# Lux to Lumens



## Bigwilly (Oct 2, 2015)

Is there a way to convert lux into lumens? Using an Android app to measure lux, can you convert it to lumens or is there an app for android to use my Galaxy S4's light sensor to measure lumens?


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## reppans (Oct 2, 2015)

Assuming you have a good way to collect and homogenize the light (ie, integrated sphere, DIY lightbox, etc) then just use a constant/multiplier derived from a known output calibration light. Keep in mind that every manufacturer, and every CPF reviewer, uses different lumen scales... you'll probably develop you own based on the lights you own. 

There is only one reviewer here I've seen that claims true ANSI with laboratory tested calibration lights (ti-force), and I think he's right, but you'll need matching lights to calibrate.


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## Bigwilly (Oct 2, 2015)

reppans said:


> Assuming you have a good way to collect and homogenize the light (ie, integrated sphere, DIY lightbox, etc) then just use a constant/multiplier derived from a known output calibration light. Keep in mind that every manufacturer, and every CPF reviewer, uses different lumen scales... you'll probably develop you own based on the lights you own.
> 
> There is only one reviewer here I've seen that claims true ANSI with laboratory tested calibration lights (ti-force), and I think he's right, but you'll need matching lights to calibrate.


My question is if there is a calculation to derive lumens from lux. I understand using a light sphere or box to measure the lumens.


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## Lynx_Arc (Oct 2, 2015)

Bigwilly said:


> My question is if there is a calculation to derive lumens from lux. I understand using a light sphere or box to measure the lumens.


Try googling lux to lumens conversion


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## Bigwilly (Oct 2, 2015)

Lynx_Arc said:


> Try googling lux to lumens conversion


I did but all I see is a complicated formula involving area and a convoluted explanation. I try to not ask questions readily answered by googling.


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## reppans (Oct 2, 2015)

Bigwilly said:


> My question is if there is a calculation to derive lumens from lux. I understand using a light sphere or box to measure the lumens.



Yes, as above, there are online calculators - I think they might be reasonably useable with uniform beams like from a mule, but I'm curious how lux can be formula-converted to lumens with anything that has focused hotspot?


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## more_vampires (Oct 2, 2015)

Sticky thread on this: http://www.candlepowerforums.com/vb...-Easy-to-Understand-Lumens-Vs-Lux-Explanation


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## Swedpat (Oct 2, 2015)

The difference between lux and lumen is similar to the difference between pressure and force: Pressure=force/area, and in the same way lux=lumen/area. Therefore there is no standard conversion number between them. If you have 1lumen evenly spread across 1m2 you get 1lux over that area. 1lumen across 1dm2 will be 100 lux. To get 100 lux over 1m2 demands 100lm, and so on.


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## more_vampires (Oct 2, 2015)

Lumens is more like "all the photons," while lux is the concentration of them at a single point.

If you shined a light into a lux meter and panned the light side to side, you'd see different lux readings in the hotspot, spill, etc.

To get lumens, you must perform math and have a device called an "integrating sphere." The sphere must be "calibrated," but this doesn't really involve changing the sphere but coming up with the calibration math. It's kind of a bumpy road to get started.


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## drmaxx (Oct 2, 2015)

Bigwilly said:


> I did but all I see is a complicated formula involving area and a convoluted explanation. I try to not ask questions readily answered by googling.


Sometimes physics makes life complicated. However, google is really your friend here. It doesn't get simpler - see for explanation why in the threads above.


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## more_vampires (Oct 2, 2015)

If you're solving a circuit involving reactance (inductors, capacitors,) for example, it doesn't get simple. You gotta nerd-man up, get the pocket protector and graphing calculator, put tape on your glasses, cancel your dates, break up with your girlfriend, and face "imaginary numbers" head on.

Sound like I'm talking smack? Nope.
https://en.wikipedia.org/wiki/Imaginary_number


> An *imaginary number* is a complex number that can be written as a real number multiplied by the imaginary unit _i_,[note 1]​ which is defined by its property _i_2​ = −1.[1]​ The square of an imaginary number _bi_ is −_b_2​. For example, 5_i_ is an imaginary number, and its square is −25. Except for 0 (which is both real and imaginary[2]​), imaginary numbers produce negative real numbers when squared.
> 
> An imaginary number _bi_ can be added to a real number _a_ to form a complex number of the form _a_ + _bi_, where the real numbers _a_ and _b_ are called, respectively, the _real part_ and the _imaginary part_ of the complex number.[3]​[note 2]​ Imaginary numbers can therefore be thought of as complex numbers whose real part is zero. The name "imaginary number" was coined in the 17th century as a derogatory term, as such numbers were regarded by some as fictitious or useless. The term "imaginary number" now means simply a complex number with a real part equal to 0, that is, a number of the form _bi_.


You cannot solve a circuit involving reactance without this. To become the Flashlight Alpha Geek, you've got to wrap your head around math or else you're flying blind.

http://www.regentsprep.org/regents/math/algtrig/ato6/electricalresouce.htm


> In order to analyze AC circuits, it became necessary to represent multi-dimensional quantities. In order to accomplish this task, scalar numbers were abandoned and complex numbers were used to express the two dimensions of frequency and phase shift at one time.



Only then do you get Mountain Dew and pizza at 4 am.


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## Bigwilly (Oct 2, 2015)

Swedpat said:


> The difference between lux and lumen is similar to the difference between pressure and force: Pressure=force/area, and in the same way lux=lumen/area. Therefore there is no standard conversion number between them. If you have 1lumen evenly spread across 1m2 you get 1lux over that area. 1lumen across 1dm2 will be 100 lux. To get 100 lux over 1m2 demands 100lm, and so on.





more_vampires said:


> Lumens is more like "all the photons," while lux is the concentration of them at a single point.
> 
> If you shined a light into a lux meter and panned the light side to side, you'd see different lux readings in the hotspot, spill, etc.
> 
> To get lumens, you must perform math and have a device called an "integrating sphere." The sphere must be "calibrated," but this doesn't really involve changing the sphere but coming up with the calibration math. It's kind of a bumpy road to get started.





drmaxx said:


> Sometimes physics makes life complicated. However, google is really your friend here. It doesn't get simpler - see for explanation why in the threads above.





more_vampires said:


> If you're solving a circuit involving reactance (inductors, capacitors,) for example, it doesn't get simple. You gotta nerd-man up, get the pocket protector and graphing calculator, put tape on your glasses, cancel your dates, break up with your girlfriend, and face "imaginary numbers" head on.
> 
> Sound like I'm talking smack? Nope.
> https://en.wikipedia.org/wiki/Imaginary_number
> ...


Thanks guys. I think the pain meds is warping my brain. I don't know why I couldn't comprehend that, even though I understood lux and lumens individually but not together in context. I got it now. The explanations connected the missing dots. Thanks again.


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## more_vampires (Oct 2, 2015)

I like how you pieced that together. Smooth flow. Good work.


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## Bigwilly (Oct 2, 2015)

more_vampires said:


> I like how you pieced that together. Smooth flow. Good work.



Thanks again for the explanation.


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## more_vampires (Oct 2, 2015)

:thumbsup:


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## leon2245 (Oct 2, 2015)

> Lux to Lumens



Sounds like an Atari 2600 game title.


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## Bigwilly (Oct 2, 2015)

leon2245 said:


> Sounds like an Atari 2600 game title.



Or a bad 70's porno. Lmao


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## TeaSipper (Oct 2, 2015)

Lumen is the total amount of light while Lux is the intensity of light. For example, a thrower will show more Lux than a flooder but the flooder has more lumen than the thrower.


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## Bigwilly (Oct 2, 2015)

TeaSipper said:


> Lumen is the total amount of light while Lux is the intensity of light. For example, a thrower will show more Lux than a flooder but the flooder has more lumen than the thrower.



That's not quit accurate. I have a thrower with more lumens than a flooder. And a flooder with more lux than a thrower. You need to rethink your description


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## TeaSipper (Oct 2, 2015)

Bigwilly said:


> That's not quit accurate. I have a thrower with more lumens than a flooder. And a flooder with more lux than a thrower. You need to rethink your description



Seems I got something mixed here. What's CD?


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## Bigwilly (Oct 2, 2015)

Candela.


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## TeaSipper (Oct 2, 2015)

Ok, I looked up lux and candela and they seem to be analogous? I guess I won't get it.


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## KeepingItLight (Oct 2, 2015)

TeaSipper said:


> Ok, I looked up lux and candela and they seem to be analogous? I guess I won't get it.




Lux measures lumens per square meter at a given distance. The ANSI FL 1 distance rating for a flashlight, for instance, gives the distance at which peak beam intensity is 0.25 lux.

Candela gives the number of lumens per square meter, i.e., the lux, at a distance of 1 meter. Measurements of candela are usually made by measuring lux at distances greater than 1 meter, and normalizing back to 1 meter. This is so that a flashlight beam can focus properly before the measurement is taken. 

Note: Checking with Wikipedia, I see that candela has a more complex definition than the one given above. For flashlight usage, however, I think the one above will suffice.


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## Bigwilly (Oct 2, 2015)

KeepingItLight said:


> Lux measures lumens per square meter at a given distance. The ANSI FL 1 distance rating for a flashlight, for instance, gives the distance at which peak beam intensity is 0.25 lux.
> 
> Candela gives number of lumens per square meter, i.e., the lux, at a distance of 1 meter. Measurements of candela are usually made by measuring lux at distances greater than 1 meter, and normalizing back to 1 meter. This is so that a flashlight beam can focus properly before the measurement is taken.
> 
> Note: Checking with Wikipedia, I see that candela has a more complex definition than the one given above. For flashlight usage, however, I think the one above will suffice.



That pretty much sums it up.


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## lumen aeternum (Oct 3, 2015)

"Lux measures lumens per square meter at a given distance. The ANSI FL 1 distance rating for a flashlight, for instance, gives the distance at which peak beam intensity is 0.25 lux."

So if I'm standing in the dark, illuminated by some far off light source and 0.25 lux is shining upon me -- what do I see? How functionally bright is that?

If I am using binoculars to see a target 500 yards away being so illuminated, and they are really good binoculars wrt transmission losses -- what do I see?


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## lumen aeternum (Oct 3, 2015)

Uh oh. Now I want a "moonlight" level flashlight which has a distance sensor. I point the light at some object some distance away, adjust the brightness, and then the sensor maintains that lux as I move the light around, pointing it at things different distances away.

So I can point it at a tree over there, and then point it at my map, and then the ground in front of me -- and my eyes experience a constant level of brightness.


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## Bigwilly (Oct 3, 2015)

lumen aeternum said:


> Uh oh. Now I want a "moonlight" level flashlight which has a distance sensor. I point the light at some object some distance away, adjust the brightness, and then the sensor maintains that lux as I move the light around, pointing it at things different distances away.
> 
> So I can point it at a tree over there, and then point it at my map, and then the ground in front of me -- and my eyes experience a constant level of brightness.



Checkout the Nitecore Sens CR.


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## KeepingItLight (Oct 3, 2015)

lumen aeternum said:


> So if I'm standing in the dark, illuminated by some far off light source and 0.25 lux is shining upon me -- what do I see? How functionally bright is that?



If 0.25 lux is what shines on and around you, it will be roughly as bright as a full moon on a clear night. 

You've found the weakness in my hand-waving explanation. Lux does not really require a distance. That comes in because we are flashlight people, shining our lights from a certain distance away. 

If you check Wikipedia, you will see that the definition is more complicated than I described. Given a surface in space, lux measures how many lumens per square meter are striking that surface. In general, each point on the surface will have a different lux. One lux is equal to one lumen per square meter.

There are some vectors involved as well. In the flashlight world, we always assume our lights are striking a flat target that is perpendicular to the beam. If the target is not perpendicular to the beam, however, then it will receive less lumens per square meter, i.e., less lux!

This is easy to understand if you visualize a distant wall as the target. Suppose the hot spot of a flashlight has expanded to a diameter of 10 meters when it strikes the wall. If the wall is perpendicular to the beam, then all the lumens from the hot spot will hit along a 10-meter section. 

Now suppose the wall is strongly angled to the beam. If the angle is large enough, it might be that the hot spot lights up a section of the wall that is 100 meters long. You have the same number of lumens, but this time they are spread over a 100-meter section. On average, the lux at any point where the hot spot hits must be 1/10 of what is was when the wall was perpendicular to the beam.




lumen aeternum said:


> If I am using binoculars to see a target 500 yards away being so illuminated, and they are really good binoculars wrt transmission losses -- what do I see?



I think the answer here depends on the binocular. Those with wide lenses gather more light than those with narrow lenses.


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## drmaxx (Oct 3, 2015)

lumen aeternum said:


> "Lux measures lumens per square meter at a given distance."


It already was established that this is wrong. There is no given distance. It is just the light intensity at a given spot. 



lumen aeternum said:


> So if I'm standing in the dark, illuminated by some far off light source and 0.25 lux is shining upon me -- what do I see? How functionally bright is that?


The easy answer is: Go outside on a clear night with half a moon. There is probably about 0.25 lux around you. 
The long answer is: If you have 0.25 lux at a specific spot and you are looking at it from a distance, then this spot acts as a light source that reflects the light back to you. What you see depends on how much is reflected and how far you are away = how much of this light reaches your eye. E.g. The dark bark of a tree might get 10 lux from a flashlight - but you won't see anything, because the light gets adsorbed and not reflected into your eyes. 



lumen aeternum said:


> If I am using binoculars to see a target 500 yards away being so illuminated, and they are really good binoculars wrt transmission losses -- what do I see?


The binoculars don't change how much light (energy in form of photons) reaches you - it just makes it visually bigger. There might be a biological effect, that if you have a bigger light source you will excite more light receptors in your eye and therefore make it 'brighter'.


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## KeepingItLight (Oct 3, 2015)

lumen aeternum said:


> If I am using binoculars to see a target 500 yards away being so illuminated, and they are really good binoculars wrt transmission losses -- what do I see?





KeepingItLight said:


> I think the answer here depends on the binocular. Those with wide lenses gather more light than those with narrow lenses.





drmaxx said:


> The binoculars don't change how much light (energy in form of photons) reaches you - it just makes it visually bigger. There might be a biological effect, that if you have a bigger light source you will excite more light receptors in your eye and therefore make it 'brighter'.





> Objective diameter: The diameter of the objective lens determines how much light can be gathered to form an image. This number directly affects performance. When magnification and quality is equal, the larger the second binocular number, the brighter the image as well as the sharper the image. *An 8×40, then, will produce a brighter and sharper image than an 8×25, even though both enlarge the image an identical eight times.*
> 
> Source: Wikipedia



Using a wide objective lens is akin to opening the aperture wide in a camera. Doing so lets in more light, which is then focused to create an image. Obviously, more light means more photons, despite the fact that the magnification remains unchanged.


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## Fireclaw18 (Oct 5, 2015)

more_vampires said:


> Lumens is more like "all the photons," while lux is the concentration of them at a single point.
> 
> If you shined a light into a lux meter and panned the light side to side, you'd see different lux readings in the hotspot, spill, etc.
> 
> To get lumens, you must perform math and have a device called an "integrating sphere." The sphere must be "calibrated," but this doesn't really involve changing the sphere but coming up with the calibration math. It's kind of a bumpy road to get started.




Or, for a much rougher calculation of lumens, you could try the "integrating bathroom" instead of an integrating sphere.


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## lumen aeternum (Oct 5, 2015)

"Lux measures lumens per square meter at a given distance."



drmaxx said:


> It already was established that this is wrong. There is no given distance. It is just the light intensity at a given spot.



IIRC, If it is a point source and you want to use that intensity to calculate the lux at other distances, then you need the distance.


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## Bigwilly (Oct 5, 2015)

Fireclaw18 said:


> Or, for a much rougher calculation of lumens, you could try the "integrating bathroom" instead of an integrating sphere.



What do you use as a sensor or what device measures the lumens?


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## reppans (Oct 5, 2015)

Eyeball, smartphone app, manual camera, photog light meter, lux meter, etc (I've used them all), but as many have mentioned above, they all require calibration from a known/trusted output.


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## Bigwilly (Oct 5, 2015)

reppans said:


> Eyeball, smartphone app, manual camera, photog light meter, lux meter, etc (I've used them all), but as many have mentioned above, they all require calibration from a known/trusted output.



What's the cheapest somewhat accurate way to measure lumens? I have a lux meter app on my phone that I have calibrated to be somewhat accurate.


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## more_vampires (Oct 5, 2015)

lumen aeternum said:


> Uh oh. Now I want a "moonlight" level flashlight which has a distance sensor. I point the light at some object some distance away, adjust the brightness, and then the sensor maintains that lux as I move the light around, pointing it at things different distances away.
> 
> So I can point it at a tree over there, and then point it at my map, and then the ground in front of me -- and my eyes experience a constant level of brightness.


Surefire tried that with their Intellibeam, but CPF reports that it's flaky and kind of a lemon at this time. Maybe SF will clean up the problems, maybe the NLA it. Who knows?



Bigwilly said:


> What's the cheapest somewhat accurate way to measure lumens? I have a lux meter app on my phone that I have calibrated to be somewhat accurate.


http://www.candlepowerforums.com/vb/printthread.php?t=200334&pp=30&page=1


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## reppans (Oct 5, 2015)

Bigwilly said:


> What's the cheapest somewhat accurate way to measure lumens? I have a lux meter app on my phone that I have calibrated to be somewhat accurate.



I personally like the [URL="https://farm8.staticflickr.com/7310/11524977296_39c8145b17_z.jpg]$5 BLF lightbox[/URL]. It's plug and play.

If you can, add ~$30 for a BLF favorite lux meter (LX1330B). With 1.5" PVC piping, my conversion factor comes out to a nice even 0.1x . It pegs my HDS 325 at both max and min, and also closely matches all tested modes (moonlight through max) for my 2 matching lights with ti-force (again, only reviewer on CPF to claim true ANSI and use laboratory tested calibration lights... he's about a third lower than SB in the <500 lm range I care about). 

Note that it is best to calibrate from lower modes since max tends to be much more dependent upon sample, and of course battery age and state of charge. Well except for HDS, which are individually calibrated and with stone flat output/runtime curves.


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## MAD777 (Oct 5, 2015)

reppans said:


> I personally like the [URL="https://farm8.staticflickr.com/7310/11524977296_39c8145b17_z.jpg]$5 BLF lightbox[/URL]. It's plug and play.



That's the first time I've seen that approach. I may have to have some fun with it. I guess I would need the inside diameter to match my largest reflector. 

Thanks for the tip.


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## Bigwilly (Oct 5, 2015)

reppans said:


> I personally like the [URL="https://farm8.staticflickr.com/7310/11524977296_39c8145b17_z.jpg]$5 BLF lightbox[/URL]. It's plug and play.
> 
> If you can, add ~$30 for a BLF favorite lux meter (LX1330B). With 1.5" PVC piping, my conversion factor comes out to a nice even 0.1x . It pegs my HDS 325 at both max and min, and also closely matches all tested modes (moonlight through max) for my 2 matching lights with ti-force (again, only reviewer on CPF to claim true ANSI and use laboratory tested calibration lights... he's about a third lower than SB in the <500 lm range I care about).
> 
> Note that it is best to calibrate from lower modes since max tends to be much more dependent upon sample, and of course battery age and state of charge. Well except for HDS, which are individually calibrated and with stone flat output/runtime curves.



Thank you very much. I'll look into this.


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## Bigwilly (Oct 5, 2015)

reppans said:


> I personally like the [URL="https://farm8.staticflickr.com/7310/11524977296_39c8145b17_z.jpg]$5 BLF lightbox[/URL]. It's plug and play.
> 
> If you can, add ~$30 for a BLF favorite lux meter (LX1330B). With 1.5" PVC piping, my conversion factor comes out to a nice even 0.1x . It pegs my HDS 325 at both max and min, and also closely matches all tested modes (moonlight through max) for my 2 matching lights with ti-force (again, only reviewer on CPF to claim true ANSI and use laboratory tested calibration lights... he's about a third lower than SB in the <500 lm range I care about).
> 
> Note that it is best to calibrate from lower modes since max tends to be much more dependent upon sample, and of course battery age and state of charge. Well except for HDS, which are individually calibrated and with stone flat output/runtime curves.



It looks like your using an app on an Iphone? Does it measure lumens?


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## more_vampires (Oct 5, 2015)

No just lux. There is no little handheld device like a lux meter for lumens, afaik. Someone would win a science award if they came up with one.


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## Bigwilly (Oct 5, 2015)

more_vampires said:


> No just lux. There is no little handheld device like a lux meter for lumens, afaik. Someone would win a science award if they came up with one.



What's the point of the bended PVC pipe then. Some throwers require a good deal of distance for the beam to form. So wouldn't that setup give lower figures than say a setup where you are 7 meters away and calculate back to 1 meter?


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## more_vampires (Oct 5, 2015)

A lux meter tells you intensity at one point. An integrating spehere collects it all together, sort of. You point the lux meter into the sphere, basically. It's an attempt to find "combined lux at all points" I guess you could say.


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## Bigwilly (Oct 5, 2015)

more_vampires said:


> A lux meter tells you intensity at one point. An integrating spehere collects it all together, sort of. You point the lux meter into the sphere, basically. It's an attempt to find "combined lux at all points" I guess you could say.


So i was just reading Jmpaul360's post for OTF lumen and lux measurements and he links to where he got the info to build the sphere. That poster and Jmpaul360 seem to be using just a lux meter and then using a "corrective factor" to determine lumens. I looked on Amazon for a meter that measures lumens but all I see are lux meters. So when I originally started this thread, my intent was to find the calculation / relationship between the two. So if i'm thinking correct i could build the PVC tube, put in multiple known lumen flashlights and then divide the lux number from the meter to get the "correction factor" and then apply that correction factor for testing a light with unknown lumens? This would get me a closely correct lumen figure? 
If this is correct what is the relationship between the two figures? Is it arrived at because all of the light is in the integrating sphere or in this case PVC pipe and makes its way into the lux meter? 

Am i missing something ?


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## reppans (Oct 5, 2015)

Bigwilly said:


> ... So when I originally started this thread, my intent was to find the calculation / relationship between the two. So if i'm thinking correct i could build the PVC tube, put in multiple known lumen flashlights and then divide the lux number from the meter to get the "correction factor" and then apply that correction factor for testing a light with unknown lumens? This would get me a closely correct lumen figure?
> If this is correct what is the relationship between the two figures? Is it arrived at because all of the light is in the integrating sphere or in this case PVC pipe and makes its way into the lux meter?
> 
> Am i missing something ?



The purpose of the integrated sphere, integrated bathroom, or PVC piping, etc, is to collect, bounce around, and homogenize the light to normalize different beam profiles (flood vs throw). Then, using a light meter, you take a sample of that homogenized light and, knowing the true output of that sample, you derive a fixed multiplier to convert it to a lumens scale (the calibration). 

The app on my iPhone is a photog light meter app which I can use shutter speed (it has no lux), as my "lumen meter." I shine a trusted 100 lms into the PVC, and then vary the aperture and ISO settings on the meter until I can force a 1/100ths shutter speed as the proper exposure - the app now been calibrated. So if I show it 500 lms, the app returns 1/500ths of a second as the proper exposure (5x the output = 1/5th the time exposure); a 50 lumen mode will return 1/50th of a second (half the light = twice the exposure time); 5 lms = 1/5 sec; 0.5 lms = 5 sec, and so on. The important point here is that lumens and time are both dead linear. 

Lux is also dead linear, now I meter my 100 lumen calibration light, and I get 1000 lux from my LX1330, so my multiplier is 0.1x. So a measurement of 30 lux = 3lms, and 3 lux = 0.3 lms, etc. Simple.


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## MAD777 (Oct 5, 2015)

My guess as to a procedure to validate the PVC snake would be to check as many known lights as possible with a variety of output. If the correction factor is approximately the same from light to light, then it works. If the factors are all over the place, save the piping for fixing the kitchen sink. Lol


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## Bigwilly (Oct 5, 2015)

MAD777 said:


> My guess as to a procedure to validate the PVC snake would be to check as many known lights as possible with a variety of output. If the correction factor is approximately the same from light to light, then it works. If the factors are all over the place, save the piping for fixing the kitchen sink. Lol



That's my biggest issue. Getting enough known lights to prove or disprove the correction factor.


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## Bigwilly (Oct 5, 2015)

Bigwilly said:


> That's my biggest issue. Getting enough known lights to prove or disprove the correction factor.



I have 3 or 4 lights that were measured. Think that's enough?


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## more_vampires (Oct 6, 2015)

reppans said:


> The purpose of the integrated sphere, integrated bathroom, or PVC piping, etc, is to collect, bounce around, and homogenize the light to normalize different beam profiles (flood vs throw). Then, using a light meter, you take a sample of that homogenized light and, knowing the true output of that sample, you derive a fixed multiplier to convert it to a lumens scale (the calibration).
> 
> The app on my iPhone is a photog light meter app which I can use shutter speed (it has no lux), as my "lumen meter." I shine a trusted 100 lms into the PVC, and then vary the aperture and ISO settings on the meter until I can force a 1/100ths shutter speed as the proper exposure - the app now been calibrated. So if I show it 500 lms, the app returns 1/500ths of a second as the proper exposure (5x the output = 1/5th the time exposure); a 50 lumen mode will return 1/50th of a second (half the light = twice the exposure time); 5 lms = 1/5 sec; 0.5 lms = 5 sec, and so on. The important point here is that lumens and time are both dead linear.
> 
> Lux is also dead linear, now I meter my 100 lumen calibration light, and I get 1000 lux from my LX1330, so my multiplier is 0.1x. So a measurement of 30 lux = 3lms, and 3 lux = 0.3 lms, etc. Simple.


Right on, sir! 


Bigwilly said:


> I have 3 or 4 lights that were measured. Think that's enough?


IMHO, no. You'd only have 3 or 4 data points on your graph that you make with your spreadsheet. 3 or 4 gives you a line or a simple curve. It's not enough to reveal an erroneous result.


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## Bigwilly (Oct 6, 2015)

more_vampires said:


> Right on, sir!
> 
> IMHO, no. You'd only have 3 or 4 data points on your graph that you make with your spreadsheet. 3 or 4 gives you a line or a simple curve. It's not enough to reveal an erroneous result.



How many data points are needed for marginal accuracy?


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## more_vampires (Oct 6, 2015)

"Lots." 3 or 4 data points can fool you with something called "small sample size error."

https://en.wikipedia.org/wiki/Sampling_error
https://en.wikipedia.org/wiki/Sample_size_determination


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## reppans (Oct 6, 2015)

Getting comfortable with a lumen scale is an evolutionary process and heavily dependent upon the lights you are testing. You should also reconcile with as many independent reviewers here as you can. 10 Chinese lights purchased off eBay for <$10 each may be in a similar ballpark with each other, but you'll be off, probably by a factor of 2x, from the mid-priced ($50-$100) Chinese lights that Selfbuilt tends to test. Then, if you get into quality US lights (eg, HDS, Malkoff, McGizmo, Surefire, Etc.), whom a I believe use true ANSI, you might be off another ~30% or so from many of the mid-priced Chinese brands. 

Lumen scales are all over the map - between different manufacturers, within the same manufacturer, and even within the same flashlight, and often due to sample variation. For example, I can peg (test vs spec) 4 out of 5 modes on my favorite calibration light, but only 2 out of 5 modes on a different light from the same manufacturer... however, I'm comfortable with my readings, because I can peg 6 out of 7 tested modes from an independent true-ANSI reviewer for the same 2 flashlights (and probably miss the 7 mode due to my aged batteries). THIS is another good example (2 virtually identical lines) ET calls that 75 lms/2.5 hrs, ZL 108 lms/3 hrs, Fenix 94-98 lms, and Selfbuilt 116-120 lms/2.5 hrs. I have same lights, got the same results, and I think it's ~ 80-84lms/2.5hrs. 

In the end, whatever scale you use, it will at least give you an objective RELATIVE assessment. So unless you're big believer in truth-in-advertising (like me) it just comes down semantics. If you use a lenient scale, then Manuf. A may be accurate and B conservative; but if you choose a tougher scale, then A is exaggerating and B is accurate. 

Good luck.


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## reppans (Oct 6, 2015)

Oh yeah.... get into tailcap current measurements with a DMM/ammeter. There's a whole extra dimension of BS to dig up there too .


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## Swedpat (Oct 7, 2015)

I have found that ceiling bounce measuring with a lux meter on my living room table is a very good way to estimate the total lumen output. 
I have compared many flashlights with a known ANSI lumen output. In my case 1lux=16lm. As long the light is held 1m or closer to the ceiling practically all the light output is gathered narrow enough on the ceiling above the sensor. It's very accurate.


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## SemiMan (Oct 9, 2015)

Bigwilly said:


> How many data points are needed for marginal accuracy?



If your home built integrating sphere is working properly, then only 1 data point is required to "calibrate". If your home built integrating sphere is not working properly, then it does not matter how many lights you test, you may still have bad results:

- If your "sphere" consistently measures spot lights high, and that is what you are using for "calibration", then when you go to measure a flood light, you are going to measure wrong. Same if you use floods for calibration, then measure a spot.

- The same would be true is you have linearity issues with measurement, i.e. maybe its really accurate at 100 lux where you all your test sources were used, but at 10 lux, it's 50% off. (Most light meters, even cheap ones are pretty linear)

- If your sphere has no "bias" for the light source distribution, then one measurement is all it takes as you are just calibrating.

Best calibration source tends to be an incandescent bulb run from a DC voltage source (used only for calibration) ... just make sure your meter properly adjusts for spectrum.


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## SemiMan (Oct 9, 2015)

reppans said:


> Oh yeah.... get into tailcap current measurements with a DMM/ammeter. There's a whole extra dimension of BS to dig up there too .



Far better off using precision low value resistors and a volt meter with an accurate millivolt capability than an ammeter.

Using an ammeter, you will have two issues, voltage drop in the leads, and voltage drop in the ammeter itself. That added voltage drop can completely change the nature of what you are testing, especially direct drive circuits where every 10th of a volt can really change the drive current.

If you put a low value precision resistor into the circuit, then you do not have any lead resistance to contend with. Just measure the voltage on the resistor to get current. It's a far more accurate method of measuring current in a flashlight. Just make sure you have a multimeter that can measure in the millivolts.

Semiman


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## more_vampires (Oct 9, 2015)

reppans said:


> Oh yeah.... get into tailcap current measurements with a DMM/ammeter. There's a whole* extra dimension of BS to dig up there too *.


How right you are, reppans. Quite right.

I can't believe the claims some of these people make. Best to just test it out yourself and see what you can learn. 100% right on.


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## reppans (Oct 9, 2015)

Swedpat said:


> I have found that ceiling bounce measuring with a lux meter on my living room table is a very good way to estimate the total lumen output.
> I have compared many flashlights with a *known ANSI lumen output*. In my case 1lux=16lm. As long the light is held 1m or closer to the ceiling practically all the light output is gathered narrow enough on the ceiling above the sensor. It's very accurate.



Try the bounce/sampling approach horizontally in a narrow hallway... effectively the same thing, but the much shorter distance for the light to travel means a lot more light to work with > greater accuracy and ability to measure into sub-lumen levels. 

Very curious who you consider as "known ANSI lumen output" though. Many manufacturers claim as such, yet they are all different, and significantly so. Most reviewers here specifically DISCLAIM ANSI accuracy.... who do you think is accurate?



SemiMan said:


> Far better off using precision low value resistors and a volt meter with an accurate millivolt capability than an ammeter.



Perhaps, but that's currently beyond my electrical skills. I actually used to do actual output/runtime tests, and at the sub-/low- lumen outputs I use most (and the reviewers never test). Got a better quality DMM though, and have found its a ammeter function to tie in well with all my past runtime tests, so I'm quite happy using only it now. The efficiency differences between my lights at these low lows are quite significant, and some are off by many multiples from their exaggerated specs, so even "blunt" instruments are very revealing. 

M_V.... the other DIY/Hacker


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## Bigwilly (Oct 9, 2015)

SemiMan said:


> If your home built integrating sphere is working properly, then only 1 data point is required to "calibrate". If your home built integrating sphere is not working properly, then it does not matter how many lights you test, you may still have bad results:
> 
> - If your "sphere" consistently measures spot lights high, and that is what you are using for "calibration", then when you go to measure a flood light, you are going to measure wrong. Same if you use floods for calibration, then measure a spot.
> 
> ...



The calibration figure is to convert the lux numbers from the sensor to lumens. That's why many known data points are needed. If I have 20 lights but their lumen figures are unknown they do me no good in getting a correct calibration number.


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## SemiMan (Oct 9, 2015)

Bigwilly said:


> That's why many known data points are needed.



Just one "Known" number should be enough.


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## SemiMan (Oct 9, 2015)

reppans said:


> Perhaps, but that's currently beyond my electrical skills. I actually used to do actual output/runtime tests, and at the sub-/low- lumen outputs I use most (and the reviewers never test). Got a better quality DMM though, and have found its a ammeter function to tie in well with all my past runtime tests, so I'm quite happy using only it now. The efficiency differences between my lights at these low lows are quite significant, and some are off by many multiples from their exaggerated specs, so even "blunt" instruments are very revealing.
> 
> M_V.... the other DIY/Hacker



No electrical skills needed  ..... If you have a 100 milliohm resistor, then it's 100 millivolts = 1 amp. If you have a good quality DMM, I expect it may have a 20mV scale?

Semiman


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## Bigwilly (Oct 9, 2015)

SemiMan said:


> Just one "Known" number should be enough.



One is not enough as you need to average the results to get an accurate calibration figure which runs to several points to the right of the decimal ie 1.564876. Without multiple data points the accuracy of the average won't be acceptable.


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## MAD777 (Oct 9, 2015)

Bigwilly said:


> One is not enough as you need to average the results to get an accurate calibration figure which runs to several points to the right of the decimal ie 1.564876. Without multiple data points the accuracy of the average won't be acceptable.


Sounds like a great excuse to buy more flashlights!


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## Bigwilly (Oct 9, 2015)

MAD777 said:


> Sounds like a great excuse to buy more flashlights!


True with the S54 specs, it'll be easy to get the calibration number lol. I just need to hit the lotto. Soooo many lights, soooo little money. Lmao.


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## SemiMan (Oct 9, 2015)

Bigwilly said:


> One is not enough as you need to average the results to get an accurate calibration figure which runs to several points to the right of the decimal ie 1.564876. Without multiple data points the accuracy of the average won't be acceptable.



No, that would be based on the assumption that the lumen measurements of all your test sources average out to "right". That is highly untrue. It's almost a given that on average, the quoted lumens from vendors is going to be high, so not matter how many you test, you cannot improve the accuracy of your calibration.

Multipoint calibration only help if you have a non-linear system.

One, accurate calibration source is infinitely more accurate than 20 inaccurate calibration sources.

Semiman


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## Bigwilly (Oct 9, 2015)

SemiMan said:


> No, that would be based on the assumption that the lumen measurements of all your test sources average out to "right". That is highly untrue. It's almost a given that on average, the quoted lumens from vendors is going to be high, so not matter how many you test, you cannot improve the accuracy of your calibration.
> 
> Multipoint calibration only help if you have a non-linear system.
> 
> ...



You're assuming that the known lumen figures are correct and absolute. But it's been proven that lights vary from light to light and some manufacturers give overages and underages plus some lights were measured by other spheres and Vinh admits his figures are a little low. So again, using multiple sources and averaging them out is going to give me the best correction factor possible. And the more samples I use, the more accurate I will be.
If you you take a test and get 9 out of ten then you got 90% right. If you get 95 out 100 then you got 95%. And so on it goes as your sample size goed up the margin for accuracy also goes up.


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## reppans (Oct 10, 2015)

SemiMan said:


> No, that would be based on the assumption that the lumen measurements of all your test sources average out to "right". That is highly untrue. It's almost a given that on average, the quoted lumens from vendors is going to be high, so not matter how many you test, you cannot improve the accuracy of your calibration.
> 
> Multipoint calibration only help if you have a non-linear system.
> 
> ...



Yup, this ^^. 

A large sample might get you a good industry average, but the overall industry is skewed toward exaggeration. That said, I would stand behind a sample consisting of HDS, Malkoff, Surefire and Elzetta - ANSI is an American standard and quality American firms somehow feel obligated to stand by both their products (warranty/CS), and their word (outputs/runtime). And I'm not a diehard patriot, most of collection is made in China - but I highly respect truth in advertising and stand-up companies.


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## more_vampires (Oct 12, 2015)

reppans said:


> A large sample might get you a good industry average, but the overall industry is skewed toward exaggeration.


Kinda reminds me of an old lab concerning error analysis. 4 of us were to each measure the same exact thing, 10 times each. The results were surprising. Graphs of our data and the resulting error bars weren't something I was expecting to see. We were literally using mechanical calipers to measure the same object. Of course, the fact that most of the group had no experience with this was probably a factor as well.

A source of error can be almost anything, even something weird like needing to change the batteries on a multimeter and not realize it.
https://en.wikipedia.org/wiki/Error_analysis_(mathematics)


> In mathematics, *error analysis* is the study of kind and quantity of error, or uncertainty, that may be present in the solution to a problem. This issue is particularly prominent in applied areas such as numerical analysis and statistics.


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## Bigwilly (Oct 12, 2015)

reppans said:


> Yup, this ^^.
> 
> A large sample might get you a good industry average, but the overall industry is skewed toward exaggeration. That said, I would stand behind a sample consisting of HDS, Malkoff, Surefire and Elzetta - ANSI is an American standard and quality American firms somehow feel obligated to stand by both their products (warranty/CS), and their word (outputs/runtime). And I'm not a diehard patriot, most of collection is made in China - but I highly respect truth in advertising and stand-up companies.



Again, the multiple samples are needed to make the correction factor acurate as all factory lights will be off their ANSI spec for one reason or another. Some manufacturers are very close and some are off due to lesser manufacturing tolerances. I need the correction factor to be accurate as possible in order to conver the lux reading from the sensor into lumens. I've read numerous reviews from respected members and they've found some lights 15% lower than advertised. I have to go by the advertised figure therefore the more samples the less my correction factor is off. 

I take manufacturers ratings with some skepticism. My first expensive hobby was car audio. In the 90's there was no oversight in their advertising. My first amplifier was made by company called Boss and was rated by them at 600 watts at 4 ohms. 2 channels by 300. In reality it would've needed to be struck by lightning to put out 600 watts. It really put out just over 200 watts total. Now I have a same era Rockford Punch Amp, 2 in fact, rated at 360 watts and their birth certificates show both over 380 watts. Of course stretching stuff is par for the course for advertising departments but some companies like Boss out and out lie. 

Back to flashlights. If I use 1 Surefire light and let's say it's a poor example and is off by 25% then every light I test will be off by the same. If increase the sample size and average the correction factor then I'll have accuracy good enough for me. This method has worked for numerous reviewers - Selfbuilt, Jmpaul360, Vinh Nguyen, and others. I can only wish I had multiple lights from the companies you mention as they are very reputable but I can only measure lights in my possession. That being said, I'm using reputable factory lights and modded lights that were previously measured. The custom lights I own that haven't been measured will be excluded from the sample.

I agree about the stand up companies. I am loyal to my brands and not a fan of outsourcing.


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## more_vampires (Oct 12, 2015)

Bigwilly said:


> Again, the multiple samples are needed to make the correction factor acurate as all factory lights will be off their ANSI spec for one reason or another. Some manufacturers are very close and some are off due to lesser manufacturing tolerances.


Oh yes, "small sample size error" can really throw things out of whack. There is never any harm in comparing 10 samples of the same thing. That sounds more like science to me.


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## reppans (Oct 12, 2015)

Bigwilly said:


> Again, the multiple samples are needed to make the correction factor acurate as all factory lights will be off their ANSI spec for one reason or another.....I have to go by the advertised figure therefore the more samples the less my correction factor is off.



We are not at complete odds. What we are saying is that, if an ANSI laboratory tested a single lower mode (so batt. condition wasn't a factor) from one of your lights, and said that output is exactly X, then you be done and have your calibration light. The problem is knowing what true ANSI is, and all we are saying is that, testing more and more lights will not get you any closer to ANSI, and in fact may take you further and further away as, logically, on average, the industry is predisposed to exaggeration. 

That said, once you do find a manufacturer, or reviewer, whom you believe to use true ANSI, then I agree that you will need more than a single matching mode (data point) to eliminate the risk of sample variation, etc. In my case, for example, I can match all the lower modes from 2 lights with the reviewer that I believe to use true ANSI... and this calibration also happens to match the lumen scale of my most trusted, stand-up manufacturers. BUT this scale does NOT match the majority of my lights (that tend to exaggerate), and ONLY one manufacturer, of my collection, I find overly conservative. 

Of course, there is no certainty with any of this, but am now very comfortable with my scale, and IMHO if I where to use some sort of regression analysis from my whole collection, I'd be much worse off.


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## SemiMan (Oct 12, 2015)

You may be better off with a single incandescent bulb at a fixed voltage. It should be possible to get one that's fairly accurately plus or minus five to 10%. I have my doubts about most manufacturers or almost any manufacturer is putting every single unit they make into a integrating sphere, and I certainly have my doubts that most of them even know how to use it properly. That is based on experience with leading Chinese companies not just a guess. A lot of the Chinese lighting companies may have fairly good equipment but limited knowledge in how to use it properly.


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## Bigwilly (Oct 12, 2015)

SemiMan said:


> You may be better off with a single incandescent bulb at a fixed voltage. It should be possible to get one that's fairly accurately plus or minus five to 10%. I have my doubts about most manufacturers are almost any manufacturer is putting every single lately make into a integrating sphere, and I certainly have my doubts that most of them even know how to use it properly. That is based on experience with leading companies not just a guess. A lot of the Chinese lighting companies may have fairly good equipment but limited knowledge in how to use it properly.



The single bulb may work, I see what your saying, but how do you arrive the correct lumens with it? How do you get the fixed voltage to it?


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## SemiMan (Oct 12, 2015)

Bigwilly said:


> The single bulb may work, I see what your saying, but how do you arrive the correct lumens with it? How do you get the fixed voltage to it?



They will be specified at a given voltage. You will need a power supply to achieve that.

I will do some digging. I may be able to get some bulbs tested at say 12V, a fairly easy to get power supply voltage.


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## Bigwilly (Oct 13, 2015)

DavidW said:


> They do look similar. And Koehler-Brightstar has some flashlights and headlamps that look suspeciously like Princeton Tec products.
> 
> The Brightstar has a nicad and alkaline option, so we know it takes full size batteries. The streamlight lists a nicad sub-c battery. And the head is smaller.
> 
> ...



Excellent. Thank you for your help.


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## more_vampires (Oct 13, 2015)

In this thread: we cannot stop the error analysis.






As a direct sensor reading, lux can be close to fact, but the least light pollution or smudge on your sensor and you're off. Now we're calling the lux meter itself into question. Is it calibrated? How long ago? Is it possibly damaged?

As a calculated and experimental value, lumens are a bit tricky to pin down within +-5% even for the big boys with pocket protectors, graphing calculators, spreadsheets, and no date on Friday night. So your lux meter is fine, but is your calibration factor off? Is there a new problem with the gear that formerly worked?



Bigwilly said:


> Again, the multiple samples are needed to make the correction factor acurate as all factory lights will be off their ANSI spec for one reason or another. Some manufacturers are very close and some are off due to lesser manufacturing tolerances. I need the correction factor to be accurate as possible in order to conver the lux reading from the sensor into lumens. I've read numerous reviews from respected members and they've found some lights 15% lower than advertised. I have to go by the advertised figure therefore the more samples the less my correction factor is off.





more_vampires said:


> Oh yes, "small sample size error" can really throw things out of whack. There is never any harm in comparing 10 samples of the same thing. That sounds more like science to me.


Not just manufacturing tolerances, but different batteries can have huge impacts as well. To say a light has "one output and only one measurement is required" is not correct.

An example from our illustrious Vinh could be the many times where he has compared lux and lumens *with the same flashlight* but different batteries. We've seen raw max/min spreads in excess of 25%! I'd post a link, but this comes up so frequently and lux/lumens are said so frequently in the V54 forum that it's actually kind of hard to search for an example. 

This is a factor, particularly on current boosted lights where max/turbo is direct drive and the light becomes limited by resistances of the system and what the battery is capable of providing. In certain such lights, a protected battery that trips at 5 amps or a battery with poor maximum drain is going to get functionally stomped by something like the Sony VTC5 (30 amp continuous) and you'd never know without taking multiple data points and scratching your head over the "error bars." What was the cause of the discrepancy?

https://en.wikipedia.org/wiki/Error_bar


> *Error bars* are a graphical representation of *the variability of data and are used on graphs to indicate the error, or uncertainty in a reported measurement.* They give a general idea of how precise a measurement is, or conversely, how far from the reported value the true (error free) value might be. Error bars often represent one standard deviation of uncertainty, one standard error, or a certain confidence interval (e.g., a 95% interval). These quantities are not the same and so the measure selected should be stated explicitly in the graph or supporting text.
> 
> Error bars can be used to compare visually two quantities if various other conditions hold. This can determine whether differences are statistically significant. Error bars can also suggest goodness of fit of a given function, i.e., how well the function describes the data. * Scientific papers in the experimental sciences are expected to include error bars on all graphs*, though the practice differs somewhat between sciences, and each journal will have its own house style.


When I was partying my brains out in engineering college, error analysis was a freshman first semester sort of topic. My first reaction to error analysis math was "WTH is this???" After I wrapped my head around it, I saw that no engineering can be complete without it.

Hate it if you want, but you cannot escape error analysis. Just one measurement is the Diet Coke of analysis. Just one calorie, not enough. 



reppans said:


> We are not at complete odds. What we are saying is that, if an ANSI laboratory tested a single lower mode (so batt. condition wasn't a factor) from one of your lights, and said that output is exactly X, then you be done and have your calibration light. The problem is knowing what true ANSI is, and all we are saying is that, testing more and more lights will not get you any closer to ANSI, and in fact may take you further and further away as, logically, on average, the industry is predisposed to exaggeration.
> 
> Of course, there is no certainty with any of this, but am now very comfortable with my scale, and IMHO if I where to use some sort of regression analysis from my whole collection, I'd be much worse off.


Part of error analysis is being able to throw out obviously erroneous data, including bogus manufacturer claims.

I see what you're saying about using false maker claims as part of calibration. IMHO, one of the hardest things about calibration scales as we're discussing is getting started with valid data. Using bogus data to calibrate will definitely cause issues, I agree with you completely sir!


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## more_vampires (Oct 13, 2015)

Some links for further reading on error analysis.

Shake hands and say hello:http://astro.physics.uiowa.edu/ITU/glossary/percent-error-formula/

This link appears to be an excellent error analysis overview:
http://felix.physics.sunysb.edu/~allen/252/PHY_error_analysis.html
Random errors vs systematic errors:
As the number of trials become large, random errors should become apparent on a bell curve.

Unfortunately, systematic errors (you're doing something wrong) aren't necessarily revealed by that method.

For good error analysis, even the format of your mathematical formula is important. This concept is called "propogation of error."

The neat thing about error analysis is you're basically "proving how wrong you were" and giving yourself a chance to try again and fix it.

The more people who try it and compare notes, the larger the error bars will be. It's the nature of the beast.

Oops, the battery in trial #42 wasn't fully charged and the battery in #53 was near the end of its useful life.


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## SemiMan (Oct 13, 2015)

Bigwilly said:


> The single bulb may work, I see what your saying, but how do you arrive the correct lumens with it? How do you get the fixed voltage to it?



The great thing about a "standard" bulb, especially if using a common voltage, say 12V, especially incan, is ease of measurement.

- 12V regulated supplies are easy to obtain and cheap, <$10-20
- Most people in this hobby at least own a multimeter, and likely accurate to 0.2% DC
- You can wire up the bulb and measure the voltage at the bulb. It if says 11V or 13V, the supply is no good, the leads to the bulb is no good, or your meter is crap. Fortunately, most of us have lots of things around the house to compare to. USB chargers, fully charged batteries, etc. You are going to know if you meter is at least pretty close. Many of us have 2 (or more) meters.
- Even if you voltage is off by 0.1-0.2V, there are well defined formulas for calculating light output at those voltages with an incan to compensate for the error.

Incans require little burn-in as well.

We could calibrate an LED, could even build a simple board with an LED, some heatsinking, and the constant current circuitry on board. If you stick to Luxeons, they tend to have the least droop w.r.t. temperature. Output does change in the first 50-100 hours of operation but tends to not be large.


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## 2xTrinity (Oct 13, 2015)

SemiMan said:


> *No, that would be based on the assumption that the lumen measurements of all your test sources average out to "right". That is highly untrue. *It's almost a given that on average, the quoted lumens from vendors is going to be high, so not matter how many you test, you cannot improve the accuracy of your calibration.
> 
> Multipoint calibration only help if you have a non-linear system.
> 
> ...



I can confirm this, I am fortunate to have access to one of these handheld integrating spheres at work:

http://www.labspherestore.com/product-p/aa-00775-00x.htm

I can verify who is lying about their lumen claims by pointing one of my flashlights inside the opening and pushing a single button. All of them are lying. Some manufacturers claims are slightly over, some are insanely over. There is actaully very little relationship between advertised lumens and what you actually get, even when comparing multiple products from the same manufacturer.

Even the select few manufacturers who advertise ANSI lumens can't be used as a point of reference as they almost invariably understate their products' output to avoid lawsuits from people like me


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## reppans (Oct 13, 2015)

2xTrinity said:


> I can confirm this, I am fortunate to have access to one of these handheld integrating spheres at work:
> 
> http://www.labspherestore.com/product-p/aa-00775-00x.htm
> 
> ...



Care to share any details on your lights and/or which manufacturers you find reasonably conservative/accurate vs those that overly exaggerate? 

Any CPF reviewers here that you think is closest to true ANSI?


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## more_vampires (Oct 13, 2015)

reppans said:


> Care to share any details on your lights and/or which manufacturers you find reasonably conservative/accurate vs those that overly exaggerate?


I was also wondering if there were any pleasant surprises at all? It was all either close or massive market lies?
For example, could you find any Surefire lights that were understated?

Most of us here play with improvised stuff. It would be nice to compare notes with pro gear.


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## Bigwilly (Oct 17, 2015)

Ok question time. If you take two lights and combine their aim on a target, does the lumens and lux double? Example - i shine my X60vn and X60Mvn at a tree 100 meters away is it close equaling one light with their combine output? In this case - 14900 lumens and 71700 lux


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## scs (Oct 17, 2015)

q


Bigwilly said:


> Ok question time. If you take two lights and combine their aim on a target, does the lumens and lux double? Example - i shine my X60vn and X60Mvn at a tree 100 meters away is it close equaling one light with their combine output? In this case - 14900 lumens and 71700 lux


In general, yes.


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