Tuesday, June 20, 2006

How Bright is Bright Enough? :|: Picking the Right Projector

Today's Topic: The Basics

Today we're going to talk about every salesman's favorite stat to throw around when selling you a projector.

You guessed it... The ANSI Lumen...

"And this projector over here... It's more ANSI than my six-month-old! Hehehe."

Understanding the ANSI lumens of your video projector is a good start to knowing how bright it will be and how good it will look. And with lumens, truly the more the merrier. The only problem is this: the more lumens you get, the less full your wallet is when you leave.

Unfortunately, from what I've observed, people tend to buy video projectors based on a comparative sense of lumens. If you're last projector was 3000 lumens, your next one should be, oh, about 6000 lumens or some such wizardry.

But lumens are only half of the picture. Your screen size is the other half. And it's a very important 50%. Naturally, the manufacturer can't guess what screen size you will use, so they just list the lumens and make you feel good about getting something brighter than you had last time.

But how bright is bright enough when you factor in your screen?

I want to begin a revolution here by introducing a good friend of mine: Mr. Foot-Lambert.

A Foot-Lambert (FL) is a measurement that takes into account your screen size. With it you can compare projectors that will be shown on different size screens. Also, you can compare a projector to another reference brightness you may be more familiar with (like your TV at home).

To find out a projector's Foot-Lambert measurement for your screen, divide the lumens by the square footage of your screen.

Foot-Lamberts = ANSI Lumens/ Sq Ft of the Screen

Here's a recent example for me:

The singles ministry wanted to add two 9 x 12 screens, one on either side of our main center screen in our sanctuary. The main center screen is 15 x 20 and our main projector is 10,000 lumens. To get all the screens to be about the same brightness, how many lumens do I need the other two projectors to have?

If all I had was the number 10,000 lumens, I'd be guessing what I need. What would your guess be? 6000 lumens? 7000 lumens?

Let's do just a little math.

Main Screen FL = 10,000 / (15 x20) = 33.3 FL

Side Screen FL = 33.3 FLs = Side Projector Lumens/ (9 x 12)

Side Projector Lumens = 3596.4 ANSI Lumens

Wow! So a 3500 Lumen projector would work just fine. That saves me some cash over my initial guess.

But what if you are working from scratch? How do you know the number of Foot-Lamberts you may need? Here's some hopefully helpful comparisons that I put together with some help from friends at Clark ProMedia in Alpharetta, Georgia:
  • Your local movie theater probably has a Foot-Lamberts level of about 20 FL for its screens. But remember it always turns all the lights off.
  • A room with some light spill on the screen will probably need a brightness level of 30-40 FL to overcome the wash-out.
  • A room with fairly direct light on the screen will need 40-60 FL of brightness.
  • Your boring television at home is over 100 FL!
  • Your computer screen or HDTV is even brighter!
So, when your video creator or your pastor comes to you and says, "It just doesn't look like it looked on my computer screen and high-def TV!" you can tell them why that's the case.

When you buy a projector, buy it based on the foot-lamberts it will create on your screen, not based on its ANSI lumens rating alone.


More Posts on The Basics

5 comments:

Jason Fletcher said...

This was a helpful post. Thanks.

ron mills said...

good article - thanks.

Anonymous said...

Thanks. I'm buying a projector for our children's church ministry, so this was the perfect article for me. 1 question. I use DVI on flat screens, but will it make a difference on a projector? With the degradation of light, will the noise be noticeable? The difference could mean a few extra FL b/c of price. Thx for any help.
aking@painterfirm.com

Anonymous said...
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Rajeev CK said...

Very good explanation!!!