Understanding lumens better - AVS Forum
Digital Projectors - Under $3,000 USD MSRP > Understanding lumens better
reckless7 03:21 AM 07-24-2014
I have an ultra short throw projector rated for 3500 lumens. I want to display crisp powerpoint presentation/video in convention environments, so I'm having a custom display made to block out unwanted light. It will be shaped like a cube for the projector to throw video on display. Not sure how much difference that is going to make. Can someone tell me their opinion. Is it worth $1000 to have this custom display or should I just buy a projector screen. Not sure how bright 3500 lumens will be in low lit environment.

If custom cube idea works, can I put two ultra short projectors and shoot them on opposite sides of the screen or will there be interference?

Ftoast's Avatar Ftoast 11:55 AM 07-24-2014
Is the cube going to be like a tent/gazebo that viewers walk into that keeps light off both screen sides and both sides are being lit so viewers can watch from either side? Then the idea makes sense by keeping most outside light off the screen and a single projector should work fine if you want.

If you are only blocking one side and viewers can't watch from inside the cube..making it like a giant rear-projection TV, you'd be MUCH better off just using a plain screen with two projectors hitting it from the front and no cube at all.

Unless you can get a giant conical prism rear-projection screen (prohibitively expensive, I'd expect), blocking light from only one side isn't going to fix the wash-out and having the projector hitting it from the back which lights both sides while blocking visibility of one side is wasting lumens and effectively cutting your contrast in half.
If anyone has some ideas of how to get or make a front-side light-rejecting rearprojection screen, that'd make the giant rear-pro plan effective.

Otherwise, would it be possible to build a mount and hood contraption that holds the projector/s above the screen and out of the walkway..instead of having a thin pole coming out over the screen's top holding the projector/s, you could have a short/small "ceiling" so it both holds your PJs AND blocks some light from above.

Rear projection only makes sense if you'll have viewers seeing both sides (while using only one projector) OR it's a "proper" front-light-rejecting screen which is likely impossible to get.
AV_Integrated's Avatar AV_Integrated 01:30 PM 07-24-2014
I'm going to argue this.

The entire point of rear projection is that it allows for higher light in the viewing area compared to what a front projection setup allows. This is why rear projection televisions existed at all, and why they worked for many years (decades) with good results. The enclosure of a projection space in 100% black eliminates reflections and noise from entering the projection path. You get a screen which diffuses light, and is typically somewhat greyed, and this improves overall contrast. The front side of the screen diffuses light and allows some light to pass, but the rear projection path is far brighter, and far more focused, so that you end up with a punchier, higher contrast image, than you do with front projection. This is more and more apparent as ambient light on the viewing side of the screen increases.

The negative shot on this is that screen resolution drops. You lose a bit of sharpness as the image must pass through the screen itself. It also isn't as friendly with short throw projectors. You need a high diffusion screen for best results, but lower diffusion screens can be brighter.

For years, and continuing, the best solution in a brightly lit board room is to go with a rear projection setup when flat panels aren't feasible. You put the projectors in a rear projection control room, then the board room, or classroom, is normally lit by florescent lighting. You can have enough light in the room to actually conduct acceptable video teleconferencing and still have a nice bright image on the screen.

I would not do both front and rear projection on the same screen, and there would be little/no reason to have the back side open at all and do all this work. It is also part of the reason why 'black' is the color to use around screens. It reduces reflections and increases contrast.

Rear projection makes a ton of sense overall if you can implement it properly.

A good recommendation is not to take our word for it, but to contact a projection screen company like DaLite or Draper who would be happy to give you recommendations and provide information to you about the best materials and ways to pull this off properly.
Ftoast's Avatar Ftoast 06:13 PM 07-24-2014
My main point against rear-projection (cheap and large) is that all those good points you mentioned about rear-pro were working because of the specially designed screen that diffused light coming from behind but NOT from the front..a plain diffusing surface (both directions) will still wash-out as light hits it from the front even with a totally darkened rear.
The screens used for RPTVs diffuse light from the back but pass it through from the front so instead of turning your blacks grey, it goes into the black pit of the inside where it's absorbed (mostly).
The good ones also tightened vertical viewing-angles while leaving horizontal angles largely untouched which meant more light made it to viewers eyes and less was wastes, all while absorbing/passing 90% of frontside light instead of diffusing 50% of it into the image.

If any of the screen companies offer an affordable rear-pro screen that functions this way, that's fantastic, but I wouldn't hold my breath. I don't even know if it's possible to make in a version that isn't stiff like a giant flat-panel.

With a plain (cheaper and pliable) diffuse screen, the lit surface being visible from both sides means your lumens are basically cut in half compared to a single-sided screen. Yes, you'll be twice as dark with ambient light hitting it because half passes through and gets absorbed, but you'll also be losing half your brightness and turning out roughly the same in the end.

A proper RP screen will simultaneously triple the amount of light making it to your viewers AND absorb 5X more frontside ambient light. I also doubt you'll find one that isn't stiff, limited to 90" diagonal or less, and under $5,000 at the size you'll want. If they exist for cheap, that's awesome!

If you can experiment with it in a controlled and affordable way beforehand, I'd be happy to be proven wrong, but I certainly wouldn't bet a big presentation on it.
AV_Integrated's Avatar AV_Integrated 09:41 PM 07-24-2014
Quote:
Originally Posted by Ftoast View Post
My main point against rear-projection (cheap and large) is that all those good points you mentioned about rear-pro were working because of the specially designed screen that diffused light coming from behind but NOT from the front..a plain diffusing surface (both directions) will still wash-out as light hits it from the front even with a totally darkened rear.
The screens used for RPTVs diffuse light from the back but pass it through from the front so instead of turning your blacks grey, it goes into the black pit of the inside where it's absorbed (mostly).
The good ones also tightened vertical viewing-angles while leaving horizontal angles largely untouched which meant more light made it to viewers eyes and less was wastes, all while absorbing/passing 90% of frontside light instead of diffusing 50% of it into the image.

If any of the screen companies offer an affordable rear-pro screen that functions this way, that's fantastic, but I wouldn't hold my breath. I don't even know if it's possible to make in a version that isn't stiff like a giant flat-panel.

With a plain (cheaper and pliable) diffuse screen, the lit surface being visible from both sides means your lumens are basically cut in half compared to a single-sided screen. Yes, you'll be twice as dark with ambient light hitting it because half passes through and gets absorbed, but you'll also be losing half your brightness and turning out roughly the same in the end.

A proper RP screen will simultaneously triple the amount of light making it to your viewers AND absorb 5X more frontside ambient light. I also doubt you'll find one that isn't stiff, limited to 90" diagonal or less, and under $5,000 at the size you'll want. If they exist for cheap, that's awesome!

If you can experiment with it in a controlled and affordable way beforehand, I'd be happy to be proven wrong, but I certainly wouldn't bet a big presentation on it.
This is just not the case though. Rear projection creates an environment which allows for very strong black levels in fairly bright rooms. While the use of a Fresnel lens screen was common on CRT rear projection, the use of bright projectors is far newer and allows for rear projection setups which allow a ton of light to be transmitted through the screen, at levels which produce a very strong image in a room.

The key is that the projection side (back area) must be 100% light controlled and painted dark for this to work properly.

The light certainly hits the screen and is very visible within the projection area, but the black sucks up reflections and increases contrast dramatically. This is why this is THE gold standard for rear projection with a lot of ambient light on the other side. I have been in 50+ facilities that do this, and you can just have a ton of lights on and still have a very usable on-screen image.

A material like this is what I'm talking about: http://www.dalite.com/screen-surface...contrast-datex

1.0 gain, designed for high ambient light on the viewing side. You do have the narrow viewing angle (you described) but the surface in not terribly expensive, and with a several thousand lumen projector, you will end up with a bright punchy image in most lighting conditions (not daylight of course).

In fact, with a fast fold (portable) screen frame, this material can be ready to go for under $800.

Companies like DaLite often sell black backdrops for hiding a projector and keeping the area dark as well.
Ftoast's Avatar Ftoast 12:39 AM 07-25-2014
Cool. I'm hoping for at least a few of the situations you've seen it in use that you asked about the projector behind the screen and recognized it as a soft screen similar to the link. As long as a similarly inexpensive, large screen paired with a lower lumen PJ (or any configuration using roughly 50ftL in a strongly lit room) could create a watchable image where even short film-clips could be considered fairly watchable, that's awesome and I'll take your word for it.

The linked material certainly looks like a nice dark color to have a gain of 1.0, and the claimed viewing cone doesn't sound terrible.

I didn't dig into it enough to see the $per sqFT. About how big would $800 get you between the fabric and frame?

Anyway, looks legit; this is the being proven wrong that I can be happy about.
AV_Integrated's Avatar AV_Integrated 10:01 AM 07-25-2014
If you haven't done commercial work, it's hard to know how often this type of setup is put in place, but it is a fairly regular occurrence on the commercial side of A/V. From what I've seen, resolution takes a bit of a hit, and while I was excited about maybe doing this in my home at some point, I would not do this moving forward. But, for less demanding viewing (commercial), the slight loss of resolution is made up for by the relatively punchy image which is obtained in a less than perfect environment.

The big thing is that it maintains contrast and brightness more than anything else.

I don't know how much material costs, it's the full portable frame system which is out there for about $850 for a 125" diagonal.

http://www.bhphotovideo.com/c/produc...Fold_Port.html

It may be available for less elsewhere.
reckless7 10:51 AM 07-31-2014
I finally got around to calling Da Lite and some dealers and they mentioned to me that no one else has really asked for a tent behind the screen. I think because I am so new to projectors in general that I don't realize the difference a quality screen can make. They mentioned the product I am looking for is very common in tradeshows and usually always done as rear projection:
http://www.thefinalclick.com/Da-Lite..._p_113441.html (I am going with the Heavy Duty unit so I can raise the screen higher).
Da-Lite told me I need this screen:
http://www.da-lite.com/screen-surfac...tra-wide-angle

I am debating after getting the unit whether I should try to buy some fabric to block out unwanted light. Can anyone tell me if in theory it will make a huge difference? I think my problem has been that I have been testing the projector on a painted wall with all the light on to simulate the worst case scenario in a tradeshow. The dealer mentioned that since the projector is sitting so close to the screen the issue of ambient light interfering with projection isn't as bad.

I am also purchasing one of these to put the projector 50" off the ground:
http://www.thefinalclick.com/DaLite-...d_p_54639.html

Now I need to find a good hard case to put my projector in and a decent sound solution. I do have a Bose Soundlink II and 2 bose L1 compacts.
Ftoast's Avatar Ftoast 01:53 PM 07-31-2014
I think the dealer is underestimating how badly the light will affect the image (even that particular screen says that it is recommended for controlled ambient light conditions which the trade-show is NOT) and any specialty rear-projection screen will need a darkened "tent" between it and the projector to work its magic. Light hitting that screen from behind WILL interfere with the image regardless of the projector's throw and it's odd that they would think a shorter throw would make any difference in lessening light interference.

The darker version that AV linked will probably grant better contrast in the well-lit building. That Bose system you already have, is that the 5-6ft pole of speakers that's also marketed for live-sound performance? If so, I believe it would perform quite well for your needs and be more easily portable than many alternatives. If you need a lot of bass (I doubt you will), expect to bring an extra sub system as the Bose isn't usually enough to thump a large space.
reckless7 08:28 AM 08-02-2014
Thanks for your advice. I cancelled the order for the Da Lite screen and managed to find a phenomenal deal on starbright7 screen which multiplies the gain between 7-7.4. From what I've read it sounds like the solution for a conference or well lit environment although I am not sure if it's possible to be too bright? 3500 lumens multiplied by 7 is ~25,000 lumens. Is there such a thing as too much brightness?

https://www.youtube.com/watch?v=TZXgYA8BgsY
I don't think I will have the perfect screen for watching but think the image and colors will pop which is the effect I am looking for.
Ftoast's Avatar Ftoast 09:19 AM 08-02-2014
A reflective front-projection high-gain screen (as well as dark screens with gain around 0.8+) will require a long-throw projector to have decent uniformity and avoid severe hotspotting. Your short-throw projector will be VERY ill-suited for that screen.

AV has been around much more large venue projection than I have by the sound of things so I'm kinda hoping he'll link you to something awesome (or reaffirm the previously linked screen). If you're using a shortthrow, you'll need either a rear-projection setup or a plain/lambertian (I've totally read that as a word before, I swear) screen and as many lumens as you can afford either way.
AV_Integrated's Avatar AV_Integrated 02:58 PM 08-02-2014
The only way to use light-rejecting screens is with long throw projectors, and you will have a fair bit of image degradation, and loss of viewing angle. I have seen the Elite Black Diamond screen with a high brightness (5,000+ lumen) projector at 110" and had mixed feelings.

First, the image was bright, it popped and held up well to the ambient light in the room (board room) it was in.
Second, the image had some hot-spotting from the gain it was providing.
Third, the image had significant sparkling around the image. This is similar to how light reflects off of snow - it sparkles a bit, and this screen emphasized this anomaly.
Fourth, the screen was pretty expensive for what it was.

I would NEVER use a ambient light rejecting screen in any situation where image quality matters. That said, typical PowerPoint presentations or a trade show are not 'critical' viewing environments. So, this screen was not only ideal in the installation it was a part of, but would be ideal in your situation with the following requirement: You MUST use a longer throw projector so that the angle of incidence between the lens and the screen works within the manufacturers tolerances.

Personally, I haven't tested a covered rear projection setup vs. a ambient light rejecting screen, but would think you would have very similar results, with lower cost associated with rear projection. Given the choice between the two, I would probably go rear projection. But, both setups have limitations, and drawbacks, but deliver a very viewable image in a less than ideal viewing environment. If you can't get 12'+ of throw distance, and have the projector near, or below, the top of the screen, then it seems like a light rejecting screen won't work at all, and must be eliminated as an option unless you really want to work to get the setup right. I would likely opt for rear projection in your setup.
Ftoast's Avatar Ftoast 05:16 PM 08-02-2014
Would it be soulcrushing to suggest ordering one of the cheaper $2500-4000 90inch LCD tv's? Your size would lose 10-20"diagonal, but your contrast, brightness and viewing angles would beat most/all light-room projection setups. It sounds like the price would be about the same, the size similar, and the setup+results a lot less troublesome.

It might even be possible to rent one for the time you need it and only pay a couple hundred. There are places that rent out large displays for superbowls and events.
reckless7 02:43 PM 08-03-2014
Interesting points from everyone. The search continues. My focus is less about a clean, perfect video and more about grabbing attention and doing something different to get people curious.

It isnt soul crushing to think about LCDs but its not something I really want to haul or ship across the country. Plus, I don't think it will grab as much attention as a proper projector setup will.

Majority of the booths are 10'x10.' I am considering a long throw projector but do need to rethink how to set it up. Someone feel free to correct me but I think at the moment a super high gain screen with proper projector, may be bright enough to grab peoples attention as they walk by. I don't mind projecting a smaller image and even not having the screen cover entire projection screen. I need something very vivid that has 'life' to it. I don't want dull screen so I am willing to compromise video quality. Most of the presentation that will be looping will be a powerpoint presentation with logos/text/images and every so often short video to grab attention.

Will a high gain screen work outdoors? Yesterday, I was at an event where I thought of what it would be like to use a super high gain screen? This would be for images primarily and maybe short videos.
AV_Integrated's Avatar AV_Integrated 07:08 PM 08-03-2014
IMO, if this were me...

I may look for rear projection 'holographic' film which would work well with projectors and then 'float' glass plates in the space if possible creating an image that appears to be (somewhat) floating in space. It's very eye catching. Not a brilliant image, but as simple as it can be, almost everyone is doing projectors and flat panels now, and many places have $10,000+ budgets to work with and do one heck of a job on their setups. I still remember seeing a floating image setup and finding it to be one of the more unique presentations that I recalled from a trade show setup.

But, for best image quality, a 90" display will deliver the best/brightest setup. A rear projection will give the largest size for the lowest overall cost. A light rejecting screen won't be cheap, and really won't be brighter, but could be bigger. Not my first choice. A setup of 9 or more cheap 50" displays would be, perhaps, the most impactful setup you could have. It wouldn't be cheap, but could be done pretty nicely I think for not a ton of cash, so that would likely be my 'first' choice if I could do it and wanted 'big'. A fair bit of research on how to pull it off, but it would be a really cool setup.
reckless7 08:16 PM 08-03-2014
AV: You are a mind reader and your suggestions are valued GREATLY. I was planning both suggestions actually but waiting to test the starbright screen first.

I am trying to change my order from 92" (16:9) screen to a 146" (4:3) starbright7 screen (total cost is $430), I think that might be more impressive in a convention and fill the entire back of the booth better (10' wide x 7.5' tall). I am considering mounting the screen 2-3' off the ground and mounting projector 6-9' off the ground (so no one walks in front of it). Only issue is I won't be able to fill the entire screen because can only make a 100" screen from 9-10' away.

I am also planning on doing the transparent holographic projections in future but need to figure a mounting solution for multiple translucent glass pieces. I'll probably make a 150" screen as well out of four pieces of plexiglass In order to make it look more holographic how will the projector shoot the image? Would it be white background?

Thanks for all your help!
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