This doesn't explain it though. I'm doing tests with just as much contest all over the screen and leaving it up for a really long time, like 20+ minutes. I'm using big, bold 78point fonts in word, pitch black type on a super white background, then switch to gray after a really long time, no IR. I am duplicating the checkerboard test pretty closely and taking it to even greater extremes and still no IR. But IR shows up in the checkerboard test.
Are you staring at the thing during the whole time? if so, there is also image retention with our *real* retinas
As far as getting IR in a certain image, well
certain images are not conducive to viewing and displaying. Take those images from illusions, for example. They are tricky to see but displaying correctly and in your case you are seeing correctly but its not displaying correctly. One of the mysteries of life.
LCD's with a slow/normal refresh rate will retain images. This was the whole marketing scheme behind *beating the motion blurring* with 120 Hz TV's and now the 240 Hz TV's for 3D. I have a Samsung LCD TV with 120 Hz. But guess what? When I enable the motion blurring option, the video looks like it was taken from a home camcorder. So I never use that. I will get a Plasma since they are so thin these days, when I have to get my next TV.
So LCD TV manufacturers came up with lot of workarounds in Image processing to compensate for that. Remember when some videophiles say LCD TV"s will never be as good as a plasma or a CRT? this exactly is why and its a weakness. But its the low weight,power consumption and cost that actually pushed LCD to the forefront of display technology whereas it was the worst performer.
The LCD in a laptop is no different.
But in all fairness I agree there are variations between LG and Samsung. Samsung might be doing some tricks behind the scenes to make it appear good, but fundamentally they are the same.
The liquid in the LCD is actually a dye and my guess is Samsung has a better recipe than LG.
I returned an MBA recently due to severely washed out colors and my guess is that batch of LCD's had a bad batch of dye's when they were compounded.Some disgruntled employee diluted it more? or wasn't monitoring the process closely? Who knows?
But I am using my retina MBP daily now before the return period and I can't really seem to find any fault with it. Even the colors are perfect. Could I produce some odd results by running some programs or visiting some websites? I probably could. But, If I am going to use it as I would and I don't see any issues then all is good for me, personally.
But if you are going to be left with a nagging feeling that your monitor isn't up to your expectation's then exchange it by all means.
In the end, you have to feel good about your purchase.