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Lighting:
Liquid Crystal Displays (LCD) Lighting
By Lance Kaczorowski, Guest Writer
| Summary: Liquid crystal display, or LCD
lighting, appears everywhere - from on our watches to the
screens for computers. The technology behind liquid
crystal displays defies our understanding of typical
lighting. |
The first thing to recognize about liquid crystal display
lighting is that LCD technology is
a way of selectively blocking light, not a way of producing light.
Thus, LCD technology is not truly a light source technology, but it
is packaged in such a way that we often don't discern the
difference.
Many Different Applications
LCD technology appears everywhere from our watches to the screens
for portable computers.
In a computer screen, the light sources are actually thin
fluorescent tubes coupled with various techniques to even distribute
the light across the screen.
On watches, there is
a reflective surface under the LCD display, and the light source is
just the ambient light! Watches also have a separate light source
built in so that you can, at the push of a button, read your watch
in total darkness.
Affected by Temperature
"Liquid
crystal" sounds like a contradiction in terms. Yet some substances
at the right temperature are liquid yet still maintain numerous
microscopic rod-like structural shapes. Note that this special
state of matter is a function of the temperature. Thus, the screen
on your portable PC may behave oddly in very cold or very warm
environments.
Polarizing Filters
The orientation of these rod-like shapes is influenced by
electric currents. The rods can collectively act as a polarizing
filter.
Most of us are familiar with what happens when you use one or two
polarizing filters. Polarized sunglasses (a single polarizing
filter) significantly reduce glare. If you place two polarizing
filters together (one behind the other),
the amount of light that passes through depends on the alignment
between the two filters.
If the two filters are aligned together,
then light passes through as if there was only one filter. If you
rotate the two filters so as to be 90 degrees out of alignment, then
almost all of the light is
blocked.
The amount of light that is blocked depends on the angle of
rotation between the two filters.
Effects of the Filtering Process
An interesting effect takes place if you introduce a third
polarizing filter.
Place the first and third filter so that they are at 90 degrees
to each other. You would expect most of the light to be blocked.
However, the amount of light that passes through now depends on the
angle of rotation of the middle filter. In some positions, most of
the light is blocked, and in other orientations, the light passes
through.
In an LCD display, the liquid crystal material acts as the middle
polarizing filter. The liquid crystal actually also possesses a
complex twisting behavior (like multiple stacked polarizing
filters), but the simplified description here is sufficient.
How Colors are Displayed
The various colors are made by having very tiny areas of the screen
tinted red, green, and blue.
Thanks to our
guest lighting expert - Lance Kaczorowski,
who brings a wealth of expertise to the site:
Kaczorowski, a native of New York City, now resides in Fort Wayne,
IN. Kaczorowski has a 4-year degree in Mechanical Engineering from
the University of Texas at Austin, and also a 2-year degree in
Electronics Engineering Technology from the Community College of the
Air Force. Kaczorowski's broad work history includes
(chronologically): Three years as a Mercedes-Benz mechanic; six
years as an electronics technician with the Air Force; three years
as a new product development engineer with General Electric Lighting
in Cleveland; seven years as a new product development engineer and
an engineering analyst with Grote Industries in Madison, IN; and
currently as an engineering analyst with International Truck and
Engine Corporation in Fort Wayne.
The first two years
of Kaczorowski's employment with General Electric consisted of
extensive training in light source sciences and engineering under
GE's Edison Engineering Program. Kaczorowski's experience with
lighting was broadened at Grote Industries, which is a supplier of
vehicle lighting for heavy duty trucks.
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