A video display terminal (VDT) is a computer screen that displays text and images. VDTs can be part of a computer or separate hardware devices. They use pixels to reproduce images, and different technologies like CRT, LCD, and gas plasma. Flat panel displays are lighter and thinner than CRTs, and LCD screens are commonly found in laptops. Plasma displays work using gas and have improved energy efficiency.
A video display terminal, or video display terminal (VDT) is a computer screen. The VDT displays computer-generated text and images. VDUs can be part of a computer or separate hardware devices connected to a computer with a cable. These separate devices are sometimes called computer monitors.
When personal computers were first commercialized in the mid-1980s, the first video terminals displayed a single color, usually green or orange. Today’s VDTs can reproduce millions of colours, all created by mixing the primary colors red, green and blue.
Displays reproduce text and images using pixels. A pixel is the smallest unit of color reproduced by a video terminal. The pixel size depends on the resolution of the screen. The higher the resolution, the smaller the pixel and the sharper the image. VDTs project pixels onto the screen using different types of technology.
These include the cathode ray tube (CRT), liquid crystal display (LCD) and gas plasma technologies. A CRT is a vacuum tube similar to the picture tube in a television. Electricity is moved back and forth across the screen, striking phosphor dots within the tube. Like televisions, VCRs that use these tubes are bulky and heavy.
The advent of new technologies, which followed the CRTs, allowed for the creation of much lighter and thinner video displays, known as flat panel displays. Flat panel displays can be a few inches wide, compared to CRT displays which can be over a foot wide. LCD and gas plasma are two common types of flat panel displays.
LCD screens have been used since the 1980s in digital watches and calculators. LCD screens are now commonly found in laptops and other small computers. These screens are backlit using either a fluorescent light or a light emitting diode (LED). The backlight is always on and images are reproduced on the VCR by blocking portions of light.
Electricity passed through the liquid crystals inside the screen changes the polarity of the crystal. Polarized crystal blocks light. A filter placed in front of the backlight changes the color of the light which is not blocked, and is projected onto the VCR.
Plasma displays work using gas instead of liquid crystals. They have small screen chambers filled with plasma gas. Color is added to the gas by mixing phosphorus and electricity, similar to how color is projected on a CRT screen. Originally, plasma screens used more energy than LCD screens. Updated technology has since improved the energy efficiency of plasma VDT.
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