How Does a CRT TV Work?

by David Dunning

Cathode ray tube (CRT) TVs employ different technology from liquid crystal display (LCD) and plasma TVs. In fact, it is the presence of a CRT -- a funnel-shaped glass tube -- that gives CRT TVs their characteristic depth and weight. Essentially, CRT TVs work by bombarding a phosphor coating on the inside of the screen with negatively charged particles called electrons or, originally, cathode rays.

Electron Gun

Inside a CRT, a device known as an electron gun (which consists of a negative electrode, or cathode), a series of computer windings known as steering coils and a heater generate a beam of electrons. The steering coils create a magnetic field, which guides the beam so that it scans back and forth across the screen, starting at the top. Air is withdrawn from the CRT so that air molecules don't interfere with the passage of electrons between the electron gun and the screen.

Phosphor

Phosphor is the name given to any substance that emits visible light when exposed to radiation, such as ultraviolet light, or, in this case, a beam of electrons. The electrons collide with the phosphor atoms, causing them to gain energy or become "excited." When the phosphor atoms lose the energy gained during the collisions, they emit particles, or photons, of visible light.

Black-and-white and Color

Older CRT TVs use just a single color phosphor and so can only produce black-and-white, or monochrome, pictures. Later CRT TVs use phosphors colored in the three primary colors -- red, green and blue -- and therefore can produce full color pictures. In the latter case, manufacturers apply multiple color coatings to the screen through a device known as an aperture mask, made from perforated metal, to create thousands of narrow, colored lines of phosphor.

Considerations

There's nothing inherently wrong with the way CRT TVs work. In fact, CRT TVs render colors very well and produce high quality pictures, which scale easily to various resolutions. However, their main drawback is their physical size and weight; a large CRT TV can weigh several hundred pounds, whereas a much larger LCD or plasma TV can be light enough to hang on a wall. CRT TVs also produce more noticeable flicker than their flat-screen counterparts and consume significantly more power. Furthermore, the nature of a scanning electron beam means that it diverges as it approaches the edge of the screen, so the viewable area of a CRT TV screen is always an inch or two less than the actual physical size.

About the Author

A full-time writer since 2006, David Dunning is a professional freelancer specializing in creative non-fiction. His work has appeared in "Golf Monthly," "Celtic Heritage," "Best of British" and numerous other magazines, as well as in the book "Defining Moments in History." Dunning has a Master of Science in computer science from the University of Kent.

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