Switchable Backlight Unit With Graded Index Films
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Solution Overview
Problem
Current backlight units face challenges in achieving a flat-top intensity profile across a range of viewing angles while maintaining high uniformity and efficiency, especially in low to medium etendue scenarios, and struggle to provide sharp transitions between viewing and non-viewing regions, leading to issues with private and public viewing modes.
Innovation Solution
The proposed solution involves a backlight unit with a light guide and angle-dependent diffuser layers, comprising graded index films that homogenize light within specific acceptance angles and transmit light outside these angles without diffusion, allowing for the creation of distinct eye boxes for narrow and wide viewing modes, enabling a flat intensity profile and sharp transitions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If conventional diffusers are used to homogenize light across wide viewing angles, then light uniformity is improved, but the ability to provide sharp transitions between viewing and non-viewing regions deteriorates
Solution Approach 1:
The backlight unit is divided into multiple independently controllable light source groups, each associated with specific viewing angle ranges. This segmentation allows different regions of the display to provide light for different viewing modes (private vs public) simultaneously, enabling sharp transitions between viewing and non-viewing regions while maintaining uniformity within each mode through targeted light homogenization in specific angular ranges.
Solution Approach 2:
The system dynamically switches between different viewing modes by selectively activating specific light source groups. The backlight unit can transition between private viewing mode (narrow angular range), public viewing mode (wide angular range), and mixed modes by controlling which light sources are active, providing sharp transitions between different viewing states while maintaining optimal light uniformity for each mode.
2Adaptability or versatility
If multiple light sources with different acceptance angles are used, then viewing mode versatility is improved, but device complexity increases
Solution Approach 1:
Multiple light sources with different acceptance angles are integrated into a single backlight unit that can serve multiple viewing modes. The system provides universal functionality by supporting private viewing mode, public viewing mode, and mixed modes within one device, allowing the same backlight unit to adapt to different viewing scenarios without requiring separate hardware systems.
Solution Approach 2:
Different regions of the backlight unit are assigned different light source characteristics (narrow vs wide acceptance angles) to provide locally optimized performance for specific viewing modes. This local quality differentiation enables the system to achieve viewing mode versatility while managing complexity through spatial organization of light source properties rather than requiring complex control mechanisms.
3Illumination intensity
If light is homogenized across all angles, then viewing uniformity is improved, but the ability to create distinct eye boxes for different viewing modes deteriorates
Solution Approach 1:
Light homogenization is segmented by angular range rather than applied uniformly across all angles. The system homogenizes light within specific acceptance angle ranges corresponding to different viewing modes, creating distinct eye boxes for private and public viewing modes simultaneously. This angular segmentation allows each mode to have its own optimized eye box while maintaining uniformity within that mode's angular range.
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 provides a flat angular light intensity profile within the eye box region with sharp transitions at the edges, effectively supporting both private and public viewing modes by controlling light distribution based on viewer position, enhancing viewing experiences.
Implementation Method 1
an angle-dependent diffuser layer comprising a first graded index film configured to receive light from the second light interface of the light guide, homogenize received light that is incident on the graded index film from within a first range of acceptance angles
Implementation Method 2
configured to receive light at a first light interface located at an end of the light guide and output light via a second light interface located at a face of the light guide
Implementation Method 3
A backlight unit may be used to illuminate display panels by directing diffuse light toward the panel at a range of angles
Implementation Method 4
output light via a second light interface located at a face of the light guide
Data Source
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AI summary
Embodiments for a backlight unit are provided. In one example, a backlight unit comprises a light guide configured to receive light at a first light interface located at an end of the light guide and output light via a second light interface located at a face of the light guide, and a plurality of light sources configured to inject light into the light guide at the first light interface. The example backlight unit also comprises a graded index film configured to receive light from the second light interface of the light guide, homogenize received light that is incident on the graded index film from within a range of acceptance angles and not homogenize light incident on the graded index film from outside of the range of acceptance angles, and direct the homogenized light toward an eye box.