Film-Tech Forum ARCHIVE: 3200 Lumens Enough?

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Posted by Robert E. Allen (Member # 1351) on 10-29-2009, 08:35 PM:

I'm loking at a consumer video projector to use for a film ministry to churches. It puts out 3200 lumens. Do you think that would be enough for the average church auditorium with a screen of about 8 x 20'? (I'm not talking St. Patrick's Cathedral here.)

Posted by Brad Miller (Member # 2) on 10-29-2009, 08:52 PM:

Not unless you want it to look like ass. Go for at least double that, and consider a gain screen if the room permits it.

There are plenty of portable projectors under $5k that could work acceptably for this purpose.

Posted by David Zylstra (Member # 4230) on 10-29-2009, 09:27 PM:

At my Church we use a 3,000 lumen projector on a 10' wide screen and so far it is sufficient on both 4:3 and 16:9 - looks good enough with a lot of ambient light (we are not showing high quality content), looks great when we don't have sunlight streaming in and looks really good when we do a game night and can section off a semi-private dim area for a WII.

Judging from our 10' screen you definitely need at least twice that for a 20' screen, more if you have high ambient light and want to have any fine detail visible.

Posted by Randy Stankey (Member # 64) on 10-29-2009, 10:00 PM:

We used an Eiki LC-X1100 projector for about 5 years before we bought the Christie.

http://www.eiki.com/Products/LC-X1100/

It puts out 4100 lumens.
We used a long-throw lens to shoot a 13 ft. tall screen (17 ft. wide) from almost 100 feet away. It made an acceptable image if you turned the house lights down to half.

When we installed the Christie HD-8K we took the Eiki down and moved it to another venue where it is still in use today. It now shoots a 10 ft. tall screen using a shorter lens from about 25 feet away. It can produce a good image with the house lights all the way up and, with the house lights off, it will make an image as good as can be had with that type of projector.

Given this experience, I would say that a 3200 lumen projector on an 8 X 20 screen would produce the bare minimum acceptable image and, if you turned the lights off, you could get a passable image from it.

But, if the lights are on, your projector will probably struggle to produce a good image.

Posted by Justin Hamaker (Member # 2165) on 10-29-2009, 11:01 PM:

Part of the equation for this is the throw of the projector and the light level around the screen.

I have projected Schindler's List in an auditorium on a ~50' screen with about a 30' throw using an 1800-2000 lumen projector (the projector was set up in the seating area of the auditorium). Granted this was in a theatre auditorium with the lights down, but the picture was perfectly acceptable for the purpose - a high school history class that would have otherwise watched it in class on a TV.

Posted by John Wilson (Member # 269) on 10-29-2009, 11:36 PM:

Do you mean a 50ft screen or 50inch?

50inch = OK, but 50ft with an 1800 to 2000 lumen projector?

I must be misunderstanding you.

Posted by Randy Stankey (Member # 64) on 10-29-2009, 11:40 PM:

All other things being equal, throw has very little to do with brightness or picture quality. I include it simply to give the reader a scale of the room the projector and screen are installed in.

Outdoors where haze, fog and rain might affect picture, throw is more important so you will understand how vulnerable you are to picture degradation due to the elements. Shooting a picture through 50 feet of fog versus 200 feet will make a difference but, in clear air, there is very little.

Throw, by itself, does not affect picture brightness or quality.
The main determining factor of picture quality (assuming an ideal lens) is the size of the screen area over which you spread the light from the projector.

Posted by Justin Hamaker (Member # 2165) on 10-30-2009, 01:17 AM:

quote: John Wilson
Do you mean a 50ft screen or 50inch?

I mean 50 foot. The picture didn't fill the screen edge to edge, but it was probably 85-90%. The picture was a little washed out, but if much better than just "watchable". We did this 4-5 years in a row and the final year we finally had a DVD to use - before that it was just VHS.

Posted by Paul Mayer (Member # 355) on 10-30-2009, 01:20 PM:

The only time throw becomes an issue is if you are forced into using excessively long or short lenses to get the image size you need. Very short or very long lenses will be slower (higher f numbers) and therefore won't let as much light through.

As for the equation itself, it's 1 lumen = 1 foot Lambert/square foot on a unity gain (1.0) screen. So if you're shooting for 16 fL on a plain ol' matte screen you'll need 16 honest ANSI lumens for each square foot. Since many projector manufacturers embellish their output numbers with non-ANSI lumens, more lumen output than indicated by this formula is more-than-likely better.

As mentioned, screen gain helps a lot too (divide your total needed matte-screen lumens by the screen gain to see how many lumens you'll need for the gain-screen). If you're having room light issues, especially things like light from side windows, a directional gain (e.g. lenticular) screen works well.

Posted by Scott Norwood (Member # 30) on 10-31-2009, 08:29 PM:

I will differ with the crowd here and say that 3500 lumens should be fine, given a proper screen, a darkened room, and a video projector that is capable of actually delivering 3500 lumens (i.e. new bulb, correct lens, correctly stated specifications).

Assuming that the aspect ratio is 1.77:1, the picture on screen will be about 8x14'. That is 112 square feet. With a 1.0 gain screen, you can get 16fL with just under 2000 lumens. If the above assumptions hold, then you should have an image that is 50% brighter than the standard.

What's wrong with that?

If there is any question, you can rent or borrow the model that you are considering and test that.

Posted by John Hawkinson (Member # 1135) on 11-01-2009, 01:54 AM:

Well, remember you want to engineer for when the bulb isn't new, too. Etc.

--jhawk

Posted by Paul Mayer (Member # 355) on 11-01-2009, 02:37 AM:

I forgot to mention pixel count. The stated lumen output of a video projector assumes all pixels operating and putting out light. If you're running letterboxed sources, you will not have full light output from your machine.

If you're running mostly 1.77 or 1.85 widescreen stuff, you probably don't want to go with a machine that uses 4:3 imagers unless you can use anamorphic sources and lenses to maximize the number of working pixels. If you're running mostly 1.33 or 1.37 stuff, a 4:3 imager machine will work fine.

Nowadays most newer projectors are equipped with 16:9 imagers. These will let you run widescreen without having to use anamorphics (you will lose some pixels when running 1.85 though). But these machines will lose light output when running 1.33 or 1.37 stuff.