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[Jordan Wolf]

What I find hard to decipher is how to figure out what size image I can get at what distance. For example, determining if a particular unit will be suitable for
6' wide screen at 14' or
10' wide at 30'

I know I need 3000 to 4000 lumens for my applications.

We routinely use 5500 lumen projectors to throw about 55ft.-60ft. for 9x12 screens, and with the house lights at 100%, I feel that the brightness level is acceptable.  I, however, would prefer them to be brighter - I think a 7500 lumen projector is a better fit, personally…but I'll take what I'm given if it works well enough.

In your case, I'd say 35ft.-40ft. would be the max I'd want to throw for a 4000 lumen projector - and I'd aim for a 9ft. x 16ft. screen if possible…or a 9ft. x 12ft. screen if you need to stick with 4:3 AR.  If you have total control of the ambient lighting, those limits may be exceeded by a good bit, but you will always have the most brightness when the projector is as close to the surface as the lens will allow.

The 3500 lumen projectors at my job have 1.8-2.2 lenses - others are available, those are what we have in-house, so we're stuck with them.  Multiplying those numbers by the screen width gives me the minimum and maximum distances I can be from the screen surface.

I find that the 3500 lumen units are fine for a 7.5x10 screen with house lights at 100%, but find them lacking for a 9x12 with the same ambient lighting.  This "lacking" is both a decrease in apparent brightness on the screen surface (judged by my eyes), and also a graininess/lack of clean lines from needing to magnify the LCD pixels so  much to adequately fill the surface.

Hope that helps some…

[Gerry Seymour]

Jordan, I think his question was more a matter of what size he can produce at a given distance, rather than how large and how far away.

I, however, have learned something I didn't expect. I didn't think a 4,000 lumen projector was capable of an image that size under full ambient lighting. I'm starting to wonder just how badly my current projector sucks.

[Brad Weber]

I, however, have learned something I didn't expect. I didn't think a 4,000 lumen projector was capable of an image that size under full ambient lighting. I'm starting to wonder just how badly my current projector sucks.

This seems to possibly get into an area that I questioned when a 10:1 image contrast ratio was being taught and that was how that number was determined.  One reason that was asked is that InfoComm itself was routinely making presentation with lower contrats images than they were teaching were required yet people found those image quite usable.
 
The fairly recent InfoComm/ANSI Standard for image contrast ratio apparently had a number of subject matter experts assess different types of images at different image contrast ratios and determine the minimum contrast ratio deemed to provide an acceptable (in their assessment) result for each type of image.  My concern there is that while the people making that assessment are well trained in viewing, they may also have greater expectations than many real world users.  That is why I tend to use that information as a goal but to temper it with the reality that in many cases a lower image contrast ratio may be acceptable.
 
This is a long way of saying that there are some guidelines for image brightness based on the associated image contrast ratio but in the end it is a subjective determination that may vary.  Adding to that are potential variations in what terms such as "full ambient light" and "house lights at 100%" actually represent as far as the light levels on the screen.
 

In your case, I'd say 35ft.-40ft. would be the max I'd want to throw for a 4000 lumen projector - and I'd aim for a 9ft. x 16ft. screen if possible…or a 9ft. x 12ft. screen if you need to stick with 4:3 AR.  If you have total control of the ambient lighting, those limits may be exceeded by a good bit, but you will always have the most brightness when the projector is as close to the surface as the lens will allow.

Just so others don't get confused, it is the image size rather then the throw distance that directly affects the image brghtness.  Theoretically, a projector producing a certain size image will produce the same image brightness regardless of how far it is located from that image as it is still providing the same total brightness over the same image area.
 
There can be an indirect effect of throw distance in that different lenses, and different points along the zoom range of a zoom lens, incur different losses in the optics themselves which can thus affect the actual brightness provided by the projector.  It is a generalization but for lenses of comparable quality long throw lenses often incur greater losses.

[Jordan Wolf]

...potential variations in what terms such as "full ambient light" and "house lights at 100%" actually represent as far as the light levels on the screen.

Yes, and I can't say that I have any objective measurements to provide...we don't have a light meter - thus the lack of lux/footcandle data from the ambient lighting.

Just so others don't get confused, it is the image size rather then the throw distance that directly affects the image brghtness.  Theoretically, a projector producing a certain size image will produce the same image brightness regardless of how far it is located from that image as it is still providing the same total brightness over the same image area.

I think that most people would agree that getting the projector as close as possible to the screen surface is best practice.  Even if using a zoom lens, there is still noticeable dropoff in the image brightness when compared to a screen that has a projector mounted closer to it...isn't that why a projector with a higher lumen rating would be desired for a greater throw distance?

I still don't know hardly as much as I'd like about the industry standards for brightness, etc., and I will gladly defer to your knowledge and expertise on the subject.  If I've said anything incorrect, or that needs clarification, please fix my mistake(s) - I'd love to learn more (and I certainly don't want to confuse others who are reading along).

[Bojan Bajsic]

I think that most people would agree that getting the projector as close as possible to the screen surface is best practice.  Even if using a zoom lens, there is still noticeable dropoff in the image brightness when compared to a screen that has a projector mounted closer to it...isn't that why a projector with a higher lumen rating would be desired for a greater throw distance?

In short. No.

The projector with a higher lumen rating would be desired for greater screen width and for better contrast in non-dark conditions.

The projected light doesnt loose enough energy on a ie. 50ft journey to be considered detrimental to the image.

[Brad Weber]

I think that most people would agree that getting the projector as close as possible to the screen surface is best practice.  Even if using a zoom lens, there is still noticeable dropoff in the image brightness when compared to a screen that has a projector mounted closer to it...isn't that why a projector with a higher lumen rating would be desired for a greater throw distance?

The simple concept is that image brightness is a factor of having a certain number of lumens from the projector spread over a certain image area and if the projector brightness and image area remain constant then then the throw distance is not a factor.  Throw distance can become a factor if it changing causes the image area or projector output to change.
 
So say you had a 4,000 lumen projector creating a 9' wide by 12' high image, that's 4,000/(9x12) or just over 37 ftL (footLamberts).  It doesn't matter where the projector is, if the image size and projector brightness remain the same you get the same result.
 
The other factor in image brightness is screen gain or how the screen affects the light hitting it.  However, you do not really have to consider that in assessing the image contrast as screen gain tends to affect both the projector output and ambient light about the same.
 
What can happen in some cases is that a different lens or different point in the zoom range may resulting in a reduction in the projector output.  Obviously most projector manufacturers are going to rate their products based on the most favorable condition and it is possible that a long throw lens or a lens zoomed in tight may actually reduce the projector output.

[Gerry Seymour]

The simple concept is that image brightness is a factor of having a certain number of lumens from the projector spread over a certain image area and if the projector brightness and image area remain constant then then the throw distance is not a factor.  Throw distance can become a factor if it changing causes the image area or projector output to change.
 
So say you had a 4,000 lumen projector creating a 9' wide by 12' high image, that's 4,000/(9x12) or just over 37 ftL (footLamberts).  It doesn't matter where the projector is, if the image size and projector brightness remain the same you get the same result.
 
The other factor in image brightness is screen gain or how the screen affects the light hitting it.  However, you do not really have to consider that in assessing the image contrast as screen gain tends to affect both the projector output and ambient light about the same.
 
What can happen in some cases is that a different lens or different point in the zoom range may resulting in a reduction in the projector output.  Obviously most projector manufacturers are going to rate their products based on the most favorable condition and it is possible that a long throw lens or a lens zoomed in tight may actually reduce the projector output.

Hmm...since we all (myself included...in fact, I may have started it) have long since hijacked this thread, let the festivities continue!

What about screen selection? I know the screen has an effect upon brightness, but are some screen types better than others in high ambient lighting? Is it just a matter of highest gain (since a given % loss has a much higher impact on the brighter projection source than the dimmer ambient light)?

[Bojan Bajsic]

In my experience, i would sooner go with the opposite! A gain screen will help the projected light, sure. But it remains a highly reflecting white screen and it will reflect ambient light at the same rate.

In ambient light conditions, if given the chance i would either go for:
 - high contrast grey screen (to get better blacks and improve contrast. But be careful as these are usually 0.5-0.9 gain screens, so one needs a proportionally higher output projector)
 - rear projection (but this depends on space and the viewing angle of presenters, usually not easy to implement if you don't know ahead of time what kind of place you will come to. Really unsuitable for wide viewing angles/auditoria)

[Brad Weber]

What about screen selection? I know the screen has an effect upon brightness, but are some screen types better than others in high ambient lighting? Is it just a matter of highest gain (since a given % loss has a much higher impact on the brighter projection source than the dimmer ambient light)?

The gain affects both the projected and ambient light the same thus if the ambient light is setting the black level it has no effect on the resulting image contrast ratio.

There are 'high contrast' screen surfaces that can help reduce the apparent black level and some of these are very effective, actually making the image appear brighter due to the greater image contrast ratio.  However, I have found many churches do not like the typically gray color of the high contrast screens when they are not in use.

Also consider the viewing angle or half gain angle of the screen surfaces as that indicates how the reflected light falls off as the viewers get off-axis of the screen.

Rear projection is often a very good option as it addresses several issues but it can be more expensive and you have to have the space for it.

[Gerry Seymour]

So, that's two recommendations (with qualifications) for the high-contrast screens. I have never really looked at these. Since the main issue I've seen in high-ambient light conditions is the contrast (blacks), this might be well worth it. I'll have to look around and see if I can rent one in the area for one run, just to try it out before I buy.