No, he obviously meant the lux calculated back to 1m. Seriously, you don’t expect the meter really showed 144k reading at 100m do you, because that would mean he’s doing 1.44 Gigalux @1m, and it throws 75km. :bigsmile:
Getting higher calculated reading as the range increases is understandable, as light collimation is completed. Multi emitter normally have longer collimation range.
No, that is a fact. I promise you. The stronger the thrower, the longer the distance needed to properly test the light for lux. Nothing wrong with the meter. Do some research here and on the other forum you’ll that’s how it’s done.
For an example, a test of my sr90 (dedomed) measured 78 lux at 50m. To calculate the true lux you multiply the distance towards itself, then multiply that with the measured lux. So here 50 x 50 = 2500, 2500 x 78 = 195,000. That’s how you have to do the throwers.
Now for the reverse. Mr sr90 will do 195k. To got the throw in meters from that number, you divide it by the desired lux target, .25L in our case, and the find the square root of that number. So 195,000 divided by .25 = 780,000, and the square root of 780,000 = 883m. That is how to get the ANSI rating from your Lux.
Yes, I am saying the lux after calculation back to 1m. Now we are talking about single emitter. If his meter is linear, he should get result below:
X = 2m test, lux calculate back to 1m
Y = 5m test, lux calculate back to 1m
X>Y
But now his meter shows that Y>X after calculate back to 1m.
It doesn’t make sense as at 5m, more lights get out of the hotspot. Only explanation is his meter is not linear.
I am not challenging ANSI or other so called fact.
But I think if you think your SR51 is 50kcd and the meter is measuring it correctly, then you should be able to measure your SR90 which you think is about 195k at 2m. Because at 2m, your meter should measure about 50kcd, times 4 will calculate back to about 200kcd.
I believe all these low cost meter has a sweet spot, it is not calibrated from 0.25 to 200kcd, they might not be uniquely calibrated at all but just loaded with generic calibration data.
i’m curious how do you guys read the meter… how far from the wall did you aim it?
did you guys set it at 100X?
It has nothing to do with the meter. It’s just simply a fact that the the more throw a light has, it will need a longer distance to get proper readings. Here are some confirmation of what I’m saying -
I do the readings at many different distances and at many different meter settings. I mean. I always test all lights at a true 1m to begin with. Out of about 50 lights I have tested, roughly 90% will read very close to their true lux numbers when done at the 1m.
For the meter settings, they always have to be adjusted to match the light and the distance. My meter measures in increments of 200, 2000, 20000, & 200000 depending on the settings. So for an example doing a lux reading at 1m with the SR90 I have to have the meter in the “up to 200,000” setting since it measures about 90,000 at that distance. But if I test it at say 50m, I can keep it the “up to 200” setting since it measures 78 lux at that distance.
So a test at 1 meter needs no adjustment. But that reading is also very inaccurate for the big lights. Now with the 50m 78 lux reading I simply multiply the distance times itself (50 x 50) and multiply that towards the reading (78). So 50 x 50 = 2500. 2500 x 78 = 195,000. Thus the 195kcd reading.
All lights get calculated like this - distance x distance x reading. You just have to have the meter at the proper setting to match the lights potential lux at the tested distance.
You can actually get pretty accurate numbers on throwers at distances of 100m, 200m, & more. But usually I go with -
Lights under 30K, 1m test is fine
Lights 30K –60k, 5m is a good distance
Lights 60k - 100k, 15m is good
Lights 100k - 200K, 15-50m is usually good
These numbers are not concrete however. Beam types, amount of LED’s, etc. can effect those testing ranges needed. That’s just the way it is.
But again, because all these numbers can get tricky to find the best testing distance or to find the “sweet spot” on the spot, we also do true throw testing. Meaning one person stands at 0m and shoots at the meter at distances of 100m, 200m, 300m etc up to the lights can only post a reading in the .2’s with the meter.
And 95% of the time, those numbers I get by actually measuring the true throw match with in a few percent of the calculated throw we also got testing in the 1m-50m readings.
I do know how to do these readings guys. And I do know how to use my meter properly. No guess work here.
You just proof my point is correct with the 2nd CPF link. mudman cj of the original post found the “sweet spot” for his meter. His meter is not linear, that is why when he measure high intensity above 18k lux, the measurement is not correlate well with inverse square law, so he deleted those points. No way he suggested to test at 15m though, his experiment was from 1m to 6m.
This points out to one thing. You need to find the sweet spot of your meter that follow inverse square law. For example, mudman cj’s meter is before 18k lux. When you found the sweet spot, then you just need to adjust the distance to make your meter to read around that sweet spot.
And I don’t think measure at long distance so that meter read very low lux is good idea as it is close to noise floor.
Measure in long distance can have two problems. The multiplier is large, for example 50m will be 2500. And loss of light in air particles will result in lower lux.
Again, that was cause by the beam itself, not meter. That simply proved the FM3x beam wasn’t fully converged 1.5m, 2m, and 2.5m. After that, the beam follows the inverse square law, so that’s the minimum convergence point.
If it was the meter, then his first reading for the TK20 would also has to be adjusted. But that wasn’t the case.
I believe you base on manufacturer or forums information to judge your lux reading.
And you found that for 30k lux, 1m is fine. So I am thinking your meter sweet spot is below 30k lux. But you haven’t do the same analysis comparing with inverse square law. Very possible your meter is good at 15k lux.
Measuring instrument has limitation. Many effort are put into them to calibrate them. Very expensive proper calibrated light source traceable to NIST needed to calibrate them. Don’t bet on those USD40 lux meter do calibration from 0 to 200k lux. They are usable for relative comparison or rough estimation.
so if i put my meter at 80’ away and shine it with the light… and if the meter read 34,
is that mean the light is 217600 kcd? that would be cool especially coming from $10 HD2011 flashlight 
His TK20 measure about 6k lux which is below 18k lux, that is the reason it is good at 1m because it is in linear range for his meter. It is the meter causing problem. Light travel in straight line. It won’t bend. Of course, I am not talking about measuring at 1cm as reflector design will be affecting. I think 3m will be adequate for all hand holdable flashlights.
You won’t read 34 if it is 80m away with your HD2011. :bigsmile:
I try to point out, the bigger the multiplier, the bigger the error get magnified. All test instruments have error.
No. 80’ is 24.38m. So 24.38 x 24.38 x 34, equals 20.2K. Too low so either you didn’t find the hot spot or your distance is off.
Guys I’m not guessing with this crap. If you don’t believe me that this is the proper way to use a meter for throwers - then I give up. I know its correct.
It’s not the meter. My numbers and testing numbers match what the manufactures ANSI rate their lights at. It’s not guess work, its all about beam angles, reflector size, emitter qty, lumen output, and beam convergence.
sorry rdrfronty… not doubting your methods of using light meter… i was just trying to learn it myself…
i always shoot the meter from 1M away just to see high the #s is :bigsmile: , had no idea how to calculate the lumen…i always thought the higher the #s that’s mean it’s brighter… but some people in here pointed that out that’s not always the case
i guess i learned something tonight 
It’s all good man. And generally what your saying is true - testing most lights by shining at your meter sensor at 1 meter will tell which one will be the best thrower. Buts its not a 100% rule though.
We we started in this we also thought it was adequate. But then a few lights were were reading off from what they should be - the sr90, derelight, A60, & 35wt hid. With more research we discovered why - true throwers need more distance for their beam to converge into its true concentrated hotspot. Now since we discover that, the numbers ALWAYS come very close to real life throw and the ANSI rated throw. The tn31 and btu we’ve now added to that list of our lights that need more meters to read correct. Even some of the better zoomies will need more than a meter.
some interesting pictures comparing the tk70 and btu
i think these heads were most likely made by fenix as seen by the extreme high quality threading. probably the fenix engineers were doing trials with 18650s to make their final product the th75 .and these left over ones were auctioned off to our Ric
apparently the bighter one is the btu on turbo 
Turbo on the BTU is 3 minutes… The 70 holds the 2200 for like a hour and a half
yes true ,I think a higher quality circuit /Toughened ultra-clear mineral glass with anti-reflective coating and may be the reflector as well are whats holding the btu back from its full potential.
It could easily get 3200 lumens with u2 and up to 140000 lux readings with Integrated “Precision Digital Optics Technology” that provides extreme reflector performance” used by high end manufactures .
tk70 on turbo and on the right is btu on “high” mode
The Btu’s 2000 lumen high mode seems to compete wih the TK 70s 2200 lumen turbo mode for 1.5h
distence shots may tell a diffrence or may be :weary: not
