A computer monitor is an output device that displays information in pictorial form. A monitor usually comprises the visual display, circuitry, casing, and 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.
When It Emerged?
Early electronic computers were fitted with a panel of light bulbs where the state of each particular bulb would indicate the on/off state of a particular register bit inside the computer. This allowed the engineers operating the computer to monitor the internal state of the machine, so this panel of lights came to be known as the 'monitor'. As early monitors were only capable of displaying a very limited amount of information and were very transient, they were rarely considered for program output. Instead, a line printer was the primary output device, while the monitor was limited to keeping track of the program's operation. Computer monitors were formerly known as visual display units (VDU).
Cathode Ray Tube Monitors
A CRT has a large vacuum tube in the back, with a cathode containing a heated filament pointing forward, toward the viewer. This heated filament becomes an electron gun, firing off streams of electrons in response to the visual signal it receives from the computer. Ahead of the cathode, ringing it, is a set of electromagnets which activate in response to the same signal. These magnets alter the course of the electron stream, aiming it. At the front of the monitor is a glass plate. On the back of this plate are millions of tiny phosphor dots. These dots are combined into groups of three--one red, one blue and one green. These groups are called pixels. When the electron stream touches the pixels, the correct combination of the phosphor dots will light up and different intensities to create any color in the spectrum. The stream passes over the entire monitor at a rate of 50 to 100 times per second to create the continuous interactive image that we see.
Liquid Crystal Display Monitors
An LCD monitor is composed of two specially treated plates of polarized glass pressed together. Between these plates is a liquid crystal material which responds to an electrical current by allowing different wavelengths of light through at various points across its surface. Instead of creating points of light, the entire premise of an LCD monitor is to block out the majority of light, to allow only specific wavelengths, interpreted as colors by our brains, through the front of the monitor. A backlight emits a continuous stream of light covering the entire back of the monitor, at all visible wavelengths. The electrical current created by the visual signal sent from the computer causes the liquid crystal material to block out different wavelengths of light across its face to create the general shapes and colors of an image. Behind the monitor's face but in front of the liquid crystal is an enclosed matrix of transistors connected to pixels on the screen's face. This matrix is so thin that it appears to be transparent. But when a varying current runs through it, the same current as the one manipulating the liquid crystal, it causes certain pixels to light up, adding definition to the overall color passing through from the backlight.
Function
The cathode ray tube receives an electronic signal from a power source which causes the cathode, or negative electrode, to release a set of electrons corresponding to this signal which travel toward the anode, or positive electrode. These transmitted electrons travel to the anode in a vacuum, created through enclosure by a picture tube, and strike phosphor stripes which display a certain color according to the electron signal. This signal must be constantly refreshed, even if the color doesn't change, as the phosphor glows for less than a second.
The larger picture is created through a process called deflection. The electron beam shot by the cathode sweeps horizontally across the screen to create the continuous picture visible on a CRT monitor.
Uses
Cathode ray tubes, or CRTs, have been applied in numerous pieces of imaging equipment because of their ability to produce a picture. Cathode ray tubes have long been used in both televisions and computer monitors. Besides their varied applications within the broad category of monitors, cathode ray tubes are also utilized in oscilloscopes, a piece of laboratory equipment which uses the deflection of electrons to measure voltage over different frequencies.
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