Think of it this way. If a friend holds a book open and shows it to you from 100 yards away, all you see is a gray blob. If you were to move closer, you could read words. If you stayed in the same spot and the book were enlarged, you could read words. If you're staying in the same spot, though, and the book is going to stay the same size. . .does the book even need words? You get the same amount of visual benefit whether the item in question is, in fact, a book, or an actual blob of gray ooze.

Screens are the same. If you have a television screen that you view from a distance, you're able to benefit from a smaller amount of information, so the screen doesn't need as much detail. The closer you go, the more information the screen needs to display in order to prevent you from seeing the pixels, instead of the picture. At a certain size and distance, SD looks exactly the same as HD. You can increase the level of detail (the resolution) in the picture as high as you want, but, without binoculars, it won't look any different.

So. Your comment:



...is actually half right, and half wrong. If you make your screen bigger, then yup, you probably need a higher resolution. If you move it further away, though, then you need a LOWER resolution. At 100 yards, you would need a truly enormous screen even to need SD resolutions. It's all a matter of how big, and how close. Another experiment you could do would be to switch back and forth between HD and SD stations again, and move closer and closer to your TV until the HD looks noticeably better. Now look at the screen, and get a feel for how much of your field of vision it fills. In order to see the same benefit from your usual viewing spot, you would need a tv big enough to occupy the same amount of space in your visual field at that distance.

Does that make sense?