Why can fast liquid crystal switching be useful in digital camera viewfinders and projection systems?
In nematic arrangements the crystals are randomly positioned with all their long axes pointing in essentially the same direction, given by a vector known as the director. In smectic arrangements the crystals are further constrained to parallel planes; in smectic A the director is perpendicular to these planes, while in smectic C the director is at some other angle to the planes.
Fast liquid crystal switching is particularly valuable for digital camera viewfinders and projection systems because it enables the use of time-sequential colour systems.1
In these systems, instead of using traditional, costly colour filters, a coloured backlight flashes red, green, and blue in rapid succession—typically at a rate of about 100 cycles per second. Because the liquid crystals can switch states in tens of microseconds, they can synchronize with these flashes, alternating between transmissive and nontransmissive states to modulate the light. This allows the human eye to perceive a composite colour image, such as yellow, by averaging the rapid sequence of red and green light.1
This high-speed response is essential for maintaining image quality in these compact devices, as it prevents the motion blurring that can occur when liquid crystals respond too slowly to electric charges.12