Thursday, August 12, 2010

Phosphor burn-in

Phosphor burn-in is localized aging of the phosphor layer of a CRT screen where it has displayed a static bright image for many years. This results in a faint permanent image on the screen, even when turned off. In severe cases, it can even be possible to read some of the text, though this only occurs where the displayed text remained the same for years.

This was once a common phenomenon in single purpose business computers. It can still be an issue with CRT displays when used to display the same image for years at a time, but modern computers are not normally used this way anymore, so the problem is not a significant issue. The only systems that suffered the defect were ones displaying the same image for years, and with these the presence of burn-in was not a noticeable effect when in use, since it coincided with the displayed image perfectly. It only became a significant issue in three situations:

when some heavily used monitors were reused at home,
or re-used for display purposes
in some high-security applications (but only those where the high-security data displayed did not change for years at a time).
Screen savers were developed as a means to avoid burn-in, but are unnecessary for CRTs today, despite their popularity.

Phosphor burn-in can be gradually removed on damaged CRT displays by displaying an all-white screen with brightness and contrast turned up full. This is a slow procedure, but is usually effective[citation needed].

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