Video Projection Formulas
– a Primer by Anthony D. Coppedge, CTS
The screen height will be the same if the aspect ratio is 4:3 or 16:9 as
only the width is different (if done correctly, anyway). Make sure that the closest seat is twice the
distance from the screen in comparison to the screen height. Example - 6' tall = 12' away for
closest viewer.
Next, measure the distance from the screen to the closest audience seat that is in line-of-sight to
that screen. The screen should be no taller than twice that distance. This isn’t always possible,
but it is preferable. Remember, the furthest viewers take priority, as it is better for the screen to
be “too big” for those close than “too small” for those in the back.
Determine square footage of the screen surface.
Take the screen height (in feet) and multiply it by the screen width (in
feet). Ex. 6' x 8' = 48 sq. ft.
Take the number of lumens that is estimated will be needed (this is the ONLY time we'll estimate
lumens).
Example - 1000 (lumens) divided by 48 (sq. ft.) = 20.83
ANSI specifies that 18 (+ or - 2) is the acceptable number. This is assuming NO light is hitting the
screen. Pitch black area. Dark. No light. Nada.
So we now know that 20.83 is our number for this example, and our next
measurement is the screen area itself - the amount of foot-candles hitting the screen surface from
lights, windows, etc.
Let's assume 8 foot-candles is hitting the screen surface. We now take our number (8) and
multiply it by 5 (our next formula). The answer? 40, of course.
THAT (40) is the number we must now reach to have adequate lumens being
projected onto the screen surface. In other words, we must project at least 40 lumens per square
foot onto the screen.
So, going back to our first example, we have 48 sq. ft. of screen area. If we project 2000 lumens
onto the screen surface, and divide that by 48, we get 41.66, which is enough to accomplish our
goal.
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