Types of Visual-Display Units

Visual displays vary in resolution, construction and power consumption.

Visual Display Units are more commonly known as monitors, the electronic visual displays used by computers. Televisions use the same various visual-display technologies as computer monitors. Most VDUs consist of screens, circuitry and inner workings and a protective decorative enclosure. The most common VDU unit types are CRT, LCD and plasma displays.

CRT

A CRT computer monitor

CRT, or Cathode Ray Tube, technology is the oldest technology among visual-display units. Invented in the late 1800s and first used in televisions in the 1940s, CRTs were the dominant visual-display unit until the late 1990s, when they began to be replaced by LCD technology. In CRT monitors, a funnel-shaped glass tube projects electron beams back and forth across the inside of the screen, illuminating phosphor dots in a series on many lines that appear on the outside of the screen--these lines compose an entire screenful of imagery. CRTs are the largest and heaviest of monitor types, usually sporting large display surfaces and smaller, boxier back ends (to house the tube). Screen surfaces on CRT displays are curved; in general appearance, these monitors resemble nonflatscreen television sets, and their screens feature a 4:3 ratio (square-shaped) rather than widescreen format. CRTs use the most power of all displays (around 150W for a 17-inch monitor), cannot be used with laptops and have a subtle "flicker" in their display, which causes eyestrain. However, CRT displays feature simple and solid technology, can be seen from a wide viewing angle and are manufactured at significantly lower cost than alternative display units .

LCD

A 4:3 display ratio LCD monitor

Liquid crystal displays (LCDs) began as display units for calculators and laptop screens, but started to quickly replace CRT monitors in the latter part of the twentieth century. In LCD technology, light shines through a combination of liquid crystals and polarized glass to create an onscreen image. LCD screens are flat rather than curved and generally housed in slimmer, smaller and lighter casings than CRT displays. LCD offers a higher resolution and better image contrast than CRT, and because LCD technology doesn't flicker, it causes less eyestrain. These displays often come in widescreen format as televisions, and both widescreen and 4:3 ratios as monitors. LCDs generate less heat and consume as little as a third of the power of CRTs. However, LCDs feature a higher price and a smaller viewing angle than CRT screens.

Plasma

A plasma-screen television

Plasma screens create a high-resolution picture by lighting up thousands of tiny dots (or "pixels") with a high-energy electron beam. Plasmas combine three pixel colors (red, green and blue) to create the entire spectrum of colors, resulting in richer colors than LCD or CRT displays. Plasma displays are often very large widescreens generally used as televisions, but many plasmas can be used as computer displays. Though they are larger and heavier than LCDs, plasmas are generally only about six inches thick. Plasma display units usually consume slightly more power than LCD displays, depending on the resolution. Plasma viewing angles are very wide, but this technology comes at a higher cost than other visual-display units.

References

• PC Tech Guide: CRT Monitors
• Hardware Secrets: Everything You Need to Know About LCD Monitors
• Energy Star: LCD Basics
• Plasma TV Science: Inner Workings of Plasma Displays
• CNET: HDTV Power Consumption Compared