Tailored Phosphor Layers for Uniform LCD Backlight Color
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Solution Overview
Problem
Existing LCD backlight systems fail to maintain consistent color output across the screen due to varying light attenuation by LCD layers versus wavelength, even when white points of white light LEDs are matched, leading to non-uniform color perception.
Innovation Solution
Tailoring the phosphor layer thickness and density over blue LEDs to adjust blue light leakage, ensuring that shorter wavelength blue LEDs leak more blue light to compensate for greater attenuation, while maintaining consistent red and green light components, resulting in uniform white points across the backlight.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the phosphor layer thickness and density are made uniform across all blue LEDs, then the manufacturing process is simple, but the color output becomes non-uniform due to wavelength-dependent attenuation by LCD layers
Solution Approach 1:
The patent applies local quality by varying the phosphor layer characteristics (thickness and/or density) according to the specific dominant wavelength of each blue LED bin. LEDs with shorter dominant wavelengths (420-440nm) receive thicker or denser phosphor layers to increase blue light conversion, while LEDs with longer dominant wavelengths (440-460nm) receive thinner or less dense phosphor layers. This localized customization compensates for the wavelength-dependent attenuation by LCD layers, ensuring uniform color output across the entire display.
2Illumination intensity
If the phosphor layer is tailored to each blue LED bin to achieve uniform color output, then color uniformity is improved, but the manufacturing complexity and cost increase
Solution Approach 1:
The patent implements preliminary action by pre-characterizing blue LEDs according to their dominant wavelengths and organizing them into bins before phosphor layer application. This preliminary classification allows the manufacturing process to efficiently apply the appropriate phosphor layer characteristics to each bin without requiring complex real-time adjustments. The bins are established in advance, and corresponding phosphor layer parameters are predetermined, streamlining the overall manufacturing process while achieving uniform color output.
3Use of energy by moving object
If blue LEDs with shorter dominant wavelengths are used, then more blue light is available to compensate for attenuation, but the white point of the LED shifts and causes color non-uniformity
Solution Approach 1:
The patent applies parameter changes by adjusting the phosphor layer characteristics (thickness and/or density) as a function of the blue LED's dominant wavelength. For LEDs with shorter dominant wavelengths (420-440nm) that emit more blue light, the phosphor layer is made thicker or denser to increase the conversion of blue light to other wavelengths, effectively reducing the excess blue light. For LEDs with longer dominant wavelengths (440-460nm), the phosphor layer is made thinner or less dense. This dynamic adjustment of phosphor parameters compensates for the white point variations among different LED bins, ensuring uniform color output across the display.
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 ensures consistent color output across the LCD screen, regardless of the blue LED bin used, by adjusting the phosphor layer characteristics to account for wavelength-dependent attenuation, thereby achieving uniform red, green, and blue light outputs.
Implementation Method 1
tailoring the phosphor layer thickness and density over blue LEDs to adjust blue light leakage
Implementation Method 2
varying light attenuation by LCD layers versus wavelength
Data Source
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AI summary
A backlight for a color LCD includes white light LEDs formed using a blue LED die with a layer of red and green phosphors over it. The attenuation by the LCD layers of the blue light component of the white light is typically greater as the blue wavelength becomes shorter. In order to achieve a uniform blue color component across the surface of an LCD screen and achieve uniform light output from one LCD to another, the blue light leakage of the phosphor layer is tailored to the dominant or peak wavelength of the blue LED die. Therefore, the white points of the various white light LEDs in a backlight should not match when blue LED dies having different dominant or peak wavelengths are used in the backlight. The different leakage amounts through the tailored phosphor layers offset the attenuation vs. wavelength of the LCD layers.