The size of an approximately
rectangular display is usually given as
the distance between two opposite screen corners, that is, the diagonal
of the rectangle. One problem with this method is that it does not take
into account the display aspect ratio, so that for example a 16:9 21 in
(53 cm) widescreen display is far less high, and has less area, than a
21 in (53 cm) 4:3 screen. The 4:3 screen has dimensions of
16.8 × 12.6 in (43 × 32 cm) and area 211 sq in , while the widescreen
is 18.3 × 10.3 in (46 × 26 cm), 188 sq in (1,210 cm2).
For many purposes the height of the display is the main parameter; a
16:9 display needs a diagonal 22% larger than a 4:3 display for the
This method of measurement is inherited from the method used for the
first generation of CRT television, when picture tubes with circular
faces were in common use. Being circular, only their diameter was
needed to describe their size. Since these circular tubes were used to
display rectangular images, the diagonal measurement of the rectangle
was equivalent to the diameter of the tube's face. This method
continued even when cathode ray tubes were manufactured as rounded
rectangles; it had the advantage of being a single number specifying
the size, and was not confusing when the aspect ratio was universally
A problematic practice was the use of the size of a monitor's
imaging element, rather than the size of its viewable image, when
describing its size in publicity and advertising materials. On CRT
displays a substantial portion of the CRT's screen is concealed behind
the case's bezel
or shroud in order to hide areas outside the monitor's "safe area" due
to overscan. These practices were seen as deceptive, and widespread
consumer objection and lawsuits eventually forced most manufacturers to
instead measure viewable size
The performance of a monitor is measured by the following parameters:
- Luminance is measured in candelas per square meter (cd/m2 also called a Nit).
- Viewable image size is measured diagonally. For CRTs, the viewable size is typically 1 in (25 mm) smaller than the tube itself.
ratios is the ratio of the horizontal length to the vertical length.
the standard aspect ratio, for example, so that a screen with a width
of 1024 pixels will have a height of 768 pixels. If a widescreen
display has an aspect ratio of 16:9, a display that is 1024 pixels wide
will have a height of 576 pixels.
resolution is the number of distinct pixels in each dimension that can
be displayed. Maximum resolution is limited by dot pitch.
- Dot pitch is the distance between subpixels of the same color in millimeters. In
general, the smaller the dot pitch, the sharper the picture will appear.
pitch is the number of times in a second that a display is
illuminated. Maximum refresh rate is limited by response time.
- Response time is the time a pixel in a monitor takes to go from active (black) to
inactive (white) and back to active (black) again, measured in
milliseconds. Lower numbers mean faster transitions and therefore fewer
visible image artifacts.
- Contrast ratio is the ratio of the luminosity of the brightest color (white) to that
of the darkest color (black) that the monitor is capable of producing.
- Power consumption is measured in watts.
- Viewing angle is the maximum angle at which images on the monitor can be viewed,
without excessive degradation to the image. It is measured in degrees
horizontally and vertically.
- High dynamic range (up to
around 15,000:1), excellent color, wide gamut and low black level. The
color range of CRTs is unmatched by any display type except OLED
- Can display natively in almost any resolution and refresh rate
- No input lag
- Sub-millisecond response times
- Near zero color, saturation, contrast or brightness distortion. Excellent viewing angle
- Usually much cheaper than LCD or Plasma screens.
- Allows the use of light guns/pens
- Large size and weight, especially for bigger screens (a 20-inch unit weighs about 50 lb (23 kg))
- High power consumption
- Generates a considerable amount of heat when running
- Geometric distortion caused by variable beam travel distances
- Can suffer screen burn-in
- Produces noticeable flicker at low refresh rates
- Normally only produced in 4:3 aspect ratio (though some widescreen ones, notably Sony's FW900, do exist)
- Hazardous to repair/service
- Effective vertical resolution limited to 1024 scan lines.
- Color displays cannot be made in sizes smaller than 7 inches
(5 inches for monochrome). Maximum size is around 24 inches (for
computer monitors; televisions run up to 40 inches).
- Very compact and light
- Low power consumption
- No geometric distortion
- Little or no flicker depending on backlight technology
- Not affected by screen burn-in
- No high voltage or other hazards present during repair/service
- More reliable than CRTs
- Can be made in almost any size or shape
- No theoretical resolution limit
- Limited viewing angle,
causing color, saturation, contrast and brightness to vary, even within
the intended viewing angle, by variations in posture.
- Bleeding and uneven backlighting in some monitors, causing brightness distortion, especially toward the edges.
- Slow response times, which cause smearing and ghosting artifacts.
However, this is mainly a problem with passive-matrix displays. Current
generation active-matrix LCDs have response times of 6 ms for TFT
panels and 8 ms for S-IPS.
- Only one native resolution.
Displaying resolutions either requires a video scaler, lowering
perceptual quality, or display at 1:1 pixel mapping, in which images
will be physically too large or won't fill the whole screen.
- Fixed bit depth,
many cheaper LCDs are only able to display 262,000 colors. 8-bit S-IPS
panels can display 16 million colors and have significantly better
black level, but are expensive and have slower response time
- Input lag
- Dead pixels may occur either during manufacturing or through use.
- In a constant on situation, thermalization may occur, which is when
only part of the screen has overheated and therefore looks discolored
compared to the rest of the screen.
- Not all LCD displays are designed to allow easy replacement of the backlight
- Cannot be used with light guns/pens
- High contrast ratios (10,000:1 or greater,) excellent color, and low black level.
- Virtually no response time
- Near zero color, saturation, contrast or brightness distortion. Excellent viewing angle.
- No geometric distortion.
- Softer and less blocky-looking picture than LCDs
- Highly scalable, with less weight gain per increase in size (from less than 30 in (760 mm) wide to the world's largest at 150 in (3,800 mm)).
- Large pixel pitch, meaning either low resolution or a large screen. As such, color plasma displays are only produced in sizes over 32 inches.
- Image flicker due to being phosphor-based
- Heavy weight
- Glass screen can induce glare and reflections
- High operating temperature and power consumption
- Only has one native resolution. Displaying other resolutions requires a video scaler, which degrades image quality at lower resolutions.
- Fixed bit depth. Plasma cells can only be on or off, resulting in a more limited color range than LCDs or CRTs.
- Can suffer image burn-in. This was a severe problem on early plasma displays, but much less on newer ones
- Cannot be used with light guns/pens
- Dead pixels are possible during manufacturing
Phosphor burn-in is localized aging of the phosphor
layer of a CRT screen where it has displayed a static image for long
periods of time. This results in a faint permanent image on the screen,
even when turned off. In severe cases, it can even be possible to read
some of the text, though this only occurs where the displayed text
remained the same for years.
Burn-in is most commonly seen in the following applications:
- Point-of-service applications
- Arcade games
- Security monitors
were developed as a means to avoid burn-in, which was a widespread
problem on IBM Personal Computer monochrome monitors in the 1980s.
Monochrome displays are generally more vulnerable to burn-in because
the phosphor is directly exposed to the electron beam while in color
displays, the shadow mask provides some protection. Although still
found on newer computers, screen savers are not necessary on LCD
Phosphor burn-in can be "fixed" by running a CRT with the brightness
at 100% for several hours, but this merely hides the damage by burning
all the phosphor evenly. CRT rebuilders can repair monochrome displays
by cutting the front of the picture tube off, scraping out the damaged
phosphor, replacing it, and resealing the tube. Color displays can
theoretically be repaired, but it is a difficult, expensive process and
is normally only done on professional broadcasting monitors (which can
cost up to $10,000).
Burn-in re-emerged as an issue with early plasma displays, which are
more vulnerable to this than CRTs. Screen savers with moving images may
be used with these to minimize localized burn. Periodic change of the
color scheme in use also helps.
Glare is a problem caused by the relationship between lighting and
screen or by using monitors in bright sunlight. Matte finish LCDs and
flat screen CRTs are less prone to reflected glare than conventional
curved CRTs or glossy LCDs, and aperture grille CRTs, which are curved on one axis only and are less prone to it than other CRTs curved on both axes.
If the problem persists despite moving the monitor or adjusting
lighting, a filter using a mesh of very fine black wires may be placed
on the screen to reduce glare and improve contrast. These filters were
popular in the late 1980s. They do also reduce light output.
A filter above will only work against reflective glare; direct glare
(such as sunlight) will completely wash out most monitors' internal
lighting, and can only be dealt with by use of a hood or transreflective LCD.
With exceptions of correctly aligned video projectors and stacked LEDs,
most display technologies, especially LCD, have an inherent
misregistration of the color channels, that is, the centers of the red,
green, and blue dots do not line up perfectly. Sub-pixel rendering depends on this misalignment; technologies making use of this include the Apple II from 1976, and more recently Microsoft and XFree86
RGB displays produce most of the visible color spectrum, but not all. This
can be a problem where good color matching to non-RGB images is needed.
This issue is common to all monitor technologies that use the RGB
model. Recently, Sharp introduced a four-color TV (red, green, blue,
and yellow) to improve on this.
Much software and video hardware supports the ability to create additional, virtual pieces of desktop, commonly known as workspaces. Spaces is Apple's implementation of virtual displays.