A CRT monitor is similar to older types of televisions. A large glass tube known as a "Cathode Ray Tube" is used as the display. The front of the tube is covered with a type of phosphor. At the back is an "electron gun." This gun shoots electrons at varying intensities, causing the phosphors cells to glow. Each phosphor cell contains three color phosphors, red, green, and blue. When different colors are needed to be displayed, the gun charges up two or more of the colors, as well as dithering with other cells to create even more colors.