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Brightness Enhancement Reflective Liquid Crystal Displays

IP.com Disclosure Number: IPCOM000079976D
Original Publication Date: 1973-Oct-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 2 page(s) / 44K

Publishing Venue

IBM

Related People

Schlig, ES: AUTHOR

Abstract

Reflective liquid crystal displays operating in the indirect mode suffer loss of contrast through two mechanisms: (a) Scattering of light by the unexcited liquid crystal and by the surfaces of the display; and (b) Specular reflection from the mirror-like background of the display, resulting in the viewer seeing an image of his face and surroundings in the unexcited parts of the display surface. This is distracting as well as a deteriorating contrast.

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Brightness Enhancement Reflective Liquid Crystal Displays

Reflective liquid crystal displays operating in the indirect mode suffer loss of contrast through two mechanisms: (a) Scattering of light by the unexcited liquid crystal and by the surfaces of the display; and (b) Specular reflection from the mirror-like background of the display, resulting in the viewer seeing an image of his face and surroundings in the unexcited parts of the display surface. This is distracting as well as a deteriorating contrast.

Loss of contrast due to specular reflection is normally minimized by: (1) Tilting the display surface so the back surface reflects a matte black surface; or
(2) Attaching a circular polarizer to the front of the display to attenuate light passing into the display, specularly reflecting and passing out again. This virtually eliminates the reflection from the display. Tilting the display is unsatisfactory for human factors (particularly for large displays) and makes proper illumination more difficult. Employing a circular polarizer is very effective; however, the brightness of the display for a given illumination is reduced, since incident light must pass through the circular polarizer before impinging on the display, which attenuates it by about 60%.

What is here suggested is the separation of the display and the circular polarizer to permit illumination of the display by light which has not been attenuated by the circular polarizer, to markedly increase the br...