Light valves, such as liquid crystal (LC), digital micromirror device (DMD), and light grid valve (GLV), reflect or allow light to pass through. LCs polarize light and are used with a polarizer, while GLVs modulate diffraction of light. DMDs use hinge-mounted arrays of microscopic mirrors to turn on or off, with one chip for each primary color in high-end units. DMDs have a faster response time than LCs but are slower than GLVs.
A light valve is a device that reflects light or allows light to pass through the shutter. Light tubes have a wide range of uses from televisions to top secret military applications. A light valve can be liquid crystal (LC) or a nanomechanical device. Nanomechanical devices include the digital micromirror device (DMD) and the light grid valve (GLV).
Liquid crystals, a naturally occurring substance, were originally identified in 1889 by Friedrich Reinitzer working at the Charles University in Prague. LCs remained little more than a novelty until 1969, when major steps towards a commercially viable material were made. The property of LCs that allows them to function as light tubes is their ability to polarize light. LCs are used with a polarizer, which either lets light through or reflects it, based on its polarity. An electric current applied to the device determines the polarity.
GLVs were developed at Stanford University by Dr. David Bloom and some of his graduate students. One of Bloom’s students, Raj Apte, outlined the technology’s potential commercial viability in his 1994 doctoral thesis. Dr. Bloom founded a start-up the same year to commercialize the technology. GLV devices are mechanical gratings that modulate the amount of diffraction light experiences as it encounters them. These devices are found in televisions and also used in military, technological and industrial applications.
DMDs were created by Texas Instruments in 1987 under the direction of Larry Hornbeck. The original concepts were aimed at detecting military objects, such as tanks and armored personnel carriers, during surveillance. A DMD is a light valve made up of hinge-mounted arrays of up to 1.3 million microscopic mirrors. Each chip corresponds to a pixel on a screen, and each can be turned on or off, either by passing light or by reflecting it. Many applications, such as TVs, home theater systems, and business projectors, use a one-chip system combined with a color wheel, and the speed and duration of each color shift are coordinated based on the color being displayed.
Very high picture quality requires a three-chip DMD unit. One chip is used for each primary color, with the same effect as the single-chip system. These high-end units are used in movie theaters, some televisions, and some military settings where very high resolution is needed. DMDs have a much faster response time than LCs, but are measurably slower than GLVs.
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