A light valve (LV) is a device for varying the quantity of light, from a source, which reaches a target. Examples of targets are computer screen surfaces, or a wall screen in the case of a light projector. There are two basic principles of achieving this. One is by deflecting the light on its way to the target (a

reflective Reflection is the change in direction of a wavefront at an interface between two different media so that the wavefront returns into the medium from which it originated. Common examples include the reflection of light, sound and water waves. The ' ...

LV). The other method is to block the light (a transmissive LV). The blocking method has found its way into liquid crystal flat screens ( LCDs),

video projectors A video projector is an image projector that receives a video signal and projects the corresponding image on a projection screen using a lens system. Video projectors use a very bright ultra-high-performance lamp (a special mercury arc lamp), X ...

and rear projection TVs. In this type of screens and projectors, the source light is first polarised by a filter in one direction and then passed on to another filter, filled with

liquid crystals Liquid crystal (LC) is a state of matter whose properties are between those of conventional liquids and those of solid crystals. For example, a liquid crystal may flow like a liquid, but its molecules may be oriented in a crystal-like way. Th ...

. By changing the voltage applied to this crystal filter, it will work as a switching polarising filter, giving different gray scales of the light coming out. The light is changed only once for each image frame. The light valve thus consists of the two polarising filters, where one has a voltage controlled switch function thanks to the properties of the liquid crystals. This type of valve is often referred to as a ''liquid crystal light valve''. The other principle, the reflective LV, works by either reflecting the light towards the target or deflecting it away. The portion of light that is reflected on the target decides the gray scale. This re- and deflection occurs many times a second. Should this happen at too low a frequency, the human eye and brain would perceive it as flickering, but due to sufficiently high frequency, a human will be "tricked" into viewing it as a continuum, a smooth shift in brightness. Examples of the reflective LV type are the

Digital Micromirror Device The digital micromirror device, or DMD, is the microoptoelectromechanical system (MOEMS) that is the core of the trademarked DLP projection technology from Texas Instruments (TI). Texas Instrument's DMD was created by solid-state physicist and ...

(DMD),

Eidophor An Eidophor was a video projector used to create theater-sized images from an analog video signal. The name Eidophor is derived from the Greek word-roots ''eido'' and ''phor'' meaning 'image' and 'bearer' (carrier). Its basic technology was th ...

's oil-film based system,Light valve
and the Grating Light Valve.

References

Display technology Optics {{physics-stub

See also

References