BIG Screen Brightness Survey/Questions - AVS Forum
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post #1 of 71 Old 10-24-2013, 06:37 AM - Thread Starter
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Good Morning AVS. Please let me know about your setup (Projector Model and Screen Size - Image Brightness), if you are running a screen that is taller than 72" high in 16x9 or 2.35. What projector? What screen? Image brightness measured in fL on 100ire window.

Looking at the JVC line, it looks like there are a few options that will provide a stated 12fL on 82"H, but most are much lower light. I am curious as to your satisfaction with 8-12fL systems in a dedicated theater with a BIG screen.

Thanks for your input

Jeff in Detroit
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post #2 of 71 Old 10-24-2013, 06:45 AM
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Originally Posted by jbryngelson View Post

Good Morning AVS. Please let me know about your setup (Projector Model and Screen Size - Image Brightness), if you are running a screen that is taller than 72" high in 16x9 or 2.35. What projector? What screen? Image brightness measured in fL on 100ire window.

Looking at the JVC line, it looks like there are a few options that will provide a stated 12fL on 82"H, but most are much lower light. I am curious as to your satisfaction with 8-12fL systems in a dedicated theater with a BIG screen.

Thanks for your input

Jeff in Detroit

With a 72" high 16:9 screen, I would want a screen with 1.3 gain. Even at 1.5 gain, a 72" high 2.35 is too much screen for a JVC.

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post #3 of 71 Old 10-24-2013, 09:45 AM
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If a Dalite HP2.4 screen can fit optimally in your arrangement, then you should be able to get sufficient brightness with a JVC.
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post #4 of 71 Old 10-24-2013, 10:04 AM
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Planar 8150, eco, Iris off, 110" HP 2.8 18+ fl at 200 hours on the lamp. See below for room image..
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post #5 of 71 Old 10-24-2013, 10:57 AM
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I am curious as to your satisfaction with 8-12fL systems in a dedicated theater with a BIG screen.

I personally find no satisfaction under 16 foot lamberts. I prefer more like 18 - 20 foot lamberts. smile.gif
And since I also do not like the side effects / artifacts of high gain screens, I went with a 60" high ( 16:9 ) and 50" high 2.35:1 screens.
YMMV.

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post #6 of 71 Old 10-24-2013, 11:03 AM
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Most people are watching the projector brighter than they claim, they are just measuring it wrong.


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post #7 of 71 Old 10-24-2013, 11:18 AM
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Most people are watching the projector brighter than they claim, they are just measuring it wrong.

Most don't measure at all. When I finally bought a light meter and discovered that my Optoma H79 was so dim I was only getting 6 - 8 foot lamberts, I immediately went out and bought a projector with two lamps! eek.gifsmile.gif

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post #8 of 71 Old 10-24-2013, 11:19 AM
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Quote:
Originally Posted by coderguy View Post

Most people are watching the projector brighter than they claim, they are just measuring it wrong.

What would be the proper way to measure it? My assumption is 100% white pattern at eye level in the seating location.
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post #9 of 71 Old 10-24-2013, 12:26 PM
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Originally Posted by airscapes View Post

What would be the proper way to measure it? My assumption is 100% white pattern at eye level in the seating location.

You want to know what you are getting (at least close) before you buy, not find out after buying. Best way is to read reviews of projectors and screens and then using math, figure out how many Foot Lamberts you will get off the screen. You play with screen size, gain Another way would be to call AV Science and talk to them. smile.gif

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post #10 of 71 Old 10-24-2013, 12:38 PM
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Originally Posted by AV Science Sales 5 View Post

You want to know what you are getting (at least close) before you buy, not find out after buying. Best way is to read reviews of projectors and screens and then using math, figure out how many Foot Lamberts you will get off the screen. You play with screen size, gain Another way would be to call AV Science and talk to them. smile.gif

That would be calculating it.. What is the proper way to measure it after the fact.. Am I doing it correctly?
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post #11 of 71 Old 10-24-2013, 12:58 PM
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Originally Posted by airscapes View Post

What would be the proper way to measure it? My assumption is 100% white pattern at eye level in the seating location.

I think that's right. I move the meter (which I hold just in front of the screen) around to different positions to see which gives the highest value.
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post #12 of 71 Old 10-24-2013, 01:04 PM
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Sorry, thought you asked about calculating it. Coderguy answered measuring it.

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post #13 of 71 Old 10-24-2013, 01:16 PM
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Originally Posted by airscapes View Post

That would be calculating it.. What is the proper way to measure it after the fact.. Am I doing it correctly?

You need a light meter first.
lx1010b ($13) or the lx1330b ($35) are the cheap ones many have, and they can be found on Amazon. CA-813 would be the next step up, about $160. Then the Minolta T-10 for about $1000.

You have to stand at the screen with the light meter facing the projector, technically you measure 9 squares (like a tic tac toe pattern), then you take the average LUX reading of all those. After you have the lux reading, you can convert it to Foot Lamberts based on your screen size (there is a free Excel spreadsheet to do it, just search excel conversion lux in the forums).

I personally don't bother measuring 9 squares, I measure 5 (depends). 9 takes too long. Just measure a straight diagonal line from top left to bottom right (3 measurements), then take the top right measurement and bottom left measurement and average all 5 of them. If you do 9, the patience of not flicking your wrist enough will skew the measurement more than doing 5 and flicking the wrist more often. You have to keep moving your wrist to change the angle of the light meter until you find the highest number (about 15-30 seconds per position), that's why so many people mess up.

You can also use a colorimeter like a C6 or D3, though it will give far less accurate results because it is too sensitive to angle and no-one has the patience to wait for its slower readings compared to the LUX meter.


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post #14 of 71 Old 10-24-2013, 01:37 PM
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Quote:
Originally Posted by coderguy View Post


You can also use a colorimeter like a C6 or D3, though it will give far less accurate results because it is too sensitive to angle and no-one has the patience to wait for its slower readings compared to the LUX meter.

Really? My i1pro spectro and C6 read 100% white instantly and since you have to adjust the meters on their mount to get the max reading before you profile them for a calibration, I don't really get what you are saying.. Far as I know reading the checker board is to calculate contrast ratio not max fl.. Maybe I missed something in the original post.. I will go back and read it again..
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post #15 of 71 Old 10-24-2013, 01:44 PM
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ANSI lumens is based on measuring 9 points on a screen, not a checkerboard pattern, but an imaginary grid (or use a real grid with 100 IRE white divided by black lines). This is the standard method of measuring ANSI Lumens. Projectors vary by as much as 35% or more by unevenly illuminating the screen, that is why you have to measure different points.

The C6 or D3 will not provide the correct results, you cannot find the max lumens point unless you take 15-20 minutes at each imaginary square. You may think you've found the right max fL point, but you haven't, not only does angle affect it, but so does distance to screen, so there are literally hundreds of possibilities to try to find the max reading.

No-one measures brightness with a colorimeter if they want to be accurate.

This is one reason why some reviewers using colorimeters to measure contrast have ridiculous results. That said, you can measure contrast somewhat accurately with a C6 by taking the peak reading with the cheap light meter, but taking the black floor reading AMP'd up at the lens with the c6, or you can just use a white piece of paper in front of the lens. This will provide the most accurate measurement of contrast within the limitations of the C6. I personally would do two methods if wanting to read contrast and then average the error of the two to be honest.


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post #16 of 71 Old 10-24-2013, 01:57 PM
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Originally Posted by coderguy View Post

ANSI lumens is based on measuring 9 points on a screen, not a checkerboard pattern, but an imaginary grid (or use a real grid). This is the standard method of measuring ANSI Lumens.

I guess that is what is confusing me..I thought we were talking about FL you get with a given projector on a given screen.. not contrast ratio..

OP asked "Image brightness measured in fL on 100ire window."
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post #17 of 71 Old 10-24-2013, 02:05 PM
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Originally Posted by airscapes View Post

OP asked "Image brightness measured in fL on 100ire window."

It's an invalid way for comparison, he needs to use a light meter, regardless of what he asked. Lamps also change their illumination balance over time, meaning one area of the screen may get brighter. A single fL reading is not a good indication of how much light your eyes are receiving, period.


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post #18 of 71 Old 10-24-2013, 02:14 PM
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Originally Posted by coderguy View Post

ANSI lumens is not related to contrast ratio, you cannot get an accurate fL with the D3 or C6. To get the amount of fL you are seeing, you have to use a light meter to first measure the LUX converted to lumens, for the reasons I stated above. Once you have the lumens, you can calculate fL by knowing the gain of your screen and the square footage.

This is the only proper way to calculate fL. This is not something I am pulling out of a hat, this is common knowledge.

I added the comment in about contrast later but that is not what we are talking about.

Well I guess this was left out of every thing I have read and learned about calibration.
Whats the point in doing a calibration if the Y reading is not accurate? I may be missing something really silly here but every time I set up my gear, the fl output number is the same as it was the last time.. Yes If I sit off axis to my HP screen I know the output is not the same as when I sit in my seat where the measurements were taken..
Please point me to some documentations that will explain in detail why the reading we take with calibrations software that tell us the fl output is xxx is wrong. I get the fact you are talking about averaging it out but my eyes only see what they see from where they are .. wink.gif

I also said to set the meter up where you sit not 4" from the screen. The C6 is measuring a large diameter circle at the distance where it is set.
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post #19 of 71 Old 10-24-2013, 02:20 PM
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You don't need to get the exact peak Y reading to get an accurate color balance reading, you only need it close enough for govt. This is entirely different than measuring how much light our eyes receive.

The light reading has to be almost EXACT at 9-points to get an accurate white point fL that your eyes are receiving. The eyes receive the light from the screen non-uniformly due to non-uniform white balance from the lamp + screen + room. Your meter also measures it inaccurately from a single point due to the angle vector. The 9-point reading not only reduces the error margin of the reading overall since the reading is repeated 9 times, but it also reduces the non-uniformity error that ALL our lamps have.

A single point on the screen is NOT how much foot lamberts your eyes are receiving, nor is it a consistent method to compare between someone else (because their screen will not illuminate at the same white uniformity as your screen, nor will their lamp as it ages, nor will the reflections in their room).

Your eyes do not perceive how bright the image is from a single TINY point that the colorimeter gives, they actually receive the light from a larger area and some from the entire screen even if you are not looking at the entire screen while viewing. The ANSI Lumens method much better and more accurately assesses how our eyes receive the light from the screen than a single fL point, and I am not talking small errors, the errors can be huge if you use a single fL reading.


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post #20 of 71 Old 10-24-2013, 02:31 PM
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Quote:
Originally Posted by coderguy View Post

You don't need to get the exact peak Y reading to get an accurate color balance reading, you only need it close enough for govt. This is entirely different than measuring how much light our eyes receive.

The light reading has to be almost EXACT at 9-points to get an accurate white point fL that your eyes are receiving. The eyes receive the light from the screen non-uniformly due to non-uniform white balance from the lamp + screen + room. Your meter also measures it inaccurately from a single point due to the angle vector. The 9-point reading not only reduces the error margin of the reading overall since the reading is repeated 9 times, but it also reduces the non-uniformity error that ALL our lamps and screens have.

A single point on the screen is NOT how much foot lamberts your eyes are receiving, nor is it a consistent method to compare between someone else (because their screen will not illuminate at the same white uniformity as your screen, nor will their lamp as it ages).

Ok, I understand. The inaccurate method of reading a 30" diameter spot in the center of the screen (FOV of the c6 from 9') is good enough for me but not the most accurate means of determining the output of reflected light.smile.gif
Comparing one persons setup to another is about as useful as a screen shot.. I get that as well.
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post #21 of 71 Old 10-24-2013, 02:33 PM
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Right, but many people assume it is close and will report in the forums that they are getting 12 fL, but they might be getting 16-18 fL if they used a lux meter. That is why no-one should use a colorimeter to determine the amount of fL coming off the screen from a single point, it is less accurate than playing horse shoes.

When I say ANSI Lumens is the standard, I mean it is what every pro reviewer goes by (or should), Art and PR both use Ansi Lumens, if they took the fL reading with a colorimeter at a point and then reverse converted that number back to lumens, their readings would be off-the-chart inaccurate, not that they are even perfect now, the last thing they need to do is add even more error. Zombie also uses Ansi Lumens as well in his reviews, for this very reason.

We all use it, comparing fL at a single point is just pointless.


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post #22 of 71 Old 10-24-2013, 03:12 PM
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Quote:
Originally Posted by coderguy View Post

To get the amount of fL you are seeing, you have to use a light meter to first measure the LUX converted to lumens, for the reasons I stated above. Once you have the lumens, you can calculate fL by knowing the gain of your screen and the square footage.
As an example, if somebody measured say 560 lumens with a T-10 or CA813 and they have a StudioTek 130 that is 56 square feet, how would you suggest they calculate their ft-lamberts?

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post #23 of 71 Old 10-24-2013, 03:50 PM
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Lumens to fL = (lumens/sq.ft.) * gain = foot lamberts
fL to Lumens = fL x sq.ft. / Gain = lumens
Lux to Lumens = (lux*SqFt)/10.76


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post #24 of 71 Old 10-24-2013, 04:03 PM
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Quote:
Originally Posted by coderguy View Post

Lumens to fL = (lumens/sq.ft.) * gain = foot lamberts
fL to Lumens = fL x sq.ft. / Screen Gain = lumens
Lux to Lumens = (lux*SqFt)/10.76
While you may have stated things that are true, you are applying them incorrectly. You went through a bunch of stuff about how wrong it was for people to not take the whole image into accournt and then it seems like you are suggesting they make the same mistake with screen gain.

I didn't tell you how far the person or the projector was away from the StudioTek 130. The gain from that screen can vary significantly from the brightest part to the dimmest and make your calculations (or those of the person you are advising) wrong for much the same reason as you were stating they were wrong if a person didn't measure over the whole image to get the lumens.

If a person took your advice and plugged in 1.3 for their gain while using your equation they would get the wrong value.

If a person is only getting the ft-lamberts for the center of the screen then they should say so. I don't believe that getting the ANSI lumens and then incorrectly using screen gain to calculate ft-lamberts helps the situation.

If you want the kind of accuracy you seemed to be for earlier with ft-lamberts then you would need to go to greater lengths than calculating lumens and then applying one gain value. For an accurate value you wouldn't even calculate the whole ANSI lumens, but would need to combine the light level for a spot to the gain for that spot and do that over the whole screen.

--Darin

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post #25 of 71 Old 10-24-2013, 04:05 PM
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This is total BS, the formula is the formula, I did not tell them how to calculate screen gain, I simply said use the REAL Gain.

Stop being a joker, you know as well as I do that every post in the world is not going to qualify every variable, them depending on their variables of non-uniform gain screens is why I told them to use a spreadsheet smile.gif

I also already mentioned that you measure LUMENS with LUX, not by reversing fL, I specifically said not to do it. You asked me how to do something I said NOT to do, and then corrected me for it. You are a nice guy...

Also Lumens is an absolute number, it has to do with the lens, not the screen, that is why I said we use Lumens.


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post #26 of 71 Old 10-24-2013, 04:10 PM
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Quote:
Originally Posted by coderguy View Post

This is total BS, the formula is the formula, I did not tell them how to calculate screen gain, I simply said use the REAL Gain.

Stop being a joker, you know as well as I do that every post in the world is not going to qualify every variable, them depending on their variables of non-uniform gain screens is why I told them to use a spreadsheet smile.gif
Honestly, I don't think you know what you are talking about and want to blame me. I asked you a question:
Quote:
As an example, if somebody measured say 560 lumens with a T-10 or CA813 and they have a StudioTek 130 that is 56 square feet, how would you suggest they calculate their ft-lamberts?
If you didn't want them to apply those equations you posted why did you post them?

If you think I'm wrong then answer the question correctly. For the StudioTek 130 what gain should they use in your formula?

--Darin

This is the AV Science Forum. Please don't be gullible and please do remember the saying, "Fool me once, shame on you. Fool me twice, shame on me."
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post #27 of 71 Old 10-24-2013, 04:11 PM
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Everyone can see you're being a smart aleck, don't pretend to not be.

I don't have the gain uniformity % or angle of uniformity % on me, so I don't have the number, their is a spreadsheet which does that for them I believe, which I told them to use.

I'm done, keep playing the joker... smile.gif


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post #28 of 71 Old 10-24-2013, 04:13 PM
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This should be good. Let me get out my popcorn

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post #29 of 71 Old 10-24-2013, 04:14 PM
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I'm not being pulled in, he's trying to set me up with baited questions, can he be any more obvious?

I've seen some pretty sneaky baiting attempts, but this is not one of them, this is so obvious it is like shooting the neighbor's dog in broad daylight and then saying "who me"...


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post #30 of 71 Old 10-24-2013, 04:14 PM
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Quote:
Originally Posted by coderguy View Post

OK foo, everyone can see you're being a smart aleck, don't pretend to not be.

I don't have the uniformity % or angle of uniformity % on me.
Interesting that you come up with that now, but when I asked the question you acted like people could use your simple formula. I was not being a smart alec. I was wondering if you really understood the subject matter and I think it was pretty clear from your responses that you did not.

You don't have a problem trashing others for doing things in a way you consider incorrect, but when I point you that you are making the same kind of mistake based on what you posted yourself you seem to have trouble handling that. Not my fault you have that trouble.

Do you at least understand enough now to comprehend that calculating the lumens the way you suggested and then applying even a non-uniform gain doesn't work? If you know the subject matter you should understand why that is.

--Darin

This is the AV Science Forum. Please don't be gullible and please do remember the saying, "Fool me once, shame on you. Fool me twice, shame on me."
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