CRT Monitors are very common in the computer world. They are the most popular type, and the least expensive, while still delivering great performance and detail. CRT stands for Cathode Ray Tube. This is the most important part of the monitor, because it is what makes the image. The Cathode Ray Tube has three major parts inside it. These include the Electron Gun, the Deflection Yoke, as well as either the Shadow Mask or the Aperture Grill (depending on the type of monitor you have).

Viewsonic's E790 19" Monitor
© 2001 by www.viewsonic.com
Modified by the TQ Team "Gates of Creation"

Just like most TVs, CRT Monitors use an Electron Gun and Deflection Yoke. The Electron Gun has three electron streams used to represent three colors, which are red, green and blue. On a Monitor with a 24-bit depth, each of the streams can have 256 different intensities, which allows for more than 16 million color combinations. These three electron streams have to be fired at every single pixel on the monitor, one pixel at a time. In order to refresh the whole screen on a typical 19" monitor, the electron gun has to fire at almost two million pixels.

This is where the Deflection Yoke comes in. It is really an electromagnet that surrounds the Electron Gun. By activating a certain part of an electromagnet, the electron streams move closer to that part of the electromagnet, which lets them hit a different pixel. On a monitor with a resolution of 1600 X 1200, there are 1200 rows, and 1600 columns. The Deflection Yoke has to draw the electron streams to hit all 1600 pixels in one row, go to the next row down, and repeat the process. Once the whole screen refreshes, this has to be done again. The operation is done so fast that the human eye cannot even see the monitor refresh.

A typical CRT monitor refreshes at 60-75 Hz, which means that the whole screen refreshes 60-75 times in one second. Here is a demonstration which shows how a CRT monitor refreshes the screen using the Electron Gun and Deflection Yoke. Note that it is only refreshing at either 0.25Hz or 1Hz (depending on which speed you choose), so that it is slow enough for the human eye to see the refresh.

Full Screen

As you can see, the streams are constantly changing their intensities while refreshing the picture. If this did not happen, the whole screen would be one color. Also, you can see how the top of the Deflection Yoke lowers its power to let the electron stream go down, and then the lower part of the Deflection Yoke intensifies its power to draw the electron stream to the bottom pixels. Now that we know how these two parts work, it is time to learn about the part of the CRT Monitor that actually lets us see the colors.

Right behind the glass on the front of a CRT monitor is a metal plate as well as a thin coat of phosphorus. After the Electron Gun has been aimed and fired, it passes through holes in the metal plate, and hits the phosphorus, causing it to glow. There are two variations of the metal plate commonly used today. The first is the Shadow Mask, which is filled with circular holes to let the electrons through. The second is the Aperture Grill, which consists of a series of parallel vertical slots to let the electrons through.

The Shadow Mask is the more popular type. It has three holes for each pixel on the screen, because of the three streams of electrons. Here is an illustration of what a monitor with a Shadow mask would look like up close:

The other common type is the Aperture Grill. As stated earlier, it features a series of parallel vertical slots to let the electrons through. It was developed by Sony, and is used by any monitors which use Sony's Trinitron technology, such as Mitsubishi, NEC, as well as Sony itself. One major advantage is that the Aperture Grill allows for more tightly packed pixels than the Shadow mask. This is evident when comparing the illustration of the Aperture Grill to the Shadow Mask. Notice that there is almost no spacing between the slots in the Aperture Grill, while there is much more spacing in the Shadow Mask:

There are many advantages to having a CRT Monitor. The first, and most obvious one, is the price. A CRT Monitor can be 3-4 times less expensive than a LCD Monitor. CRT Monitors are also much brighter than LCD Monitors, which lets the user see the screen more easily from farther distances and bigger angles than LCD Monitors. Lastly, they have an excellent refresh rate. Although this is not very obvious when working in Microsoft Word, or surfing the net, it is very obvious when watching high quality movies, as well as playing 3D games on the computer.