Robert Boschgmbh

Wolfgang Ziegler

Peter Knoll

Peter Rapps

Hans Petermann

Winfred K/o/ Nig

Arrangement to remove reflection from liquid crystal displays (LCD's)

Apparatus for illuminating passive liquid crystal displays (LCD's)

In the assembly of a liquid crystal cell indicator of which the covering glass plates are sealed together by edge bonding provided by an adhesive applique, a fixed information display is provided by supplementary adhesive appliques taking the place of some of the liquid crystal material inside the edge bonding perimeter. The display is optically inactive at the fixed information location, but the same appearance is provided as in the case of a display optically produced by electric signals. The fixed information is thus mechanically protected and is also visible when the electronic circuits are shut off.

LCD Indicator with built-in fixed information display

The disturbing residual transmission of a liquid crystal display device which is particularly noticeable in negative contrast devices is reduced by reference to the fact that the residual transmission is colored. The entire display surface of the liquid crystal device is provided with a transparent covering of a color complementary to the residual transmission color when the liquid crystal is not turned on. The transparent colored covering can be applied by printing as well as otherwise. In another embodiment, color shifts between turned-on and not turned-on displays are counteracted by mixing into the liquid crystal material a dichroic coloring material which has much lower absorption when the display is turned on. A light blue dichroic coloring material is suitable for LCDs which have residual transmission in the red region.

Method of making color-neutral LCD indicators of low residual

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.

Growing community of inventors

Furth, Germany

Wolfgang Ziegler