Video Projection Formulas
– a Primer by Anthony D. Coppedge, CTS
I’m frequently asked to explain how much ‘horsepower’ (brightness) a projector needs to have in
order to make the image on a screen look good. In a moment, I will give some formulas that are
very necessary in determining projector brightness and screen size. However, two 'red flags'
popped into my head.
First, it's a bit technical, and some will not understand the concept.
Second, while the formulas are not a big secret, they are a necessary part of how I make a living
as a consultant. However, I can honestly say that MOST firms that I've run across do not perform
all of the math required to make the estimates for screens and projectors as accurate as possible.
How do MOST do it? They guess.
Trust me, I'm about to get to the formulas, but this is important.
Most A/V firms 'guess' in that they have done several (if not dozens) of
installations. Some of these individuals have developed an 'eye' for guessing approximate
values. Some are even very good at this, and, to be honest and try to sound
humble, I usually am very close by guessing myself.
But how much money is being invested here? Is that money worth a good
'guess-timate', or is it worth an accurate, calculated proposal? I prefer the latter.
So, here are the basic math formulas necessary:
Determine screen placement
Sightlines are paramount in determining screen location. Make sure everyone (especially those
far away) have a clear, unobstructed view of the screen. In some cases, more than one screen is
required.
I won't go into screen viewing angels, as this has a lot to do with screen gain (or lack thereof) and
front vs. rear.
Determine screen orientation (front or rear).
Rear is always best, but requires space behind the screen that is
essentially useless for anything EXCEPT the projector (and possibly a
mirror).
Determine screen size.
Measure the distance from the screen to the furthest seat that is in
line-of-sight to that screen. If the majority of the content is video, divide that number by 8. That is
the screen height. Remember that this is just one of many possible formats that will determine
which number to achieve the screen height.
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