Direct-Lit Backlight Polarizer Layout for Uniform Thin Displays
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Solution Overview
Problem
Current display systems, particularly those using direct-lit backlight units, are bulky and often produce non-uniform illumination due to the arrangement of light sources and lack of efficient light recycling, which affects brightness and light use efficiency.
Innovation Solution
A backlight system with discrete spaced apart light sources arranged two-dimensionally on an optically reflective surface, incorporating a reflective polarizer and optical film with multiple polymeric layers, which recycles and collimates off-axis light for improved uniformity and brightness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If direct-lit backlight units are used, then brightness can be achieved, but the backlight becomes bulky and illumination becomes non-uniform
Solution Approach 1:
The patent segments the backlight unit into distinct functional layers: light sources arranged in a matrix pattern, reflective polarizer layer, and optical film layer. This segmentation allows each component to be optimized independently for its specific function while maintaining overall compactness.
Solution Approach 2:
The patent transitions from traditional linear or edge-lit arrangements to a two-dimensional matrix arrangement of light sources. This dimensional change enables more uniform illumination distribution across the display panel while reducing the overall backlight thickness.
2Illumination intensity
If light sources are arranged in conventional patterns, then brightness is provided, but illumination uniformity deteriorates
Solution Approach 1:
The light sources are segmented into a matrix pattern with specific spacing, allowing independent optimization of brightness and uniformity. The reflective polarizer and optical film are also segmented into multiple thin layers to precisely control light distribution.
Solution Approach 2:
The patent applies different optical properties to different layers: the reflective polarizer has high reflectance for p-polarized light while the optical film has angle-dependent transmittance. This local quality differentiation enables simultaneous achievement of brightness and uniformity.
3Device complexity
If off-axis light is not recycled, then device complexity is reduced, but light use efficiency decreases
Solution Approach 1:
The patent converts the previously wasted off-axis light into a useful resource by using the reflective polarizer to redirect it. The optical film then controls this recycled light to improve uniformity, transforming what was harmful (light loss) into beneficial (enhanced uniformity and efficiency).
Solution Approach 2:
Instead of discarding off-axis light that would normally be lost, the system recovers it through the reflective polarizer and optical film combination, improving overall light use efficiency without significantly increasing device complexity.
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 solution enhances light use efficiency and uniformity of illumination, reducing the thickness of the backlight while maintaining performance balance between brightness and uniformity compared to similar thickness backlights.
Implementation Method 1
the plurality of polymeric layers of the reflective polarizer has an average optical reflectance of at least 60% when the incident light is p-polarized and an average optical transmittance of at least 60% when the incident light is s-polarized
Implementation Method 2
the plurality of polymeric layers of the optical film has an average optical transmittance T1 for a first incident angle of less than about 5 degrees and an average optical transmittance T2 for a second incident angle of greater than about 35 degrees, T1/T2≥1.5
Implementation Method 3
a plurality of discrete spaced apart light sources arranged two-dimensionally on an optically reflective surface
Data Source
AI summary
A backlight includes a plurality of light sources, a reflective polarizer disposed on the plurality of light sources, and an optical film disposed between the reflective polarizer and the plurality of discrete spaced apart light sources. For a substantially collimated incident light, for a visible wavelength range, and for a first incident angle of less than about 5 degrees, the reflective polarizer has an average optical reflectance of at least 60% when the incident light is p-polarized and an average optical transmittance of at least 60% when the incident light is s-polarized. For the average of p-polarized and s-polarized incident lights and the visible wavelength range, the optical film has an average optical transmittance T1 for the first incident angle, and an average transmittance T2 for a second incident angle of greater than about 35 degrees, such that T1/T2≥1.5.