Abstract: A device for detecting a frozen image on a liquid crystal display screen comprises at least one photoelectric cell capable of delivering a luminance signal l(t) to means (8) for processing this signal. The cell is placed facing a display area (A) of the screen. In this display area, a variable pattern is displayed at a characteristic frequency fc. The processing means are capable of detecting the characteristic frequency in the signal l(t). If this signal is not detected, they trigger a corresponding alarm.

Abstract: The invention relates to a display device with a secured electronic architecture for aeronautical applications. Each device comprises an electronic computer and an associated matrix-type display device. The invention applies essentially to display systems having a small number of large-sized screens. The invention proposes to structure the display device as two independent display zones and the computer as two electronic subassemblies, which are also independent, in such a way that a failure of one of the elements entails, at most, only the failure of just one zone of the display device. The invention applies essentially to liquid-crystal active-matrix display devices having a lighting system based on fluorescent tubes. Two embodiments of the display zones are described. In the first embodiment, only one part of the area of the screen is lost in the event of a failure. In the second embodiment, the resolution of the display screen is simply downgraded by a factor of 2 in the event of a failure.

Abstract: To obtain improved readability of a liquid crystal display screen under varied conditions of ambient luminosity, it is possible to increase the dynamic range of variation of the polarizing voltage. However, this leads to an increase in the electrical power consumption and to contrast reversal defects. To prevent this phenomenon, it is proposed not to modify the dynamic range of variation of polarizing voltage but to shift this range towards the lower voltages when the ambient luminosity increases or towards the higher voltages when the ambient luminosity diminishes. Thus, the white level is favored under high ambient luminosity and the black level is favored under low or normal luminosity.

Abstract: A display device with a liquid crystal cell including a layer of twisted nematic liquid crystal placed between two polarizers and including, between the liquid crystal layer and each of the polarizers, a structure for compensating for cell contrast variations according to the observation angle which has an orientation in the plane of the cell. The pass directions of the polarizers are separated by an angle of 90+A degrees, in which A is not zero, and the orientations of the two compensation structures are separated by an angle of 90+B degrees, in which B is not zero. Such a structure may find particular application to a liquid crystal screen, especially for avionics.

Abstract: The invention relates to a device for illuminating a liquid crystal screen. The device comprises a light box (1) located behind the screen (2). The light box (1) comprises a plurality of light sources (4). The device further comprises first means (3) to power the light sources (4). The first means (4) comprise second means enabling, under steady conditions, at least one of the light sources to be extinguished while the other sources remain lit.

Abstract: A display panel having compensation using holographic birefringent films. Due to the natural birefringence of liquid crystals, contrast suffers when a liquid crystal cell is viewed at an oblique incident angle. Compensation devices made of birefringent media are used to correct this deficiency. The compensation devices include at least one film, the birefringence of which is induced by the recording of a volume hologram consisting of parallel fringes. The choice of the optical birefringent axes depends only on the orientation of the fringes so that it is easy to achieve compensation using uniaxial films which are inclined with respect to the plane of the film.

Abstract: A display screen for improving the angle of view from which displayed images can be perceived accurately. An illumination device produces light which is collimated along a plane YOZ orthogonal to the plane XOZ in which the screen has its best characteristics in terms of contrast and/or levels of gray. The collimated illumination device is on the front face of a cell. A device for distributing the light (by diffraction or scattering) in the plane YOZ is placed at the output of the cell. One or more compensation films can be placed at the output of the cell to increase the angle of view in the plane XOZ. This device may be used in avionics and the display of video images.