Flashlight beam distance always be a measurement of the performance. For Luminous Flux, we have Intergrating sphere. However, how to quantify the distance should be various.Here is to ask any professional method to conduct this test?
ANSI FL-1 defines it as sqrt(candela/0.25).
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And candela itself is usually measured as lux at 1m, since there exist many devices that measure lux (lm/m^2). This works by small-angle approximation.
However, the above quantities/measurements are based on an assumption that the flashlight’s beam is a cone that shrinks to a fine point at the source, which becomes increasingly untrue for throwier lights due to their very large reflector. For these lights, the beam looks like a cylinder that never spreads out at a short distance, rather than a cone.
Thus, literally measuring the lux at 1m yields inaccurate measurements as the beam needs more distance to attain the right shape to be approximable by emission from a point source.
For this reason, one often needs to measure the intensity at, say, 10m, and scale it up to obtain “effective” intensity at 1m. The resulting measurement (say C candela) should be interpreted as, “if a point source matches the flashlight’s intensity at very far distances, then that point source would have C candela”. Or equivalently, “then that point source would have an intensity of C lux if measured at 1m”.
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I guess I’ve been here long enough to justify buying a lux meter … Whats the current reccomenation from the BLF hive mind? Looking budget end of the spectrum (value for lowish money) rather than super high precision…
WT81B: Fairly high resolution for its price, high sensitivity, high range, temperature compensation and bluetooth.
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Great I’ll check that out, thanks!
Out of interest, what’s the use of the BT?
Intergrating sphere is enough. Sensor itself cannot suffer that strong lux. The intergrating sphere coating with diffuse reflection material inside to reduce and test. Should be fine for general use. And I saw some example of making a sphere with low cost using our daily materials in the forum. Suggest you to check.
Oh Thank you! Roughly calculation that almost commercial light with a wrong distance…
Appreciate that!
In this case, there can be some cheats to obtain high lux but actually with not that good using experience, which means design only for good performance on the paper.
Yep–whenever a measurement methodology comes out, people will always find a way to cheat it. A great example is the infamous 10% rule for ANSI runtime measurements.
With lux readings, I don’t see an easy way to cheat, but have seen many examples of reviewers getting obvious incorrect numbers due to faulty methodology, with the most common mistake being a too short measurement distance.
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I noticed those formulas really work in theory only, my e10 green beam is 675m, according to acebeam, but i could not reach that far in real world. I also noticed it greatly depends on air conditions, with high humidity suspended water droplets really screw your range
Agree.
Lux is based on the stuff which exposed in the light AND it is not about that stuff. So it is measurement of “brightness” of light in another aspect.
However, as a consumer, we always don’t care about so much tech criteria but only do the comparison. That’s why we always see 2000m range and 1000lm…
Definitely right. Although it has a theoretical number, it really depends on the actual using condition, which exactly can be technically translated to reflection and refraction.
The formula makes no claims about real-world visibility–it’s just a number. How to interpret this number is entirely up to the user.
A user with very good eyesight trying to spot large objects may find the ANSI m a good estimate of usable distance. A user with poor eyesight or looking for details may find 1/4 the ANSI distance more appropriate. And as you pointed out, things like backscatter can easily complicate the situation.
I’m not sure if I understood what you said.
I’ll assume that a language other than English is your primary language, and that you are using a translation service. I suggest also including your message in the original language, in addition to a translated copy. This prevents information from being lost by your translation service, and allows the reader to use our own translation service (or our own fluency in your language!) to understand what you mean.
0.25lux as a beam distance might have worked back in the day when lights were less powerful, but who’s going to be able to see something lit up with the equivalent of moonlight 600+m away…?!
I normally just half the distance to get a more reasonable value.
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I’m talking about definition of lux and it is using a translator on my mind…Keep going with more communications.
The question, in short, is what is the bearing or standard which a target subject has on lux reading? I.e., vantablack surfaces would read close to 0 lux at most ranges.
**In real world usage, it’s difficult to find a subjective standard, as 10k lux looks different on different surfaces
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Not to mention, at closer ranges, the cumulative lux of atmo scattering ends up being brighter than whatever lands on target at that lux…from the viewer’s perspective, the beam may be brighter than the subject, lol
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I just realized, the title asks how to measure, not how to calculate it, a laser rangefinder would be ideal for that, shine your light at distant object and use a rangefinder to measure the distance, keep moving the beam to spots farther and farther. or use google earth. This way you can measure actual useful throw in real world.
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