Gradient-free illumination of passive readout display devices

US4502761A · kind A · utility

Assignee

• Robert Bosch GmbH · DE

Inventors

• Peter Knoll · Ettlingen, DE
• Winfred K/o/ nig · Karlsruhe, DE
• Wolfgang Ziegler · Waldbronn, DE

Key dates

• Filing date: Feb 8, 1982
• Grant date: Mar 5, 1985
• Expiry date: Feb 8, 2002

Classification

• Technology area (CPC G): Physics
• CPC primary: G02F1/133604
• WIPO field: Optics
• WIPO sector: Instruments

Abstract

Compensating darkening is provided over the area at the back of liquid crystal displays, so that light from one or more concentrated sources near the back of the display may result in essentially uniform illumination of the display through the LCD from the back. The compensating screen may be a developed film of suitable selected gradation, or a raster of points produced by half-tone process from such a film and printed either on a transparent foil or on the back of a translucent circuit board. Instead of being based on an exposed film, the density of the size of the raster points may be generated by a point-by-point light measurement recorded in computer memory and translated to point dimensions applied automatically by a plotter to a screen. A raster of circles with progressively wider spacing is useful for illumination by a single lamp. The layout of circles can be drawn according to a simple formula, keeping the ratio of line width to line spacing proportional to the third power of the cosine of the illumination angle.