Monday, December 13, 2010

HDTV screen size and viewing distance

If you have decided on the type of HDTV that suits you, the next big question will be the size. The general answer will be to get the biggest screen size that you can afford. The only caution here is that make sure you have enough space to view your HDTV at a comfortable distance from the front.

A few general facts on the HDTV screen size. TV sizes are always quoted using the length of the diagonal across the screen. For HDTV, many advise that 32" is a minimum size for your bedroom or those with space constraint and 40" as a minimum for a normal living room. If you are getting a HDTV to replace your existing CRT TV, do not get one with the same size. This is because normal CRT TV has an aspect ratio of 4:3 while HDTV has an aspect ratio of 16:9 and for the same height, the new TV is wider than the old TV or we say the new TV is widescreen and the old TV is squarish. Thus the same image will look smaller on the new TV and to get the same size picture (i.e. same height for the 4:3 picture) on the new TV, the screen has to be bigger. As a very rough rule of thumb, multiply the old screen size by 1.2 to get the equivalent new screen size.

For example, old 27" x1.2 =32" and old 32"x1.2=38". Since the HDTV only come in certain standard sizes, take the next higher one if you don't have an exact match after your calculation. Thus replace your 32" CRT TV with a 40" HDTV. For the budget conscious, the price increases as the screen size gets bigger but an exception may be for older or discontinued models. A 40" HDTV may sound and look big initially but after a while, may users feel that they should have bought a bigger set after the thrill of watching HD movies. Hence the early advise of getting the biggest set that you can afford.

However, the bigger the size of the set, the bigger the size of each individual pixel so a 60" set will look blockier than a 50" set at the same viewing distance. Thus you need to sit further away to watch a bigger display. The general advice is that the maximum distance is 2.5 times the size of the screen (always quoted as the diagonal across) so for a 40" screen, this will be 100" or almost 8 and a half feet away. Personally I find this a bit too far away. Some give the minimum distance as 1.5 times the size of the screen so for the same 40" example, this will be 60'' or 5 feet away. Thus you can sit anywhere from 5" to 8" away for a 40" HDTV to enjoy your show. This is just a rough guide and you can choose to sit any distance you want but if you sit too close, you'll start to see the pixels and if too far, you'll feel like missing the action. The choice is again personal preference and comfort.

I have mentioned in my earlier post that LCD TV has generally a more limited viewing angle when compared to Plasma TV. Thus the height of mounting the TV will be more important in the case of the LCD. So apart from strain necks if the LCD TV is mounted too high, you'll also get a poorer image. You may have to rearrange your furniture and wall decor to suit your new HDTV to have the best seat in the house.

Related to the size of the HDTV is the resolution that boils down to what the marketing guys call Full HD or HD Ready. By definition, the maximum HD resolution is 1920x1080 pixels and the minimum is 1280x720 pixels so Full HDTV has a resolution of 1920x1080 and HD Ready has less than that, usually with 1366x768 pixels for LCD and only 1024x768 for Plasma. They are HD Ready not because they can be upgraded to full HD but that they are ready to accept Full HD materials and downscale them to display on their lower resolution screens. For LCD TV, most models are now Full HD except for a few 32" and below. In the case of Plasma TV, quite a number are HD Ready only even up to size of 50" and you should check the specs carefully if this is important for you. However, experts say that you cannot really tell the difference if they are viewed at the correct distance, especially those of smaller screen size. But if the price difference is not much, you might as well go for Full HD or you may feel uncomfortable afterwards. But if budget is a real issue, get a HD Ready as it is good enough. Again, let your eyes be the judge.

So after picking the right size HDTV for your room, you would have completed your choice but only if you do not have other requirements or fussy about inputs/outputs, refresh rates, contrast ratio, etc. These will be discussed in the next post.

Ronald Kwok

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