The initials LCD stand for Liquid Crystal Display. LCD
screens have been used for a number of years in calculators, but over the last five years
their use has increased considerably due to the development of computers (both desk top
and lap top), mobile phones, digital cameras and especially televisions. It is likely that in a
few years all televisions will have screens of this type.
The screen of an LCD TV is
made of millions of liquid crystals. Each crystal is like the shutter of a camera either blocking
the light or allowing it to pass through. You can control the amount of light that passes
through by applying a voltage to a crystal or pixel. It does this by rotating the plane of
polarisation of the light. A much-simplified diagram of this action is shown in Figure 1.
Colour is added to the signal
by a red, green or blue filter that is added to sections of each pixel.
The light is
provided by a light source behind the screen with a diffusion panel that scatters the light to
ensure that all pixels in the screen are lit evenly.
They are extremely energy-efficient; using 60% less power than a similar
sized cathode ray type TV tube. They are also much lighter than conventional screens which
makes them not only much more versatile but also much more portable. They also do not
suffer from the high altitude problems that can affect plasma screens. Another advantage is
that the LCD screen uses filters and not phosphor dots to give the colour. This means that
there is no 'burn in' (a permanent change of colour of part of the screen due to defects or if
the image on the screen remains the same for long periods.
One of the biggest
problems of TV manufacturers is to make the pixels respond rapidly to the changing voltages
so that they switch on and off quickly. If they don't then any moving images on the screen will
be blurred.