Approach 1:
The patent applies merging by combining transparent beads (for light transmission) with colored glass beads (for color control) within the same phosphor layer matrix. This hybrid approach merges the functional benefits of both bead types: transparent beads maintain blue light transmission and overall efficiency, while colored beads provide off-state color customization. The synergistic combination resolves the contradiction between maintaining efficiency and achieving color control
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 approach allows for a wide range of off-state colors, including neutral shades, without significantly affecting the on-state color or efficiency, with a potential 20% reduction in efficiency due to light blockage by magenta and cyan beads, and transparent beads help maintain efficiency by allowing blue light to pass through.
Implementation Method 1
The YAG phosphor emits a yellow light (also sometimes characterized as a yellow-green light) when energized by the blue light
Implementation Method 2
Some beads contain a dye, a powder, or other form of pigment to make some beads appear magenta and other beads appear cyan under white light
Implementation Method 3
the beads contain quantum dots or other wavelength shifting material that causes the beads to emit magenta or cyan under white light
Implementation Method 4
Other beads are clear. In another embodiment, the beads contain quantum dots or other wavelength shifting material
Data Source
AI summary
LED dies, emitting blue light, are provided on a first support substrate to form a light emitting layer. A mixture of a transparent binder, yellow phosphor powder, magenta-colored glass beads, and cyan-colored glass beads is printed over the light emitting surface. The mixture forms a wavelength conversion layer when cured. The beads are sized so that the tops of the beads protrude completely through the conversion layer. When the LED dies are on, the combination of the yellow phosphor light and the blue LED light creates white light. When the LEDs are off, white ambient light, such as sunlight, causes the conversion layer to appear to be a mixture of yellow light, magenta light, and cyan light. The percentage of the magenta and cyan beads in the mixture is selected to create a desired off-state color, such as a neutral color, of the conversion layer for aesthetic purposes.