The LCDs built in projection systems are usually small reflective or transmissive panels set off by a forceful arc lamp source. A line of lenses magnifies the reflected or transmitted image and then displays it on the screen. In front-projection systems the LCD is located on the same side of the screen as the viewer, however in rear-projection systems the screen is lit from behind. Projectors of greater cost and capability might be found with three distinct LCD panels, casting separate red, green, and blue images that blend to form a coloured display on the screen.
The growing desire for film displays has granted a special emphasis on the switching speed of liquid crystals. This has necessitated the development of items build with smectic liquid crystals, certain types of which have a speedier electro-optical response than nematic liquid crystals. The surface-stabilized ferroelectric liquid crystal (SSFLC) display is at this point the most developed smectic device. In it the liquid crystal molecules are cast in layers that are perpendicular to the substrate planes, which are separated by one or two micrometres, and inside the layers the molecules are slanted, as demonstrated in the figure. The host liquid crystal contains optically active molecules, and a minor result of the optical activity and the angle of the molecules is the presence of a permanent charge separation, or ferroelectric dipole, similar to the ferromagnetic dipole of a magnet. The direction of this dipole is perpendicular to the tilt direction of the molecules and in the plane of the layers. Thus, there must be a permanent charge separation across the liquid crystal layer in the SSFLC, and its sign is directly paired to the tilt direction of the molecules. An applied voltage of the right sign can reverse the direction of this dipole in tens of microseconds and hence reverse the tilt direction of the molecules. The resultant change in optical properties can make a change from light to dark in the case that one or more polarizers are employed.
SSFLC devices have been produced for large passive-matrix presentations, but their expensiveness and complexity has impeded them from having any great effect on the market. Small transmissive and reflective active-matrix SSFLC displays, however, have shown some probability for use as parts in projection systems or as viewfinders in digital cameras. Their immediate reaction allows them to be utilised in time-sequential colour systems, in which highly expensive colour filters are removed for a coloured backlight that flashes red, green, and blue in quick pace (approximately 100 cycles a second). For example, the liquid crystal can be switched to a transmissive state for the red and green periods then to a nontransmissive state in the blue period, having the upshot that the eye sees an average of red and green light, or the colour yellow.
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