A computer monitor is an output device that displays information in pictorial or text form. A monitor usually comprises a visual display, some circuitry, a casing, and a power supply. The display device in modern monitors is typically a thin film transistor liquid crystal display (TFT-LCD) with LED backlighting having replaced cold-cathode fluorescent lamp (CCFL) backlighting. Previous monitors used a cathode ray tube (CRT) and some Plasma (also called Gas-Plasma) displays. Monitors are connected to the computer via VGA, Digital Visual Interface (DVI), HDMI, DisplayPort, USB-C, low-voltage differential signaling (LVDS) or other proprietary connectors and signals.
Originally, computer monitors were used for data processing while television sets 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 computer monitors, has changed from 4:3 to 16:10, to 16:9.
Modern computer monitors are easily interchangeable with conventional television sets and vice versa. However, as computer monitors do not necessarily include integrated speakers nor TV tuners (such as digital television adapters), it may not be possible to use a computer monitor as a TV set without external components. The aspect ratio of computer monitors in industrial, medical and scientific applications, such as X-ray tube positioners or electron microscopes, is particularly important.
Given the age of the technology, computer monitors are used by a wide variety of people for a wide variety of purposes. However, only a relatively small percentage of computers have monitors installed in them.
In the late 2000s, computer monitors available for sale were mostly TN LCDs, while IPS monitors were the highest-resolution type of LCD that cost nearly twice as much. In 2007, LCD use was widespread in the corporate sector and for personal computers. While LCDs have higher static contrast ratios than cathode ray tube (CRT) screens, they use a lot more power and break much more easily. This has led to a shift among manufacturers from CRTs to LCDs since the late 2000s.
Monitors are available in all sizes ranging from small 2-inch pocket screens to massive 42-inch behemoths capable of displaying Full HD 1080p. LCD monitors are available in various resolutions, measured in either dots per inch (dpi) or pixels per inch ( ppi ).
The earliest monitors were television receivers with a screen divided into small individual cells. A front-end circuit consisting of a mixer and driver circuits controlled the timing and brightness of each cell. These simple cells were later superseded by vacuum tube monitors; the visual display used cathode rays to scan a video screen with a video signal to create an image.
In the early 21st century, flat panel monitors evolved from computer displays, which had been used for decades as part of a command-line interface. As these displays had become smaller and more powerful, using them for computer tasks became more practical for individuals. This led to the development of flat panel monitors for home and office computers.
Most computer monitors these days employ a thin film transistor liquid crystal display (TFT-LCD), which was invented by Japanese engineer Hideo Kodama in 1975. A sequence of four electrodes (a matrix of pixels) is controlled by a low-voltage power supply through a switching transistor. This switching transistor turns on and off to control the electrical signal received from the power supply; it switches on and off rapidly, modulating the voltage on each pixel. By cycling the power on and off very quickly, an entire screen can be refreshed quickly enough to display video. The complete picture is painted in a short burst of a duration typically around 1/60th of a second.
The active area of a flat-panel monitor contains all the circuitry that drives the display, such as TFT or OLED transistors, switching power supplies and timing control equipment. The backplane has the necessary signals to create such a display.
The backplane consists of rows of conductive pads (positive connections), separated by intervening non-conductive plates (negative connections). All cells are connected through these conductors. Typically, the two halves of the display are connected to different parts of the backplane; however modern chipsets connect all pixels to common signal lines.
This defines how information is manipulated by the chip. CCDs were replaced by transistors in the 1970s, and replaced by small LEDs in the 1980s. In the 1990s, “LED-backlit LCDs” became common.
In this type of LCD, each pixel is lit by a single-color red, blue or green LED that does not produce a wide spectrum of colors. Some monitors in the 21st century have a “white LED backlight”, which produces a brighter image in greater contrast. The red, green and blue LEDs may be controlled independently to improve color reproduction and brightness at the expense of overall image contrast.
The backlighting comes from a sheet of light-emitting diodes (LEDs) behind the liquid crystal layer. The purer colors are created by passing different colors through red, green and blue filters. A color filter for this purpose is called an RGB filter, which can also pass other colors not used in order to improve image quality. This process reduces the brightness of the display by adding filtering layers between the image source and the pixels. However, the effect of electronic filters on this type of display is small.
Today, LED backlighting is used for nearly all LCD monitors, with the exception of computer screens adopted for general public use. The backlight source is smaller than an incandescent filament bulb.
The screen pixels are formed by a combination of red, green and blue light-emitting diodes (LEDs), each emitting one narrow color range. For example, the red LED (also referred to as a “red” or “R” LED), emits light at wavelengths of about 660 nm. The green LED emits light at about 550 nm, and blue LEDs emit light between 435 nm and 450 nm. All three colors are usually combined in one pixel.
The backlight sources are usually discrete (single-color LEDs, which all emit the same color), fluorescent lamps, white LEDs or metal-halide lamps. White LEDs are most common, but all backlit displays use LEDs, with the exception of the white-light-emitting LED in “white” LED backlit LCDs.
The RGB LEDs are usually arranged in a matrix pattern on the bottom of the display, with separate red, green and blue segments. Individual sheets of LEDs are commonly mounted on a transparent glass substrate to protect them from scratches or other damage that may occur during shipping or handling.