Back to the Samsung F5300 for a sec (for those who may still be interested
I spent some more time yesterday looking at the uniformity of the F5300s at a different store with darker overhead lighting, and both the 51" and 60" displays appeared to be slightly brighter and also "cooler" (ie more blue-red) at that bottom of the screen than at the top.
There appeared to be a very diffuse hot spot centered at the bottom of the screen on both displays, so maybe that's where the panels connect to the power supplies. And perhaps the voltages are running a little higher in that area as a result.
That raises an interesting calibration question btw... If there's a difference in color and brightness at the top and bottom of the screen, then do you adjust the white/gray balance so it's more accurate in the middle of the screen, or at the top, or bottom? Before answering that question though, I think you'd also have to look at the balance near black on different parts of the screen, to see which way the shadow detail might be skewing.
My guess is that all of the F5300s and and F4500s have this "hot spot" feature to some degree. It's probably a little more noticeable on the larger displays though because the pixels at the top of the screen (esp. the top corners) are farther away from the supply of power at the bottom, and not receiving quite as much "juice", and hence somewhat darker. That's my theory anyway.
Tinkering with the voltages might help a little. But I have some doubts about whether it would make a really noticeable improvement, because it looks like this is probably a characteristic of the displays' design, and power supply. And my guess is that Mark's 3rd, 4th, 5th, 6th... F5300 panels would probably all have looked about the same. (I'm not Joe Electrician though, so I could be wrong about this.)
Given the frequency/consistency of this issue, I'd probably have to downngrade my uniformity rating on the F5300 displays from "outstanding" to merely "very good" for a low cost display. The uniformity is still significantly better on the F4500 and F5300 panels than on my 1080i CRT though, which has a fairly pronounced hot spot and color shift in the middle of the screen. And if my theories above are correct, then the uniformity is probably best on the smallest and least expensive model, namely the 720p 43F4500, and the "hot spot" is probably most noticeable on the 1080p 64F5300, since it's biggest.
I think this also proves that Mark's eyes are better at identifying these kinds of flaws than mine, so it's probably a good thing he's the one doin the reviews.
I still think he would've enjoyed the calibrated picture on the 51F5300 more in controlled lighting than the F8500 though, and that he probably would've tuned out/gotten used to the subtle hot spot at the bottom of the screen in time. The F8500 might be a better tool for doing reviews though, because it looks more like an LED than the F5300,... albeit one with better motion and blacks than a typical LED.
I disagree a little with his description of the F5300s as "dark room" displays though. In my opinion, these are "dim room" displays at best, because the blacks just aren't deep enough to really look "black" in a room with no lighting. (I'm a little spoiled on this issue by the deep inky blacks on my CRT though.)
Issues like the hot spot above will probably also stand out more in a darker room. Imo, these displays will probably look best in a room with dim to average lighting, provided that most of the room light is behind/around the display rather than in front of it, as I described earlier. I think the PQ on a well-calibrated 51F5300 would be hard to beat in these kinds of ideal lighting conditions, esp. for the price.
Also, as far as I can tell, the hot spot issue above has nothing to do with the display's color decoding (which is also quite good btw), so it wouldn't really be considered "red push". You could say that the panel appears to be "driving" a bit more blue and red near the bottom of the screen than at the top though.
Red and green "push" are usually associated with color decoding errors rather than white/gray balance issues. Manufacturers will often deliberately tweak the color decoding on their equipment to either punch up the luminance ("green push"), or to give flesh tones a more reddish hue to compensate for the cooler white balance in their Vivid picture modes. I saw no signs of either red or green push on the 51F5300 in my HDMI Blu-ray tests though, when the color settings were properly configured on both the player and display. The color decoding looked pretty much on the money using the "RGB Only" feature with a variety of different color bar tests at different stimulus levels.
The overall white/gray balance on the display looked like it could use some adjustment though, since none of the Color Tone temperature settings looked especially accurate out of the box.