The LCDs utilised in projection systems are most often small reflective or transmissive panels set off by a powerful arc lamp source. A line of lenses enlarges the reflected or transmitted image then sends it on the screen. In front-projection systems the LCD is situated on the side of the screen as the viewer, however in rear-projection systems the screen is lit from behind. Projectors of more expense and performance can be found with three discrete LCD panels, reflecting separate red, green, and blue images that combine to create a coloured display on the screen.
The growing need for film displays has had a particular emphasis on the switching speed of liquid crystals. This has demanded the development of objects utilizing smectic liquid crystals, particular types of which give a better electro-optical response than nematic liquid crystals. The surface-stabilized ferroelectric liquid crystal (SSFLC) display is at this point the most sophisticated smectic device. Inside it the liquid crystal molecules are managed in layers perpendicular to the substrate planes, which are separated by one or two micrometres, and within the layers the molecules are tilted, as demonstrated in the figure. The host liquid crystal holds optically active molecules, and a minor turn up of the optical activity and the angle of the molecules is the presence of a permanent charge separation, or ferroelectric dipole, comparable to the ferromagnetic dipole of a magnet. The direction of this dipole is perpendicular to the tilt direction of the molecules and within the plane of the layers. Hence, there exists a permanent charge separation through 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 correct sign can reverse the direction of this dipole in tens of microseconds and by doing so reverse the tilt direction of the molecules. The resultant change in optical properties can create a change from light to dark in the case that one or more polarizers are employed.
SSFLC devices have been marketed for large passive-matrix presentations, but their expensiveness and complexity has hindered them from creating any great progress on the market. Small transmissive and reflective active-matrix SSFLC displays, however, have some probability for use as parts in projection systems or as viewfinders in digital cameras. Their speedy reaction allows them to be made use of in time-sequential colour systems, in which highly expensive colour filters are replaced with a coloured backlight that flashes red, green, and blue in fast speed (about 100 cycles every second). For example, the liquid crystal might be switched to a transmissive state for the red and green periods but 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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