Many enthusiastic consumers like to go for the biggest and costliest TV which they can afford. However this sort of approach may backfire as the budget planning is not the sole thing to follow, particularly when one is going for a large screen TV. It is because there is a direct relationship between the optimum screen size and the available viewing distance.

There is a stress on the viewing distance for LCD TVs because one may feel the difference by watching TV sitting too close or too far from it. Sit too close to a TV and one will be able to see the image build-up structure - scanning lines or pixels forming the image, thus distracting your attention and spoiling your home theater experience. Yet, sit too far away, and the impact will be lost.

There are differing opinions on the best way to determine the optimum TV viewing distance for a specific screen size. However there are a few guidelines that one can follow.

The Society of Motion Pictures and Television Engineers (SMPTE) recommends that the screen size for home theater use should occupy a 30 degrees field of view - in the horizontal plan - for the audience. Alternatively, the ideal TV viewing distance should be such that the screen width occupies an angle of 30 degrees from the viewing position.

This 30-degree viewing angle seems to have been accepted by many as the standard in home theater and motion picture viewing.

THX certification: This SMPTE guideline is also in line with the THX certification standards in that the latter recommends that the back row of seats should have at least a 26 degrees viewing angle and while recommending an optimum viewing angle of 36 degrees.

It is believed that within these viewing angle limitations, the viewer will be better immersed into the action movie itself.

There is also the issue of TV viewing distance based on visual acuity. This does not represent the optimum viewing distance - rather, this relates to the maximum viewing distance beyond which some picture detail will be lost.

Technically speaking, visual acuity is a measure of the eye spatial resolving power and indicates the angular size of the smallest detail that a person visual system can resolve.

From a TV viewing distance perspective, visual acuity represents the point beyond which some of the picture detail will no longer be resolved by the viewer vision system, as it will appear to blend with adjacent picture information.

So how do these rules apply in practical terms?

Here is a rule-of-thumb that can help put in practice the guidelines detailed above. This rule for TV viewing distance refers to the screen width rather than the screen diagonal since all is tight up to the subtended viewing angle. Further more, referring to the screen width has a further advantage - namely that these rules-of-thumb apply to both 4:3 and 16:9 display formats.

A primary consideration for the viewing distance - based on SMPTE/THX and visual acuity guidelines - is that the nearest TV viewing distance should be limited to approximately twice the screen width (more precise 1.54 x screen width for a subtended angle of 36 degrees detailed by THX). On the other hand, the furthest distance should being no more than five times the width of your screen.

This should give a fairly good approximation for your TV viewing distance. Note however that it does not necessarily represent the ideal viewing distance in a home theater setup; rather it represents the limits within which your TV viewing distance should theoretically be out of the trouble zone.

In other words, move closer than twice the screen width size, and the picture scanning lines, pixel breakup and any other video artifacts will become too visibly intrusive - leading to distractions that will spoil your movie watching experience. Move further away than 5 times the screen width and your vision system will no longer be able to resolve all the picture detail.