LCD (Liquid Crystal Display) is a
transmissive technology. As used in projectors it is essentially
the same technology as used in calculators, watches, and more
recently, televisions and flat panel TFT monitors. In the case
of an LCD projector, a light source shines through a grid array
panel, each individual cell thereof corresponding to a pixel.
If the projector (for example) is an XGA projector the grid will
be 1024 pixels wide by 768 high. The light levels passing though
each pixel can be manipulated between fully white and fully closed
(This is not quite true black in most LCD projectors). This is
achieved by some technical wizardry - There are 5 layers, 1 of
liquid crystal, 2 each of polarising filters & 2 transparent
electrodes. The polarising filters are typically arranged to allow
the light to pass through each pixel unless an electrical charge
is applied which "twists" the light passing between
the filters and thus blocks its passage through the pixel.
Most LCD projectors use three of these
LCD panels which each process a different primary colour (Red,
Green & Blue). By varying the amounts of each of these three
colours and then optically combining them each pixel can be
coloured as required. (100% Red, Green & Blue = White Light).
REAL LIFE
USAGE
LCD projectors are certainly the most popular type of model
out there due to their low power consumption and small size.
Over the years the colour rendering and contrast ratio of LCD
units has certainly improved, although DLP still offers a superior
contrast ratio. One drawback of LCD systems is the "barn door
effect" which can be seen when an LCD projector is used to project
a very large image. It is caused by the fact that pixels become
large enough to be seen, along with the grid between them. This
can be reduced by slightly de-focussing the projector.
We have range of LCD projectors in our hire & demo stock.
Please call or email us for details.
MORE INFO
For more detailed info on Liquid Crystal Display click
here for wikipedia defintion
For more info on Polarizing Filters click here
