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HDTV Size vs. Viewing Distance

December 28th, 2010 Leave a comment Go to comments

While making decision for HDTV to decorate your room, one fundamental thing need to consider is the viewing distance. It can be a safe range of seating distance between the viewer and the TV to get a maximum immersive experience in home or outdoor environment. There is no strict rule with regard to the viewing distance. The range is flexible depending on the resolution of HDTV, screen size and the functional limits of human visual system.

Key points

– If you sit too close to TV you will see scanning lines, pixelization effect. Your eyes can stress with excessive brightness and will spoil your viewing experience.

– If you sit too far, you will loose “details” of the picture, because of the inability of your eye to resolve close pixels.

– For a given size of TV, with 1080p resolution TV you can afford to sit closer to the TV than to a 720p resolution TV.

– As a rule of thumb you should sit at a distance between 2 to 5 times the width of the TV.

That being said, viewing distance is also a matter of personal preference. Some will prefer to see from a close things so that they can “see the things big big”. Others will like to keep their eyes relaxed and prefer seeing from a farther distance.

SMPTE Society of Motion Picture and Television Engineers) and THX put the theoretical specifications with regard to viewing distance. According to SMPTE, if you keep coming closer to the TV, the angle subtended by the eyes along the width of the TV increases. If you come too close, the angle will increase. According to SMPTE the optimal angle for viewing is 30 degrees. This corresponds to a viewing distance 1.87 times that width of the TV.

Notice that most of the TVs give the diagonal size of the TV. It is easy to calculate the width of the TV of a given size on a widescreen HDTV with aspect ration of 16:9. Use the formula

Width of the TV = Diagonal Size of the TV / 1.147

For example if the (diagonal) size of the TV is 54 inch, its width will be 47 inch. According to SMPTE, you should be seeing the TV at a distance of 87 inches.

THX plays with the visual angle to determine the viewing distance. According to them a minimum angle of 26 and maximum of 36 degrees creates great HDTV experience.

A number of viewing distance guides are available from the manufacturers as well as the shopping sites. Bestbuy and amazon list out the distance Vs TV size where they list a range of the distance for a given TV size.

We recommend that you follow a simple rule that the viewing distance should be 2 to 5 times the width of the TV. Sit closer than twice the width and you will see pixelization effect, moving line and excess brightness effecting eyes. Move too far and your eyes will not be able to resolve the adjacent details of the picture.

While comparing the screen size with viewing distance, HDTV with higher screen size and a high resolution creates delightful moments with the TV. In the case of 720p models, close viewing distance creates the problem of visible square pixels that makes the screen image. 1080p models can support closer and wider viewing. In simple word the visual range is best with a high resolution optimum sized screen.

According to THX the screen size can be divided by 30 to find the number of viewer rows which can be effectively placed. For example a screen size of 100” can support three viewer rows approx. While arranging displays for group viewing this is need to be considered before choosing HDTV.

The visual angle is another great thing connected with the viewing distance. It is the angle subtended by viewer eye and the television screen. Optimum value comes around 30 degrees. The concepts of Vernier angle stereo acuity are used to calculate the visual angle. This range gives soothing effect and comfort for human eyes.

A straight level seating, making the eyes of viewer and the center of screen on a straight level reduces the disturbance and creates maximum immersive vision. Normal human eye has 20/20 or 6/6 vision with a capability to resolve an object of 2mm size from 6 meters away. Usually people with visual corrections prefer a close or far level viewing to exempt the use of contact lenses or spectacles while viewing TV. A distance closer than 1.5 times the screen size spoils the viewing experience by making the individual pixel cells or scan lines visible.

Sometimes diagonal screen width is used as a base for measuring optimum viewing distance. This is popularly known as the 2.5X method. Here the viewing distance is calculated as 2.5 times the diagonal screen width. There are difference in opinion between different manufacturers and retailers in context of viewing distance and screen size. You need to calculate the distance between the actual place in your mind for mounting your new HDTV and where in the room you’re supposed to sit. By matching this with your room size and the guidelines mentioned in this article find the optimum distance for viewing. This is much useful in making a good choice.
Closer viewing is a problem while making large display units. The resolution improvement has a limit. On the other hand the level of resolution that human eye can recognize has also the limit. Vector image concept is still not applicable for HDTV. The process is like a raster or bitmap image on your computer which is consisted of numerous small squares. Within these limits we need to choose a better television entertainment option.

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