A cathode ray tube (CRT) monitor is an analog computer display or television set with a large, deep casing. This type of monitor uses streams of electrons that activate dots or pixels on the screen to create a full image. In contrast to this, liquid crystal display (LCD) monitors and plasma television sets, or flat panel displays, use newer digital technologies. While flat-screens have become increasingly popular, there are still some advantages to CRT models that can make them better for some situations.
How a CRT Monitor Works
Inside a CRT monitor is a picture tube that narrows at the rear into a bottleneck. In the bottleneck area is a charged filament or "cathode" enclosed in a vacuum tube. When electricity is supplied to this, the filament heats up and a stream or "ray" of electrons pours off of it. The negatively charged electrons are attracted to positively charged "anodes" which focus the particles into three narrow beams, accelerating them to strike a phosphor-coated display screen.
Phosphor glows when exposed to radiation, absorbing ultraviolet light and emitting visible, colored light. Materials that emit red, green and blue light are used in a color monitor, arranged as "stripes" made up of dots of color. The three beams are used to excite the three colors in combinations needed to create the various hues that form the picture.
To precisely direct the beams of electrons, copper steering coils are used to create magnetic fields inside the tube. The fields move the electron beams vertically or horizontally. By applying varying voltages to the steering coils, a beam can be positioned at any point on the screen. Each image is "painted" onto the screen numerous times each second by scanning the electron beams across the screen. This must be done even when the picture being displayed is unchanging, because the phosphor only glows for a very short time.
Color Displays on a Monitor
These colored dots are not technically pixels, but the term is frequently used to refer to them. The more lines of dots on a screen, the numerically higher and clearer the resolution. Therefore 1024 x 768, the number of columns by the number of rows, resolution is sharper than 800 x 600 resolution due to a denser, more detailed picture. Higher resolutions are important for displaying the subtle detail of graphics and crisp text.
The "refresh rate" indicates how many times per second the beams paint an image on the screen. Though monitors differ in their capabilities, lower resolutions normally have higher refresh rates because it takes less time to paint a lower resolution. Therefore, a setting of 800 x 600 might have a refresh rate of 85 Hertz (Hz), meaning the CRT monitor paints or refreshes an image 85 times per second, while a resolution setting of 1024 x 768 may have a refresh rate of 75 Hz.
Large screen sizes also require higher refresh rates, and anything less than 75 Hz is generally considered inadequate. When the rate is less than this, people watching the CRT monitor can often detect "screen flicker." Generally speaking, high-end monitors have higher refresh rates overall than lower-end models.
Strengths and Drawbacks of CRT Monitors
One of the biggest advantages of these monitors over other technology is the range of colors they can display. While newer models of LCD and flat-screen monitors have improved, a CRT monitor can typically display a greater range of colors more accurately and with more detail. Their contrast is also better, with deeper blacks. CRT monitors also have a wider viewing angle and are usually less expensive than similarly sized LCD models.
LCDs are significantly smaller and lighter in weight than CRTs, however, which makes them better for small offices and similar settings. They also give less glare and consume much less power than CRT monitors. LCDs also do not have flicker problems and can run quite well at lower refresh rates.
Measuring a Monitor
A CRT monitor usually ranges from 17 inches (43.18 centimeters) in size up to about 22 inches (55.88 cm), though the actual viewing screen is about 1 inch (2.54 cm) smaller than the rated size. This is because part of the case covers up part of the screen. Screens are measured diagonally from corner to corner.