Conventionally, to utilize a field-effect liquid crystal display device where the liquid crystals are in the twisted nematic mode, nematic liquid crystals of high positive dielectric anisotropy are utilized. The interior surfaces of the plates constituting the cell which holds the liquid crystal material are each unidirectionally rubbed with a material such as cotton, and the plates are mounted so that the rubbing directions of the opposed plates are at 90.degree. to each other. The molecules immediately adjacent to the inner surfaces of the plates orient themselves in the rubbing directions, and the molecules intermediate the plates form themselves into a helix of one-quarter turn. It is believed that minute grooves are formed by the rubbing and that the liquid crystal molecules fall into the grooves with the molecular axes parallel to the direction of the grooves. Where the rubbing directions, as indicated, are at right angles to each other and the liquid crystal cell is between crossed polarizer plates, then, in the absence of an electric field, light is transmitted through the system. However, if an electric field of sufficient strength is imposed across the cell, utilizing transparent electrodes on the inner surfaces of the cell wall and suitable voltage source connected to said transparent electrodes, then the molecules align themselves with their axes parallel to the imposed field and the optical activity of the liquid crystal material drops to zero. Under such circumstances the crossed polarizing plates prevent any light from passing through the system.
Conventionally, the transparent electrodes do not cover the entire surfaces of the cell plates so that portions of the plates to which the voltage is applied through the use of said electrodes will appear to be dark and opaque while the remainder will be illuminated and transparent. Conversely, if the liquid crystal cell is inserted between polarizers having parallel axes of polarization, that portion of the plates to which the voltage is applied will appear to be illuminated and transparent, and the remainder will be dark and opaque. Generally, the system is mounted so that the polarization axes of the polarizer plates are at 90.degree. to each other, such an arrangement having proved to be the most useful due to the visibility of the display.
Nematic liquid crystals of positive dielectric anisotropy when oriented transverse to the transmission axis of the incident light are birefringent. When the optical axis of the light incident on the liquid crystal layer conforms approximately to the direction of vibration of the incident light, then, in general, the extraordinary beam is the one which is transmitted and used for the display. However, nematic liquid crystals, in general, absorb short-wavelength light so that gradual deterioration and darkening of the liquid crystal material takes place, resulting in decreased visibility of the display provided by the system. It would, therefore, be desirable to eliminate this difficulty.