Colour

In a colour CRT, things work just a little differently. Instead of a single electron beam, as in a monochrome CRT, there are actually three beams. Since the phosphors are grouped into blue, green, and red pixels (take a close up look at your television screen and you can see them), the colour CRT is constructed to direct beams at each group.

By varying the intensity of the three beams or turning one or more of them off completely, thousands of colour schemes can be achieved. When all three of the pixels are struck simultaneously with the same level of power, then the pixels mix to form white light. When they are all shut off, a black effect is achieved.

In both colour and monochrome CRTs, the phosphor pixels are separated by a device known as a shadow mask. A shadow mask is simply a filter devised to keep the electron beams from spilling into other pixel groups. A shadow mask is like a metal plate covered with rows of tiny holes. Each tiny hole lines up with a pixel grouping.