I have not seen anything written about this anywhere. So, I thought I'd take a crack at it. There are all sorts of places offering help in choosing the size of TV (both High Def and Conventional) that you ought to buy given how far you sit from the screen. There are also a number of sites offering help in figuring out all the abbreviations and buzz words that surround the changes due to TV technology improving in the digital and high definition realms. But one thing hasn't been covered and it is going to lead to a lot of disappointment to people moving to a new high definition TV from their old conventional TV.
I noticed the problem when I got a new computer at work. It was one of the new wide screen monitors that has the same proportions as the new high definition TVs. You can see in the diagram at the right that conventional TVs have a width to height ration of 4 to 3. That means if you divide the width by the height, you get the same value as if you divide 4 by 3: 1.333 but the manufacturers sell them by measuring from the upper left corner to the lower right corner. But no matter what size TV you buy, the proportions are always the same. So, if you buy a 27 inch set, the width will be about 21.6 inches and the height will be about 16.2 inches. Divide 21.6 by 16.2 and you get - 1.333 ! No matter what size TV you buy, the width and height will have the same ratio.
Now, for high definition TVs, the ration is 16 to 9 (similar to the proportions for a movie screen). With these proportions, the screen is a little wider compared to the height. This all fine but you have to realize that the manufacturers still tell you the size of the screen as measured from the upper left corner to the lower right corner. So, if you buy a 27 inch high definition TV, you might think you're getting the same area of screen as you would get with a conventional TV. But instead, you get a TV that is about 13.23 inches high and 23.49 inches wide.
Compare the areas. The conventional TV area (width multiplied by height) is 349.92 square inches. The high definition TV area would be about 310.77 square inches! The conventional TV is about 12% bigger for a given diagonal measurement. The thing I especially noticed, with my new computer monitor, was the missing height.
Next time I'll write a bit more about how to get the same height in your new high definition TV as you now have with your conventional TV.