Types of Computer Monitors
Monitor or visual display unit is the most common output device of a computer. It comprises a 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 primitive monitors used the Cathode Ray Tubes (CRTs), until they were replaced by LCD monitors.
A cable connects the monitor to a video adapter (video card) that is installed in an expansion slot on the computer’s motherboard. This system converts signals into text and pictures and displays them on Monitor. The computer sends a single to the video adapter, telling it what character, image, or graphic to display. The video adapter converts that signal to a set of instructions that tell the display device (monitor) how to the image on the screen.
We need to understand separte concepts to understand how a Monitor works:
Cathode Ray Tube
Cathode Ray Tube (CRT) was invented by German physicist Karl Ferdinand Braun in 1897. It is the device that was long used in most computer displays, video monitors, televisions radar displays and oscilloscopes. The CRT has undergone numerous development until the advent of plasma screens, LCD , TVs, DLP, OLED displays, and other technologies. Technically, CRT has an electronic vacuum tube employing a focused beam of electrons.
That most common type of graphics monitors employing a cathode ray tube are the raster-scan display based on television technology. In such a system, the Electron beam is swept across the screen, one row at a time from top to bottom. As this beam moves across each row, the beam intensity is turned on and off. This would create a pattern of illuminated spots.
There is a memory area called refresh buffer or frame buffer where the picture definition is stored. This memory area holds the set of intensity values for all the screen points. These stored intensity values are then retrieved from the refresh buffer and “painted” on the screen one row (scan line) at a time. Such each screen point is referred to as a ‘pixel’ or pel (shortened forms of picture elements). The capability of a raster-scan system to store intensity information for each pixel makes it well suited for the realistic display of scenes containing subtle shading and colour patterns.
LCD TFT Display
Liquid Crystal Display television (LCD TV) is television that uses LCD technology for its visual output. The technology used is generally TFT. TFT refers to a Thin Film Transistor, which is a special kind of field effect transistor made by depositing thin films for the metallic contacts, semiconductor active layer, and dielectric layer. The channel region of a TFT is a thin film that is deposited onto a substrate (often glass, since the primary application of TFT is in liquid crystal displays).
LCD panels are made of two layers of transparent material, which are polarized, and are “glued” together. One of the layers is coated with a special polymer that holds the individual liquid crystals. Current is then passed through individual crystals, which allow the crystals to pass or block light to create images. LCD crystals do not produce their own light, so an external light source, such as florescent bulb is needed for the image created by the LCD to become visible to the viewer. Thus, LCDs use a strong backlight as the light source and control how much of this light is allowed to reach the pixels by selectively allowing the light to reach each pixel. LCDs achieve this by taking advantage of a key property of ‘twisted’ liquid crystal molecules, which have the ability to naturally block polarized light but then let it through by degrees when a small electric field is applied. LCD cells are accurately controlled and arranged in a flat matrix of rows and columns.
Plasma Display Panel
We have read above that LCD crystals do not produce their own light, so an external light source, such as florescent bulb is needed for the image created by the LCD to become visible to the viewer. The Plasma television technology is absolutely different from this. The Plasma Display Panel is based loosely on the fluorescent light bulb. The display itself consists of very microscopic cells and within each cell two glass panels are separated by a narrow gap in which neon-xenon gas is injected and sealed in plasma form. Gas is electrically charged at specific intervals and then strikes red, green, and blue phosphors, thus creating a television image. Each group of red, green, and blue phosphors is called a pixel (picture element).
Due to presence of its own source of light, PDP suffers from the issues such as heat generation and screen-burn of static images.
Why are screensavers used in computers?
Screensavers are designed to prevent phosphor burn-in on CRT and plasma computer monitors by blanking the screen or filling it with moving images or patterns when the computer is not in use are programs that display images when the computer is idle for a specified time. In early CRT monitors when the same image would be displayed for a long time, the phosphors used to make the pixels in the display glow at a constant rate for so long a period that they would discolor the glass surface of the CRT.
But now, the advances in display technology and energy-saver monitors have solved this problem. So now we use screensavers for entertainment or security and they are perceived as works of art and used to prevent others from viewing confidential data when the user is away.
Thus, we note that Plasma display panel (PDP) is an emissive flat panel display where visible light is created by phosphors exited by a plasma discharge between two flat panels of glass. The gas discharge contains no mercury (contrary to the backlights of an active matrix LCD), an insert mixture of noble gases (neon and xenon) is used instead.
Dead Pixels, Hot Pixel, Stuck Pixel
A dead pixel is a defective pixel that remains unlit on an LCD screen, monitor, camera, charge-coupled device or CMOS sensor. A permanently lit pixel is a hot pixel, and a pixel that stays on a solid colour is a stuck pixel. Dead pixels can also occur in clusters and these are particularly annoying and in most cases these can be sent back to the manufacturer. The majority of dead pixels are only noticeable on a solid colour background, for example through the use of the “Dead Pixel Checkers” which consist of four-five solid-colour images.
All types of monitors are a strain on our eyes. EFT, or Eye Fresh Technology, monitors have a vital coating on the rear that emits anions and far-infrared rays that serve to make the environment fresh and ease the strain on the eyes and relax the eyes and body J