Display device for displaying light images on a dark background

Claim 1

In a display device for displaying bright images on a dark background, said device including a liquid crystal cell having a liquid crystal layer which is electrically switchable by zones between an operative state and an inoperative state, said layer being enclosed by two carrier plates with a predetermined wall orientation; means for individually switching zones of the layer between the operative and inoperative states; and a light trap in the form of a body containing fluorescent particles, said body being made of material with a refractive index of more than 1 and being provided with a light emergent window disposed behind each of the switchable zones of the liquid crystal layer in the direction of observation, the improvements comprising the cell including a single linear polarizer being disposed adjacent one of the carrier plates, the liquid crystal layer having a dielectric constant with a negative anisotropy, said layer, while in the inoperative state, being oriented in a uniformly tilted homeotropic manner with a tilt parallel with the direction of polarization of the linear polarizer, said liquid crystal layer, while in the operative state, assuming an essentially uniformly homogeneous texture with a bias predetermined by the direction of tilt, and said liquid crystal layer containing at least one pleochroic dye, said dye being selected to absorb the excitation light for the fluorescent particles and the fluorescent light emitted by the fluorescent particles at a low level in each zone that is in the inoperative state and to absorb the fluorescent light at a high level in each zone in the operative state so that the zones are only placed in an operative state when the zone belongs to the background of the image.