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[David Wanat]

I'm trying to pick out a couple new projectors for our sanctuary remodel.  
Is it possible to go too bright?

Screen size is ~6 x 10.6  (H x W)
That would make it 64 sq/feet.

One rule of thumb I've seen is 150 - 200 lumins per foot of projection distance.
So....  200 x 19.5 = 3900 lumins

Another rule of thumb (SMTPE) says 12-22 foot Lambert's at the screen in darkness, or 50 foot Lambert's in ambient light.
Formula:  projector lumins / screen sq. ft
So....  4000 x 64 = 62.5 foot Lambert's


If I use Hitachi CP-X600 (4000 lumins, 1000:1 contrast ratio)
Am I too bright?




Reference:
Projector link:
http://www.projectorpeople.com/projectors/projdtls.asp?itemi d=23070&itmname=Hitachi%20CP-X600&tab=summary

SMTPE rule:  about half way down
http://www.practical-home-theater-guide.com/projector-screen s.html

[Brad Weber]

David Wanat wrote on Mon, 01 October 2007 12:38

Screen size is ~6 x 10.6  (H x W) That would make it 64 sq/feet. One rule of thumb I've seen is 150 - 200 lumins per foot of projection distance. So....  200 x 19.5 = 3900 lumins Another rule of thumb (SMTPE) says 12-22 foot Lambert's at the screen in darkness, or 50 foot Lambert's in ambient light. Formula:  projector lumins / screen sq. ft So....  4000 x 64 = 62.5 foot Lambert's If I use Hitachi CP-X600 (4000 lumins, 1000:1 contrast ratio) Am I too bright?

Several things to take into account.  First, while this may be a little confusing, that is a native 4:3 projector so while you can display a 5.9625' high x 10.6' wide 16:9 image, that would actually be a letterboxed 16:9 image within a larger 7.95' high x 10.6' wide overall 4:3 image.  Or you can look at is as that you are actually using only the middle part of the native 4:3 chip to display a 16:9 image.  Since the projector rating is based on the full 4:3 native area of the chip, the image brightness should also be based on the full 4:3 image area, in your case 84.3 square foot rather than the ~64 square feet of the letterboxed 16:9.

Next, the projection distance has absolutely nothing to do with it, the issue is the image area.  So skip any calculations that base the image brightness just on projection distance and not the resulting image size (which can differ with different projectors and lenses).

SMPTE actually recommends 16 ftL for cinema applications, but that is based on a darkened cinema.  What is really being addressed is the image contrast ratio, which is not the projector contrast but rather the ratio between the projected image brightness and the ambient light levels on the screen.  For most presentation systems in classrooms, sanctuaries, etc., the ambient light levels are much higher than in a cinema, therefore those applications typically require a brighter image to maintain the same image contrast.  The usual goal is to have the image brightness 10 times the level of the ambient light on the screen for a contrast ratio of 10:1.  Obviously, the ambient light levels are a major factor here and they can vary tremendously, especially when you get into rooms with windows and/or no light control.  This is also an area where the typical church or commercial application differs significantly from the typical home theatre application.

Screen gain is another factor.  The level of light reflected off the screen is based on both the brightness hitting the screen and the screen gain, which may vary with the angle the viewers are off the centerline of the screen as well.  So the screen you are using can impact the results.

Finally, keep in mind that 4,000 lumens is the best that projector will do.  That is in high brightness mode, in "eco" mode that would likely give you a longer lamp life it is rated at 3,200 lumens.  The brightness will also drop off some at the edges.  And you can always turn it down.

Once you take all these factors into account, I seriously doubt that it will be too bright unless you are in a completely darkened room, even then you could drop the projector into "eco" mode and/or lower the brightness.

[Arnold B. Krueger]

[quote title=David Wanat wrote on Mon, 01 October 2007 17:38]I'm trying to pick out a couple new projectors for our sanctuary remodel.  
Is it possible to go too bright?

If your picture is too bright, you can always turn the brightness down. If your picture is not bright enough...


One important item that simple calculations don't seem to address is ambient light, whether spill from room lighting or windows.

[Ole Anderson]

Has anyone ever seen a front projection screen in a HOW too bright?  I can't imagine.

[John North]

Take a deep breathe....

Here is what I have learned along the way. Most of which can be found through searching. I claim none as my own, just delivering what I have gleaned.

Screen size:
Measure the distance from the screen to the farthest seat. If the majority of content leans to video or is video divide distance by 8 to get the screen height. If you are going to be using the screen to display data – web sites, excel spreadsheets, etc your divisor will be closer to 4. So if you have room for a screen larger than the “8” calculation you will gain visibility of what you are displaying.

Measure the distance from the closest seat to the screen. Ideally you do not want the screen height to be more than half of the distance away – 10’ away = 5’ high screen. Now this is an ‘ideal’, that plays second fiddle to the people at the back of the house, because too big is easier to deal with than too small.

Whether you are 4:3 or 16:9 the height calculation still works. If you are letterboxing a 4:3 to get your widescreen then you will need to rethink the above calculation for screen size.

Screen area:
Plugging in your screen height calculation to your aspect ration determine your screen width to get the square footage of the screen. Eg height = 6, aspect ratio of 4:3, width =8, area = 48’ sq.

Base illumination:
Multiply screen area X 20 lumens = 960 lumens.
Now in a BLACK room to adequately light up the screen you need 960 lumens. Next we need to find out how many lumens we need to give away to all the ambient light, and there will be ambient light.

Ambient illumination:
With a light meter, what photographers use, measure the ambient light at the screen at a time of day and or house lights set at typical service time. Suppose that number is 10 ft candles of light at the screen surface. Multipley ft. candles (10) X 5 = 50. This is the new lumens number we must meet to maintain that same illumination as above. So take the screen area (48) X ambient lumens per sq ft (50) to get 2400 lumens output from the projector.

So now you need a projector rated at 2400, but remember that the lamp assembly does not get brighter or even stay the same with time – it gets dimmer. So the first hours of use you are burning through the ambient light but as the lamp assembly ages the image is getting dimmer, and you are asking the projector to push out at 100% all the time which is impossible. This is where I would try to get something with a margin, AND the ANSI specs allow projector manufacturers to use a better lens on their projectors than what they sell the projector with. This will give a higher output reading than you will likely ever see, plus they will take into account the hot spots or zones rather than a true average of the display area, so your calculated spec may in reality mean a 3000 lumen unit or more.

With an actual applied calculation you now have enough info to ask for demos. What you really need might be a ‘3300’ lumen projector from X and a ‘3800’ projector from Y when you do an actual demo in your building. Seeing 3 or 4 projectors in your building at the service time of day, perhaps the brightest time of year will give you the best idea of what you really need.

And no you can’t get too bright, within reason.

[Ole Anderson]

Our situation:

Distance to rear pew = 80', 85% sit within 60' of proposed screen location.
Song lyrics, Imag, video clips, announcements primary use. No Excel training, thank you.
Ambient light on screen 8 fc
Max screen size, only available location is over altar = 150" diag (87'x116") area = 70 sf
Projector recommended by vendor: Hitachi CP-X605  4000 lumens    
4000/70 = 57 fc = 7:1 ratio screen brightness: ambient
Height ratio at 80' =10.7, at 60' =8

Looks like this should work, do you agree?
             

[John North]

Yes it looks like it should be capable of meeting the specs to demo the model to see if it works. Remember manufactures are given some latitude in how there specs actually play out on the 'big screen.' Specs and math look good but does it really look good in your room on your screen in typically lighting? Now if you already know that the edges don't trail off, or there are typically no hot spots, the math suggests that even after a few hundred hours you should have enough light output even if the lens supplied cuts into the specs compared to the lens they used to generate their 'specs.' I find you can create just about any slide you need to make even a dim set-up legible, but if you try and play a video clip, then you will know that your machine is either up to the task or not.

[Brian Kent Tennyson]

Standards call for 10:1 contrast ratio for computer and 25:1 for video, so you are coming up short with a 4000 lumen projector, plus that 4000 projector is probably more like 3000 and after a year will be around 2000. 6000-8000 lumen projectors are well withing the grasp of most budgets and LCD technology has advanced to the point where this kind of light output won't destroy the LCD panel.

I would look at Christie (hint: the LX Line http://www.christiedigital.com/AMEN/Markets/HousesOfWorship/ ), Sayno or Mitsubishi.

[Ole Anderson]

With some light fixture shielding and darkening the close side windows with smoked clear pull down shades I would be able to further reduce ambient even with the lights on in order to get a 10:1 for slides, and then do video with the lights dimmed to bring the ambient down farther.  Bottom of the screen is above the tops of the windows.

We would love a big Christe or Barco , but even a CHRISTIE LX66A at 6600 lumens is $15,000 vs $3500 for the Hitachi.  Typical attendance is 130, that would be a tough sell when we REALLY need an elevator at $100k.

[Rain Jaudon]

David - Any follow up on the install?
Rain

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