Found this article from a few weeks ago:
extremetech.com
Flat panel display technology:
Every time you look into a cathode ray tube (CRT) in a computer monitor or
television, you're looking at technology that is over 100 years old. While CRT
manufacturers have made some amazing improvements, the fact remains that thin is
in, and people really want the lightweight, small footprint, and sharp image that you
get with a flat panel display.
But there are a lot of different types of flat panel displays, and some are better suited
for some tasks than others. To understand these differences, it helps to know a bit
about how flat panels work and how they are manufactured, what is available now and
what is just over the horizon, and how all this adds up to affect your current and future
display purchase decisions.
LCD Technology
The number 2 technology--and gaining--behind CRTs is clearly liquid crystal display
(LCD) technology. This approach takes many forms, and is the mainstay for
notebook and handheld computers. It also plays a central role in data projectors, is
making inroads into the desktop monitor market, and is even finding applications in
head-mounted and other near-to-eye uses.
LCD Background
The technology itself is older than you might expect. The special properties of liquid
crystals were discovered by an Austrian botanist, F. Renitzer, in 1888. It took 85
years for these properties to be commercially exploited, with Sharp Electronics in
Japan releasing the first product: an electronic calculator with a digital display in
1973.
Nematic Materials
Liquid crystals get their name from the fact that the molecules are crystals, but they
form a liquid instead of a solid. The most commonly used compounds are made up of
an alkyl group and a biphenyl group (often with fluorine or cyano-terminal groups).
The liquid nature of these crystals makes their two
most useful characteristics possible. If you run an
electric current through a layer of liquid crystals,
they will orient themselves in relation to the
positive and negative poles of the current. In the
absence of a current, they will try to line up in
parallel with each other, but if you provide a
surface with fine grooves, the layer next to the
surface will line up with the grooves.
A third characteristic completes the magic that
makes liquid crystals useful; a layer can bend light
waves. A liquid crystal layer acts as a polarizer,
which means that it can filter out all the light waves
except those that are oriented in a specific
direction. Furthermore, if the crystals in the layer
are twisted, the light waves will actually follow the
twist, and come out the other side of the layer with
a different orientation than when they entered.
Taken together, these three attributes let liquid
crystals be used as a switch that can either block
or transmit light. The bottom surface of the liquid
crystal cell is made with tiny ridges that cause the
molecules next to this layer to line up in parallel. A top surface also has ridges that
make the molecules adjacent to it line up. The molecules between these two layers
then line up in parallel, but if the ridges in the top and bottom surfaces are at an angle
to each other, the liquid crystals try to line up with both surfaces, and so twist
slightly in between. The result is a spiraling layer that can twist light as it passes
through.
If an electrical current is run through the liquid crystal layer, all the molecules will line
up to match the flow of the current, which eliminates the twist of the light. Stated
another way, an electric current effectively lines up the top and bottom layers to
eliminate the twist effect. If a polarizing filter is placed on top of the liquid crystal layer
so that it lets the twisted light pass through, the untwisted light will be blocked. As a
result, the presence or absence of the electrical current can determine whether or not
the light will be transmitted or blocked. In other words, the electricity can be used to
turn the light on and off. In some designs, with the application of electricity, no light
passes, but with no electricity, light passes through (from the backlight)...
...(and a whole lot more at the above link!!) |
