ViewSonic: Monitor University: Monitor Technology 101: CRT Basics

CRT Basics

How does it work? A CRT monitor operates much like your regular television set. A cathode ray tube (CRT) uses an electron gun to shoot electron beams through a metal grille or mask on the inside of a glass monitor screen. The screen is coated with phosphor dots that glow red, green, or blue to create any color and produce the image you see on your monitor. Shooting the gun at the appropriate colors in differing intensities produces the full color spectrum. There are three types of grilles for CRT monitors, and each has its own benefits.
Aperture grille Aperture grille tubes send their electron beams through an array of thin vertical wires. The grille is supported by one or two horizontal wires that may cause a faint line to appear on a white screen. Most users don't notice this effect unless they look for it. Virtually all aperture grille models have a flat face. Though they cost more, flat-faced models repay the investment, because they present a clear, undistorted image and reduce glare from ambient light. Aperture grilles deliver bright, saturated colors ideal for desktop publishers and graphic artists.
Shadow mask Shadow mask displays use a metal sheet perforated with small holes to filter out stray electrons and focus the electron beam that illuminates phosphors on the inside of the tube. Because shadow mask monitors tend to render accurate straight lines, they're generally the monitor of choice for CAD/CAM and drawing applications. A shadow mask tube also provides sharp detail for precision graphics or text-heavy applications.

Slot mask
Slot mask displays are a hybrid of aperture grille and shadow mask technologies. In order to allow a greater number of electrons through the mask, the standard round perforations are replaced with vertically aligned slots. The phosphor dots are arranged to make best use of the increased electron traffic and produce a higher brightness level.

Screen size
ViewSonic CRT screen sizes range from 15 to 22 inches. CRT screen size is based on the diagonal screen measurement of its picture tube and is usually an inch larger than its viewable image size. A 17" CRT, for example, typically has a 16" viewable image size, with the edge of the picture tube covered by the bezel of the monitor.

Resolution
A monitor screen is made up of individual dots of color, or pixels. Resolution refers to the number of pixels contained on a display. Resolution is typically expressed by identifying the number of pixels on the horizontal axis (rows) and the number of lines on the vertical axis (columns), such as 1024x768.

A higher resolution generally results in smoother graphics and can fit more information on a screen at once.

Color depth
Color depth indicates how many colors can be displayed on a monitor's screen. CRT technology allows for potentially unlimited color depth. The combination of the display modes supported by your graphics adapter and the color capability of your monitor determine how many colors can be displayed.

Dot pitch
Dot pitch is the spacing between pixels on a CRT, measured in millimeters. Generally, the lower the number, the more detailed the image.

Refresh rate
Refresh rate is the number of times per second that a CRT's picture must be redrawn. For most monitors, a rate of at least 75Hz will avoid flicker. For larger monitors, 19 inches and up, an 85Hz rate may be needed to avoid eyestrain.

Screen technology
CRT screens vary in their degree of flatness. Conventional CRT screens have a slight curve. Flat square tube (FST) screens are flatter than conventional screens. And CRTs with ViewSonic's PerfectFlat^® screen technology are absolutely flat, creating realistically proportioned images and reduced distortion and reflection.

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