# Revised Selfbuilt beam intensity measures: new NIST-calibrated Extech EA31 lux-meter



## selfbuilt (Jul 25, 2012)

If you have been following my recent high-output/multi-emitter light reviews recently, you may have noticed some discussion (on my part) of the accuracy of my standard lux light meter for throw measures.

I have a custom set-up with a permanently-mounted sensor for my lightbox, where I continually monitor the internal calibration for my relative output measures. I derived estimated lumen conversions from that setup using the method discussed here: How to convert Selfbuilt's Lightbox values to Lumens

But in terms of direct beam intensity measures and beam distance, I have been using one of the inexpensive lux lightmeters available at a number of deal sites (the common Ceto model). The problem with these sorts of meters is you never know how good their internal calibration is. :shrug: Note that all meters will go off calibration with time, but I can compensate for that with my reference standards. I recently picked up a second inexpensive meter (the V&A VA800), and found it typically gave ~15% higher lux readings than my long-standing Ceto meter. 

As a result, I decide the break open the piggy bank and get a good quality Extech light meter (the EA31 in this case). But I also paid the extra $75 to have its specific calibration tested and certified according to NIST standards. :thumbsup:

Note that there is nothing magical about NIST certification - it just means this specific unit has been tested (and tuned if necessary) so that its calibration matches an agreed-upon reference standard. But I do have a nifty looking calibration certificate (good for one year). :laughing: Again, all meters will drift out of calibration over time, but at least I have a good starting point with this meter - and I can monitor its performance over time to reference standards I've set up.

The other thing I've done recently is to invest in a copy of the ANSI FL-1 testing standard. The actual standard is a protected document, and details the laboratory methodology used for testing (available from NEMA for $60). Although I am most definitely not a proper laboratory, I can at least try to follow the methodology as closely as I can in my testing. The details matter here - the closer I can replicate testing conditions, the more consistent my results will be.

Up until now, I've been working back from intensity measures at 5m (for convenience sake) using my old Ceto meter. From now on, all beam measures will be taken at the full 10m distance and worked back, using the NIST-certified Extech EA31 meter. To designate this change, I will be color-coding my summary tables with orange-highlights for the new measures.

Below is a comparison of my high output lights, broken down by single or multiple emitters. Let's see how the new meter and methodology compares. *Note: blue is the old Ceto meter, orange is the new EA31-NIST meter*.












I'm showing the percent change for each light, as I believe it is instructive. I know from directly comparing various lights using the same technique that my Extech EA31-NIST reports about ~10-12% brighter than my Ceto meter (and ~3-5% dimmer than my V&A VA800 meter). 

However, when using this new 10m measuring distance, I am seeing anywhere from ~10-25% increase in raw lux measures (converted back to 1m). In particular, the multi-emitter lights are all showing a fairly consistent 21-26% increase in beam intensity. I suspect a big part of the reason for this is how long it takes the beams to fully converge in multi-emitter lights - 5m just wasn't enough. This is likely also a contributing factor for some of the higher output single-emitter lights.

The other factor is the larger hotspot when projected to 10m - this gives me more opportunity to hunt around for the area of peak intensity. Recall that the ANSI FL-1 standard for beam intensity/distance is based on absolute peak values. I suspect some of my earlier 5m measures were lower because the diffuser cup over the light meter sensor was integrating too wide an area. 

You can really see this effect on aspherics - my peak intensity measures from regional hotspots are much higher now (one example is shown above). That said, I believe you really need to go out to 30m to get a true measure of aspherics - these 10m readings are just too heavily influenced by those hotspots. But it illustrates the principle of why some lights are increasing in intensity readings at 10m compared to 5m.

I will begin updating all my tables in upcoming reviews with the new measures, and wanted to provide a reference here for those who were curious about the change.

Keep in mind one thing hasn't changed – I typically only have one sample of each light I test. ANSI FL-1 requires a minimum of 3 lights be tested for beam intensity/distance (under fully controlled conditions). As always, you should NOT take my results as representative of a given model. It is simply the most accurate picture that I can provide of the one given sample in my possession.

:wave:


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## Burgess (Jul 25, 2012)

*Re: Reivsed Selfbuilt beam intensity measures: new NIST-calibrated Extech EA31 lux-m*

Thank you, once again, for all your dedication and hard work ! ! !


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## biglights (Jul 25, 2012)

*Re: Reivsed Selfbuilt beam intensity measures: new NIST-calibrated Extech EA31 lux-m*

Very nice thanks for your time and the effort that you put into this!!!


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## Up All Night (Jul 25, 2012)

*Re: Reivsed Selfbuilt beam intensity measures: new NIST-calibrated Extech EA31 lux-m*

I thought it couldn't get any better, then you go and up the ante! Hats off to you!:bow:
A heartfelt thanks to yourself and all others who provide in-depth reviews on this forum. You guys add a dimension to this hobby that can't be quantified.
Where you find the time,......well, lets just say I can't imagine.
Thanks for all your work!
Don.

P.S. 
Can you post a copy of that calibration certificate?............:laughing:


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## orbital (Jul 25, 2012)

*Re: Reivsed Selfbuilt beam intensity measures: new NIST-calibrated Extech EA31 lux-m*

+

selfbuilt at it again,,being outdone only by _himself!!_:thanks:


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## kj2 (Jul 26, 2012)

*Re: Reivsed Selfbuilt beam intensity measures: new NIST-calibrated Extech EA31 lux-m*

Thanks, for all the work you put in 

Had my SR95UT tested at my local dealer. Don't know the numbers, but they said; that the throw was around 860meters.


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## ergotelis (Jul 26, 2012)

*Re: Reivsed Selfbuilt beam intensity measures: new NIST-calibrated Extech EA31 lux-m*

Well done selfbuilt, really nice effort!I love the fact that you try to get the perfect results!

(Now try to calibrate a bit the lumen, I saw more flashlights, especially the smaller ones, that seem to be overrated, like rofis jr20, might find more if i search! Sorry for insisting, i am pretty sure their calculations are wrong, i am doing this just to help you, because your reviews have very high impact on thousands of people. If i am getting annoying sorry for that, i won't bother you again, but you will remember me in future!  )


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## frosty (Jul 26, 2012)

*Re: Reivsed Selfbuilt beam intensity measures: new NIST-calibrated Extech EA31 lux-m*

Thanks again for all your time and effort.


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## Gunner12 (Jul 26, 2012)

*Re: Reivsed Selfbuilt beam intensity measures: new NIST-calibrated Extech EA31 lux-m*

Nice work Selfbuilt! Now your reviews are NIST traceable :laughing:


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## selfbuilt (Jul 26, 2012)

Gunner12 said:


> Nice work Selfbuilt! Now your reviews are NIST traceable :laughing:


Well, I suppose the beam intensity/distance measures will be. :laughing:



Up All Night said:


> Can you post a copy of that calibration certificate?............:laughing:


I'm not keen to post the whole thing (given the personal identifying info listed for myself and the calibration technician), and it does say that the certificate "cannot be reproduced other than in full, except with prior written approval of Extech". 

But they appear to have done a thorough job comparing my unit to their reference standard (i.e., repeated measures, at a variety of intensities, using a tungsten source of specific color temperature). I don't suppose I'm revealing any state secrets to say that the calibration data reveals they are using a Konica Minolta T-10 as their illuminance standard and a Minolta XY-1 as their chromaticity standard (both with certified calibration dates). 



ergotelis said:


> (Now try to calibrate a bit the lumen, I saw more flashlights, especially the smaller ones, that seem to be overrated, like rofis jr20, might find more if i search! Sorry for insisting, i am pretty sure their calculations are wrong, i am doing this just to help you, because your reviews have very high impact on thousands of people. If i am getting annoying sorry for that, i won't bother you again, but you will remember me in future!  )


The general question of the accuracy of the lumen estimation method is a valid one. While I trust the lux values from the EA31-NIST for beam intensity/distance, and I know I can trust the consistency of the relative output values (ROV) of my lightbox (because I maintain an internal calibration), the lumen conversion estimate is only as good as the reference light-lumen data I used. Again, see my lumen estimation thread for more detail.

But the key point here is that it is not _individual_ lights that are over-rated (e.g. Rofis JR20 or Nitecore EC2). Rather, _ALL_ lights within a given output range would have to be over (or under) estimated. Since the lumen conversion method is power relationship based on the calibrated lightbox data, the _relative_ relationship between lights is consistently maintained. The question is whether the absolute value is right, across the board.

As such, I don't think its appropriate to cherry-pick individual lights to suggest they are high (or low). If the Rofis JR20 is "wrong" at 390 estimated lumens, then ALL lights in my tables around this value are likely similarly "wrong". There are a few caveats here in terms of the exact performance of individual lights (i.e., throwers vs flooders in my lightbox), but as a general rule the relative relationships still hold.

For those who interested, I decided to go back this morning and compare four lights using the same emitter in my lightbox. These four lights were originally tested last month, six months ago, 1.5 years ago, or 2 years ago. Below is their original calibrated lightbox ROV (and lumen estimate using my standard power conversion), and the new calibrated lightox ROV (and subsequent lumen estimate) today.






When you consider variation in the specific battery used, the exact placement of the light in the lightbox, the current calibration status of my lightbox, and the potential changes in emitter/circuit performance of the lights over time, etc., it is actually pretty surprising that all the ROV data remains as consistent as it does (i.e. less than 2.5% variance for each these lights). 

At some point in time, I would like to build a proper integrating sphere for better relative measures of my lights. But again, that still won't tell us anything about true lumens unless I can calibrate it to a properly maintained NIST-certified sphere of appropriate size, characteristics, etc. That would mean testing my inidividual lights in both devices, and developing a calibration standard. If/when I manage to to do this, I will be sure to let you all know (and revise my lumen estimates accordingly).

Again, the point it that I don't know what the "true" lumen value is for any of these lights - but the approximate relative difference between them remains consistent over time in my testing. I would use my lumen estimates as just that - estimates to gauge relative output performance between lights I examine.


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## Colonel Sanders (Jul 26, 2012)

Thanks, now I know that my EA30 is correctly calibrated. I got pretty much the same throw values done at 10m as you did on the X10. However, I have now tested three of these lights and there were variances. One was in the 28k range, one about 24.5k, and one close to 27k. The tailcap current readings also varied a bit (about .1-.2a if I recall.) Emitters and circuits vary.


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## Oztorchfreak (Jul 26, 2012)

What is this?

A war against a guy doing a great job.

Are one of you turkeys going to step into his shoes?

Give him a break!!!

Selfbuilt has allowed myself and many others decide on which flashlights will do the job we are looking at when most of us flashaholics don't have the time, experience, test equipment or just plain knowhow to help all of us here and at other review sites and forums.

Lights vary in so many ways that he can't be expected to know how your individual light is going to behave.

There are variants in LEDs, drivers, reflectors etc to name a few.

Why this sudden attack on this guy, what is your grudge?

Are you jealous that he is good at what he does or what?



You Morons!!!


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## selfbuilt (Jul 26, 2012)

Colonel Sanders said:


> Thanks, now I know that my EA30 is correctly calibrated. I got pretty much the same throw values done at 10m as you did on the X10. However, I have now tested three of these lights and there were variances. One was in the 28k range, one about 24.5k, and one close to 27k. The tailcap current readings also varied a bit (about .1-.2a if I recall.) Emitters and circuits vary.


Thanks for the variance data. That's exactly what we need more of, but it's hard to get repeated light samples with any one given meter. The range you reported seems quite believable to me.



Oztorchfreak said:


> A war against a guy doing a great job.


No, there's no attack here.  Unless there's some discussion going on elsewhere that I am not aware of. 

I certainly take no offence to anyone quering the methodology - it is important it be discussed. If I seem long-winded in my responses, it is not because I feel defensive - I just want to make sure that I am clear in my explanations, so people accurately understand the limitations (i.e., what can be controlled, and what can't). That's the purpose of these sorts of threads - a place to give people an overview of my methods, and a chance to discuss (rather than gum up the actual individual reviews).

Lumen estimation remains a constant problem for all us hobbyists. Personally, I would have preferred to just stick with my lightbox ROV values, but I know they aren't linear for perceived lumens. The lumen estimate calibration method is subject to limitations, but I know it produces better relative magnitude differences. It is mainly the absolute values that are most suspect. Of course, that's true for anybody's integrating source.

I encourage anyone to express questions/concerns, challenge underlying assumptions, etc. A chain is only as good as its weakest link! :wave:


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## Oztorchfreak (Jul 26, 2012)

selfbuilt said:


> Thanks for the variance data. That's exactly what we need more of, but it's hard to get repeated light samples with any one given meter. The range you reported seems quite believable to me.
> 
> 
> No, there's no attack here.  I certainly take no offence to anyone quering the methodology - it is important it be discussed. If I seem long-winded in my responses, it is not because I feel defensive - I just want to make sure that I am clear in my explanations, so people accurately understand the limitations (i.e., what can be controlled, and what can't).
> ...



You are so humble Selfbuilt and do not let emotions take over your responses, but I feel anger at these people as I have followed your reviews for many years now.

It is not just about distance, lumens and peak throw etc.

It is your detailed examination of the products and the great photos that you take that clearly help us decide on which light will do the job and if it has any potential problems.

Good work and keep doing a terrific job.


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## selfbuilt (Jul 26, 2012)

Oztorchfreak said:


> It is not just about distance, lumens and peak throw etc.
> It is your detailed examination of the products and the great photos that you take that clearly help us decide on which light will do the job and if it has any potential problems.


Thank you, I appreciate the support. And the support of all the members here. :grouphug:

I too believe the value of the reviews is more than just the quantitative measures (although they are important for comparing relative performance). From the beginning, my main goal has always been to provide as accurate as possible comparator data, so people can make their own decisions based on objective testing (relative to other known lights). The reviews have grown longer in qualitative comments (with pics, videos, etc.) mainly at the request of other members. Sometimes, I'd like to go back to just doing simple runtimes (which would drastically shorten my review times!). :laughing:

But again, I also appreciate the chance to have these methodological examinations on occasion as well.


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## madecov (Jul 26, 2012)

very nice Selfbuilt. Your reviews are always great and most importantly* consistent*. I appreciate the time you take on them.


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## Colonel Sanders (Jul 26, 2012)

Oztorchfreak, I'm not really sure who you are referring to as attacking our very respected selfbuilt but I certainly hope you didn't get any impression that I was...because I wasn't in any way shape form or fashion.  And if I thought for a minute that someone was bashin' on selfbuilt, believe me, I'd be the first one to his defense.


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## GordoJones88 (Jul 26, 2012)

Oztorchfreak said:


> What is this?
> 
> Are one of you turkeys going to step into his shoes?


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## orbital (Jul 26, 2012)

Oztorchfreak said:


> What is this?
> 
> A war against a guy doing a great job.
> 
> ...



What the _XXXXXXX_____ are you taking about!??



..................


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## Bullzeyebill (Jul 26, 2012)

orbital said:


> What the _XXXXXXX_____ are you taking about!??
> 
> 
> 
> ..................



Ok guys, enough re Oztorchfreak's comments. Selfbuilt handled the situation, so that's the end of it.

Bill


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## Mr Floppy (May 30, 2013)

Sorry to bring back this thread but I was just wondering about what the raw lux reading is in your lightbox tend to be?

Basically, I am making a "milk carton" lightbox (which I assume is 2 litres? We don't have milk in 2 litre cartons but fruit juice comes in 2 litres).

I'm building a light meter using TSL2561 ambient light sensor from Adafruit and a Raspberry Pi. The problem is that the TSL2561 only goes up to 40,000 Lux so some of the higher powered lights may be over that in the box I'm guessing?


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## selfbuilt (May 31, 2013)

Mr Floppy said:


> Sorry to bring back this thread but I was just wondering about what the raw lux reading is in your lightbox tend to be?


To be honest, if I were starting out today, I wouldn't recommend the milk carton lightbox approach (which was common when I started). Although I was able to calibrate my lightbox to estimate lumens (based on my fairly extensive dataset and comparators), it is not starting out with the best tool. While a sphere would be better, I am personally intrigued by the twisted PVC "tube" designs people are experimenting with today. Whatever method used though, you will need to develop your own calibration standard (i.e., none of the home-made contraptions are going be properly linearly integrating over all ranges). 

In terms of the raw lux measures, 40K range should be fine. Due to the fact that the sensor is only receiving indirect reflected light (i.e., in any design, the emitter should not be "visible" to the sensor), even heavy output lights are well below that (with most designs).


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## Mr Floppy (Jun 2, 2013)

selfbuilt said:


> Whatever method used though, you will need to develop your own calibration standard (i.e., none of the home-made contraptions are going be properly linearly integrating over all ranges).



The main reason why I was going to go a milk carton was to try and get as close to your set up and calibrate off your numbers as I have a subset of the lights you have tested. In the past I've tried other homemade designs, including sphere type ones, tents, cardboard boxes, eskys, but my graph points stretch and curve away from yours way too much. I know it wasn't going to be linear but at the high output end, they curve!

Cheers for the confirmation of the raw lux numbers. It saves me from having to build an ADC as the sensor above has one built in.


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## selfbuilt (Jun 2, 2013)

Ah, well, then you should definitely see my comments on the lightbox design that I use (on my Methods page). One thing I may not have mentioned - I modified Doug's original design from flashlightreviews.com to have my lights enter from the bottom of the carton, with the sensor located on the side just up from the base. This way, the light's own bezel acts a baffle, and I have various size cut-outs that I use to surround the bezel (and prevent too much light from escaping back out of the box). This arrangement facilitates my ability to automate runtimes easily, since the light lies on the ground.


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## Mr Floppy (Jun 3, 2013)

selfbuilt said:


> One thing I may not have mentioned - I modified Doug's original design from flashlightreviews.com to have my lights enter from the bottom of the carton, with the sensor located on the side just up from the base. This way, the light's own bezel acts a baffle, and I have various size cut-outs that I use to surround the bezel (and prevent too much light from escaping back out of the box). This arrangement facilitates my ability to automate runtimes easily, since the light lies on the ground.



I did notice that and I've done the same thing. The only difference is that there is a pouring hole at the other end that I have taped over and painted the inside white to get it as uniform as I can. I didn't realise that you lie the light on the ground though. So the cut outs are not in the centre? Just wondering about that as I was considering various holders and platforms to raise the light to the centre of the light box.


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## tobrien (Jun 7, 2013)

madecov said:


> very nice Selfbuilt. Your reviews are always great and most importantly* consistent*. I appreciate the time you take on them.



consistency is key and selfbuilt never wavers


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## Capolini (Aug 12, 2013)

Good job! You are a hard working, giving and dedicated Man! Before I joined here I would see your reviews when I "googled" one torch vs. another.

I can see that your accuracy has improved with your new equipment! I have a Jetbeam BC-40 and your revised ratings are very close to theirs 

My other Three great lights are the original TK-75 and the "New" TK-75 [I think I am crazy!!] which I just got today, and the Black Shadow Terminator[newest one].

Keep up the good work!!

p.s. when I get a job, I will gladly contribute to your battery fund. I need one soon!! Buying flashlights without a job is not too logical! Nor is it conducive for a good relationship with the wife!! Don't tell the Wife!!

ciao,,,,Roberto,,,,"Capo di Capo"


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