A monitor or display (sometimes called a 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 about as deep as the screen 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).
Aspect ratios 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.
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.

The size of a display is usually by monitor manufacturers given by the diagonal i.e. the distance between two opposite screen corners. This method of measurement is inherited from the method used for the first generation of CRT television.

Until about 2003, most computer monitors had a 4:3 aspect ratio and some had 5:4. Between 2003 and 2006, monitors with 16:9 and mostly 16:10 (8:5) aspect ratios became commonly available, first in laptops and later also in standalone monitors. Reasons for this transition was productive uses for such monitors, i.e. besides widescreen computer game play and movie viewing, are the word processor display of two standard letter pages side by side, as well as CAD displays of large-size drawings and CAD application menus at the same time.[6][7] 2008 16:10 became the most common sold aspect ratio for LCD monitors and the same year 16:10 was the mainstream standard for laptops and notebooks

The resolution for computer monitors have increased over time. From 320×200 during the early 80s, to 800×600 during the late 90s. In March 2011 1920×1080 became the most common used resolution among Steam users. The earlier most common resolution was 1680×1050.

Power saving

Most modern monitors will switch to a power-saving mode if no video-input signal is received. This allows modern operating systems to turn off a monitor after a specified period of inactivity. This also extends the monitor‘s service life.

Some monitors will also switch themselves off after a time period on standby.

Most modern laptops provide a method of screen dimming after periods of inactivity or when the battery is in use. This extends battery life and reduces wear.

Integrated accessories

Many monitors have other accessories (or connections for them) integrated. This places standard ports within easy reach and eliminates the need for another separate hub, camera, microphone, or set of speakers. These monitors have advanced microprocessors which contain codec information, Windows Interface drivers and other small software which help in proper functioning of these functions.

Glossy screen
Some displays, especially newer LCD monitors, replace the traditional anti-glare matte finish with a glossy one. This increases color saturation and sharpness but reflections from lights and windows are very visible.

Directional screen
Narrow viewing angle screens are used in some security conscious applications.

Polarized 3D monitor
The LG computer monitor 1920×1080 with screen 21.5-inches to 25-inches have feature the company’s Film Pattern Retarder coating that ditches the heavy active shutter glasses used by many other manufacturers for the lighter passive variety will give flicker-free 3D. Although the screen is Full HD 1080p, but to see 3D images with 3D polarizing glasses we may only get a half portion of it (HD 720p) due to the pixels should be divided for the left and right eyes.

Autostereoscopic (3D) screen
A directional screen which generates 3D images without headgear.

Touch screen
These monitors use touching of the screen as an input method. Items can be selected or moved with a finger, and finger gestures may be used to convey commands. The screen will need frequent cleaning due to image degradation from fingerprints.

Tablet screens
A combination of a monitor with a graphics tablet. Such devices are typically unresponsive to touch without the use of one or more special tools’ pressure. Newer models however are now able to detect touch from any pressure and often have the ability to detect tilt and rotation as well.

Touch and tablet screens are used on LCD displays as a substitute for the light pen, which can only work on CRTs.

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