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The most important component in a
monitor is the picture tube, also called a cathode ray tube
(CRT) or liquid crystal display (LCD) . The CRT or LCD is what
makes the image that you see on the screen, and its
characteristics primarily determine the quality of the
image you see. A good monitor has a good CRT or LCD. Fancy controls
and
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other features can not make up for a bad
tube. Another consideration of the monitor is the size. Next
to the computer itself, selecting good monitor is an
investment. In fact, a good monitor will not depreciate as
fast as the computer you select and as fast as technology
changes you may want to use it with your next computer
purchase. Of coarse, the better and bigger, the more expensive
too.
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Analog CRTs
All monitors today are called analog monitors,
while the circuitry that controls it is still digital. What makes
them analog is the color signals that are received from the video
card called the RAMDAC. Originally, monitors used digital color
signals, meaning each color had only a certain pre-set number of
color levels that were supported. This was the case for CGA and
EGA video cards and the monitors that work with them. IBM started
the VGA standard allowing for shades of three primary colors. An
analog signal can use a range of 256 different color values for
each color. Calling a monitor "digital" refers to the
type push button controls it uses. Dial type controls are analog.
LCD Flat Screen
LCDs (liquid crystal display) are used for displays in
notebook and in flat screen monitors. LCDs allow displays to
be much thinner than cathode ray tube technology. LCDs consume
much less power than LED and gas-display displays because they
work on the principle of blocking light rather than emitting it.
An LCD is made with either a passive matrix or an active matrix
display display grid. The active matrix LCD is also known as a
thin film transistor (TFT) display. The passive matrix LCD has a
grid of conductors with pixels located at each intersection in the
grid. A current is sent across two conductors on the grid to
control the light for any pixel.
An active matrix has a transistor located at each pixel
intersection, requiring less current to control the luminance of a
pixel. For this reason, the current in an active matrix display
can be switched on and off more frequently, improving the screen
refresh time (your mouse will appear to move more smoothly across
the screen, for example).
Note: Flat LCD monitors should not be confused with flat
CRT monitors.
Viewable Sizes
The viewable size represents the diagonal
width of the monitor screen from one corner of the screen to the opposite corner of
the screen in inches. CRT monitor sizes, however, are normally advertised as a single number
as the diagonal width of the monitor in inches. 15-inch monitors can have a viewable size
of 13.6 inches to 14 inches 17-inch monitors can have a viewable size of 15.7
inches to
16.2 inches.
Dot Pitch
Monitor size is advertised with a dot pitch
specification, usually from 0.22 to 0.28 in mm (millimeters). The CRT screen is made up of
small elements of red, green and blue phosphorous material, called
dots or pixels. The dot pitch is
the distance between adjacent sets of red, green and blue dots. The dot pitch of the
monitor indicates how fine the dots are that make up the picture. The smaller the dot
pitch, the more sharp and detailed the image. Each dot is illuminated to a specific
intensity based on the video signal, and the use of red, green and blue dots allows the
creation of a large number of different colors. Each time a dot of material is struck by
the electron beam in the CRT, it glows for a fraction of a second and then fades.
Refresh Rates
In order to maintain a stable image a
electron beam must sweep the entire surface of the screen and then return to redraw it
many times per second. This process is called the refreshing of the screen. If the
electron beam takes too long to return and redraw a pixel, the pixel will begin to fade in
brightness and then return to full brightness when redrawn. Over the full surface of the
screen, this becomes visible as a flickering image. The refresh rate is the number
of times per second that the screen is refreshed. Refresh rates 72 Hz or above produce
acceptable results. Although, refresh rates set too high can damage a monitor. Microsoft
Windows has drivers for your monitor to properly set refresh rates to match screen
resolutions.
Screen Size Resolution
Monitors support a wide range of screen
sizes. The most popular is 640x480, 800x600, 1024x768, 1280x1024 and 1600x1200. A 640x480
will show a partial one page document in 100% mode, while expanding your screen to 800x600
will show the entire document. On a 15-inch monitor, however, a larger resolution may make
the words too small. |
