White LED Backlight Using Preformed Phosphor Platelets
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Solution Overview
Problem
Existing white light LEDs for LCD backlighting face challenges in achieving color uniformity due to variations in phosphor thickness, density, and spectral distribution, leading to low color gamut and light transmission, as well as nonuniform color across the screen.
Innovation Solution
The use of preformed red and green phosphor platelets, precisely controlled in thickness and density, affixed over a blue LED to create a consistent white light with ideal RGB components, ensuring uniform color emission and matching the spectral requirements of LCD filters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If YAG phosphor is coated on blue LED to create white light, then white light is produced, but color gamut and light transmission are reduced due to poor matching with RGB filters
Solution Approach 1:
The patent applies local quality by using different phosphor materials for different wavelength regions. Instead of a single YAG phosphor coating, the invention uses red phosphor (K2SiF6:Mn4+) and green phosphor (β-SiAlON:Eu2+) with specific characteristics tailored to match the transmission characteristics of red and green color filters in LCDs, thereby optimizing color gamut and light transmission for each spectral region.
Solution Approach 2:
The patent employs composite materials by combining multiple phosphor types (red phosphor and green phosphor) on the blue LED chip. This composite phosphor structure enables the generation of white light with optimized spectral distribution that better matches the RGB color filter characteristics, improving both color gamut and light transmission compared to single-phosphor solutions.
2Power
If phosphor thickness and density are increased to improve color conversion, then more white light is produced, but color uniformity deteriorates due to variations across the LED surface
Solution Approach 1:
The patent applies preliminary action by pre-forming phosphor plates with precisely controlled thickness and density before mounting them on the LED chip. This pre-forming process ensures uniform phosphor properties across the entire plate surface, eliminating variations that would occur with conventional coating methods and thereby maintaining color uniformity while achieving high white light output.
Solution Approach 2:
The patent replaces the mechanical coating process (which creates thickness variations) with a precision fabrication process for phosphor plates. By substituting the coating mechanism with a controlled plate formation process, the invention achieves uniform phosphor thickness and density across the entire active area, ensuring consistent color output.
3Ease of manufacture
If blue LED variations are tolerated to reduce production costs, then manufacturing is simpler, but white light color points vary across the backlight
Solution Approach 1:
The patent applies parameter changes by selecting phosphor materials with specific emission characteristics and optimizing their thickness and composition to compensate for blue LED variations. The red phosphor (K2SiF6:Mn4+) and green phosphor (β-SiAlON:Eu2+) are chosen for their ability to provide stable color output that can mask variations in the blue LED wavelength and intensity, thereby maintaining consistent white light color points.
4Stability of the object's composition
If deep backlight boxes are used to improve color mixing, then color uniformity improves, but device size increases and cost increases
Solution Approach 1:
The patent applies preliminary action by pre-forming phosphor plates with precisely controlled thickness and uniform phosphor distribution before mounting on the LED chip. This pre-characterization ensures that color mixing is optimized at the source, eliminating the need for deep backlight boxes and complex mixing optics to achieve color uniformity.
Solution Approach 2:
The patent extracts the color mixing function from the backlight box structure and relocates it to the phosphor plate itself. By incorporating the color conversion and mixing characteristics directly into the phosphor plate material and structure, the invention eliminates the need for additional space dedicated to color mixing, thereby reducing backlight box depth.
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 results in high color gamut, high light transmission, and consistent white points across the LCD screen, eliminating the need for complex color mixing and reducing production costs, while allowing for precise control of RGB components to achieve accurate image reproduction.
Implementation Method 1
A white light emitting diode includes a blue light emitting diode and red and green phosphors. The red phosphor may be K2SiF6:Mn4+ and the green phosphor may be beta-SiAlON:Eu2+.
Implementation Method 2
A white light emitting diode includes a blue light emitting diode and red and green phosphors
Data Source
AI summary
A white light LED for use in backlighting or otherwise illuminating an LCD is described where the white light LED comprises a blue LED over which is affixed a preformed red phosphor platelet and a preformed green phosphor platelet. In one embodiment, to form a platelet, a controlled amount of phosphor powder is placed in a mold and heated under pressure to sinter the grains together. The platelet can be made very smooth on all surfaces. A UV LED may also be used in conjunction with red, green, and blue phosphor plates. The LED dies vary in color and brightness and are binned in accordance with their light output characteristics. Phosphor plates with different characteristics are matched to the binned LEDs to create white light LEDs with a consistent white point for use in backlights for liquid crystal displays.