Truth Patrol: Screen Sizes

HDTV Truth Patrol
According to a story on chinapost.com.tw, the German consumer magazine Test advises that you should sit no closer to an HDTV than three times the screen’s diagonal measurement. So for a 32″ model, you should sit at least 96″ away, which is eight feet.

Now, I’ll admit that this is a second-hand reference, but the facts are so simple that it’s difficult to think that the reporter misquoted it. And it’s wrong.

First, it’s wrong because it treats 720p and 1080p displays the same, which is not the case at all. The pixel size of a 32″ 1080p screen is one-third smaller than that of a 32″ 720p screen. So you are more likely to see the dots of a 720p than a 108p screen at a given distance.

But the bigger question is how close do you have to be to see the individual dots at all? As a rule of thumb, a person with average eyesight can see details as small as 1/60th of a degree of their field of vision. In order to see the dots, they must be at least big enough to fit 1,800 of them in 30 degrees of your field of vision. So to see the 1,280 horizontal dots of a 720p display, you need it to fill at at least 21 degrees of your field of vision. For the 1,920 horizontal dots of a 1080p display, it must fill 32 degrees. Do the math, and you’ll find that you must be sitting much, much closer than eight feet for a 32″ screen before you’ll be able to see the dots.

For a 32″ screen, this works out to six feet for a 720p screen, and just four feet for a 1080p screen. If you watch a 32″ 1080p screen from eight feet away, you won’t be able to tell the difference between it and a 720p screen, and you’re wasting the money you spent for the extra resolution. It is important that you get a set big enough for you to see the HDTV detail from the normal viewing distance in your room.