Displays are limited by resolution. So First all the Calculation then the Gyan
The human eye can resolve details down to 1/60° (so if pixels get bigger than this they will be noticed).So let’s do some calculation here:
viewing distance = 8 ft = 96 in
max pixel width / viewing distance = tan (1/60)
max pixel width = tan (1/60) x viewing distance
max pixel width = tan (1/60) x 96 in
max pixel width = 0.028 in
For true HD 1080p resolutions is 1920 x 1080 pixels
1920 pixels x 0.028 = 54 in (screen width)
For a widescreen display aspect ratio is 16:9
diagonal = sqrt ( 16^2 + 9^2 ) = 18.4 aprox
54/16 x 18.4 = 62 in diagonal
Notice that if we calculate for vertical resolution the result will be the same:
1080 pixels x 0.028 = 30 in (screen height)
30/9 x 18.4 = 62 in diagonal again
Then 62″ is the biggest screen size you could use from that distance (8 ft) without pixels noticed when it’s a full HD 1080p display.
Nevertheless, for real cinema experience and image impact (the closer to the real cinema) recommended viewing angle is 26° minimum. This will require 51″ from 8 feet and it will be like being seated in the back row of a comercial theater. And a recommended viewing angle of 36° which will require 72″ from 8 feet like being seated in the middle row of a comercial theater – actually the best seats.
If we use this larger screens then pixels will be noticed but this is not a big deal up to some size (about 40° viewing angle – 80″) because.
If we do the same for standard definition we will obtain maximum 22″ from 8 feet away. This is why in 25″ or bigger TV’s with standard definition is easier to notice scan lines when seen from 8 feet away or less. Anyway people have always wanted bigger screens and actually they do improve image impact no matter scan lines being noticed. Anyone can prove this: compare side to side a 14″ standard TV with a 32″ TV and notice that 14″ is shaper and scan lines are barely noticed while 32″ shows scan lines and picture doesn’t look sharp anymore, but overall 32″ is way better to watch movies on it.
And a major drawback of small screens is that they cause eye straining when viewed on darkened rooms because of reduced viewing angle. And dark rooms are desired to watch movies (some people could say that this is important only when watching terror movies but this is a must for cinematic experience to be inmersive) so this is another reason to prefer bigger screens.
If we do the same calculation for 720p resolution:
720p is 1280×720 pixels
1280 x 0.028 = 36 in (screen width)
36/16 x 18.4 = 42 in diagonal
Then 42″ is the biggest screen size you could use from that distance (8 ft) without pixels noticed when it’s a 720p display.
If your TV is not full HD then probably it’s 1366×768 which means it have a resolution between 720p and 1080p, but it will be ok to assume as 720p. Then you are ok because if you seat closer pixels will be noticed. Then 8 ft is good for TV watching and regular movie viewing. But you can see what image impact is all about if you just try a movie (not TV) with dark room from 5 ft away, you will notice soon how you can see the entire image easier in a natural way (like if the film was recorded using your own eyes). This is not joke.just try it. Anyway a bigger screen always works better than seating closer than 6.5 ft with a smaller one.
TV Screen Size (in) ÷ 8 = Minimum Distance (ft)
TV Screen Size (in) ÷ 4 = Maximum Distance (ft)