Burn in is more properly known as "uneven phosphor wear".
What causes burn in?
CRTs (or plasma phosphors) "wear/age" as they are used. If the same part of the TV is "hit" with the same image for long periods of time, it will "wear" differently from the other parts of the CRT that are being "hit" with varying images.
After a while, this results in uneven phosphor wear, or "burn in". You will be able to see the image that was 'static' on your TV - for example, a logo, a black bar, a ticker...
CRT-based Direct View TVs, CRT-based RPTVs and Plasmas are susceptible to burn in.
Burn in, can happen in as little as 6 months and is PERMANENT. It cannot be "reversed"
You can prevent burn in by not having any fixed images (like opaque logos, or tickers, black bars, etc) on the TV for extremely long periods of time. Short periods of time are perfectly acceptable. Burn in is cumulative. This means that you can't burn in an image in hours or days. It takes months, but it can happen.
TV setup also plays a major role in Burn-in. Many TVs come shipped with the default picture mode being "Vivid" or "Dynamic" - see the Digital Home FAQ What you need to do to your new HDTV
This doesn't mean that you can't watch any 4:3 HD or 2.35:1 DVDs, but that you should keep any static image to less than about 20% of your overall viewing on a "susceptible TV". Burn in is something you should be aware of, but not paranoid about. This post is not intended to "frighten" but educate.
The order of susceptibility to burn in, from most likely to least likely, is as follows:
CRT-based Direct View TVs
LCD-based TVs (not susceptible)
LCoS-based TVs (not susceptible at all)
DLP-based TVs (not susceptible at all)
For LCDs it's possible
to encounter greyscale degradation (or image persistence) under severe service - as in commercial service where the TV is on all day, on the same channel, but it's not a concern under normal home use, where the TV is not on the same channel 24/7 and is turned off occasionally). Remember that LCDs have been used for computer monitors for many years and there the image is almost always static, without burn in issues. (Some people have
reported burn in on LCDs if 4:3 images have been on the TV almost exclusively, although I have not encountered it...
Although grey bars mimic the phosphor wear of colour images, you cannot be assured that you will not see burn in, especially at the interface of the 4:3 image and the "bars". I know this from experience, on a calibrated CRT-based RPTV, after watching 4:3 almost exclusively for only 6 months. Luckily I noticed when the lines were very faint and they are now gone after several years of appropriate viewing. Black bars are the worst since there is no wear at all where the black bars are being displayed and after a long period there will be a difference between the area where the black bars were and where the 4:3 image was.
Sometimes people will notice "short term image retention", especially on plasmas. This may come from watching the same channel for hours, or perhaps days. It can also happen if you bring up a channel or IPG that has writing on it for even a short time. This is not burn in and should go away if you watch something different and look for it again in a day or two (or even in a couple of hours if it was on screen only briefly).
Recently there has been a lot of discussion about the fact that burn in is no longer a concern on newer plasmas. This is simply not true since the phosphors do
age with time and therefore, will age differently depending on what's displayed on screen. A black bar will not age phosphors at all (while the rest of the image does age). Therefore, if you accept that phosphors age, you must accept the possibility of burn in on new plasmas, even if the likelihood has been decreased from older plasmas since they age less rapidly. As stated above, burn in takes a long time to see - many months or a year for example. Varying the programming you watch and not watching too much 4:3 programming should be fine. Since there is a lot more HD programming available today than there was years ago, burn in is less of an issue with people who watch a lot of HD.
One thing that you cannot do is turn on a susceptible TV to a channel like CP24 in the morning and have it on that channel for hours a day. You will
get burn in.
Some people recommend operating a plasma (burning/breaking it in) for 100-200 hours to prevent future burn in. This is simply not true - it would be equivalent to putting your car on rollers for the first 5,000km instead of driving it properly. Taking the plasma off the default "torch mode" is the most important thing to do, and then watch it (and optimize it at some point) as discussed above. Operating a TV while not watching is also a waste of energy and nothing more.
Discussed by calibrators/optimizers in link below:
The only reason to wait for a while to calibrate would be if you're going for a professional calibration and don't want to run into the bother of infant mortality on the TV. If break in were
required, it would be covered in the operating manual.
If you would like to make additional contributions to this post or have corrections/clarifications, please PM me.