Backlight Unit Polarization Alignment for LCD Brightness
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Solution Overview
Problem
The optical characteristics of liquid crystal displays, particularly the lower polarizer, lead to reduced backlight efficiency and display brightness due to the transmission of only a fraction of scattered light from the light guide layer.
Innovation Solution
Incorporating a quarter wave plate between the light guide layer and the backlight reflector, along with a turning film and a half wave plate, to align the polarization of light with the pass axis of the polarizer, thereby minimizing light loss and enhancing backlight efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a conventional backlight unit with a light guide layer and polarizers is used, then the display structure is simple, but the backlight efficiency and display brightness are reduced due to the lower polarizer transmitting only a fraction of scattered light
Solution Approach 1:
The patent introduces wave plates (quarter wave plate and half wave plate) as intermediary optical elements between the light guide layer, turning film, and polarizers. These wave plates mediate the polarization state of light to ensure optimal transmission through the polarizers, thereby improving backlight efficiency without fundamentally changing the basic backlight unit structure
Solution Approach 2:
The patent changes the polarization parameters of light by incorporating wave plates with specific optical axes and retardation values. The quarter wave plate converts linearly polarized light to circularly polarized light, and the half wave plate rotates the polarization direction, optimizing the light transmission parameters through the polarizer system to enhance display brightness
2Loss of energy
If the lower polarizer is used in the conventional configuration, then the manufacturing process is simple, but the optical efficiency is reduced due to transmission loss of scattered light
Solution Approach 1:
The wave plates serve as intermediary elements that transform the polarization state of scattered light before it reaches the polarizers. The quarter wave plate positioned between the light guide layer and turning film, along with the half wave plate between the turning film and lower polarizer, ensures that light transmission losses are minimized by optimizing polarization alignment
Solution Approach 2:
The patent optimizes energy transmission by changing the polarization parameters of light through wave plates. The specific retardation values and optical axis orientations of the wave plates are designed to maximize the transmission efficiency of scattered light through the polarizer system, reducing energy loss while adding optical elements
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 improves the transmission of scattered light, increasing the brightness and efficiency of the display by aligning the polarization of light with the polarizer's pass axis, thus optimizing backlight illumination.
Implementation Method 1
The quarter wave plate below the light guide layer may be used to rotate the polarization of light emitted from the bottom of the light guide layer into alignment with the dominant polarization
Implementation Method 2
The half wave plate may be interposed between the turning film and the reflective polarizer. The half wave plate may be used to rotate the dominant polarization into alignment with a pass axis of the reflective polarizer
Implementation Method 3
The light that is emitted into the edge of the light guide layer may be distributed throughout the light guide layer in accordance with the principle of total internal reflection
Implementation Method 4
The light guide layer may be provided with light scattering features that scatter the light that is traveling within the interior of the light guide layer
Data Source
AI summary
A display may have an array of pixels that display images for a user. The backlight unit may have a light-guide layer. An array of light-emitting diodes may emit light into an edge of the light-guide layer. The light guide layer may overlap a backlight reflector. A quarter wave plate may be interposed between the light guide layer and the backlight reflector. A turning film may be interposed between a lower polarizer in the array of pixels and the light guide layer. The lower polarizer may be a reflective polarizer. Light exiting the upper surface of the turning film may have a dominant polarization. A half wave plate may be used to rotate the dominant polarization into alignment with a pass axis of the reflective polarizer.