When following instructions, you find the formula dictates inverting the fraction and multiplying, so 30 divided by 1/2 (30 * 2) + 10 is indeed 70. So many people get in a hurry, don’t pay attention, and end up with the wrong answer. Including teachers.
Kudo’s to those caught paying attention. 
Edit: FWIW this question is a serious stumbling block when asked where no calculator is present.
About the math question. People are on the same page. That is a good thing right? I think so. :)
[quote=DBCstm] Do you know, for instance, that rdrfronty himself built my lightbox, Tom E's lightbox as well as RMM's lightbox? All of ours are FROM rdrfronty. [/quote]
I had a feeling about that, but I was not 100% sure. And based on your guys numbers its not that hard to notice. The issue is that you guys are not on the same page as many others. You guys are generally higher or much higher when it comes to lumen. Who else have as high lumen numbers as you guys? Who have higher numbers?
Who gets higher lux readings?
The only way for others to get those high numbers are either to try and adjust their calibration accordingly, or get the same lightbox/tube thingy you guys are using. As far as I know, its just form of tube with bends or something, not even a round sphere, so most would never agree to use such a device even if they could agree on the calibration.
When is the last time you bought a light from a well respected premium manufacturer and measured similar numbers or lower that was stated? How often have you measured lower compared to how often you measure higher? I have a good feeling you are used to be measuring higher.
I know your K50 numbers kcd numbers are more than 50% higher than Supbeams claimed number. I know your K50 lumen numbers are about 4% higher. I know your TK61 lumen number is about 20% higher compared to Fenix. I dont know what your TK61 kcd number is, but I bet it was higher compared to Fenix. Its not ideal for everyone to try and get a calibration as high as you guys because then they would purposely have to increase their numbers beyond what many manufacturers do. Manufacturers that many use as reference. And the purpose for non modders and reviewers are generally to be close to manufacturers numbers. Which supposedly have expensive calibrated equipment following the same standards.
One guy, rdrfronty, built your lumen boxes/tube thingys (and did the calibration?). Your boxes generally produce higher numbers. What is the point of only having comparable numbers with each others high numbers, when you could be having numbers that are comparable with so many others while having comparable numbers with each other?
Many others have individually done calibration work, and been able to match each other fairly well. You guys are typically higher. So it would make more sense for rdrfrontys box to match those other guys right? I mean, wouldn't that make it easier for everyone to compare numbers from different people?
The point is, me, Tom and Richard build lights for rdrfronty and manxbuggy1. So we all know what each other is getting and how/why. That was the original point.
These numbers have always been shared as a YMMV point of interest.
I have actually had lights fall below the manufacturer’s advertisted numbers. And my lux numbers have zip to do with my light box, obviously, aside from using the same meter. So if the meter was faulty, wouldn’t it also show up in the box?
I’m not trying to be argumentative, and have no feelings one way or the other. Just want to to know what is right and how to go about making it happen.
I will look into how I perform my 5M lux testing and see if I’m doing something wrong there that would account for what you say. I AM new at this, and also very forgetful, so it’s likely to be some part of my process at fault. Worst comes to worst I can take the light outside and do a 800M test. By the way, rdrfronty and manxbuggy1 did just that, at 895M they tested about 15 lights previously tested at shorter distances and found them to be accurate on the meter even at that range. I usually always try to include beamshots to show just what the light is doing to verify what my box shows, I don’t touch up the photo’s, but I do take pics in RAW and apply sharpening and noise filters. My base photo settings were derived originally by optimizing the photo to represent what I saw at the time and setting with my own eyes. After doing that quite a bit, I standardized those settings and use them all the time, even when the big throwers are blowing out my 97yd test subject with their intensity.
It’s all relevant, as you well know, and seeing a picture, reading the numbers, it’s never going to replicate holding the light and seeing the result from behind the battery tube. The real problem is that we’re trying to put subjective findings to black and white numbers.
Let me also say this, might clear some of the confusion concerning my numbers. I read the lightbox at start up and after a timed period, and list the numbers as such. When I take a lux reading I observe the 1st numbers to hit the meter, and also take into consideration how that number changes from start to finish of the test. BUT, I list what I saw. If I saw it, then the meter said it and that’s what the light did. I look at it in terms of being an end user. If I’ve got fresh cells in the light, and the light comes on making 479393Kcd then that’s what I say I saw. That’s what an intruder in my house will see when I hit him with it. That’s what the coyote 311 yds away sees when I fire up the light. In the real world, there just ain’t nobody waiting around 30 seconds for the light and batteries to stabilize. In 30 seconds, when ANSI is satisfied, the light has been off and the blood is being cleaned up…
I do move the light around, look for the most stable reading, and usually that’s the one I post.
In my little lights, 30 seconds into the ANSI test the cell is dead. How do you compute that? With a 300mAh cell giving 3.34A, what’s a 30 second ANSI test? Irrelevant, that’s what. It’s the sheer power that first puts spots in your eyes that matters, how fast the lumens are falling after that is really of no significance.
Perhaps my end user point of view is the reason my numbers differ from the bookworms.
I definitely agree with RaceR86 that getting everyone on the same page would be desirable, IF and only if that actually means the readings would be more consistently accurate. But I see no clear evidence that would be the case…he is just assuming that the “ANSI people” are correct. There are people on both the high and low ends who have done an amazing job of calibrating, comparing, and double checking their numbers…to assume that either camp is simply doing a better job than the other is not really going to help matters. I think some of the minutiae that has already been covered is missing the bigger picture…every system, even NIST certified ones, will have some variation, because the lights (and the cells, and the testbeds) all have some variation as well. Garbage in, garbage out…it is not possible to reduce variation to nothing except for substituting guesses for reality (which would be a step backward).
I for one still greatly appreciate the effort that goes into home testing, because it is useful for RELATIVE comparisons…you can at least determine if a light is dramatically under-performing, and possibly take steps to address the issue. My general thought is that more data is better…if you want one number, than you can average all readings for a given light. If you have a large enough data set, that is likely to give a reasonable estimate of lumens. And really, for most of us, that is the goal.
This thread was certainly an interesting read. I’ve been a member of CPF for a while, and finally decided to get in on the action here too. Can never have too much information!
Max Output (Lumens) is measured in an integrating sphere or home-made lightbox.
Peak Throw (kcd) - the ANSI FL1 standard requires measures be taken at 2m, 10m, or 30m from surface of the lens, as appropriate for the size of the flashlight head and output width. It seems to me that this measurement does not involve a lightbox or integrating sphere but requires a dark space with the appropriate distance available. For big head throwers, the appropriate distance would be 30m.
The calibration of the lightbox and the calibration of the lightmeter affects the measurement of Max Output (Lumens).
The proper procedure/setup and the calibration of the lightmeter affects the measurement of Peak Throw (kcd).
RaceR86 seems to be concerned with Peak Throw (kcd) numbers so the distance used should be the major factor not the lightbox calibration.
Selfbuilt says he used 1m to 5m. What distance do others use?
But recently I’ve discovered, through modding the TK61, that it will take at least 15M to really get an accurate reading. 30M is going to be tough for a lot of people. I can probably swing it fairly easily in one of our barns or even outside under optimum conditions, but it will take some set-up of course. I might go ahead and set it up for easy consistent results in our barn. I’ll check it out, now that the family of foxes have moved on…
thedoc007, welcome to the forums!
Glad you found the thread interesting and joined the discussion. :beer:
[quote=GeoCan46] RaceR86 seems to be concerned with Peak Throw (kcd) numbers so the distance used should be the major factor not the lightbox calibration. [/quote]
How the lightbox/sphere, etc is calibrated is a concern when it comes to lumen. How the lux meter is calibrated is a concern when it comes to kcd numbers. This thread is about both of those numbers. Some of the guys with the highest lumen numbers also have the highest kcd numbers. In some cases I talk about both at the same time. Sorry if im not being clear.
IMO lux meters needs to be calibrated as well. Most guys seems to just go with what the meter tells.
I do lux readings at 10m. After 30 seconds. Usually between 30 seconds to 1 minute, but as close to 30 seconds as possible. I either use live view or a recording DSLR to see what happens/happened at the lux meter all the way from startup to one and a half minute while im searching for the highest readings.
I think you need to get your numbers calibrated to ANSI standards and not "real life in texas". 0:)
I use a LX1330B for throw and lumens… I agree - if anything the throw is a little bit high on both the LX1330Bs I have… FWIW I do get a reading of 938kcd on the deft x that Michael certified at 931k.
I will be the first to admit that my sphere is quite crude - its made from paper mache and spraypaint… I have fairly high confidence in it though since I used a number of ANSI lights to calibrate it and they all landed within a few % of each other in terms of a corrective factor. Aside from buying a professional integration sphere, its as good as it gets for now. I can reproduce the same numbers - usually within 1% every time. If nothing else the database I have over on vinhs forums has grown large enough that it should be able to serve as a relative comparison of many lights that hopefully can be useful to the community 
And yes - I would rate the FET driven securitying T6 4c model as 3800 ANSI OTF - but remember - I have a UCL installed on mine… stock should be a little lower with a regular glass lens
JMpaul320, im curious. Have you measured stock TK61 and stock K50?
How would you compare your lumen and kcd numbers compared to selfbuilt? Or compared to others?
I’m a bit late to the party (er, thread)… but I’m totally onboard with trying to get better calibration for everyone.
I have a cheap HS1010A lux meter and so far have only made a simple milk carton light box. Also, for really really low readings (too dim for the light box), I’ve found that it works reasonably well to simply hold a medicine bottle cap over the lux meter and press a light directly against the cap. Yes, it’s prone to errors due to beam pattern, but it’s better than any other really-sensitive approach I’ve tried.
The plan is to make a proper sphere sometime, but I’ve been busy.
As for calibration, I use the lux readings directly (tested first with some lights of relatively well-known throw, decided the values were close enough). For lumens, I’m using a simple linear correction factor chosen to most closely match my Zebralights. It’s not the greatest calibration, but so far it has been surprisingly okay for “ballpark” purposes.
I hope to do a better calibration curve like what selfbuilt did, but again have been too busy so far and don’t really have enough data points to do it properly.
On a related note, I made a publiclab spectrometer… and getting meaningful readings from it is surprisingly difficult! Tiny changes in the angle of the light or the meter can produce huge changes in both the magnitude and the shape of the spectral histogram, and it gets overexposed pretty easily. I mean, looking at a red XP-E2 it gave me a clean result totally within Cree’s spec… but comparing two different white LEDs is really difficult even if one is 65CRI and the other is 90+.
Ansi FL1 “standard”, extreme example chart.
if one take it on 30 seconds, other using 1 minute and another one on 120 seconds, what is the number for this one ?
It’s from Chloe’s review for Olight ST25 , about same pattern with Bigmac_79’s
Imo, the best measurement should be like this
I do not have a stock tk61 or stock k50 to compare to unfortunately…
most of the lights I have measured so far have been modded lights (aside from the ANSI lights used to calibrate the sphere)
I would be very interested to test some of the SAME lights that selfbuilt measures (or other members measure) with my setup and equipment - just to see how they compare. I think that would be informative. The few OSTS lights that I tested from Michael were with 4-5% of his ANSI readings he sent along with the lights. (TN31mb & deftx). Also - I was able to reproduce the Tom E lux measurement on a Modded Maxtoch he sent me within 3%.
This could all just mean we have the same light meters though LOL.
JMpaul320, just curious, again.
You have measured many ANSI rated lights in order to get your lumen calibration. Did you try to calibrate your lux meter in the same way, using the ANSI rated lights as reference?
Im not surprised your lux reading were close to Tom E. Did you compare lumen as well?
No - I did not calibrate for lux the same way - I could try I guess - I just thought I would get a wider range of lux across lights… I guess it could be my next project
Tom E Maxtoch numbers
Panasonic PF
lumens: 1,615 at start, 1,540 at 30 secs,
throw: 358 kcd, measured at 5 meters (did get 344 kcd on an earlier test)
Jmpaul320:
Samsung 20r
1538@ turn on
1425@ 30 sec
626 mid
266 low
Throw - 358,000 lux
Perhaps we all just need to take a trip where we bring our meters over to someone with a lot of lights and then all measure the whole set, and calibrate our results to each other. At least then it’d be relatively consistent. But then, I think a few BLF members have already done that, more or less, with nearly-identical spheres and a single set of lights shipped around. And the results still vary.
Was that taken with the cells at 4.19V or 4.21V? What was the ambient room temperature? How deep into the IS aperture was the light, and was it dead-on or tilted? Did you measure at 30 seconds or 28 seconds? Did you let the light cool down between measurements? Etc… Even with just one light and one meter, the results still vary… especially if two different people operate the equipment.
Each person’s results are really only comparable to the same person’s other results, assuming they spend the effort to do things the same each time. I can’t say whether my D25A XM-L2 is actually 201 lumens or 141, but I can at least say it puts out about 78% more light than a L3 L10-219A.
So, to make one’s measurements more meaningful, it is very helpful to include results from several different lights at the same time, to provide context for what the numbers actually mean. The person reading it can then scale the values accordingly, if they have any of those lights available as a reference point.
Would certainly be interesting to see what you ended up with on your lux meter if you tried to calibrate it based on your stock ANSI rated flashlights. :)
No surprise to see that Tom E`s lumen number were higher compared to yours on the exact same light (About 8% higher at 30 sec).
I was expecting at least 8% difference, but strange that people who use so many ANSI rated lights can have such a "large difference". Especially when you say that you can usually be within 1% when you measure your lights and that ALL your ANSI rated lights were within a few percent in terms of corrective factor.
Just sharing observations...
All this reminds me of the story of the dolphin(porpoise?) that was found young, weak, injured. They took it in, gave it medical care, nursed it back to good health…spent 10’s of thousands on getting it ready to return to the ocean. They made a huge deal of it, had various news agencies present to document it’s release and had it tagged so they could follow it’s progress, the whole 9 yards.
When they released it, it swam off and leaped out of the water and right in front of all the cameras and scientists, an Orca ate it.
I hope there was a petition put out to get rid of all Orcas.
Point being, all the effort to be perfect is taking place in an imperfect world.
