The functioning of a computer system is based on the combined usage of both input and output devices. Using an input device we can give instructions to the computer to perform and action and the device reverts back to our action through an output device.
A piece of equipment/hardware which gives out the result of the entered input, once it is processed (i.e. converts data from machine language to a human-understandable language), is called an output device. For example printer, monitor, etc.
The commonly used output devices have been listed below with a brief summary of what their function is and how they can be used.
- Monitor (VDU)
- Printer
- Headphones
- Computer Speakers
- Projector
- GPS
- Sound Card
- Video Card
- Braille Reader
- Speech-Generating devices
Monitors, commonly called as Visual Display Unit (VDU), are
the main output device of a computer. It forms images from tiny dots,
called pixels that are arranged in a rectangular form. The sharpness of
the image depends upon the number of pixels.
There are two kinds of viewing screen used for monitors.
- Cathode-Ray Tube (CRT)
- LCD
Cathode-ray tube (CRT)
The CRT display is made up of small picture elements called pixels. The
smaller the pixels, the better the image clarity or resolution. It takes
more than one illuminated pixel to form a whole character, such as the
letter ‘e’ in the word help.
The cathode-ray tube (CRT) is a vacuum tube containing one or more electron guns, the beams of which are manipulated to display images on a phosphorescent screen. The images may represent electrical waveforms (oscilloscope), pictures (television, computer monitor), radar targets, or other phenomena. CRTs have also been used as memory devices, in which case the screen is not intended to be visible to an observer.
A finite number of characters can be displayed on a screen at once. The screen can be divided into a series of character boxes - fixed location on the screen where a standard character can be placed. Most screens are capable of displaying 80 characters of data horizontally and 25 lines vertically.
There are some disadvantages of CRT −
- Large in Size
- High power consumption
LCD (Liquid-Crystal Device)
The flat-panel display refers to a class of video devices that have
reduced volume, weight and power requirement in comparison to the CRT.
You can hang them on walls or wear them on your wrists. Current uses of
flat-panel displays include calculators, video games, monitors, laptop
computer, and graphics display.
The flat-panel display is divided into two categories −
Emissive Displays − Emissive displays are devices that convert electrical energy into light. For example, plasma panel and LED (Light-Emitting Diodes).
Non-Emissive Displays − Non-emissive displays use optical effects to convert sunlight or light from some other source into graphics patterns. For example, LCD (Liquid-Crystal Device).
A liquid-crystal display (LCD) is a flat-panel display or other electronically modulated optical device that uses the light-modulating properties of liquid crystals combined with polarizers. Liquid crystals do not emit light directly, instead using a backlight or reflector to produce images in color or monochrome.
LCDs are available to display arbitrary images (as in a general-purpose computer display) or fixed images with low information content, which can be displayed or hidden, such as preset words, digits, and seven-segment displays, as in a digital clock. They use the same basic technology, except that arbitrary images are made from a matrix of small pixels, while other displays have larger elements.
LCDs can either be normally on (positive) or off (negative), depending on the polarizer arrangement. For example, a character positive LCD with a backlight will have black lettering on a background that is the color of the backlight, and a character negative LCD will have a black background with the letters being of the same color as the backlight. Optical filters are added to white on blue LCDs to give them their characteristic appearance.
LCDs are used in a wide range of applications, including LCD televisions, computer monitors, instrument panels, aircraft cockpit displays, and indoor and outdoor signage.
Small LCD screens are common in LCD projectors and portable consumer devices such as digital cameras, watches, digital clocks, calculators, and mobile telephones, including smartphones.
LCD screens are also used on consumer electronics products such as DVD players, video game devices and clocks.
LCD screens have replaced heavy, bulky cathode ray tube (CRT) displays in nearly all applications. LCD screens are available in a wider range of screen sizes than CRT and plasma displays, with LCD screens available in sizes ranging from tiny digital watches to very large television receivers.
LCDs are slowly being replaced by OLEDs, which can be easily made into different shapes, and have a lower response time, wider color gamut, virtually infinite color contrast and viewing angles, lower weight for a given display size and a slimmer profile (because OLEDs use a single glass or plastic panel whereas LCDs use two glass panels; the thickness of the panels increases with size but the increase is more noticeable on LCDs) and potentially lower power consumption (as the display is only "on" where needed and there is no backlight). OLEDs, however, are more expensive for a given display size due to the very expensive electroluminescent materials or phosphors that they use. Also due to the use of phosphors, OLEDs suffer from screen burn-in and there is currently no way to recycle OLED displays, whereas LCD panels can be recycled, although the technology required to recycle LCDs is not yet widespread. Attempts to maintain the competiviveness of LCDs are quantum dot displays, marketed as SUHD, QLED or Triluminos, which offer similar performance to an OLED display, but the quantum dot layer that gives these displays their characteristics can not yet be recycled.
Since LCD screens do not use phosphors, they rarely suffer image burn-in when a static image is displayed on a screen for a long time, e.g., the table frame for an airline flight schedule on an indoor sign.
LCDs are, however, susceptible to image persistence. The LCD screen is more energy-efficient and can be disposed of more safely than a CRT can. Its low electrical power consumption enables it to be used in battery-powered electronic equipment more efficiently than a CRT can be. By 2008, annual sales of televisions with LCD screens exceeded sales of CRT units worldwide, and the CRT became obsolete for most purposes.
Various different LCD technologies are used today, including:
- In Plane Switching (IPS) Panel Technology: These panels are considered to have the best color accuracy, viewing angles and image quality in LCD technology.
- Super Plane to Line Switching (PLS): Developed by Samsung, this LCD panel is very similar to the IPS panel but reportedly, it is 10 percent brighter, has wider viewing angles and is cheaper to produce.
- Vertical Alignment (VA) Panel Technology: These panels are considered to be in the middle of TN and IPS technology. Compared to TN panels, they offer wider viewing angles and better color quality but have slower response times. They have higher contrast ratios, compared to the other panels but have a downside, in terms of color shifting, where the brightness display is unevenly distributed throughout the screen.
- Twisted Nematic (TN) Panel Technology: These panels are the most commonly used type of panel in LCD technology. They are cheaper and offer faster response times, making them a preferred choice for gamers. The downside is that the viewing angles, contrast ratios and color production are considered the lowest of LCD panel types.
LCD monitor vs. LED monitor
Until
2014, plasma displays were the most commonly manufactured displays. But
then the LCD took over. LCD stands for liquid crystal display. We’ll go
over what that means in a minute. But first, it’s important to note
that an LED also uses liquid crystals, so the name is somewhat
misleading. Technically, an “LED monitor” should really go by the name,
“LED LCD monitor.”
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