Here is a link to a relatively sophisticated seating distance calculator: http://referencehometheater.com/2013/commentary/4k-calculator/
It is crucial that people have their vision tested before they make decisions about UHDTV and whether it benefits them. The calculator's results are highly dependent upon the acuity of one's vision.
The most important thing to understand about 20/20 vision is that it is only perfect in the sense of being a goal for optometrists. When they correct for faulty vision, they attempt to correct it to 20/20.
Because someone with 20/10 vision literally only needs a 42 inch screen to get the same benefit that an 84 inch set provides to someone with 20/20 vision. That is a dramatic difference.
In my case, based on my (recently measured) vision, the ideal distance for watching 2160p on a 55 inch set is 8 feet! Furthermore, 1080p pixels on a 55 inch set become visible (to me) at 16 feet. I am glad I found the 4K calculator, because for a while I thought it was going crazy.
Later today, I should have an article about resolution and visual acuity and viewing distance. After doing a bit of research, one of the things that came up is that 90% of children and young people have better than 20/20 vision. That's why they can see the difference in 5 inch telephone screens, even the difference between 720p and 1080p.
The pixels on a 55" 1080 display become "visible" to you at 16 feet? So if you stand on the 5 yard line on a football field and I put a 55" 1080 tv on the goal line you can make out the individual pixels?
Oh, you mean the image that is composed of the pixels? Yeah, they're visible to you and everyone else who is not blind.
As for discerning the actual individual pixel structures on a 55" 1080 set at 16' feet? Yeah, sure. Me too...and I'm "just" 20/15. I just KNOW I can.
Hopefully your "article" will be/is better backed with actual valid data and reference as almost ALL children's vision is WORSE (most times, considerably so) than 20/20 until they're 6-7 years old. And nearly 50% of children aged 15 are or should be acuity-corrected. Ref: Goh PP, Abqariyah Y, Pokharel GP, Ellwein LB. Refractive error and visual impairment in school-age children 2005;112:678–685
But yeah, some people do have vision more acute than 20/20...and, like so much else, tacking on the years does not help, but acuity trends beyond secondary school are also very uniform and predictable. I can provide references for those as well, if desired.
EDIT: and just so you're aware your assertion that a person with 20/10 vision only needs a 42" screen to see 4k instead of a 84" screen for a 20/20 viewer at distance "x" is completely false (hint: screen area and therefore pixel size does not increase linearly as the diagonal measurement increases). It would be much closer to 60"
Edited by mastermaybe - 5/13/13 at 12:08pm