I induced IR by displaying a letterbox 4:3 image so there were gray side bars and black bars above and below the image. Let the display run this way for 90 minutes or so. Confirmed with a black screen that there was obvious IR (there was - just like EVERY A550 panel, I've checked 12 of them now and they ALL have IR to exactly the same degree so people who aren't seeing it either don't know what to look for or they are in denial). The object of this was to see if IR disappears overnight with the TV turned off.
I did turn the TV off after confirming what the IR looked like. I did not turn the TV on again for more than 12 hours. The IR was exactly the same as I when I turned it off the previous night.
The next test was to see whether a black screen dissipates IR as well as a white screen or the scrolling eraser pattern... I have to say a black screen DOES remove IR almost as well as all-white or the scrolling eraser. Must be something about the cells being "activated" that knocks down the IR. In an hour or so of sending a 0% white test pattern to the A550, the IR was gone. So IR doesn't disappear with the TV off, but a black screen does eliminate IR over time - and it uses a lot less electricity doing so than the all-white screen or the scrolling eraser. How fast is IR eliminatd? By 20-30 minutes you had to look real hard to see it on a black screen, and it was invisible with moving images covering the entire screeen. By 1 hour or so, I couldn't find it on the black screen any more.
I've seen "no image retention" before... on a Pioneer Kuro... and these panels (and every other brand) are NOT in the same league with the Pioneer Kuros re. image retention. That said, this amount of IR is not a terrible thing - though I find myself distractedly looking for it all the time after a movie or 4:3 programming. So I wish there wasn't any IR, but it doesn't interfere with viewing in any significant way. And if it is visible, after 20 minutes or so, it has abated to the extent only a true obsessive would be able to find it. The only time I've seen it for more than 20 minuted was when the disc menu image was retained and the movie itself was 2.0:1 format with black bars top and bottom... I could see retained image from the disc menu in the black bars for about an hour, but I think that's about the worst it will ever be and it didn't really affect watching the movie as long as I didn't look closely at the black bars trying to find the IR.