And another update. Tech came today and switched my LG panel. They held true to their word and actually did send an AUO panel instead of switching it for another LG panel.
Comparison of my panels, I'm going to give highly subjective ratings from -4 (really bad, could hardly be worse) over 0 (average) to +4 (outstanding, hard to get it better). I'm judging them as IPS panels.
___________
Dependency of illumination on viewing angles:
LG: -4
My biggest grime with it. I posted some pictures before. While the pictures slightly exagerate the effect compared to how I perceive it in nature, it's still very strong.
AUO: 0
Notperfect either. Watching straight on, you can see that whites get noticeably darker towards the horizontal sides. Depending on how you turn/tilt the display, you can see shifts of brightness that are stronger than I know it from desktop IPS panels.
HOWEVER, the effect is much weaker than on the LG panel. I'm simply mentioning it to state the facts. Still, it's night and day compared to the LG! Might not be the perfect choice for someone who really wants a panel that shines in this area, but it's good enough for me. The effect is there, but it totally lacks that "in your face" momentum. Changing the viewing angle by 5° no longer results in extreme brightness shifts and you can actually tell whether you see an image with a gradient or not.
___________
IPS glitter / "snow"
Don't know if there's a better term for this effect. It's not exactly unsharpness but it gets really annoying to look at after a while. For me it also has the effect that the picture appears slightly unsharp even when the panel actually isn't once you look at single pixels.
LG: -3
After a while, my eyes always started to feel a bit like when you look at a bright light source after being acclimated to darkness. Whenever I looked somewhere else, I've seen some slight retinal bright patches for a few seconds. I really don't know how to describe it better, I know this description is quite vague.
AUO: +3
Yeah it has glitter too, but it's very minor. If you just look at it and not closely examine it, my guess is you won't notice it. Very nice.
___________
Backlight bleed:
LG: +2
Minor at best. It's not like an OLED panel, but still no problem at all. If you look at a black picture in a dark room, you can see some unevenness, but then again, why would you...
AUO: +2
Has some edge bleed, not uncommon for edge lit LEDs (which is like every LED LCD today). Still, the effect is minor. Black screen, maximum brighness, normally lit room, I can't see it. Once I turn off the light and shut the blinds a bit, it becomes visible. This might be the case as well if you use it to watch a movie in the evening/night. Still, you have to be really picky to consider that a real issue.
___________
Contrast:
LG: +3
Not OLED like, but still really good
AUO: +3
Quite comparable to the LG
___________
Brightness:
LG: +1
Good, but not especially good. If brightness is a top priority for you, there are better panels. Bright enough to be used outside, but you should avoid direct sunlight.
AUO: +1
Yet again, quite comparable. However, the brightness is actually of much more practical use since it doesn't get ruined by viewing angles.
___________
Colors:
LG: +3
If you're able to look past the glitter and the huge brightness shifts, this panel actually had quite good colors. Unfortunately, it's very hard to do so.
AOU: +2
Some people reported a significantly warm picture, some others a yellow or brown taint. While it might be slightly warmer, I cannot second the yellow/brown taints (unless this is your general perception of a warm image). The main reason why I rate it slightly lower than the LG is that the color balance noticeably shifts when you change the brightness. At lower levels, whites get a noticeable green/blue taint. While it's possible to calibrate against it, you really would have to recalibrate whenever you change brightness. I can handle it since I don't care about color accuracy that much with lower brightness settings.
Beyond that, colors are good and accurate. At least adequate for an IPS panel and much better than most laptop panels. I wouldn't be surprised if scientific measurements of the panel would hint towards giving a slightly worse rating, I don't have the subjective impression that the colors are off when I look at the screen.
___________
Mattness:
LG: -1
Still clearly matte, yet reflecting more than I would like. Not sure if this might be related to the strong glitter.
AUO: +3
Not moth eye panel quality, but still, it's a good matte panel. Direct light sources will be visible slightly blurred, beyond that, reflections are vague at best. Also, the matte coating doesn't let the picture appear grainy or unsharp.
___________
Conclusion:
The two panels are quite compareable in many aspects. But the very bad viewing angles and the strong glitter totally spoil the overall decent results for the LG panel. While AUO doesn't have perfect viewing angles either, it doesn't have any strong flaws and most results are at least solid or better. The issue with non linear color balance to brightness might be annoying for some, but for me it doesn't break the overall good to very good impression.
The AUO panel definitely swims with the best in the pool of laptop panels.
So overall, I'm really happy with the new panel, finally, I can use the laptop without constantly being annoyed by retilting and turning the screen whenever I move my head. The AUO panel isn't perfect in every aspect, but its a pleasure to look at and a steep upgrade over any other ThinkPad panel I've seen so far (mostly TN panels and some old IPS panels).
As a side note, also at Lenovo: You might want to think about streamlining the process of screen replacement regarding the bezel. My technician just had the panel with him and he was simply told to install it. While he seemed to have quite some experience with ThinkPads in general, it was the first time he worked with a T440s. He was quite surprised that it was just glued. He really had a wild time rumbling with it until he got it all off. A lot of the glue stuff got wasted in the process.
When I told him that the HMM recommends that the bezel gets replaced with the panel as well, he wasn't the least bit surprised and agreed that this seems to be the smart call.
Given the circumstances, the end result doesn't look too bad though, he was somewhat careful when reattaching the new panel to the bezel. But still, the bezel is slightly loose in some areas now, while it was quite solid before. As long as it stays like this, I'm fine with it, but he already told me that I might want to request a new bezel somewhen in the future, in case that it does start to come off.
We will see. Still, overall I'm happy with the result, especially since the screen delivers what I expect.