| 摘要 |
<p>The screen comprises a series of parallel strips the desired absorbency or transparency of each being individually controlled by varying the voltage applied to it. The voltage level may be varied, or an alternating voltage may be applied at variable frequency. In one embodiment, the screen is a layer of liquid crystal material sandwiched between two layers of electrically conductive material which have been etched to produce the strip pattern. The crystal material may be nematic, opt. also contg. a small amt. of cholesteric material, and may be contained in a twisted nematic cell opt. located between two sheets of polarising material. The screen is also claimed in combination with a cathode ray tube, the screen being so oriented that the strips arealigned with the writing direction of the raster. The strips are interconnected with tube circuitry so that each strip is transparent when the raster is writing on the area of tube display face behind it. Preferably the screen is transparent when no voltage is applied to the strips. The invention is applied to the instruments in an aircraft cockpit to ensure their readability even in conditions of high ambient illumination.</p> |
