Screenburn Prevention On Panasonic TH42PX70
Since the technology of plasma was introduced a few decades ago, the single biggest worry of potential owners has been that of screenburn. This refers to the permanent ghosting of images on the screen due to prolonged use displaying the same image over and over again.
Physics Behind Screenburn
What makes up a plasma TV is a lot of cells containing phosphor gas, which will be charged up by voltage as instructed by video signal sent either from your aerial or DVD player. The phosphor in these cells will be consumed to emit certain light frequencies, which eventually produces the picture you see.
A problem arises when a static image is displayed on the plasma screen for a long time. The phosphor in the cells making up a portion of the static image will be used up more quickly than the phosphor in the cells that don't. Over time, the cells with less phosphor will become dimmer than the rest, resulting in a "ghosting" of previous static image which overlay all images displayed now on the screen. This is known as screen burn.
Typical examples of screen burn are Sky TV logo, BBC logo, and the Windows bottom bar (if you're using a HTPC with your plasma). Plasma TVs are most susceptible to this phenomenon during the first couple of hundred hours of their use because the phosphor has not yet stablised, therefore it is very important for you to take certain precautions after you unpack your shiny new TV.
How To Prevent Screenburn
It's obvious: you need to look after your plasma especially in the first 200 hours of its life. Do not display a static image for over 30 minutes (to be on the safe side keep it under 15). Switch off the TV when you go to grab a snack etc, and let your family member know about the risks too so that your effort is not wasted.
To prevent the phosphor in the cells from being used up too fast and causing screenburn, it's wise to reduce the contrast and brightness on your plasma TV. Usually plasma TV's ship in the Dynamic mode where the contrast and brightness has been increased... a sales tactic to attract more attention in showroom. For the first 200 hours, make sure your contrast and brightness is at most half of the maximum allowed in the adjustment bar.
With so many cheap LCDs around with higher resolution, hopefully you didn't buy a plasma to play a lot of console or computer games. But if you do, the same advice apply. Because there are quite a lot of potentially static icons on such games (life bar, console bar, etc), it's best to take a break after a couple of hours, switch of the plasma for 30 minutes, and then resume your session.
Some sensible use and appropriate precautionary measures will go a long way towards ensuring that your plasma serve you well over the years. Good luck!