The LCDs put in projection systems are most often small reflective or transmissive panels lit up by a forceful arc lamp source. A line of lenses enlarges the reflected or transmitted image then displays it on a screen. For front-projection systems the LCD is situated on the side of the screen as the viewer, although in rear-projection systems the screen is set off from behind. Projectors of more expense and performance might utilise three discrete LCD panels, forming separate red, green, and blue images that blend to create a coloured picture on the screen.
The growth in need for film presentations has put a special emphasis on the switching speed of liquid crystals. This has necessitated the creation of objects build with smectic liquid crystals, certain ones of which emit a faster electro-optical response than nematic liquid crystals. The surface-stabilized ferroelectric liquid crystal (SSFLC) display is currently the most progressive smectic device. With it the liquid crystal molecules are set out in perpendicular layers to the substrate planes, which are separated by one or two micrometres, and throughout the layers the molecules are on a tilt, as shown in the figure. The host liquid crystal holds optically active molecules, and a subtle outcome of the optical activity and the shape of the molecules is the appearance 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 through the plane of the layers. Therefore, there exists a permanent charge separation over the liquid crystal layer in the SSFLC, and its sign is directly coupled to the tilt direction of the molecules. An applied voltage of the corresponding sign can reverse the direction of this dipole in tens of microseconds and therefore reverse the tilt direction of the molecules. The resultant change in optical properties can cause a change from light to dark in the case that one or more polarizers are used.
SSFLC devices have been commercialized for big passive-matrix displays, but their high cost and complex detail has stopped them from enjoying any particular movement on the market. Small transmissive and reflective active-matrix SSFLC displays, however, have displayed some probability for use as parts in projection systems or as viewfinders in digital cameras. Their speedy responding allows them to be utilised in time-sequential colour systems, in which high cost colour filters are emulated by a coloured backlight that flashes red, green, and blue in rapid pulsing (about 100 cycles per second). For example, the liquid crystal may be switched to a transmissive state for the red and green periods then to a nontransmissive state for the blue period, displaying the outcome that the eye sees an average of red and green light, or the colour yellow.
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