Backlight Retarder Layer Eliminates RPRM Moiré
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Solution Overview
Problem
The combination of reflective polarizers and prism films in liquid crystal display backlights often results in an optical artifact known as Reflective Polarizer Reflective Moiré (RPRM), which appears as alternating dark and bright bands, and existing solutions have not effectively mitigated this issue.
Innovation Solution
A backlight configuration that includes an extended light source, a reflective polarizer, a prismatic film with a structured surface, and a retarder layer, where the retarder layer is positioned between the reflective polarizer and the prismatic film to provide tuned retardance, minimizing RPRM by optimizing the polarization state of incident light and maintaining minimal variation in retardance across different wavelengths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a reflective polarizer and prismatic film are combined to maximize axial luminance, then brightness in the normal direction is improved, but Reflective Polarizer Reflective Moiré (RPRM) artifacts appear as alternating dark and bright bands
Solution Approach 1:
A circular polarizing converter is introduced as an intermediary component between the reflective polarizer and the viewer. This converter consists of a linear polarizer and a half-wave retarder layer that work together to convert the linearly polarized light from the reflective polarizer into circularly polarized light, thereby eliminating the RPRM artifacts while preserving the axial luminance enhancement provided by the reflective polarizer andprismatic film combination
Solution Approach 2:
The invention changes the polarization state parameter of the light from linear polarization to circular polarization by adding the half-wave retarder layer. This parameter change in the polarization state transforms the light properties to eliminate the interference patterns (RPRM) that occur with linearly polarized light while maintaining the desired brightness characteristics
2Illumination intensity
If prism films are added to enhance brightness, then axial luminance is improved, but the complexity of the optical stack increases
Solution Approach 1:
The circular polarizing converter serves multiple functions simultaneously: it eliminates RPRM artifacts, maintains axial luminance enhancement, and works with standard reflective polarizer andprismatic film components. By making the converter a multi-functional element that addresses both artifact elimination and brightness maintenance, the overall system complexity is managed more effectively
Solution Approach 2:
The circular polarizing converter acts as a mediating layer that reconciles the conflicting requirements of brightness enhancement and artifact elimination. Rather than requiring complex redesign of the entire optical stack, the intermediary converter layer provides a relatively simple addition that resolves the contradiction between usingprismatic films for brightness and avoiding RPRM artifacts
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 significantly reduces the appearance of RPRM, ensuring uniform illumination and minimizing angular variations in color coordinates, thereby enhancing the display's brightness and color consistency.
Implementation Method 1
the reflective polarizer reflects at least 60% of the incident light having a first polarization state and transmits at least 60% of the incident light having an orthogonal second polarization state
Implementation Method 2
the retarder layer has a retardance nW, where n is an integer ≥1 and W is a wavelength between about 160 nm and about 300 nm
Implementation Method 3
The firstprismatic film is disposed between the extended light source and the reflective polarizer and includes a structured major surface. The structured major surface includes a plurality of substantially parallel first linearprisms
Implementation Method 4
The extended light source is adapted to emit light through an emission surface thereof
Data Source
AI summary
A backlight includes an extended light source adapted to emit light. A reflective polarizer is disposed on the extended light source, such that for substantially normally incident light and for at least a first wavelength in a range from about 420 nanometer (nm) to about 650 nm, the reflective polarizer reflects at least 60% of the incident light having a first polarization state and transmits at least 60% of the incident light having an orthogonal second polarization state. A first prismatic film is disposed between the extended light source and the reflective polarizer. A retarder layer is disposed between the reflective polarizer and the first prismatic film, such that for substantially normally incident light at a wavelength of about 550 nm, the retarder layer has a retardance nW, where n is an integer ≥1 and W is a wavelength between about 160 nm and about 300 nm.