The present invention is directed to a liquid crystal display device having a liquid crystal cell with a layer of liquid crystal material, which is switchable on a zonal basis between various optical states, interposed between front and rear carrier plates and a fluorescent plate disposed behind the rear carrier plate of the liquid crystal cell in the path of observation and provided with exit windows which are disposed behind the switchable liquid crystal zones.
Liquid crystal displays are passive displays and consequently have to be provided with supplementary lighting when used for certain purposes, for example, in clocks or watch faces that are to be read during both the day and night. In German Offenlegungsschrift 25 03 663, which corresponds to U.S. Pat. No. 3,984,176, a display device is disclosed in which a plate of carrier material having an index of refraction greater than 1 is disposed behind a liquid crystal cell in the path of observation. This plate is silvered on the back surface and the carrier material of the plate contains a large number of transparent particles having an index of refraction which is different than that of the carrier material. Light, which is artificially generated is directed into this plate and is refracted into a wide variety of directions. If one wishes to obtain an attractive optical quality level with such a plate, and above all else illuminate the face of the screen uniformly, the light reflecting particles must be distributed very carefully and in certain circumstances with a specific concentration gradient.
A liquid crystal display with a fluorescent plate which has silvered edges and acts as a light trap has been suggested in German patent application P 25 54 226. In this suggested arrangement, ambient light is received by fluorescent centers and causes or excites a fluorescent light which is fed by the plate in an amplified form to individual segment electrodes. However, this arrangement has no provision for any supplementary lighting.
In U.S. patent application Ser. No. 747,035 filed Dec. 2, 1976, which application includes the disclosure of the above mentioned German application P 25 54 226 and additional German applications, a suggestion for providing supplemental lighting for a fluorescent plate of a liquid crystal display device was made.
USPTO Backgrounds
USPTO Backgrounds