The LCDs utilised for projection systems are usually small reflective or transmissive panels lit up by a forceful arc lamp source. A series of lenses enlarges the reflected or transmitted image and sends it onto a screen. For front-projection systems the LCD is situated on the same area of the screen as the viewer, although in rear-projection systems the screen is lit up from behind. Projectors of higher cost and capability might use three separated LCD panels, reflecting separate red, green, and blue images that mesh to form a coloured display on the screen.
The growth in need for film presentations has put a special emphasis on the switching speed of liquid crystals. This has demanded the invention of devices employing smectic liquid crystals, certain ones of which emit a speedier electro-optical response than nematic liquid crystals. The surface-stabilized ferroelectric liquid crystal (SSFLC) display is at this point 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 slant, as illustrated in the figure. The host liquid crystal has optically active molecules, and a minor outcome of the optical activity and the tilt of the molecules is the presence of a permanent charge separation, or ferroelectric dipole, analogous 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. So, 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 right sign can reverse the direction of this dipole in tens of microseconds and so reverse the tilt direction of the molecules. The respective change in optical properties can create a change from light to dark if one or more polarizers are utilised.
SSFLC devices have been marketed for bigger passive-matrix displays, but their high cost and complex nature has prevented them from creating any particular progress on the market. Small transmissive and reflective active-matrix SSFLC displays, however, have displayed some probability for use as aspects in projection systems or as viewfinders in digital cameras. Their immediate responding allows them to be used in time-sequential colour systems, in which expensive colour filters are emulated by a coloured backlight that flashes red, green, and blue in fast pace (approx 100 cycles per second). For example, the liquid crystal can be switched to a transmissive state during the red and green periods and then to a nontransmissive state during the blue period, with the upshot that the eye sees an average of red and green light, or the colour yellow.
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