Video Projection Formulas
– a Primer by Anthony D. Coppedge, CTS
Therefore, assuming no screen gain, we will need 2,000 lumens projected onto the screen
surface from the projector in order to overcome ambient light.
Here’s another item to think about: contrast ratio. In a pitch-black room, lower contrast ratios are
not nearly as important. But in a lit room, the better the contrast of the projector, the better the
image will be. Contrast, in layman’s terms, is how black the blacks are in comparison to how
white the whites are. We call this contrast ratio.
Contrast ratios are normally listed (if at all) in one of two ways on a projector spec sheet: ANSI
contrast and ON/OFF contrast. The number to pay attention to is ANSI contrast.
I’ll give another example to help illustrate contrast ratio.
Let’s say you have two projectors: Projector A is 2000 lumens with a 150:1 ANSI contrast ratio.
Projector B is a 1400 lumen projector with a 500:1 ANSI contrast ratio. We’ll also say they are
using the exact same lenses projected onto the exact same size screens, side by side in a well lit
room.
For an easy simulation, let’s also assume the screens are the 4’ x 6’. Now, which image will
appear brighter?
If you said Projector A, you’re wrong.
You see, the human eye perceives brightness in comparison to something dark. Therefore,
because Projector B had a much greater contrast ratio, the whites would seem brighter next to
those blacks. To our eye, Projector B would seem brighter.
Don’t believe me? Try duplicating this test with similarly equipped projectors and see for yourself
that this is in fact true.
Beyond this, it gets quite complicated, and I probably have lost 85% of the readers
four paragraphs ago anyway. In fact, there's much more to it than what I've typed here.
Therefore, I'm wrapping this up.
I do ask this one thing: if it's important enough to do, do it right – the first time - hire a consultant
or design/build firm.
To Contact Mr. Coppedge:
Anthony D. Coppedge, CTS
Church Media Consultant
WEB: www.anthonycoppedge.com | EMAIL: anthony@anthonycoppedge.com
PHONE: 817.819.7288 | FAX: 817.887.3700
Copyright 2001-2003 Do not duplicate in any form whatsoever without the written permission from Anthony D. Coppedge.
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