Does anyone know at what distance from the projector do they (Manufacture) make the light output measurement? - AVS Forum
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post #1 of 23 Old 08-20-2012, 10:54 AM - Thread Starter
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I know contrast measurements are all over the board and somewhat overstated but I have not seen much on how they rate their light output.of a projector.

Is there a spec or given distance from the projector to make this measurement?

Don't think I have ever seen anything on this other than after color calibibration it is usually less than whats called out.

Thanks
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post #2 of 23 Old 08-20-2012, 11:38 AM
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The manufacture wants the number as high as they can get it. They use the brightest mode which is normally not even close to the best mode for HT. I do not have the answer to your question but don't put to much faith in the spec numbers and know it will be less..
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post #3 of 23 Old 08-20-2012, 11:47 AM - Thread Starter
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Yes, This I know, Just trying to find some rhyme or reason to eval their claims on light output.

Sure do which they would just be honest about it so one could make a good decision on what you may need. or want.

Thanks
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post #4 of 23 Old 08-20-2012, 02:30 PM
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There are many ways to measure how bright something is. For a lumen measurement it is usually measured at source i.e. the light leaving the lens, so screen distance/size is not relevant.
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post #5 of 23 Old 08-20-2012, 04:50 PM - Thread Starter
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Quote:
Originally Posted by andysm View Post

There are many ways to measure how bright something is. For a lumen measurement it is usually measured at source i.e. the light leaving the lens, so screen distance/size is not relevant.

Of course, except the farther you are away from the lens output, the less the brightness, measures in lumen's.

But the question is at What is the the distance used by most manufacturer's to rate their pj.

I realize it will be probably be somewhat different for each; but given they publish them they must be somewhat similar or they would have a war
not only for specmanship but also for dishonesty in advertising. In their circle there would be some common ground. What though?

Maybe that's just wishful thinking but...........?

Rew
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post #6 of 23 Old 08-20-2012, 06:07 PM
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If you think about it, the measurement of light output would be taken for a few inches/feet facing the lens. I can do this with either of my meters but the measurement is not really helpful. What is needed is the light level reflected from the screen at the seating area. The bigger the screen the lower the light level 13 foot Lambert being the rule of thumb. If I stick my C6 or i1pro in front of my projector with the the ambient defuser on, the output measured will be the same if it is 1 foot or 5 foot in front of the the lens..
If you want to know the real output look at the pro reviews, many will give you the output once calibrated which will of course drop off after a few hundred hours..
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post #7 of 23 Old 08-21-2012, 05:30 AM - Thread Starter
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I totally agree with you but when one is shopping for a pj we all look at the specs sheet but have no idea what to believe.

I was hopping that we could find out what technique or technique's some of the manufactures use to rate their light output.

It just seems crazy that we have not pushed them for more honesty in their spec's. It seems even worse than a car's rated mpg.

At least then we could compare with some degree of confidence of what you are purchasing.

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post #8 of 23 Old 08-21-2012, 07:28 AM
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Quote:
Originally Posted by Rew452 View Post

I totally agree with you but when one is shopping for a pj we all look at the specs sheet but have no idea what to believe.
I was hopping that we could find out what technique or technique's some of the manufactures use to rate their light output.
It just seems crazy that we have not pushed them for more honesty in their spec's. It seems even worse than a car's rated mpg.
At least then we could compare with some degree of confidence of what you are purchasing.
Rew

The previous poster (airscapes) already told you the better way - checking for the pro reviews. It is not uncommon that two projectors rated at the same lumens can behave very differently in terms of light output after calibration. A projector rated at 1500 lumens can only output 500 lumens after calibrated to D65; another projector rated at 1200 lumens can output 700 lumens after calibrated to the same D65. Would you buy the 1500 lumens projector or the 1200 lumens (assuming light output is a concern for you).

Every pro in this forum is trying to convey the same message to you - ignore the manufacturer spec. Do some homework and check on some trustable review sites.

Of course, next step is to see it by yourself after narrowing down to a few of those that you're interested.
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post #9 of 23 Old 08-21-2012, 08:12 AM - Thread Starter
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Excuse me please, I know what you are all saying. I have owned my share of projectors and well understand what each of you are saying.

But here we are as the more experienced users and we still don't know a very key point of a projector. It almost sounds as if you support the manufactures way of specing their products. You say read the reports, but what I don't get is why are we are just accepting this type product spectmanship?

If anything we should know how each measure and rate their machines, be it at 1 meter from the lens or what ever but I have never heard any definitive answer other than what each of you have presented. Which is my whole point, you go over to Projector Central they give you estimates of it's light output based on screen size and Manufactures Specification.

Again a lot of info based on what????

Don't get me wrong, I am not against pro/user reports, I use them frequently but why are we accepting these discrepancies? As "That's the way they do It."

I would have thought someone here would have some insight on how they make their measurement.

For an example there are a number of manufactures using 230 watt lamps and their light out put can range from say 1100 - 2000 lumen's. Granted if you are talking dlp and the color wheel has a clear segment you will get a higher reading. But why the allusiveness?

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post #10 of 23 Old 08-21-2012, 08:34 AM
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Can you say MARKETING? The job of the marketing department is to get people to buy the crap the company is making, so make it look as good as you can without down right lying.. or if you do lie make sure you don't tell anyone how you got the results so they can not prove you wrong.. Lots of more important things to find out.. Such as "What (who) really controls the price of gas??" What do we do about global warming now we have screwed up the weather patterns? How do you get people who have been killing each other for centuries to be nice to each other? ...
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post #11 of 23 Old 08-21-2012, 01:55 PM
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I suggest you look up lumens on wikipedia. The lumen output does not vary with distance from the source. A PJ which produces 500 lumens produces 500 lumens, the position of the screen or measuring equipment does not change that. It is a bit complex but try wikipedia to start with. A lumen measurement does not simply measure an amount of light, but also takes the angle over which the light is emitted into account.
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post #12 of 23 Old 08-21-2012, 02:02 PM
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By the way, the brightness of a PJ screen is not measured in lumens but in foot-lamberts. The brightness of a screen also depends on pj-screen distdance and screen reflectivity, which are outside of the control of the PJ manufacturer.
Edit - I just noticed that the wikipedia article explains how ANSI lumens are measured.
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post #13 of 23 Old 08-21-2012, 05:03 PM - Thread Starter
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Yes andysm,

I agree you are right on units used to express light measurement. And yes, lumen are the measure of the device's ability to illuminate and foot- lambert is reflected light.

Thanks for the ANSI reference.

But my original question still stands; regardless of the units used to expressed it.
Quote:
Originally Posted by Rew452 View Post

I know contrast measurements are all over the board and somewhat overstated but I have not seen much on how they rate their light output.of a projector.
Is there a spec or given distance from the projector to make this measurement?
Don't think I have ever seen anything on this other than after color calibration it is usually less than whats called out.
Thanks
Rew
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post #14 of 23 Old 08-22-2012, 08:44 AM
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Rew452, you're right there is no standardization on distance from projector to screen when making illumination measurements. The ANSI standards outline many requirements for testing but NOT distance. Even the new standards being proposed by the Society for Information Display (SID) do not address this issue.

http://www.3lcd.com/news/press_release.aspx?bot=true&release_id=467

Personally I think it's time that a standard screen size (rather than distance) is applied to ALL projector light measurements. The default size i would suggest is 100" (16:9) since anything smaller than that is just like watching a very large TV set (my opinion of course). The screen would be white and a screen gain of 1.0.

As an example let's take two popular LCD projectors, the Epson 8350 and the Panasonic AR100U.

Working off the Projector Central Calculator:

On a 100" screen the Epson has a throw range from 9' 9" to 20' 10". It produces 20 fL at mid range (13' 4").
On a 100" screen the Panasonic has a throw range of 9' 8" to 19' 6". It produces 26 fL at mid range (12' 11").

In the DLP class let's try the Acer H6500 and the Viewsonic Pro8200.

On a 100" screen the Acer has a throw range from 10' 11" to 13' 1". It produces 32 fL at mid range (11' 11").
On a 100" screen the Viewsonic has a throw range from 10' 2" to 15' 7". It produces 29 fL at mid range (12' 4").

If you were to standardize the distance (at say 12') you would end up with varying screen sizes.

To maximize the lumen measurement touted by manufacturers I suspect that all measurements are taken at the closest distance attainable from projector to screen.

For the Epson the closest distance is 6' 2" which produces a 47" screen.
For the Panasonic the closest distance is 8' which produces a 62" screen.
For the Acer the closest distance is 5' which produces a 42" screen.
For the Viewsonic the closest distance is 5' which produces a 41" screen.

I doubt very much we will ever see a TRUE standardization so it will always fall to the consumer to research their projector choice wisely.

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post #15 of 23 Old 08-22-2012, 10:01 AM - Thread Starter
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Mr. G

I really like your idea of a given screen size and measurement! it makes sense but as you say It probably won't happen anytime soon.

You did give me another point I had not considered; performing the measurement at the smallest given screen size for the projector. This would maximize light readings and since pretty much every projector has a somewhat unique lens. throw range - that would account for the many different light readings.

Thanks much for your insight, I Greatly appreciate!

Rew
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post #16 of 23 Old 08-22-2012, 12:48 PM
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When measuring the ANSI lumens output from a projector the distance between projector and screen does not matter since it does not affect the ANSI lumens rating. A greater distance / larger screen size will make the image darker, but the image will also be larger. The ANSI lumens standard takes both the brightness and the size of the screen into account, so the two things sort of cancel each other out. The ANSI lumens will be the same regardless of how large or small the image is. If you have a 40 inch picture from a projector it will have the same ANSI lumens rating as a 100 inch image from the same projector. I really don't know how many times I have to say this. The image size does not affect the ANSI lumens rating. There is no standard distance or screen size because they are not relevant, they do not affect the result.
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post #17 of 23 Old 08-22-2012, 01:07 PM
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andysm, you are confusing measuring lumens straight off the lens (which is done sometimes) versus the nine point measurement on the screen.

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post #18 of 23 Old 08-22-2012, 01:25 PM
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No I am not, the 9 point measurements measure the amount of light falling on those parts of the screen, but then the size of the screen is also taken into account. When you take both the 9 points AND the size of the screen into account (which ANSI lumens do) then image size is not relevant to the ANSI lumens rating. The amount of light hitting the screen is the same, whether 'spread out' over a large picture or 'concentrated' into a smaller picture makes no difference. Two PJs with the same ANSI lumens projecting the same size image should show two images of the same brightness.
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post #19 of 23 Old 08-22-2012, 04:00 PM
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You guys are getting confused between zoom and size of the screen, as Lumens is just the baseline at a given zoom, so I would offer the below clarification:

You don't take lumens readings off the screen, that is an fL reading. Although technically you can say this fL amounts to this lumens by converting it back based on the screen size, but ANSI lumens are taken with a light meter pointing towards the projector with your back to the screen and the projector's ZOOM configured at closest throw. You cannot compare one MFR to another just by looking at ANSI lumens, but you can get some general ideas by looking at calibrated lumens. You can take lumens readings at any throw/zoom position, but you need to specify at what ZOOM position they were taken at if you did not use closest throw. However, MFR ANSI lumens themselves mean they are going to be taken with the projector at max zoom / closest throw. My issue with the explanations would be that the distance doesn't matter, well it can matter if the zoom is changed and how the lens is setup, but because it's always going to be taken at max zoom for MFR ANSI Lumens, then that is the baseline and so in that sense it does not matter (but it can matter even here between different MFR's because of the different min. throws and zooms). However, in a user based lumens reading (NON-MFR), the measurer can choose any ZOOM position, which is why throw distance needs to be specified (closest, mid, farthest), but with ANSI readings it is always closest throw unless specified otherwise. When measuring lumens the size of the screen does not matter, only the position of the zoom (hence what screen sizes are able to be produced at a given throw by changing the zoom).

fL Readings = Takes into account screen size.
Lumens = Takes into account Zoom position of lens.

There is a standard way to measure it, and the above is the method. The MFR's are always going to quote MAX ZOOM lumen measurements because that is what gives the highest reading. Whether or not the ANSI document (I haven't read it) enforces them to take the reading at closest throw doesn't really mater, because they always will anyhow.


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post #20 of 23 Old 08-22-2012, 05:07 PM
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Quote:
Originally Posted by Mr.G View Post

Rew452, you're right there is no standardization on distance from projector to screen when making illumination measurements. The ANSI standards outline many requirements for testing but NOT distance.

To maximize the lumen measurement touted by manufacturers I suspect that all measurements are taken at the closest distance attainable from projector to screen.
For the Epson the closest distance is 6' 2" which produces a 47" screen.
For the Panasonic the closest distance is 8' which produces a 62" screen.
For the Acer the closest distance is 5' which produces a 42" screen.
For the Viewsonic the closest distance is 5' which produces a 41" screen.
I doubt very much we will ever see a TRUE standardization so it will always fall to the consumer to research their projector choice wisely.

This part is correct, since ANSI lumens are measured at closest throw, one projector's closest throw is not the same as anothers and this can skew the results. However, this is usually NOT a concern because mode differences and loss in calibrated lumens is 100x more severe than this difference, and most projectors in the same lens and genre (HT, Biz, Classroom) are usually close. Overall the real reason to ignore MFR lumens is because all they are showing is the max light output capable at closest throw with no concerns for how much you will lose when calibrating or even just when using a watchable mode.
Quote:
Originally Posted by AndySM 
Two PJs with the same ANSI lumens projecting the same size image should show two images of the same brightness.
This part is incorrect, because they can produce the same size image using different ZOOM and angle factors depending on the design of the lens and the throw. Only if the two lenses are using the same throw factor at the same zoom does it perfectly equalize across manufacturers.

This is a confusing topic, but..
You guys are also arguing in a confusing method. Hence, one person is arguing about screen size when they should be talking about zoom and throw (not screen size), but the confusion in the argument seems to be how it applies between different MFR's. Andy is correct that screen size does not determine ANSI lumens, but he is incorrect in assuming that this also applies to the throw ratios not skewing the results. The skewing is minor in most cases, but the min. throw does skew the ANSI lumens. That is why my calculator bases the measurement off real readings at a given zoom and knows the min. lens throw when it does this and takes all that into account.

Note:
This type of confusion is a big reason I made my calculator instead of relying on other calculators "MFR Spec'd Numbers". In my calculator it uses the real-world results. You can see the general TRUE differences in brightness between projectors by looking at my calculator. I do have a couple readings that aren't perfect due to a lack of data, but I will fix that eventually and most readings are really close.

...


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post #21 of 23 Old 08-22-2012, 06:26 PM - Thread Starter
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Wow! Coderguy that seems to make a lot of sense. Definitely does needs some digesting.

And I hope you won't mind if after some thought I get back to you with some more questions.

Thanks much
Rew
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post #22 of 23 Old 08-23-2012, 01:07 AM
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Thanks coderguy, my pj doesn't have a zoom so I completely forgot about that.
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post #23 of 23 Old 08-23-2012, 02:43 AM - Thread Starter
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Quote:
Originally Posted by andysm View Post

Thanks coderguy, my pj doesn't have a zoom so I completely forgot about that.

Honestly? What pj do you have? I don't think I have seen one without zoom.

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