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Reflective twisted nematic liquid crystal display.
A liquid crystal display, or LCD, is a thin, lightweight display device with no moving parts. It consists of an electrically-controlled light-polarising liquid trapped in cells between two transparent polarising sheets. The polarising axes of the two sheets are aligned perpendicular to each other. Each cell is supplied with electrical contacts that allow an electric field to be applied to the liquid inside.
Before an electric field is applied, the long, thin molecules in the liquid are in a relaxed state. Ridges in the top and bottom sheet encourage polarisation of the molecules parallel to the light polarisation direction of the sheets. Between the sheets, the polarisation of the molecules twists naturally between the two perpendicular extremes. Light is polarised by one sheet, rotated through the smooth twisting of the crystal molecules, then passes through the second sheet. The whole assembly looks nearly transparent. A slight darkening will be evident because of light losses in the original polarising sheet.
When an electric field is applied, the molecules in the liquid align themselves with the field, inhibiting rotation of the polarised light. As the light hits the polarising sheet perpendicular to the direction of polarisation, all the light is absorbed and the cell appears dark.
A group at RCA, headed by George Heilmeier , demonstrated the first operational LCD based on the dynamic scattering mode (DSM) in 1968. Heilmeier's company Optel produced a number of LCDs based on this principle. In 1969 James Fergason at Kent State University in Ohio discovered the twisted nematic field effect in liquid crystals, and in 1971 his company ILIXCO produced the first LCD based on this effect. These displays superseded the poor-quality DSM types.
A nit is a unit of luminance which is often used to quote the brightness of displays, which typically have luminances of 200 to 300 nits (cd/mē).
LCDs can be used in transmissive or reflective modes. A transmissive LCD is illuminated from one side and viewed from the opposite side. Activated cells therefore appear dark while inactive cells appear bright. This type is used in high-brightness applications such as pocket television receivers. The lamp used to illuminate the LCD in such a product usually consumes more battery power than the LCD itself.
A reflective LCD, as used in pocket calculators and digital watches, is viewed by ambient light reflected in a mirror behind the display. This type has lower contrast than the transmissive type, because the ambient light passes twice through the display before reaching the viewer. The advantage of this type is that there is no lamp to consume power, so the battery life is long. A small LCD consumes so little power that it can run from a photovoltaic cellA photovoltaic cell is a device that turns light into electric energy. There are three main types of photovoltaic cells. monocrystalline cells polycrystalline cells amorphous cells Monocrystalline cells are the most expensive to make because they require.
Transflective LCDs use a combination of transmissive and reflective modes.
Just to support this ... the NIT, even though easier to pronounce, is not an approved international unit for luminance any more. cd/m2 should be used instead.
A note to the above statement: In the reflective mode of operation, a reflector is used, but not a mirror-like reflector, rather a scattering reflector (structured metal).
Also the contrast of reflective LCDs is higher than the contrast of the same LCD in transmissive mode of operation !
Transflective mode of operation means reflective mode when ambient illuminance level is high and a low-power backlight provides transmissive illumination in dark and dim situations.
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