Backlight Unit Light Shielding Member Design for LCD
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Solution Overview
Problem
Backlight units in liquid crystal display devices experience light leakage and deflection of the light diffusion sheet due to thermal expansion and contraction, which is exacerbated by the use in high-temperature, high-humidity environments and the desire for narrower frames.
Innovation Solution
A backlight unit design that includes a light guide sheet, a light source, a light diffusion sheet, a prism sheet, and a frame with a light shielding member that covers the prism and diffusion sheets, adhering to specific relationships between the light shielding member's length, the prism sheet's thickness, and the light diffusion sheet's shrinkage and expansion to prevent light leakage and deflection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the frame is made narrow to reduce size, then the device achieves reduction in size, but light leakage and deflection of the light diffusion sheet increase
Solution Approach 1:
The patent introduces a light shielding member that extends in the thickness direction (Z-axis) of the backlight unit, adding a vertical dimension to light blocking. This allows the light diffusion sheet to be positioned closer to the light source while maintaining light leakage prevention, thus enabling a narrower overall frame structure without compromising reliability.
Solution Approach 2:
The light shielding member acts as an intermediary element between the light source and the light diffusion sheet. It provides mechanical support to prevent deflection of the light diffusion sheet while simultaneously blocking light leakage through the prism sheet, resolving the contradiction between narrow frame design and reliability.
2Use of energy by moving object
If the light diffusion sheet is positioned close to the light source to improve efficiency, then light utilization improves, but thermal expansion causes deflection and light leakage
Solution Approach 1:
The light shielding member provides a counteracting mechanical support force against the thermal expansion of the light diffusion sheet. By positioning the light shielding member adjacent to the light diffusion sheet, it counterbalances the expansion forces, preventing deflection and maintaining stable composition despite thermal effects from the light source.
Solution Approach 2:
The patent modifies the structural parameters of the backlight unit by introducing the light shielding member with specific dimensions and positioning. This changes the mechanical and optical parameters of the system, allowing the light diffusion sheet to maintain stability under thermal conditions while remaining close to the light source for efficient light utilization.
3Area of moving object
If the light diffusion sheet expands due to heat, then the sheet covers more area, but it contacts the frame and becomes deflected
Solution Approach 1:
The light shielding member is pre-positioned adjacent to the light diffusion sheet before thermal expansion occurs. This preliminary positioning creates a mechanical constraint that prevents the expanded light diffusion sheet from contacting and deflecting against the frame, maintaining flatness even when the sheet area increases due to thermal expansion.
4Area of moving object
If the light diffusion sheet shrinks after expansion, then it creates space, but light leakage occurs through this space
Solution Approach 1:
The light shielding member serves as a dual-function intermediary: it provides mechanical support to prevent deflection and acts as a light barrier to block light leakage. When the light diffusion sheet shrinks and creates space, the light shielding member fills this gap optically, preventing light from leaking through while maintaining the structural integrity of the assembly.
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 design effectively reduces light leakage and prevents deflection of the light diffusion sheet, maintaining optimal performance across varying environmental conditions.
Implementation Method 1
a light guide sheet that guides incident light beams toward a front side
Implementation Method 2
a light guide sheet that guides incident light beams toward a front side
Implementation Method 3
a light diffusion sheet superimposed on the front side of the light guide sheet
Implementation Method 4
a prism sheet disposed on a front side of the light diffusion sheet
Data Source
AI summary
A backlight unit satisfies the relationship given by the following expression: S<2(A−√3T), where A (mm) represents the length along which the light shielding member covers the light diffusion sheet before shrinkage, T (mm) represents the thickness of the prism sheet, and S (mm) represents the amount of shrinkage of an end on the frame side of the light diffusion sheet in the planar direction of the light diffusion sheet. The backlight unit also satisfies the relationship given by the following expression: E<D, where D (mm) represents the distance between the end on the frame side of the light diffusion sheet before expansion and a frame and E (mm) represents the amount of expansion of the end on the frame side of the light diffusion sheet in the planar direction of the light diffusion sheet.