Lumens measuring contraption... (or just a pipe dream?)

Wanted to throw this idea out to the experts, so please humor me if you will...

Two things lacking from my reviews have been:

- PWM readings (building audio cable connected to solar cell and will use a PC soundcard oscilloscope program
- Lumens measurement. While I can do a ceiling bounce, there are usually too many factors introduced (beam shape/intensity chief amongst them)

For the latter, I've been meaning to build an IS but don't like the idea that there would not be a stable platform/holder for the light while I'm taking measurements (especially for runtime logging). Also, based upon what I've read, I felt tweaking the baffle has been one of the trickiest parts to calibrating it properly. So I came up with this idea based on the following criteria:

- must accomodate bezel head up to 4" in diam
- allow consistent repeatable measurements
- provide stable platform for light to rest on while doing runtime / logging and light must be exposed to allow fan to cool it
- not be affected by ambient lighting while logging is in progress
- no fiddling w/a baffle
- simple to build w/easily sourced parts
- reasonably budget friendly
- allow light sensor to be easily removed for other measurements
- easy for others to build/reproduce

I've read about the PVC U-pipe idea but decided to add an extra 90deg. elbow to further reduce the likelihood of any direct reflection making it to the light sensor and ended up with this:

Total parts used cost $34.40 before taxes:

- 3 x 4" 90deg. PVC elbows
- 1 x 4" -> 3" step down adapter
- 1 x 3" -> 1.5" stepd down adapter/cap

The entire contraption will be strapped/bolted onto a wood base. The end where I'm shining the light into will have a glass/plastic lens over it that can accomodate lights up to 4" and establish a platform for the light to rest bezel down on and be completely exposed to allow a fan to keep it cool. I'll cut card board/paper templates for smaller lights that will allow perfect centering thus allowing consistent repeatable measurements. The other end w/the step down adapters will need to be sanded down to fit but will hold the light sensor.

Worst case is that if this doesn't work, since no glue or alteration is involved, I can return the 3 x 90deg. elbow which was the majority of the cost for this project. The step down adapters will need to be sanded down and can not be returned but I'm sure I cand find other uses for them.

I figure if I can establish a consistent X factor/multiplier, then it should be good enough. So do you guys think this will be reasonable to effectively measure lumens w/some degree of accuracy or is it just a pipe dream?

i like this idea

That's a very novel concept! I like the thought you put into it...definitely outside the box.

The main problem I see lies in the fact that this design will heavily favor throwers. The sides of the pipe are parallel and won't properly re-direct the spill light to the meter. This is why round spheres are used for light integration to help minimize favor of one beam pattern over another.

Thx moT!

@Match - darn, I was afraid someone would say that. I was hoping that the curved surfaces in the pipes would reduce that enough by 3 bends so as not to be a factor... Maybe add yet another elbow or two?

Let me get working on this and see what the results are.

Thx for the feedback and please keep them coming!


I'm afraid more bends wont help, but only exasperate the issue. My guess is, most of the side spill will be lost before the first bend. Every time the light has to make a bounce, it'll lose some intensity...and the the number of bounces the light has to make will go up exponentially the farther away from the center axis it gets.

Then again, give it a shot.....find two lights with the same output, one a thrower and the other a flooder. If both measurements come out the same then you're definitely onto something!

I learned a new word today ...I thought you meant exacerbate.

flashlight fun for plumbers

More proof this forum is just going down the drain


@Boaz - hopefully that was tongue in cheek... if not, then as a potentially stupid idea, it was mine alone, no need to drag the rest of the forum into this.

@moT/Match - some interesting results... I Might (with a capital M) be on to something here...

Here are some lights with the mfg's claimed ANSI values and what I measured (PVC) after 30 seconds:

Icon Link

High 50
PVC - 41

Klarus XT20

High 1200
PVC - 1222 (this light uses PWM even on high so I actually should've done an avg instead of eyeballing a single value)

Niteye EYE30

Turbo 2000 / High 1000
PVC - 2117 / 1100

SureFire M3LT

High 400 / Low 70
PVC - 669 / 139.5

SureFire E2DL

High - 200
PVC - 234

Sunwayman T20C (forgot to take pic)
High - 438
PVC - 290

Sunwayman T40CS

High - 788
PVC - 745

Sunwayman V60C

Max - 728
PVC - 831

Xeno G10v2

High - 460 OTF
PVC - 440

So it seems like it's not too far off and thus far doesn't seem to be favoring throwers. There are of course a few anomalies like the V60C. I know for sure lux was lower than the T40CS thus why I'm surprised why the lumens measured this way was higher.

Anyways more testing to come!


Since light intensity falls of at the square of the distance, you would ideally want the shortest physical distance between meter and the light source that allows for complete registration. This would help minimize the differences between 'throwers' and 'flooders', as the longer linear distances would favor the lights designed for such.

Some diffusion material placed upstream of the bends in your device could help rectify the linearity issue without having to re-engineer the entire thing. I think playing with diffusion levels will ultimately give you an excellent tool with repeatable results.

This balance between emission angle, bezel size, meter and baffle placement is the difference between an OK integrating meter and a great one, IMO.

I have often toyed with the idea of making an integrating "ring" to save space over the sphere; I'm very happy to see some additional outside-the-box thinking being actualized.

Well done.


@Boaz - hopefully that was tongue in cheek... if not, then as a potentially stupid idea, it was mine alone, no need to drag the rest of the forum into this.


You need to get to know him. He's a complicated man. It's all good. I think. Maybe.

Thx ChicagoX, I'll try w/just two elbows. As an update, I've edited post #7 w/pics. For now, just as a POC for myself, I skipped the step down adapters and just placed the sensor at the lip of one end. I placed a piece of glass on the light end to hold the light in place. I noticed that I'm allowed some flexibility w/the placement of the light w/out affecting the reading drastically (the sensor however will read a bit higher once centered in the step down adapter).

Of course there's consideration to be given to the semi-glossy surface of the PVC so I may look to coat it w/IS paint.

Anyways more experimenting to come.

EDIT: Thx Langcjl, let's see... I mean, I don't mind criticisms as truth be told, I'm not even sure this would work but I don't think the forum should be disparaged on my behalf...

More i look at this the more I think a lux meter maybe in my near future. Maybe some pvc pipe as well. good work

I'm impressed with the out of the lightbox thinking involved here on your part .

I wasn't intentionally trying to dump on your idea .

The forum isn't going down the drain .it was a lame attempt at toilet humor .

Don't flush, I'm down in the basement still testing lights.

Thx Boaz! It's all good man, as I said, I don't mind criticisms levied at me/my ideas but just didn't think it would be fair to direct at the forum. Appreciate the clarification! :beer:

Are those LEDs in that toilet? Very appropriate.


Sounds like a good idea to me. Something like a sink trap would completely exclude any direct light. But losses would be high. Would be good for the silly high powered stuff though.

Repeatability is far more important than absolute accuracy for what we're doing.

So here's the deal, I was afraid that this might favor throwers, and perhaps it does to a very light degree and as much as I remain a little skeptical myself, the readings keep telling me that I just might be on to something.

I took a few more measurements of most of my lights and they are all within % of claimed ANSI or mfg claims (and again using the same set up as above as I didn't have time to sand and paint yet).

I think these two test subjects are the clearest example that this might work:

This is the eGear Focus Control headlamp, it can be focused from flood (left pic) to spot (right pic) and in spot mode, it only increased the reading marginally:

This is a LumaPower XR-E R2 w/TurboForce Kit that casts a pencil beam sized hot spot (check my beamshots threads in my sig for beam profile) and if this contraption did favor throwers heavily, then this reading should be much higher but I think it's fairly relative for a XR-E reading:

L: Lux reading | M: stepped down to show beam profile | R: diffused light at other end

I don't have time right now to post the rest of the pics but the full album is here in case you want to take a look. I tried to include most of the light in the pic so you can identify them (EDIT: forgive the bag in the pic, it's acting as a ballast to hold down the pipe).

I'm sure the readings will be different once I sand down and mount the sensor in the center of the pipe but at least this seems encouraging no? More to come!

(sorry Foy, I needed to just do this at least once during my time on this forum, but please know it's in your honor!) =o)

Tim -

LOL Very nice . . . and I thank you.

And, I also commend you - your pipe dream seems accurate. In fact, I'd like Match to chime in a bit more on this project. Specifically, does he think the light is sufficiently integrated? Your results thus far suggest that it may be. If it is, I'm thinking I would rather build this than a sphere.


OK, so I actually haven't done any further fiddling with it and literally been using it as is w/out the adapter. Where it deviates from my original requirements is that it will be affected by ambient lighting so I need to take measurements in a pitch black room. While I don't have a baffle to deal with, thx to feedback from a member, I found out that ambient temp will affect the readings. So each time before I take readings, I'll first use a Xeno G10v2 (as Xeno uses ANSI values and it immediately runs nearly perfectly regulated on medium) to calibrate the sensor's position to match as close to 158lms as possible. Then I'll check the other levels to see if they're close to 480 and 10 on High and Low respectively.

The PVC (lms) column is what I've measured for each light. The output is measured in lux but wouldn't be far-fetched to call it lumens as the readings are pretty close for most of the lights. As expected in SureFire's case, they are known for underestimating their lumens and my readings corroborate that. Judging by the measurements, Sunwayman is also a little on the conservative side as well. All my measurements are done at 31seconds after turn on but of course it's not known at what time the manufacturers take their readings since it can be done anytime between 30secs - 2min.

As you'll see, it doesn't necessarily favor throwers. Case in point, the T40CS is near~47K lux and the V60C @ ~36K lux but yet the V60C registers 904 lux (lms) vs. 814 for the T40CS.

While I wish there was some engineering formula I could provide to calculate what is happening to the output after three pipe bends to produce these results but in a way it's been great not having to. I'm now able to consistently reproduce comparative WISIWIG (What I See Is What I Get) figures of how one light is faring vs. another.

The real nice surprise aside from the Sunwayman V60C were the ThruNite TN 10 & 11 as those readings were taken on only 1 x 18650 each, I'll post 2 x 18650 config (including step down) when I get around to them.

Anyways this has been a fun experiment for me and useful for comparitive purposes. Anyone else care to give this a spin? Assembly takes all of 5 seconds after you get the 3 x 90 deg. elbows.

TurboBB .. I still like this. waiting for the kit to be offered for sale winks. great job