CRT screen burning

[Goodberry]

I see in warnings in various game manuals that displaying the same image for a long period of time carries the possibility of "burning" the image into the screen, ruining the monitor.

I would have thought computer monitors were made to cope with this sort of thing, i.e. displaying an unmoving desktop.

What are the chances of burning a monitor screen? Is it the sort of thing that happens often?

 

[Diggrr]

It used to be a problem, especially on office machines where it could be on for most of the day without the screen changing.
But now, there's degaussing built into the monitor, that takes care of it.
There's also power saving standards (the green E) that gives your monitor auto-sleep mode after a few minutes of inactivity (a windoze default)...saves energy and monitors.

I have degaussing set to fire everytime I cycle the power button on the monitor. I have my windoze power settings to use "sleep" both when the computer is turned off, and after 20 minutes of inactivity (mouse movement), so I'm only really degaussing about every week or two.

Check out your monitor's on-screen menu's to see what I'm talking about.

 

[Goodberry]

Ah... I appear to have been misled; I was under the impression that the phosphorous layer of the screen was chemically damaged , but if it is just magnetic damage then it all makes so much sense.

 

[jamespetts]

No, it is the phosphorous layer of the screen. With a CRT (the problem does not affect LCDs), the electrical signal excites the phosphor coating on the inside of the glass screen. The phosphor, being excited, gives off light. However, this process degrades the phosphor. It takes a long time, but, slowly, the phosphor coating becomes less excitable. The effect of this is that older monitors are less bright and have poorer contrast than newer monitors (assuming that the old ones were heavily used).

Screen burn occurs when the phosphor coating wears uneavenly, causing a noticable pattern of duller/lower contrast image to display. This can happen when the same image is displayed for a very long time: that shape can then be "burnt" into the phosphor coating of the screen.

To prevent this occuring, "screen savers" were invented, which turned the display blank (or displayed a moving image or text) after a specified period of inactivity. Initially, these were purely functional things, with a little box of text that changed position every ten seconds saying something like, "The display has been blanked to save the screen. Press any key to continue". In about 1993, however, a product called "After Dark" became very popular: screensavers that displayed interesting and amusing images, such as a flock of flying toasters. Later versions of Windows incorporated more diverse screen-savers (Windows 95 had only blank screen, flying windows, spacefield simulation or scrolling text; the Plus95 pack added far more), and screen savers started appearing on laptops, whose LCD screens did not need saving in the first place.

With the invention of automatic energy saving, so that monitors would not only display no static image to avoid screen-burn, but would cease firing the scanning gun at all after some time of inactivity in order to save power, screen savers became less about saving the screen, and more about expressing individuality. All sorts of whacky screensavers emerged throughout the 1990s, and screensaver trading and downloading became so popular that it was even used as a method of virus transmission.

Then, a group of scientists analysing information from radio-telescopes in search of signs of extraterrestrial life, short on supercomputer time, had an idea. All of that time that home and office PCs were not being used is time that could be used to perform useful scientific work. The screensaver was the natural medium for such a project, so Seti@Home was born. Other groups soon followed suit, and now there are a plethora of distributed computing projects that use screen-savers as their base.

From its humble beginnings as a tool to prevent screen-burn, the screensaver has evolved into an important scientific tool, whilst the issue of screen-burn itself has been overtaken with the invention of power-saving modes and LCD monitors.

 

[Goodberry]

...how long did that take to write?

Nice one, thanks.

 

[jamespetts]

You're welcome

It started out as a brief response to a screen-burn question and mutated into a potted history of the screensaver... I don't have much to do at present, can't you tell? ;-)