View Distance -- When selecting a big screen TV, what size do I need for HDTV?
How big of a TV do I need? This is the question on everyone’s mind, whether you’re finally making the move from a old analog TV into
the world of HDTV or you already own an HDTV set, and you’re upgrading or buying an additional TV.
If you visit a retailer or other websites, you may see recommended viewing distances like this:
Or a recommendation to multiply the diagonal measurement of the display by 2 or 2.5.
Since most of us don’t just
take one source as gospel, we check other sources, and eventually stumble across a website that mentions
the SMPTE (Society of Motion Picture and Television Engineers) recommendations, which recommend even close viewing distances than those
above. The same website that tells you about the SMPTE recommendations will inevitably mention the THX recommendations, which puts you
even closer still. Currently THX is recommending that your viewing distance for a 1080p resolution display should be the diagonal
measurement of the HDTV, divided by .84. That means that for a 65” HDTV you are to sit 77 inches away, a mere 6 feet 5 inches.
So here you are, more confused about what size you should be considering than when you started your research. So which recommendation
should you follow! All and none!
Huh? Consider the view point of both polar extremes: THX’s, George Lucas (the Star Wars guy), who in the 1970’s was disappointed
that movie theaters did not
have the adequate setup to allow people to view his movie optimally, created his own very high standards to
provide the movie going public with the ultimate experience. As the home theater market began, his company, THX, applied the same
standards to custom home theater setups. So if you want the ultimate view experience follow the THX recommendations. At the other
end of the scale are the recommendations from HDTV retailers, whose motivations are a little different. Then want you to buy an HDTV.
If they use the THX recommendations and tell you that you need an 86” HDTV, (assuming you will be sitting 8.5 feet from the set) that
will put HDTVs out of the range of affordability for most people.
So, how do you figure out what size HDTV you need, you use the THX and retailer/manufacturer guidelines, as guidelines. Do not
follow recommendations blindly! No one recommendation will be correct for everyone, taking into account, budgetary constraints, our
eyes and the resolution of the display we are viewing.
First of all, viewing distance recommendations are based on a bunch of factors surrounding something that is different on a person
to person basis -- our ability to see. As a teenager, I could read the 20/20 line on the eye chart, from greater than the test distance.
With age (and probably too much time staring at a computer monitor), my vision is not what it once was, I wear glasses. The THX and
SMPTE recommendations are base primarily on the field of view the human eye can see (which is about 140 degrees, but not the same for
everyone). THX feels the display should occupy 40 degrees of your field of view, while SMPTE recommends that it take up 30 degrees.
Both THX and SMPTE recommendations put us so close to the display that most of us will have no problem picking up all of the detail provided
by a 720p, 1080i or 1080p resolution.
With the retailer’s recommendations, depending on your eyesight, you may end up sitting too far from the HDTV; unable to still see the
detail your set is capable of providing. Here is the Readers Digest version of why with an illustration. (If you are good at math and want
the full explanation, click here).
If you have parallel horizontal black lines on a white background, you can see the separation between the lines when it is viewed
at close range (Figure 1). As you view the lines from further and further away,the image gets smaller, you eventually get to the point
where you can no longer see the separation between the lines, and it looks like one line. Losing the ability to see separation in the
lines is exactly what happens when you sit too far back from an HDTV set. If we apply the same principle to an HDTV, a 1080p resolution
HDTV has to fit 1920 vertical and 1080 and horizontal black lines separated by the white space on the screen, (that is the pixel grid of
a 1080p HDTV display). Furthermore the spaces between each cell of the grid need to be very small in relation to the area each cell occupies,
or you will get a screen door type effect. A bigger HDTV can increase the size of the cells and the separation between the cells,
so everything doesn’t run together when you sit further back.
Hopefully you now understand the relation between screen size and viewing distance, here is how to use that knowledge with the various
viewing distance recommendations on the showroom floor. Measure how far you plan to sit from the HDTV in your home. Match your viewing
distance to the size of HDTV display recommended by the retailer recommendations. Use the display size (e.g. 42”), and divide by .84 as
recommended by the THX recommendation, to get the THX distance. In the showroom stand in front of the size of TV you picked from the
retailers chart, at the distance you will be viewing the HDTV from at home. If you wear contacts or glasses and normally watch TV without
them, take then out or off (whatever the case). The retailer will likely be playing demo material that repeats every 3-5 minutes, watch
the entire loop from your planned view distance. When you realize the demo is repeating, move up to the THX distance. If all of a sudden
images are sharper, you can see textures on clothing or flowers, blemishes on the faces of the actors you didn’t see the first time, etc.,
then based on your eye sight, viewing habits and the resolution of the HDTV, you need a bigger TV my friend.
If you have a big room, and not a big wallet, perhaps you should be looking at a Rear Projection DLP, LCoS or CRT, instead of the sexy
(“keeping up with the Jones”) flat panel LCD or Plasma display. Rear Projection DLP, LCoS and CRT have a much lower cost per square/in than
their flat panel counter parts. If you just got to have a flat Panel HDTV, then purchase a 720p HDTV! This is where the bargains are, and
when you sit too far from a 1080p HDTV, you are effectively reducing the detail you can discern, turning it into a 720p or lower resolution
display as everything runs together.
If you would like to understand more about how to properly size your HDTV, read this follow-up article
and use the distance calculator at the bottom of the article.