The Shadow Mask technique uses the same process employed by conventional televisions. The rays in each beam scan a metal sheet perforated with thousands of round holes. Each pixel consists of three holes, one for each color (red, green, blue), set in a triangle. Near each perforation is a dot of phosphor to bring out the color. The distance between the source of the electrons and the center of the sheet is less than that between the source and the edge of the sheet. We can then observe overheating of the central dot, which causes uneven expansion and hence a read disturbance. However, the manufacturers have now found a solution to this problem. The mask of monitors using this technology is now made of Invar, a nickel and steel alloy with an expansion factor near to zero. This makes the image more readable and prevents dullness in the center of the screen.
The main drawback of this system is that the mask takes up a high proportion of the screen zone, which prevents a large amount of electrons, and thus, light, from getting through it. The image is therefore darker than a Trinitron tube monitor, for instance. Some manufacturers have taken the technology a bit further by adding a filter behind each phosphor dot. This is the case with Toshiba's Microfilter, Panasonic's RCTs, and ViewSonic's SuperClear. The technique can be explained as follows: the filter lets the ray (emitted by the electron gun) through in one direction, and at the same time, it captures the light outside. This is designed to raise its own light level and deliver a color that is still pure, but brighter.
The Shadow Mask, less expensive than other technologies, is not just efficient, but is also a solution very well designed for desktop use. It is also good for graphics work because its colors are truer.