The LCDs built in projection systems are most often small reflective or transmissive panels lit up by a strong arc lamp source. A line of lenses magnifies the reflected or transmitted image then displays it onto the screen. In front-projection systems the LCD is situated on the same side of the screen as the viewer, while in rear-projection systems the screen is illuminated from behind. Projectors of higher expense and capability sometimes use three discrete LCD panels, creating separate red, green, and blue images that come together to form a coloured picture on the screen.
The increasing need for video displays has granted a growth in emphasis on the switching speed of liquid crystals. This has led to the manufacture of objects utilizing smectic liquid crystals, some of which possess a better electro-optical response than nematic liquid crystals. The surface-stabilized ferroelectric liquid crystal (SSFLC) display is at this time the most sophisticated smectic device. In it the liquid crystal molecules are managed in perpendicular layers to the substrate planes, which are distanced by one or two micrometres, and inside the layers the molecules are on a slant, as displayed in the figure. The host liquid crystal contains optically active molecules, and a scarcely perceptible turn up of the optical activity and the angle of the molecules is the appearance 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 through the plane of the layers. Therefore, there exists a permanent charge separation throughout 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 in so doing reverse the tilt direction of the molecules. The consequential change in optical properties can cause a change from light to dark if one or more polarizers are employed.
SSFLC devices have been commercialized for big passive-matrix presentations, but their expense and detail has impeded them from enjoying any great movement on the market. Small transmissive and reflective active-matrix SSFLC displays, however, display some promise for use as aspects 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 emulated by a coloured backlight that flashes red, green, and blue in rapid pace (approximately 100 cycles per second). For example, the liquid crystal could be switched to a transmissive state during the red and green periods and then to a nontransmissive state during the blue period, displaying the end result that the eye sees an average of red and green light, or the colour yellow.
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