How does an image get burned in to a TV Screen?

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How does an image get burned in to a TV Screen?
« on: 05/12/2008 16:04:37 »
How does an image get burned in to a TV Screen, and does this happen for crt, lcd and plasma?


Offline graham.d

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How does an image get burned in to a TV Screen?
« Reply #1 on: 05/12/2008 16:43:45 »
Yes for CRT and plasma. No for LCD.

CRT tubes excite coloured phosphor dots by bombarding them with focussed beams of electrons. The continued bombardment does affect the material and if this continues in an uneven way (with a single image in one place) it will dim the perfomance of the phosphor to respond and leave a negative imprint there. Modern CRTs are actually very resilient to this and it is very unlikely to be noticable in the life of a typical TV set. It was a much bigger problem with Black and white TVs.

Plasma sets have a similar problem and, on early models, quite severe. Again it has been improved over time and, although can still occur, there are things that can be done to help alleviate the problem. Some manufacturers recommend a "burn-in" period where the screen is not used at full brightness for a while and also say that there are things that can be done to erase a burnt in image, though I am unsure how either of these things work.

I have never seen the phenomena on LCD screens and cannot see how it can occur, but some people on the web (people who seem to wish to promote plasma TVs perhaps) claim that it occurs. So there may be other opinions.


Offline techmind

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How does an image get burned in to a TV Screen?
« Reply #2 on: 07/12/2008 00:56:36 »
Some plasma screens slowly move the picture around so that any burn-in from static shapes and logos is fuzzy-edged, making it less noticeable.
I remember the LG plasmas in the shops running the manufacturers demo loop ... the LG logo jumped between all four corners of the screen during the demos, and while in any one corner was set up to wander around slightly. This is an extreme case because the demo would be running all-day every day in stores - but there was definitely evidence that the manufacturers were taking preventative steps to avoid/mitigate effects of burn-in!

While LCDs do not "burn in", they can exhibit "image sticking", which can leave a remnant or latent image of sorts (sometimes the latent image can be like an edge-map of the causing image). This can be caused by ion migration from the glass/LCD/electrodes creating a net bias on a pixel. The effects are minimised by using good quality materials in the display construction, and good process-control, but also by proper adjustment of the LC cell bias (there should be no DC bias). This VCOM bias is not always set as accurately as one might like, and can be a significant factor leading to image-sticking. I've seen many LCDs which don't seem to have any image-sticking issues, but one or two with really severe image-sticking problems (a laptop screen after just a few days of use the desktop background led to image-sticking).

Most manufacturers cover their backs in the small print by telling you to avoid displaying static images for long periods!

I would say that some degree of burn-in is inherent in plasmas (and to a lesser extent in CRTs - witness train departure indicators for extreme cases)
Burn-in ("image sticking") can occur in LCDs if they're poorly manufactured or poorly trimmed, but can be largely avoided if manufactured with care - so the problem is not inherent with LCD technology. Unfortunately that's not to say that buying from a well-known manufacturer is sufficient to guard against problems.
« Last Edit: 07/12/2008 01:03:15 by techmind »
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