Liquid Crystal
Display (LCD) monitors are based on liquid crystals acting like
shutters where they allow light to either pass through or block
it. LCD technology was introduced to computers with notebooks. They
provide superior qualtity because there is no translation from analog
to digital.
Advantages
- Crisper and
more precise picture quality
- True, more
saturated color
- Flat displays
provide less distortion
- Uses 90%
less space than a CRT monitor
- Energy efficient
due to using less power and emiting less heat
If
you are in the market for an LCD monitor, you should be aware
that even though the specifications may be close, LCD monitors
may not be equal in quality.
The most popular
sizes are 15 and 17 inches. Unlike CRT monitors, the listed
size of an LCD represents the true viewable size. A 15 inch
CRT provides about 14 inches of viewable space. A 17 inch CRT
provides about 16 inches of viewable space. So the viewable size
on a 15 inch LCD is in between a 15 and 17 inch CRT. Currently
the maximum size for a LCD is 40 inches.
How
it Works
An LCD panel
consists of five layers.
- White
backlight that provides the illumination.
- Polarizing
filter that ensures the light waves from the backlight are
aligned in one direction.
- Very small
pattern of red, green and blue colors forming one pixel.
This layer works as a filter, only allowing light through one
of the three colors. The amount of fire power issued controls
the “twist”, affecting the amount of light.
- Actual
Liquid Crystal cells. Behind the cells is a grid of wires
that can be addressed by x, y coordinates. Your video display
controller issues a command to fire at the approriate coordinates.
- Another
polarizing filter that is perpendicular to layer two.
To simplify,
polarized light gets colorized and may or may not emerge from
the last polarizing layer depending on the “twist”.
One of the
problems with LCD displays is that when viewed from a side angle,
the color intensity drops. Different technology is used in creating
the pattern alignment to improve viewing from the side. The side
angle view quality is one of the things that makes a difference
in comparing different models.
Contrast
Ratio & Brightness
Two specifications
to check in comparing LCDs is the contrast ratio and brightness.
Both of these specs have to be considered in overall quality.
Typically the higher the brightness, the lower the side
viewing angle.
The contrast
ratio is a measurement comparing the brightest (white) and darkest
(black) pixels. A good contrast ratio is at least 500:1. A
minimum contrast ratio to consider is 350:1.
Brightness
is measured in nits. The average LCD currently is in the range
of 250-280 nits. Ultra-bright models are capable of 450 nits.
A higher nit level isn’t always good.
In a darker room, 450 nits would make you reach for your sun glasses.
Viewing
Angle
A viewing
angle of 160 degrees will provide viewing by a group of people.
If you never have to view your monitor from a side angle, a
minimum viewing angle of 110 degrees is adequate.
Response
Time
This is the
amount of time required for panel pixels to turn from completely
white to black and back again. This time is measured in milliseconds
(ms). Larger values for response time represent
a slower response. A minimum response time should be
at least 25ms and 17ms is recommended. If you have a digital
video card, you can use LCDs with a 16ms response time. Most users
only have an analog video card.
Panel
Quality
Many manufacturers
use a third party firm to provide the panels. Panels are rated
as A, B or C grades. Even within a given manufacturer, different
models will use different grade panels. There
are no specs that provide information as to the panel grade.
B and C grade panels are used by mass merchant
sites who want to move a volume at the lowest price.
Bezel
Size
If you multiple
displays, the thinner the bezel the better. This allows you to
put two LCDs side by side with very little space between the displays.
Portrait
and Landscape
Allows you
to see a full-size page as you would normally view it. You can
rotate the screen between portrait and landscape mode without
having to restart your computer.
Failures
The biggest
failure with LCDs is the backlight. Backlights are not cheap to
replace. The better models come with a three year warranty.
LCD
comparison to CRT
Before digging
into each feature, perhaps a simple explanation of how a CRT monitor
displays images should be clarified.
- The image
you see on the monitor is a series of tiny dots, called pixels.
- Each pixel
contains a mixture of three colors: red, green and blue.
It would appear
that once a program defines the color mixture for a given pixel,
the monitor would not have to re-display this pixel until the screen
actually changes. Nah, that would be too simple. The monitor
is constantly re-displaying the pixels, a row at a time. The
time it takes to redisplay is referred to as the refresh rate.
Resolution
represents the number of horizontal and vertical pixels.
Resolution sizes ranges are
- 640 x 480
- 800 x 600
- 1024 x
768
- 1280 x
1024
- 1600 x
1200
Most monitors
support several ranges. By default many monitors will start at
the 640 x 480 range. Only the larger size monitors, 17 inch and
greater, can support the higher ranges of 1280 and 1600.
So what does
the resolution control? The higher the resolution values
the crisper and smaller the image. If an image required
5 x 5 pixels to display on a screen with 640 x 480 resolution,
it would take less space to show this image than on a resolution
of 1024 x 768.
Because there
are more dots on a higher resolution, you can see more on the
screen. The down side is the images are smaller in size.
This is why larger size monitors are needed to run the larger
resolutions. The confusion here is the "larger"
the resolution values, the "smaller" the image. Basically
the pixel size is reduced in order to produce more pixels on the
screen.
Graphic
Resolution
For graphic
applications, sharp images are important. Therefore a higher
resolution along with a larger screen provides the best solution.
At least 1024 or greater and 17" in size.
Non-Graphic
Resolution
For non-graphic
applications, resolution sizes up to 1024 and 15"
monitors are fine.
A special
note on resolution sizes. Having a monitor that can handle a large
resolution doesn’t always mean it will work on your system.
You must also have a video adapter card
that will handle the resolution size of your choice.
As stated
earlier, monitors are constantly re-painting the pixels. Because
a higher resolution requires more pixels, a faster refresh rate
is required in order to reduce visible flicker. The refresh
rate is the number of times per second that each line is re-painted.
It is normally expressed in hertz (Hz).
If
the refresh rate is too slow, the screen will have a flicker.
A visible flicker can be very annoying and cause excessive eye
strain.
Graphic
and Non-Graphic
A reasonable
refresh rate, at the resolution size you want to use, should
be greater or equal to 70 Hz. One of the main differences
between the lower vs. high end monitors is the speed of the
refresh rate.
Older technology,
in order to improve on the flicker problem, used a method called
interlacing. This method re-displayed every other line. This was
an attempt to reduce the appearance of flicker without actually
increase the refresh rate. Interlacing was and is used on lower
cost monitors. The new and better monitors
are non-interlaced and have a higher refresh rate to avoid flicker.
Not to be
confused with pixie dust, pixel pitch is the distance between
dots of the same color. Each pixel is made up of three color
dots: red green and blue. The distance between each red dot is
the pixel pitch or sometimes referred to as the dot pitch. This
distant is measured in fractions of a millimeter and is expressed
as .28mm. This distant is the main
factor in the apparent quality of the monitor.
It would at
first seem reasonable that the smaller the distant between each
dot, the better the image quality. The problem is as the pitch
gets smaller, the electron beam that shoots the dots has a more
difficult time hitting the target. This results in an image with
less intensity. So there is a trade off between sharpness and
intensity.
There are
basically two types of screen technologies, shadow mask
or aperture grille.
Sony Trinitron
monitors use the aperture grille method. NEC monitors
use the shadow method. Some brand monitors have either type available.
The type you choose is more a matter of personal preference.
Color calibration
controls are available on high-end monitors intended for professional
graphic applications. For the non-graphic or typical user, color
calibration is not an important feature.
Aperture
Grille CRT
Delivers superior
vertical definition as a result of striped phosphate alignment,
as well as improved brightness for more uniform image contrast without
loss of focus.
Aspect
Ratio
The ratio of
width to height of a display surface.
Bandwidth
The range of
frequencies a monitor can accept without degrading the video signal.
It is measured in millions of cycles per second, or megahertz (MHz).
Bandwidth plays an important part in determining the overall resolution
of the monitor.
Cathode
Ray Tube (CRT)
An evacuated
(i.e. a vacuum) tube containing an anode and a cathode in which
the electron beam is deflected horizontally and vertically to produce
images.
Digital
Visual Interface (DVT)
A high-speed
video interface supporting both analog and digital video signals.
Dot
Pitch
The distance
between the triads, measured in tenths of a millimeter. Each set
of triads in the monitor is separate from the next, which is called
the dot pitch. The shorter the distance, the better the resolution
and the crisper the image.
Dot
Trio
RGB phosphor
arrangement employed with a metal shadow mask.
Gamma
Comp
Automatically
converts 8-bit data from the PC to 10-bit and back to 8-bit, producing
smooth, accurate color tones.
Grille
Pitch
Measurement
of phosphor arrangement as they occur in an aperture grille CRT.
Invar
shadow mask
Holes in the
thin metal sheet behind the glass of the CRT surface corresponds
to each phosphor dot on the inner surface of the CRT's faceplate,
allowing the correct electron beam (red, green and blue) to hit
the correct color phosphor for improved focus, brightness and color.
ISO
113406-2, Class 2 requirements
Obliges the
panel manufacturer to give comparable information about the features
of the display. These include luminous intensity, contrast, reflection,
color reproduction, uniformity of intensity and color, font analysis,
flicker, pixel faults and viewing angle classification.
Multiple
Frequency Technology
Automatically
adjusts the monitor to the display card's scanning frequency, thus
displaying the resolution required.
Pivot
and Portrait/Landscape Functionality
Adds flexibility
to the user's viewing preferences by allowing them to change the
orientation of the monitor via the stand. Depending on monitor screen
size, users are able to view documents in their entirety without
having to sacrifice font, size or zoom level.
Pixel
The smallest
segment of a raster line that can be discretely controlled by the
display system. Usually referred to as pixels per line and lines
per frame.
Power-off
Timer
Automatically
turns the monitor's power off after a user-determined amount of
time (1-24 hours), thereby reducing electric power cost.
Resolution
The combination
of the number of horizontal dots per line and lines per frame in
a raster display device. This term refers to how sharply an image
can be defined on the screen of the monitor. Generally, the higher
the numbers, the finer the display.
sRGB
A recommended
default color setting that helps achieve a consistent color environment
for PC-based applications. With sRGB, the image colors seen by the
user on screen can be reproduced elsewhere, such as printers.
Tile
Matrix
Allow you to
build video walls of various configuration (up to 5 x 5) through
the advanced DSM.
Tilt
Capability
Allowing the
monitor to tilt forward and backward, this feature adds flexilblity
and comfort to user viewing.
Total
Cost of Ownership (TCO)
The total cost
of owning a product over its life cycle. For example, the cost of
owning a personal computers doesn't end with the purchase price.
The costs associated with procuring and using that computer over
its life, acquisition cost, operational cost, administration, training,
repairs, even disposal of the product when it needs to be replaced,
all contribute to TCO.
Triad
A pattern of
three phosphor colors, RGB, put on the screen in a dot pattern called
a dot triad. The arrangement of the three-color dots physically
matches the orientation of the three guns in the CRT.
USB
Hub
Device connection
ports that, allow users to easily connect peripherals such as videoconference
cameras, scanners, keyboards and mice.
Video
Electronics Standards Association (VESA)
A non-profit
member organization dedicated to facilitating and promoting personal
computer graphics through improved graphics standards for the benefit
of the end user.
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