The LCDs built for projection systems are most often small reflective or transmissive panels lit by a powerful arc lamp source. A line of lenses expands the reflected or transmitted image and then sends it onto 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 lit up from behind. Projectors of more expense and capacity sometimes have three discrete LCD panels, casting separate red, green, and blue images that mesh to form a coloured image on the screen.
The increase in desire for visual presentations has had a particular emphasis on the switching speed of liquid crystals. This has necessitated the manufacture of items employing smectic liquid crystals, certain ones of which have a better electro-optical response than nematic liquid crystals. The surface-stabilized ferroelectric liquid crystal (SSFLC) display is currently the most progressive smectic device. Within it the liquid crystal molecules are set out in perpendicular layers to the substrate planes, which are differentiated by one or two micrometres, and in the layers the molecules are slanted, as shown in the figure. The host liquid crystal has optically active molecules, and a minor outcome of the optical activity and the angle of the molecules is the appearance 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 through the plane of the layers. So, there is a permanent charge separation through 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 correct 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 when one or more polarizers are employed.
SSFLC devices have been publicized for large passive-matrix presentations, but their cost and intricacy has impeded them from having any significant progress 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 fast responding allows them to be made use of in time-sequential colour systems, in which highly expensive colour filters are replaced by a coloured backlight that flashes red, green, and blue in rapid pace (about 100 cycles a second). For example, the liquid crystal could be switched to a transmissive state between the red and green periods 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.
For help with choosing and purchasing your data projector, contact projectors brisbane and projectors gold coast.
