Measuring Lumen Output -- The Poor Man's Method

[MR Bulk]

Measuring Lumen Output -- The Poor Man\'s Method

This suggestion may sound silly, but it is predicated on the fact that few or none of us have the resources to acquire an exalted Integrating Sphere such as SureFire surely has, and even those who do are probably disinclined to shell out for one (hey, that's probably how they're able to build up their resources in the first place), so in the twisted mind of MR Bulk, I figured:

1) SureFire rates their lights by Lumen output, and

2) Flashlights (including SF's) usually throw most of their output forward.

So if one were to use the "Integrating Ceiling" idea (shine a light up at the same spot on a textured white ceiling with the light emission plane kept at the same distance below) and shine a light of a known output (say, an SF E2x at 60 Lumens or whatever it is) at the ceiling afterwards, both measured by a light meter sitting somewhere sensor up, then at least some kind of relative comparison could be made.

I do know that even in this twisted scheme the focusing ability or lack thereof (and resultant hotspots) of each light would influence readings somewhat, but what if the sensor were covered with a white diffusing material of some sort, such as white paper, to further "even out" the light dispersal?

I will go home and try this out, maybe even tonight, but in the meantime, what are your opinions? First one to post gets a broken NoviGear switch... /ubbthreads/images/graemlins/grin.gif /ubbthreads/images/graemlins/grin.gif /ubbthreads/images/graemlins/grin.gif

 

[Rothrandir]

Re: Measuring Lumen Output -- The Poor Man\'s Method

the different dispersion patterns should really affect the output, especially when comparing a led to an incan.

i think the results wouold be better if using a wall, at a much closer range.

now what's this about a switch? /ubbthreads/images/graemlins/grin.gif

btw, does anyone know how much an integrating shpere costs?

 

[MR Bulk]

Re: Measuring Lumen Output -- The Poor Man\'s Method

If the wall is used, where do you think should I place the light meter, and at what orientation? I don't want to just eyeball it, can be quite deceiving as I've already found out the hard way...

Oh yeah, just in case you haven't had a chance to sample one in person yet, the latest high-powered Luxeon mods have surprisingly similar beam patterns compared to incandescents; in fact if precisely situated in Maglite reflectors they will focus down to an intense white-hot spotlight beam with higher-binned 5W emitters, producing lux and/or foot-candle units reading in the multiples of thousands.

 

[Rothrandir]

Re: Measuring Lumen Output -- The Poor Man\'s Method

i haven't yet had the oppurtunity to use any white 5watters.

i was refering to leds in general, but of course there are some that could be quite similar. i've found that a ld in a c/d mag reflector produces a beam exactly like a sf e2e.

i just suggested the wall because it would be easier to get close, leds in general produce wider beams, so i think being close to the source would help.

 

[MR Bulk]

Re: Measuring Lumen Output -- The Poor Man\'s Method

Yeah, and then I'm thinking that placement of the light meter sensor somehow, maybe facing an opposite or at least an adjoining wall, perhaps slightly further away to diffuse/disable the hotspot of the lights' beams, might enable one to compare output fairly accurately to a certain degree.

Any more opinions?

 

[Rothrandir]

Re: Measuring Lumen Output -- The Poor Man\'s Method

i'm still up /ubbthreads/images/graemlins/twak.gif

goodnight! it's 5am here!!!

i think that is pretty much a good setup, close, but not too close...

i think a box of mirrors would work well...

have a hole for the light, the meter on a side.. everthing inside should be mirrorized...the light more or less bounces around, so not much would get lost no matter what the beam pattern.

maybe not really lumens, but possibly a way to test something /ubbthreads/images/graemlins/icon3.gif

 

[MR Bulk]

Re: Measuring Lumen Output -- The Poor Man\'s Method

Hmmm, build a squarish Integrating...Cube? Hey, that is entirely possible, and as long as the light is shone in the same hole at the same angle every time...Hmmm.

 

[Deleted member 684]

Re: Measuring Lumen Output -- The Poor Man\'s Method

Have some sort of post on the floor for holding lights. Have a piece of cone like object disperse the light. Centered above the light, so that the conical surface will disperse the light no matter if it's spot or flood. get your light meter and measure the amount of light from over 3 meters away.....

 

[Lefselight]

Re: Measuring Lumen Output -- The Poor Man\'s Method

Well...let us consider the world of photography, where they measure intensity of light all the time to get a correct exposure. You can measure reflected light (which is what in-camera meters do) or incident light (the light falling upon the subject). To measure incident light you can buy a handheld exposure meter, which measures both reflected light,and, through a translucient white dome, incident light (sometimes flash exposure also). These things can be a little expensive. Or...you can take a white styrofoam cup and stick it over the lens (I'm assuming that the camera has through the lens metering) and you have, effectively, an incident light meter. It works. I've done it many times. Just food for thought. Hopefully this will give you another perspective on how to achieve your goal.

 

[InTheDark]

Re: Measuring Lumen Output -- The Poor Man\'s Method

It wouldn't be that hard to construct your own integrating sphere, and it can produce pretty reliable results if done correctly. The reason you want to use a sphere over a box or cone or anyother shape is because you want uniform light intensity inside the sphere, if it's some odd shape, then you'll have false reading depending on the orentation of the light. Also, you want to paint the inside of the sphere with some flat white paint, not gloss, also to prevent false readings. The exact reflectivity of the paint isn't as important as getting a nice even coverage. The detector should also have some sort of baffle between it and the light source to prevent any direct light from hitting it. The easiest way would to get some sort of ball, cut it open and paint the inside, then cut two holes opposite each other, one for the detector and one for the light. Then put a white baffle in between the two to block any direct light. I might have a picture of one that i took apart, it really is nothing more than a white sphere inside.

 

[MR Bulk]

Re: Measuring Lumen Output -- The Poor Man\'s Method

I like ITD's idea. Internally white ball of some kind, holes on opposite ends, translucent baffle in middle between holes...maybe a conical white baffle? To bend the light coming from directly in front of the flashlight?

 

[InTheDark]

Re: Measuring Lumen Output -- The Poor Man\'s Method

If you want more information, check here

http://physics.nist.gov/Divisions/Div844/facilities/photo/Publications/NEWRAD97_1.pdf

just ignore all of the text, and look at the pictures. Should give you a good idea.

One thing I forgot to mention, is that this isn't going to give you a absolute reading of lumen output (unless it's calibrated), but it will allow you to compare readings from different flashlights. And you might see some problems when trying to compare LED and incandescents, just because of the different wavelenths. If you know what kind of detector you have, then you can make a rough guess as to the responsivity at different wavelengths and try and factor that in.

 

[LEDmodMan]

Re: Measuring Lumen Output -- The Poor Man\'s Method

[ QUOTE ]
InTheDark said:
just ignore all of the text, and look at the pictures.


[/ QUOTE ]

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Just like kids say! /ubbthreads/images/graemlins/yellowlaugh.gif