ORGANISATION FOR THE PROMOTION OF LIGHTS AGAINST MORK BACKGROUND AND PROCEDURE FOR THE MANAGEMENT OF SUCH ORGANISATION

摘要

A display device for representation of a bright image on a background which device has a light valve comprising a liquid crystal cell having a medium which can be switched zone-wise between at least two optical states and a light trap or body which consists of a material having an index of refraction greater than 1, contains a fluorescent material, and is provided with an outlet window for each of the switchable zones characterized by means coacting with the switchable medium to control the passage of the light through the device so that in a rest or inactive state of the medium, the medium and means allow the passage of the excitation light for the fluorescent particles and the passage of the fluorescent light therefrom and in an "on" or activated state of the medium, the means and medium are impermeable at least to the fluorescent light so that each of the switchable zones of the medium is placed in an "on" state only when it belongs to the background of the image. The means may be a pleochroic dye operating with a single polarizer or a pair of cross polarizers, which cooperate with the material of the liquid crystal which forms a twisted cell.