LCD
or flat panel computer displays are the latest and greatest offerings
in the desktop computer industry. They have been used for years in the
portable and notebook computing markets, but recent developments have
increase performance and size while reducing costs making them viable
in the desktop environment. LCD displays are lightweight, extremely
thin and use much less power than CRT based monitors.
Screen Size
Unlike CRT monitors, LCD displays are marketed by the actual
screen dimensions. This is the measurement of the displayable area of
the screen from the lower corner to the opposite upper corner of the
display. One of the more confusing aspects with LCD's is their aspect
ratio of the screen. Most CRT displays have a 4:3 ratio of horizontal
to vertical measurement.
zSB(3,3)
Some LCD screens are marketed as a wide screen display that
still have the marketed diagonal measurement, but its aspect ratio can
be similar to the 16:9 displays used by wide screen TVs. So be sure to
look for the aspect ratio or the vertical and horizontal measurements
as well.
Native Resolutions
All LCD screens can actually display only a single given
resolution referred to as the native resolution. This is the physically
number of horizontal and vertical pixels that make up the LCD matrix of
the display. Setting a computer display to a resolution lower than this
resolution will either cause the monitor to use a reduced visible area
of the screen or it will have to do extrapolation. This extrapolation
attempts to blend multiple pixels together to produce a similar image
to what you would see if the monitor were to display it at the given
resolution but it can result in fuzzy images.
Here are some of the common native resolutions found in LCD monitors:
- 14-15": 1024x768 (XGA)
- 17-19": 1280x1024 (SXGA)
- 20"+: 1600x1200 (UXGA)
- 19” (Widescreen): 1440x900 (WXGA+)
- 20” (Widescreen): 1680x1050 (WSXGA+)
- 24” (Widescreen): 1920x1200 (WUXGA)
- 30” (Widescreen): 2560x1600
Contrast Ratio
All LCD screens get their brightness from lighting behind the
actual LCD films. This light has the tendency to wash out the colors
and provide a close approximation on most colors. The contrast ratio of
a LCD flat panel is the rating of how distinguishable various shades of
color are. The higher the contrast ratio of the screen, the better the
color representation is by the monitor. When comparing monitors try to
find two models of similar size from the same manufacturer with
different contrast ratios. The screen with the higher contrast ratio
should have better color.
Viewing Angles
LCD's produce their image by having a film that when a current
runs through the pixel, it turns on that shade of color. The problem
with the LCD film is that this color can only be accurately represented
when viewed straight on. The further away from a perpendicular viewing
angle, the color will tend to wash out. The LCD monitors are generally
rated for their visible viewing angle for both horizontal and vertical.
This is rated in degrees and is the arc of a semicircle whose center is
at the perpendicular to the screen. A theoretical viewing angle of 180
degrees would mean that it is fully visible from any angle in front of
the screen. A higher viewing angle is preferred over a lower angle
unless you happen to want some security with your screen.
Response Times
In order to achieve the color on a pixel in an LCD panel, a
current is applied to the crystals at that pixel to change the state of
the crystals. Response times refer to the amount of time it takes for
the crystals in the panel to move from an on to off state. A rising
response time refers to the amount of time it takes to turn on the
crystals and the falling time is the amount of time it takes for the
crystals to move from an on to off state. Rising times tend to be very
fast on LCDs, but the falling time tends to be much slower. This tends
to cause a slight blurring effect on bright moving images on black
backgrounds. The lower the response time, the less of a blurring effect
there will be on the screen.
Connectors
Most LCD panels still use the traditional analog VGA connector
known as the DSUB-15 or HD15 connector. This is the same connector that
is used on all CRT monitors and on most PC video cards. Newer LCD
displays and video cards are starting to use the DVI connector. This is
a digital interface that is supposed to allow for a cleaner and
brighter picture compared to standard VGA connectors. Check to see what
type of connector your video card can use before buying a monitor to
ensure you get a compatible monitor. Some monitors may also come with
composite video connectors to allow them to function as a TV screen.
Technical Update 
