Browse Prior Art Database

Twisted Nematic Liquid Crystal Replacement for Overhead Transparency

IP.com Disclosure Number: IPCOM000039043D
Original Publication Date: 1987-Apr-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 2 page(s) / 51K

Publishing Venue

IBM

Related People

Wallace, SE: AUTHOR [+2]

Abstract

This article describes techniques for improving the contrast of a projection display system consisting of a twisted nematic liquid crystal display (TNLCD) used as an electronic transparency, or liquid crystal foil (LCF), on a conventional overhead projector. The LCF shares the desirable characteristics of disposable thermal film transparencies such as previewing before and during projection, as well as direct annotation. Advantages of this system over alternate projection systems for this business meeting application include portability, the inversion of contrast polarity through rotation of one of the polarizers, simple extension to color, and low system cost through the use of mature liquid crystal technology, and the widespread availability of overhead projectors.

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Twisted Nematic Liquid Crystal Replacement for Overhead Transparency

This article describes techniques for improving the contrast of a projection display system consisting of a twisted nematic liquid crystal display (TNLCD) used as an electronic transparency, or liquid crystal foil (LCF), on a conventional overhead projector. The LCF shares the desirable characteristics of disposable thermal film transparencies such as previewing before and during projection, as well as direct annotation. Advantages of this system over alternate projection systems for this business meeting application include portability, the inversion of contrast polarity through rotation of one of the polarizers, simple extension to color, and low system cost through the use of mature liquid crystal technology, and the widespread availability of overhead projectors. A problem with the direct viewing of large information content, matrix-addressed TNLCDs is the restricted viewing cone. The orientation and extent of the viewing cone depend upon the physio-chemical nature of the liquid crystal mixture, cell fabrication and the electrical fields applied to produce the electro-optical switching between states. The acceptance cone of overhead projectors is limited by the optical design and typically does not exceed about 15 degrees half- angle. The contrast of the projected image can be improved by matching the maximum contrast vectors of the LCF to the known acceptance angle of the overhead projector lens system. Fig. 1A shows a side view of an LCF which has a characteristic maximum contrast vector that is perpendicular to the plane of the LCF. The local maximum contrast vectors are parallel across the...