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#Post#: 64--------------------------------------------------
What Is an LCD Monitor?
By: Lion_Heart Date: January 22, 2013, 9:06 am
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An LCD monitor is a thin, light computer monitor that displays
images through the use of a liquid crystal display. LCD screens
are found in most laptop computers as well as in flat panel
monitors, and have replaced traditional cathode ray tube (CRT)
monitors for many users. CRTs once were preferred by many users
for their superior color presentation; improvements in LCDs have
made the difference less noticeable, but still important to
graphics and photography professionals and serious amateurs.
Inside the LCD
A color monitor is typically made up of five layers: a
backlight, a sheet of polarized glass, a mask of colored pixels,
a grid layer of responsive liquid crystal solution, and a second
polarized sheet of glass. Images are created manipulating the
orientation of the crystals through precise electrical charges
of varying degrees and voltages. They act like tiny shutters,
opening or closing in response to the stimulus, thereby allowing
degrees of light that have passed through specific colored
pixels to illuminate the screen.
As LCD technology has evolved, different techniques for
producing color have emerged. Passive matrix screens, which were
the first invented, use two transistors — one for each row and
one for each column of pixels — to activate a particular point
on the LCD grid. Active-matrix screens usually use thin film
transistor (TFT) technology, in which each point on the grid has
its own transistor; this allows only the desired pixels to be
activated. Passive matrix screens tend to respond more slowly
than active matrix screens, and are not able to produce the same
level of image quality.
Monitor Specifications
Most modern LCD computer monitors use active matrix technology.
Within this group, there are a number of specifications that set
one LCD monitor apart from another. Size, aspect ratio, and
resolution are three related features; contrast ratio,
brightness, viewing angle, and response time are also important.
The size of an LCD monitor can affect its price, resolution, and
aspect ratio. Larger monitors are more expensive; the
transistors that are used to make active matrix displays have a
high failure rate, and since bigger monitors have more
transistors, consumers are paying in part for those that are
defective and cannot be sold. Aspect ratio refers to the shape
of the screen, with standard screens usually having a 4:3 or 5:4
ratio. Widescreen monitors tend to be bigger, but allow images
to be viewed in a 16:9 (or 16:10) aspect ratio.
A bigger screen may also allow for a higher native resolution,
or the number of pixels it can display. A screen with a high
native resolution will be very sharp, and be able to display
more information than one with a lower resolution can. Most
monitors can display resolutions other than what is native, but
the image may appear blurry.
Contrast ratio relates to the display's comparative difference
between its brightest white values and its darkest black. A
higher contrast ratio will have truer colors with less washout,
and allow for a greater range of shades. The standard offering
for lower-end models is commonly 350:1, but many experts
recommend a contrast ratio of 500:1 or better.
LCD monitors tend to be bright, with standard levels being more
than adequate for everyday use. Brightness is measured in nits,
units of one candela per square meter. Anywhere from 250 to 300
nits is standard, although people who play games may benefit
from a brighter screen. If the nits are much higher, the user
will likely end up adjusting the brightness down for regular
use.
The vertical and horizontal viewing angle specifications refer
to the degree the viewer can stray from dead center before the
picture starts to wash out. Most monitors are looked at
straight-on, but wider angles can benefit people who use
multiple screens, or if the screen will be used by several
people at one time. Many experts recommend a viewing angle of at
least 140° horizontal and 120° vertical, but the wider the
viewing angles, the better.
Response time is measured in milliseconds (ms) and refers to how
long it takes pixels to turn from completely white to black and
back again. Smaller values represent a faster response time and
are more desirable, especially for playing games and viewing
videos. If the response time is slow, ghosting or trailing can
occur with fast-moving images, where images linger as the screen
refreshes. A maximum response time should be no more than 25 ms
for general use, and 17 ms is better. Many gamers report no
ghosting using an LCD monitor with a response time of 16 ms or
less.
Advantages
One major advantage of LCD monitors are their size; they are
commonly 1 to 3 inches (2.5 to 7.5 cm) thick and weigh less than
10 pounds (4.5 k). CRT monitors, on the other hand, have a depth
five times as large, and a weight of 30 to 50 pounds (13 to 23
kilograms) or more. As such, LCDs can take up 90% less space,
and are far easier to move or adjust.
A wide variety of screen sizes are available, from 15 to 30
inches (38.1 to 76.2 cm) or larger. For average sizes — 22 to 24
inches (55.88 to 60.96 cm) — the price of an LCD monitor is
about the same as a traditional CRT. LCD screens tend to last
longer, however; in addition, if a few pixels on the screen
fail, the monitor is still usable in most cases.
LCDs use relatively little electricity, especially when compared
to their CRT counterparts, and produce far less heat. They also
emit very low levels of electromagnetic radiation. LCD monitors
are also easier on the eyes; glossy or matte screens are usually
available, and matte screens reduce glare.
Disadvantages
LCD monitors have largely displaced CRTs in most monitors,
except for very cheap and very expensive models. CRTs still can
offer better color content and depth at the high end, and also
have the advantage of multisync, or the ability to keep colors
consistent even when a picture's resolution is changed. Colors
on LCDs may also change hue as the viewer moves to the outer
limits of the viewing angle, particularly on displays with
narrow viewing angles and low contrast ratios. Graphics,
photography, and design professionals, as well as medical
professionals, usually have preferred CRT monitors for these
advantages.
A potential weak link of an LCD monitor is the backlight. Since
the liquid crystals do not produce any light on their own, if
the backlight fails, the monitor is unusable. Many monitors come
with a three-year warranty, but stipulate one year for the
backlight.
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