So once you are armed with this knowledge, selecting the correct monitor should be
a snap? Well, almost. There are still other features to
consider such as price, warranty, and reliability. But hopefully
this explanation will enable you to make an accurate comparison and
understand all those weird abbreviations.
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 quality 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 emitting 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 back light that provides the illumination.
- Polarizing filter that ensures the light waves from the back light 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 appropriate 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
Two specifications to check in comparing LCDs is the contrast ratio and brightness.
Both of these specs have to be considered in overall quality.
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
Brightness is measured in nits or candelas per square meter (CD/M2).
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. Typically the higher the brightness, the lower the side viewing angle.
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 or lower response time.
Ghosting/Latency
An effect of slower response times that cause blurring of images on an LCD monitor, it's also known as latency. The effect is caused by voltage temporarily leaking from energized elements to neighboring, non-energized elements on the display.
Native Resolution
This is the actual measurement of an LCD display, in pixels, given in horizontal by vertical order.
Stuck/Dead Pixels
A pixel that is stuck either 'on' or 'off', meaning that it is always illuminated, unlit, or stuck on one color regardless of the image the LCD monitor displays. Also called a dead pixel.
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 back light. Back lights are not cheap to
replace. The better models come with a three year warranty.
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 and Size
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.
Refresh Rate
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.
Interlacing
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.
Pixel (Dot) Pitch
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.
Screen Technology
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
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 flexibility 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 video conference
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.
