(^390) PC Hardware: A Beginner’s Guide
them perfect for thermometers and mood rings. This is also why notebook computer
displays do not work exactly right after being exposed to cold or heat for very long.
More than one type of liquid crystal exists, but computer displays are what are called
twisted nematic(TN) crystals, which are rod-shaped crystals that are twisted lengthwise.
When a current of electricity is applied to a TN crystal, it begins untwisting in a predict-
able way. With enough electricity applied, the TN crystal will completely untwist. These
are the crystals used in LCD flat-panel monitors.
Without getting too technical, TN crystals are placed on layers of polarized glass filters.
Without electricity applied to the liquid crystal, light passes through the first glass filter to the
last one. When electricity is applied to an area of a filter, the TN crystals in that area begin
untwisting, which blocks the path of the light and creates a darkened area on the display.
The Liquid Crystal Display
The display is constructed from layers of different materials, all of which are designed to
play a part in using light to create an image on the display. As shown in Figure 16-12, the
layers in the LCD are (bottom to top):
Mirror The back of the LCD is a mirror for reflecting light.
Polarizing film A piece of glass coated with a polarizing film on its back.
Figure 16-12. The layers of an LCD
Polarizing film
Glass with electrode
Liquid crystal
Polarizing film
Electrode
Mirror
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