How Colour Monitors Work

There are two main methods of producing the monitor through which we control the computer and assess images before printing them out. Both require extremely high levels of precision in manufacture and sophisticated control.

Cathode-ray tube
CRT, or Cathode-Ray Tube, technology is essentially the same as that used in domestic televisions: an electron gun, the cathode, is heated up to produce electrons that are accelerated and focused onto a phosphor-coated screen, which glows when hit by the electrons. For colour images, phosphors that glow red, green, and blue are used. To ensure that the correct colour phosphor is stimulated to glow by the beam, a grid is placed between the electron beam and the phosphor. This grid consists of very fine wires or a series of holes precisely aligned to mask unwanted electron beams from the phosphors. When you consider that each phosphor dot is as little as a 0.25mm away from its neighbour, you can appreciate the high levels of precision required. Furthermore, for a phosphor to continue emitting light, it must be bombarded by electrons: after an interval, which varies with each colour, the light decays. So, for a steady screen image, each phosphor must be hit by electrons for different periods of time.

As the electron beams all originate from a small central point - the cathode - they fan out and focus on a section of a circle. However, the resulting curvature on a screen is uncomfortable to view and picks up background reflections. To produce a flat screen takes extremely sophisticated electronics and optics.


Steve J. Wilson is living in the United States and is a freelance writer since 2006, in digital photography related topics. If you are interested in some useful Digital Photography Classes, than you are in the right place.

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