Learning Resources
 

Monitors


A monitor or display (also called screen or visual display unit) is an electronic visual display for computers. The monitor comprises the display device, circuitry and an enclosure. The display device in modern monitors is typically a thin film transistor liquid crystal display (TFT-LCD) thin panel, while older monitors use a cathode ray tube (CRT) about as deep as the screen size.

Originally, computer monitors were used for data processing while television receivers were used for entertainment. From the 1980s onwards, computers (and their monitors) have been used for both data processing and entertainment, while televisions have implemented some computer functionality. The common aspect ratio of televisions, and then computer monitors, has also changed from 4:3 to 16:9 (and 16:10).


Multiple technologies have been used for computer monitors. Until the 21st century most used cathode ray tubes but they have largely been superseded by LCD monitors.


Cathode ray tube
The first computer monitors used cathode ray tubes (CRT). Until the early 1980s, they were known as video display terminals and were physically attached to the computer and keyboard. The monitors were monochrome, flickered and the image quality was poor.[citation needed] In 1981, IBM introduced the Color Graphics Adapter, which could display four colors with a resolution of 320 by 200 pixels. In 1984 IBM introduced the Enhanced Graphics Adapter which was capable of producing 16 colors and had a resolution of 640 by 350.

CRT technology remained dominant in the PC monitor market into the new millennium partly because it was cheaper to produce and offered viewing angles close to 180 degrees.

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Liquid crystal
There are multiple technologies that have been used to implement liquid crystal displays (LCD). Throughout the 1990s, the primary use of LCD technology as computer monitors was in laptops where the lower power consumption, lighter weight, and smaller physical size of LCDs justified the higher price versus a CRT. Commonly, the same laptop would be offered with an assortment of display options at increasing price points: (active or passive) monochrome, passive color, or active matrix color (TFT). As volume and manufacturing capability have improved, the monochrome and passive color technologies were dropped from most product lines.

TFT-LCD is a variant of LCD which is now the dominant technology used for computer monitors.

The first standalone LCD displays appeared in the mid-1990s selling for high prices. As prices declined over a period of years they became more popular, and by 1997 were competing with CRT monitors. Among the first desktop LCD computer monitors was the Eizo L66 in the mid-1990s, the Apple Studio Display in 1998, and the Apple Cinema Display in 1999. In 2003, TFT-LCDs outsold CRTs for the first time, becoming the primary technology used for computer monitors. The main advantages of LCDs over CRT displays are that LCDs consume less power, take up much less space, and are considerably lighter. The now common active matrix TFT-LCD technology also has less flickering than CRTs, which reduces eye strain. On the other hand, CRT monitors have superior contrast, have superior response time, are able to use multiple screen resolutions natively, and there is no discernible flicker if the refresh rate is set to a sufficiently high value. LCD monitors have now very high temporal accuracy and can be used for vision research.

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Organic light-emitting diode
Organic light-emitting diode (OLED) monitors provide higher contrast and better viewing angles than LCDs, and are predicted to replace them. In 2011, a 25-inch OLED monitor cost $7500, but the prices are expected to drop.

 

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).
  • Aspect ratio is the ratio of the horizontal length to the vertical length. Monitors usually have the aspect ratio 4:3, 5:4, 16:10 or 16:9.
  • Viewable image size is usually measured diagonally, but the actual widths and heights are more informative since they are not affected by the aspect ratio in the same way. For CRTs, the viewable size is typically 1 in (25 mm) smaller than the tube itself.
  • Display 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.
  • Refresh rate 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 (white) to inactive (black) and back to active (white) 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.
  • Delta-E: Color accuracy is measured in delta-E; the lower the delta-E, the more accurate the color representation. A delta-E of below 1 is imperceptible to the human eye. Delta-Es of 2 to 4 are considered good and require a sensitive eye to spot the difference.
  • 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.