The main criterion for choosing a screen size is one that I have not seen described in other TV buying guides: viewing area. The viewing area of a 32″ conventional TV is 492 square inches, whereas the viewing area of a 32″ widescreen TV is a mere 438 square inches! If you’re upgrading from a 32″ conventional TV you’ll want at least a 34″ widescreen to get the same viewing area.
Here’s how I arrived at those figures.
The advertised size of a TV display is the length of the diagonal. If from the diagonal we can determine the height of the display, h, and the width, w, then the viewing area is h×w. Thanks to Pythagoras we know that h2+w2 = 322. But this isn’t enough information to determine the viewing area: we also need the fact that the aspect ratio of most conventional TV displays is 4:3, which means the width of the display is four-thirds the height.
Substituting 4h/3 for w and then simplifying gives us:
h2+(4h/3)2 = 322
h2+16h2/9 = 322
25h2/9 = 322
h = √(9×322/25)
h = 3×32/5 = 19.2
Plugging that into the formula for viewing area (h×w) and recalling that w = 4h/3,
h×4h/3 = 19.2×4×19.2/3 = 491.52 square inches
Knowing that the aspect ratio of widescreen displays is 16:9 and using similar arithmetic gives a result of 438 square inches for a 32″ diagonal.
In fact, the math shows that for a given diagonal, the viewing area of a 16:9 display will always be about 11% less than the viewing area of a 4:3 display.
But wait! It’s not as simple as finding the widescreen TV that has at least the same viewing area as your conventional TV. You should also take into account the kinds of programming you watch.
Do you watch a lot of wide-format movies on your 4:3 TV? If so, you’ve certainly noticed the “letterboxing” needed to fit the wide aspect ratio of the film into the narrow one of the display. You’re not using the entire viewing area; some of it is wasted, as much as 32% of it for very wide format formats such as “CinemaScope.” With a 16:9 TV the need for letterboxing wide-format movies is decreased or eliminated.
Similarly, if you watch a lot of conventional TV programming (sitcoms, newscasts, etc.) on a widescreen TV, you’ll get “reverse letterboxing,” also called pillar boxing, where the black bars appear not on the top and bottom but on the left and right of the image to make the taller aspect ratio fit into a shorter one. Here again you’re wasting some of your viewing area.
So think about the kinds of programming you watch and consult this handy table that shows the true image size (in square inches) for various combinations of TV diagonal size, TV aspect ratio, and programming aspect ratio. Choose a TV that gives you the best image size you can afford for the types of programming you typically watch.
|Program aspect ratio|