Evenly illuminated display devices

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350201, G02F 113

Patent

active

041718747

ABSTRACT:
The molecules in a twisted nematic liquid crystal are, in general, skewed relative to the optical axis of the cell (the perpendicular to the plane surfaces defining the boundaries of the crystal cell), and their birefringent effect on plane polarized light varies asymmetrically for such light making varying angles with the optical axis of the cell. When the cell is positioned between crossed polarizers and the cell is energized so that light is supposed to be completely extinguished, some rays are nevertheless transmitted so that the transmitted intensities at different viewing angles vary. To avoid this resulting variation of intensity with viewing angle, the cell is illuminated from behind with collimated light (i.e., all rays parallel to the optical axis of the cell) so that all rays "see" the average molecular director in the same way; a solid catadroptric element is utilized to both collimate the light and achieve essentially constant luminous flux intensity upon the display. To restore a reasonably wide angle of view, a diffuser is positioned in front of the display. The invention may be used with any type of display device which has a transmission characteristic which varies with the angle of rays passing therethrough.

REFERENCES:
patent: 1740609 (1929-12-01), Lebby
patent: 2477331 (1949-07-01), Epstein
patent: 3446916 (1969-05-01), Abel et al.
patent: 3653138 (1972-04-01), Cooper
patent: 3834792 (1974-09-01), Janning
patent: 3840695 (1974-10-01), Fischer
Brown: "Modern Optics", Reinhold Publishing Corp., New York, 1965, pp. 444-446.
Wright: "An Aplanatic Reflector with a Flat Field Related to the Schmidt Telescope", Publications of the Astronomical Society of the Pacific, vol. 47, 1935, pp. 300-304.

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