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Reduction of Reflective Moiré Associated with a Reflective Polarizer

IP.com Disclosure Number: IPCOM000202524D
Publication Date: 2010-Dec-20
Document File: 6 page(s) / 707K

Publishing Venue

The IP.com Prior Art Database

Abstract

A crossed prism film construction that reduces reflective polarizer reflective moire in backlit liquid crystal displays is disclosed.

This text was extracted from a PDF file.
This is the abbreviated version, containing approximately 29% of the total text.

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Reduction of Reflective Moiré Associated with a Reflective Polarizer

Introduction:

Liquid Crystal Displays (LCDs) typically utilize Backlight Units (BLU) behind the Liquid Crystal Panel (LCP) to provide illumination. The BLU often includes one or more prism films and a reflective polarizer (RP), which serve to maximize brightness in the direction normal to the screen (axial luminance). This document describes an integrated combination of two prisms films that utilizes a properly adjusted angle bias to minimize optical artifacts.

A common construction for a BLU includes one or more LEDs that inject light into the edge of a lightguide plate (LGP). The LGP distributes the LED light across the area of the LCP through a process of total internal reflection and light extraction on one or both major LGP surfaces. Light generally exits the LGP at high polar angles above and below the LGP (measured from the major surface normal). A reflector film is typically placed below the LGP to send downward-propagating light back towards the LCP. A diffuser film is usually placed above the LGP to improve spatial uniformity and to aid with redirecting light toward the display normal. Prism films maximize luminance about the normal direction using a combination of high transmission into those angles and high reflection and subsequent recycling of higher angle rays.

The rays exiting the prism film are nearly unpolarized. In many displays, an RP is added above the prism films, and is often adhered to the LCP polarizer. The RP pass axis is aligned to that of the LCP polarizer, and reflects light polarized perpendicular to this direction for recycling. The overall effect of the RP and two prism films is a significant enhancement of the axial luminance.

The combination of an RP and one or more prism films, however, can lead to an optical moiré artifact, hereafter referred to as Reflective Polarizer Reflective Moiré or RPRM. This artifact manifests itself as alternately dark and bright bands.

Mechanism.

The basic ray path that leads to this form of reflective moiré is shown below:


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