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POLARIZED BACKLIGHT FOR IMPROVED CONTRAST OF REVERSE IMAGE IN BACKLIT DISPLAYS THAT EMPLOY REFLECTIVE POLARIZERS

IP.com Disclosure Number: IPCOM000009759D
Original Publication Date: 2000-May-01
Included in the Prior Art Database: 2002-Sep-17
Document File: 2 page(s) / 99K

Publishing Venue

Motorola

Related People

Jon L. Schindler: AUTHOR [+2]

Abstract

Abstract - Liquid crystal displays constructed with reflective polarizer films suffer from poor CODtrast in backlit mode, due to light leakage of the undesired polarization. A linear polarizer film, placed between the backlight and the reflective polarizer, would improve the contrast in backlit mode by suppressing tWs leakage. The improved contrast performance would come at the expense of overall display luminance. Increasing the light output from the backlight would overcome this drawback.

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MOTOROLA

Technical Developments

POLARIZED BACKLIGHT FOR IMPROVED CONTRAST OF REVERSE IMAGE IN BACKLIT DISPLAYS THAT EMPLOY REFLECTIVE POLARIZERS

by Jon L. Schindler and George T. Valliath

Abstract - Liquid crystal displays constructed with reflective polarizer films suffer from poor CODtrast in backlit mode, due to light leakage of the undesired polarization. A linear polarizer film, placed between the backlight and the reflective polarizer, would improve the contrast in backlit mode by suppressing tWs leakage. The improved contrast performance would come at the expense of overall display luminance. Increasing the light output from the backlight would overcome this drawback.

INTRODUCTION

Motorola portable products typically employ reflective, liquid crystal displays (LCD) to provide information to the user. These displays generally comprise a liquid crystal cell between two glass plates, polarizer sheets on the outside surfaces of the glass plates, a reflector film attached to the polarizer at the back of the display, and electrical connections.

Alternately, such displays can be constructed using a so-called reflecting polarizer sheet at the back surface in place of the separate polarizer and reflector films. A reflecting polarizer film achieves the same overall effect of reflecting the incident light and selecting a particular polarization component.

Motorola. Inc. 2000

Figure 1 depicts the behavior of a linear polarizer and a reflecting polarizer for unpolarized incident light. As shown in the figure, the reflecting polarizer transmits light with linear polarization along one axis (PtransmiJ and reflects light with linear polarization along the orthogonal axis axis (P reflecJ. The reflecting polarizer also exhibits some leakage ®5% ) of the reflected polarization component.

Ptran.mit

Leakage of

"' p ref1ed I

Incident light

Linear polarizer

Reflecting polarizer

Fig. 1

For nighttime use, portable products require some type of auxiliary lighting to illuminate the display. The reflector sheet in an LCD often permits 10 - 20% light transmission through the film to allow for auxiliary lighting from behind the display, i.e. a backlight. A...