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Thread: Lumens measuring contraption (feedback please!)

  1. #1

    Smile Lumens measuring contraption (feedback please!)

    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 a 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.

    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).

    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.

    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 but what are your thoughts on this?

    I am by no means an expert on this and can use whatever guidance and tips you guys can provide. Also, the above readings were pure lux w/no conversion done.

    Cheers,
    Tim
    Last edited by turboBB; 03-30-2012 at 07:10 PM.

  2. #2
    *Flashaholic* Flying Turtle's Avatar
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    Default Re: Lumens measuring contraption (feedback please!)

    Nice work, Tim. I look forward to seeing how this progresses. i wondered about the shininess of the PVC, too. Has anyone ever tried painting the PVC black? Maybe that wouldn't work at all.

    Good luck,

    Geoff

  3. #3

    Default Re: Lumens measuring contraption (feedback please!)

    Interesting setup Tim, curious to see where this goes.

    Can you fit a smaller adapter at the end that goes to your lightmeter? I notice a lot of light escapes the opening, so the effect of the internal reflections could be variable for different types of lights. Would probably be better if you could get that down to a much smaller opening.

    I am surprised at how well my milk carton lightbox (which has a matte internal finish) works to sum up the light. But in my case, very little light light escapes, except what isn't caught by my back-drape around the light bezel opening (i.e. my sensor is permanently embedded, in a perfectly cut hole).

    I remember when Doug tried painting his milk carton, it didn't make a difference (since already pretty matte). It may have more of an effect here, given how shiny white PCV is. I wonder how black PVC would do? You could probably find a lot of connectors in the plumbing section of your local big box hardware store, if you wanted to give it a go. But white is probably best, as long at it isn't too shiny.

    By the way, is there any way to lower the sensitivty/increase sampling time of your lightmeter so the PWM isn't a confounding factor?
    Last edited by selfbuilt; 02-26-2012 at 09:43 AM.
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  4. #4

    Default Re: Lumens measuring contraption (feedback please!)

    Thx guys.

    @selfbuilt - yes, that's what the step down adapters will be for, I just decided to do a test run w/out them for now since I don't have time to sand them. I wanted to go the milk carton route as well for the ease of setup but the only prob is as mentioned, I wanted a device that I could actually rest the light firmly on to conduct runtime testing as well as accomodate 4" bezel.

    Until I get the IS paint, I'm going to start scrubbing the inside of the PVC w/0000 steel wool and acetone to dull the finish.

    As for my light meter (Extech HD450), unfortunately there's no way to set the sensitivity (as a FYI , I had it set in the 4K range) but as mentioned, I can do an average so as to reduce the fluctuations in the future.

    I've got a bit more work to do on this thing before I can even start claiming that the numbers make sense. For now I just wanted to pitch the idea out there to see if it was just totally off the walls but based on various feedback, it does seem like it could work.

    Cheers,
    Tim

  5. #5

    Default Re: Lumens measuring contraption (feedback please!)

    Quote Originally Posted by turboBB View Post
    As for my light meter (Extech HD450), unfortunately there's no way to set the sensitivity (as a FYI , I had it set in the 4K range) but as mentioned, I can do an average so as to reduce the fluctuations in the future.
    Could you work around this by using phosphorescent paint? It would effectively act like a photon capacitor, i.e. a low-pass filter.

  6. #6

    Default Re: Lumens measuring contraption (feedback please!)

    I'll eventually tackle the PWM issue but for now my main concern is whether this might even work and thus far 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!

    Cheers,
    Tim
    Last edited by turboBB; 02-27-2012 at 10:56 PM.

  7. #7

    Default Re: Lumens measuring contraption (feedback please!)

    Tim,

    Does your meter have a peak capture on it?

    The one I use for work can be set to record the highest (and lowest) recorded readings. Essentially, I press a button that then samples for a couple of seconds, and saves the highest and/or lowest readings.

    The highest reading would allow you to grab the pulse peaks at least.

    If the PVC is channeling the throw from the lights, and you want to account for that, I'm not sure if black is best per se.


    Your estimated lumens seemed generally low, potentially due to the end with the light not being part of the box, and some light going the wrong way, etc.

    This can also favor throwers, as less of the thrown light would reflect back out towards the flashlight hole.

    The spheres I've seen are white inside, which makes me think white might be better than flat black for example.

    Being shiny means more of the total light that's emitted might make it to the sensor. Given that the purpose to to gather every lumen and turn it into lux at the sensor, the more reflective the capture mechanism, the better it should be at that.

    I think that's also why the use a sphere in the first place...to have the reflections even out/homogenize, etc.

    Otherwise, all you'd need is a sensor the same size or larger relative to the light source being emitted...attach the head of the light to the sensor, and the entire beam would shine upon the sensor for direct measurement.

    Short of that, the devices are essentially trying to simulate that concept...try to get the sensor to sample all the light, or to homogenize the intensity of the light with a sphere so that the sensor can sample a representative portion of it, and the rest be extrapolated, etc.


    By making the light have to take a torturous reflector path, it will tend to have the throwier part reflect differently than the corona or spill, etc. This leaves it less homogenized, so that what you measure is less representative. A duller surface might exacerbate that issue. Of course, the slight changes in angle, depth and rear reflectivity when the light isn't mounted as you intended for the permanent solution, would also add to the variables.

    Off the top of my head, shining the light onto a concave reflector to take the entire beam and compress it, and then perhaps measure either the output if it worked out to a convenient size, and/or shine it through a lens to make it "sensor sized".....onto the sensor, might allow collection of more of the light emitted?

    Going the other way to homogenize the light emitted, you could shine the light directly at a mirror that was faceted to break up the hot spot, etc, or convex, etc...and reflect the homogenized light back towards a sensor?

    IE: the Light could shine north at the convex mirror inside the reflective chamber, and back south towards the sensor.

    Just thinking out loud...

  8. #8

    Default Re: Lumens measuring contraption (feedback please!)

    Thx TEEJ, this was really more of an experiment to satisfy my own curiosity than anything. I do eventually still plan on building an DIY IS but wanted to see how this would work out. If nothing else, it would make an excellent platform for runtime testing (plus I have a design for this to act as a decor in my kids room). I likely won't be able to make any progress on this until the weekend but will be providing updates here whenever I do.

    I also need to send out a few of my lights for testing on a real calibrated IS before I'll even begin to know how to make sense of the readings from this thing.

    Cheers,
    Tim

  9. #9

    Default Re: Lumens measuring contraption (feedback please!)

    You asked for feedback...so I was trying to provide some.

    If you want to borrow my light meter let me know, I'm not scheduled to use it for anything in the near future.

    Also - If sending stuff out for IS measurements, if you think it will help, let me know if you could use any other lights for comparison, like the De-domed SR90 or DEFT edc LR, for throw, or a different tint Big Bruiser or a RRT-3 XML, for flood, etc.

    Last edited by TEEJ; 03-01-2012 at 08:51 AM.

  10. #10

    Default Re: Lumens measuring contraption (feedback please!)

    Thx a lot TEEJ! and I apologize if I came across as brushing aside your ideas, it was not my intention. I just realized that in order to start making sense of the readings, I need to have solid accurate data first, otherwise it'll just be guesses.

    I sanded down the step down adapter yesterday but by having that in place, it reduced the reading tremendously... this reinforces the fact that I need to establish a baseline first before I can start applying any corrective values etc.

    Really appreciate the offer to borrow some lights and will certainly take you up on it. Hopefully I can find somewhere local to get them tested (will let you know). Maybe someone w/one might be kind enough to bring it to PF18. ;o)

    Thx again!,
    Tim

  11. #11

    Default Re: Lumens measuring contraption (feedback please!)

    Quote Originally Posted by turboBB View Post
    Thx a lot TEEJ! and I apologize if I came across as brushing aside your ideas, it was not my intention. I just realized that in order to start making sense of the readings, I need to have solid accurate data first, otherwise it'll just be guesses.

    I sanded down the step down adapter yesterday but by having that in place, it reduced the reading tremendously... this reinforces the fact that I need to establish a baseline first before I can start applying any corrective values etc.

    Really appreciate the offer to borrow some lights and will certainly take you up on it. Hopefully I can find somewhere local to get them tested (will let you know). Maybe someone w/one might be kind enough to bring it to PF18. ;o)

    Thx again!,
    Tim
    That would be cool of them....does someone around here HAVE one?

  12. #12
    Flashaholic* jasonck08's Avatar
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    Default Re: Lumens measuring contraption (feedback please!)

    Very interesting project. I'd be curious to see how the readings would compare if you take a reading with the reflector on a specific light, then remove the reflector and lens completely. The reading should be higher without the glass lens and reflector, but my guess is that the reading would be lower...

  13. #13

    Default Re: Lumens measuring contraption (feedback please!)

    I actually did that w/a T40CS and the output measured w/out reflector and lens was drastically lower. But I suspect it would be the same w/a real IS since the light is simply not being directed forward (in my case into the PVC and w/an IS into the sphere).

    This has been good for comparitive purposes but I'm on the hunt for a sphere now... ;o)

    Once I have that up and running then I can revisit this to challenge the readings and see if I can actually tweak this device to make it meaningful.

    Thx a lot for the feedback everyone!

  14. #14

    Default Re: Lumens measuring contraption (feedback please!)

    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 positon 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 comparitive 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 expirement 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.

  15. #15

    Default Re: Lumens measuring contraption (feedback please!)

    THIS is one of the reasons why one of my requirements included being able to accomodate 4" bezels (sorry for the horribly blue tint, forgot to set camera to AWB):

  16. #16

    Default Re: Lumens measuring contraption (feedback please!)

    Nice Job Tim!


  17. #17
    Flashaholic* Solscud007's Avatar
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    Default Re: Lumens measuring contraption (feedback please!)

    Yes Tim, great job indeed. I got to see this thing firsthand at PF18. Im glad I didnt leave as I intended.

    We tested my Hellfighter and it is putting out 5,000 lumens!!!

    Collecting is not about what you have but rather what you DONT have . . . yet.
    ABTOMAT: "Newer Surefire lights strike me as the result of CNC programmers saying to each other "Hold my beer and watch THIS."

  18. #18

    Default Re: Lumens measuring contraption (feedback please!)

    Thx for posting solscud! That really was an amazing piece that Mac crafted for you (one more pic of your light down below).

    All,

    I took a few shots at PF18. We tested lights ranging from .3lms up to nearly 9K. Thx to the 4" opening, we were able to measure all lights although we had to remove the glass lens for ma_sha1's short arc though

    We were also able to demonstrate again that this doesn't really favor throwers since a TEEJ'S DEFT aspheric came in only around 80lms, otherwise it should've thrown the reading well off the charts. Too ba we didn't have a known calibrated light although an HDS Rotatry came in at 122lms these are known to have nearly perfectl flat regulation.

    Without further ado, here are the lights we took and since I can't remember all the details, for those that attended PF18, please feel free to pipe in and identify/correct any lights below.

    A few of Mac's Customs:


    Mac's Eagletac?:


    ma_sha1's short arc (can't remember the final ouput):


    solscud007's Hellfighter w/custom battery tube by Mac (I think this was originally over 7K and quickly dropped to roughly 5K+)


    Sorry, I can't recall whose light this was but it was around 9K on weak batteries after the quarry run:


    Same here, don't recall whose light this is:


    Anyways, PF18 was a blast and if any of you do actually put one of these together, I'd love to hear your feedback!

    Cheers,
    Tim

  19. #19

    Default Re: Lumens measuring contraption (feedback please!)

    IIRC, the Deft edc LR+ was 80 lumens,

    the DRY 3 XML was 3,300 lumens,

    the Fenix TK70 was 2,650 lumens,

    the De-Domed Olight SR90 was at 1,350 lumens (About the same as the 1,400 lumens Selfbuilt measured for the Domed version),

    the 4Sevens S12 Copper was 1,000 lumens,

    the 20 watt Stanley HID (HIDC10) was 1,300 lumens (But rated at over 2,900 lumens..a bit optimistic),

    the Nitecore TM11 came in at its 2k lumen rating,

    The Klarus XT11 was at 850 lumens after the drop (On 2 RCR123A's), didn't measure before, it was in use outside already...,

    of mine checked, that's all I remember right now. (Well, that I at least remembered to write down that night when you measured them...)

  20. #20
    Flashaholic* ma_sha1's Avatar
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    Default Re: Lumens measuring contraption (feedback please!)

    Quote Originally Posted by turboBB View Post

    ma_sha1's short arc (can't remember the final ouput):
    This is the Mega Blaster with 120W UHP lamp & a big Aspheric head, it read just over 7000 lumens.
    (7500 lumes when I dip the head in the tube a bit, didn't rest the head on the glass as I was afraid of bliding people by reflection).

    I also read my key chain 10280 Li-ion XPE light, it read 110 lumens. I think I had pretty close to two ends of the range, I had to say it worked pretty well. The UHP short arc lamp spec is 60-65 lm/watt. Which translate to 7200-7800 lumens range. Looks like I didn't lose much, most of the light managed to get focused & came out the front, I am pretty happy about that.

    I also agree that it doesn't seem to favor throwers, it it does, the readings would have been way out of wack, as the Mega Blaster has a measured candle power of 5 million lux @ 1 meter.

    Mega Blaster in action at Black hole/PF18. (Photo taken by CPFer WadeP)
    (16 million cp Moon blaster to the left & BVH 85Watt Blits spot to the right)
    Last edited by ma_sha1; 04-20-2012 at 12:13 PM.
    My Mods.. http://www.candlepowerforums.com/vb/...5&postcount=78
    Hobby only, I don't do custom mods as a service, thanks for understanding.

  21. #21

    Default Re: Lumens measuring contraption (feedback please!)

    Thx guys!

    For those who may not have had a chance to witness this first hand, I've put up two vids in my XTAR S1 review showing how the PVC LMD works:
    http://www.candlepowerforums.com/vb/...U2-1-3-x-18650)

    Cheers,
    Tim

  22. #22

    Default Re: Lumens measuring contraption (feedback please!)

    I'm currently making plans to re-design my lightbox, and PVC is looking like a pretty appealing material to use, for it's sturdiness and whiteness. Have you encountered anything so far that you would change about the way that you built yours? Specifically, with your setup does the reading change much based on how well centered the light is? I did a quick trial in Lowes the other day, with a few ways of arranging the pipe, and I found that moving the flashlight around the entrance made visible changes in the light level near the exit. I'm thinking through some different ways to even things out a bit, to make it less necessary for perfect centering and even out the playing field for throwers vs flooders.

  23. #23

    Default Re: Lumens measuring contraption (feedback please!)

    LOL, I was actually shining a flashlight into the pipe at HD although no one really paid me any attention.

    As for mods:

    - I'm looking to find a way to mount the sensor so that it's perfectly centered and allow it to adjust easily fore and aft in relationship to the mouth of the pipe.
    - have a piece of glass custom cut to fit the opening of the LMD (where the light rests on). In testing at PF18, having the light off centered did affect the readings but not too bad as having it at an angle (with the glass removed we angled the light in different directions). However w/the glass in place, you are always guaranteed the light will hit the pipe dead perfect to catch that elbow at a right angle. My original idea was to cut out thick white cardboard to act as a cover around the light (to reduce ambient lighting from getting in and help center it perfectly) but I haven't bothered since the sensor side is open and I always take measurements in the dark now.

    I have some more tinkering to do and will post updates as they happen but would love to hear your experiences with this should you decide to implement it.

    Am also still looking to send out a few lights for testing in a calibrated IS to see just how close/off this thing is but again, we did a bunch of testing at PF18 and most were in agreement it's great for relative output comparison and within close proximity of claimed/known values.

    Cheers,
    Tim

  24. #24

    Default Re: Lumens measuring contraption (feedback please!)

    Tim, what about a pocket door slide type receptacle for the sensor?

    The "Door" would have a hole the size of the sensor target dome...and a pocket the size of the sensor housing. You just insert/slide the sensor into the pocket, and its positioned.

    So, it would be a "door" that clips/attaches to the end pipe opening...and the door has a hole for the sensor dome to protrude though.

    The door would also have a pocket to hold the sensor housing...as simple as 2-3 rods angled to guide the dome in and hold it in place once inserted into the hole.

    Even one rod, formed into a long loop, would probably work.
    Last edited by TEEJ; 04-23-2012 at 11:44 AM.

  25. #25

    Default Re: Lumens measuring contraption (feedback please!)

    "Anyways more experimenting to come but what are your thoughts on this?"
    Interesting and creative experiment.

    *Call Labsphere to determine what coating they apply on the inside of of their spheres. It is not ordinary black paint. It is a special, non-reflective compound. If you don't feel comfortable about speaking with their engineers, let me know and I'll do so. I have several contacts within their organization.
    *Have your meter calibrated. Not just the meter itself, but the combination of the sensor plus the meter. The meter is simply measuring the current proportional to the output of the photodiode within sensor head.
    *Find a way to diffuse the outputs of those flashlights that are collimating their "beam" into a "hotspot." Since your luxmeter measures the peak of the value of the hotspot, it is does not, necessarily, account for the scatter values. Dispersing the beam will allow the measured value to be more indicative of the overall output rather than a peak.
    *Find a way to even out the right angles of the connect points of the PVC pipe. Angles tend to create reflection and scatter that tend to artificially pump-up the luxmeter readings.
    *Find a way to cover the entrance point of the light. You need to reduce the loss because much of the total light output of the source is lost since the large pipe opening vice the smaller flashlight head/bezel is allowing all the light to "escape."
    *Find a way to cover the point where the light meter sensor meets the pipe. Much light is also lost there.
    *If it is possible to do so and not damage the photodiode, remove that cheap, translucent, polymer prophylactic that covers the photodiode. This "cup" likely accounts for approximately 25% total (RSS not aggregated) loss in the meter reading. Polymers of this type (similar to milk jugs) typically have a Transmittance (T) value of ~25%; a Reflectance (R) value of ~3-7%: and an Absorbance (A) value of ~3-5% given the formula T + R + A = 1.
    *When making a measurement, ensure that the power supply of both your meter and the light source is as close to the nominal value as possible. Take a total of five readings. Move the flashlight [device] under test (DUT) minimally on the X and Y Axis to obtain a peak (max)meter reading then do the same for the detector. Using this technique, measure the trough (min) values. Calculate the average (mean) of the min and max value. This is known as varying the Angle of Incidence (AOI). Take the five readings, square the values, add them, divide by the number of readings (5), and calculate the square root. This is called Root Sum of the Squares (RSS).


    Good luck. Happy experimenting.

  26. #26

    Default Re: Lumens measuring contraption (feedback please!)

    Quote Originally Posted by 0dBm View Post
    "Anyways more experimenting to come but what are your thoughts on this?"
    Interesting and creative experiment.

    *Call Labsphere to determine what coating they apply on the inside of of their spheres. It is not ordinary black paint. It is a special, non-reflective compound. If you don't feel comfortable about speaking with their engineers, let me know and I'll do so. I have several contacts within their organization.
    *Have your meter calibrated. Not just the meter itself, but the combination of the sensor plus the meter. The meter is simply measuring the current proportional to the output of the photodiode within sensor head.
    *Find a way to diffuse the outputs of those flashlights that are collimating their "beam" into a "hotspot." Since your luxmeter measures the peak of the value of the hotspot, it is does not, necessarily, account for the scatter values. Dispersing the beam will allow the measured value to be more indicative of the overall output rather than a peak.
    *Find a way to even out the right angles of the connect points of the PVC pipe. Angles tend to create reflection and scatter that tend to artificially pump-up the luxmeter readings.
    *Find a way to cover the entrance point of the light. You need to reduce the loss because much of the total light output of the source is lost since the large pipe opening vice the smaller flashlight head/bezel is allowing all the light to "escape."
    *Find a way to cover the point where the light meter sensor meets the pipe. Much light is also lost there.
    *If it is possible to do so and not damage the photodiode, remove that cheap, translucent, polymer prophylactic that covers the photodiode. This "cup" likely accounts for approximately 25% total (RSS not aggregated) loss in the meter reading. Polymers of this type (similar to milk jugs) typically have a Transmittance (T) value of ~25%; a Reflectance (R) value of ~3-7%: and an Absorbance (A) value of ~3-5% given the formula T + R + A = 1.
    *When making a measurement, ensure that the power supply of both your meter and the light source is as close to the nominal value as possible. Take a total of five readings. Move the flashlight [device] under test (DUT) minimally on the X and Y Axis to obtain a peak (max)meter reading then do the same for the detector. Using this technique, measure the trough (min) values. Calculate the average (mean) of the min and max value. This is known as varying the Angle of Incidence (AOI). Take the five readings, square the values, add them, divide by the number of readings (5), and calculate the square root. This is called Root Sum of the Squares (RSS).


    Good luck. Happy experimenting.
    I thought they used a Reflective WHITE coating?

  27. #27

    Default Re: Lumens measuring contraption (feedback please!)

    "I thought they used a Reflective WHITE coating?"
    Not in the way most people understand reflection. An integrating sphere uses the relevant property of diffusion and scattering to minimize the original direction of the light incident to any part of it. Light applied to the sphere is distributed over all angles by minimizing specific angles such as what a mirror does.

    I should have clarified this in my original post.

  28. #28

    Default Re: Lumens measuring contraption (feedback please!)

    Thx for feedback guys!

    @0dBm, the paint that Labsphere uses (Spectralon) is prohibitively expensive so not an option for me at this time and if I were to splurge on that kind of money, I may as well save up for a real IS.

    For creating better diffusion, I'll likely sand down the inside w/steel wool and acetone. This should scruff up the surface enough to provide a nice matte finish, besides it'll be hard to evenly coat the insides w/paint anyways (which has also been a challenge for styrofoam spheres as well).

  29. #29

    Default Re: Lumens measuring contraption (feedback please!)

    Quote Originally Posted by 0dBm View Post
    "I thought they used a Reflective WHITE coating?"
    Not in the way most people understand reflection. An integrating sphere uses the relevant property of diffusion and scattering to minimize the original direction of the light incident to any part of it. Light applied to the sphere is distributed over all angles by minimizing specific angles such as what a mirror does.

    I should have clarified this in my original post.
    Labsphere's description of their coating is a reflective white - not a non-reflective black coating as you SEEM to describe. This IS very unclear in your post, as your post implies the exact opposite. IE: To a lay person, the difference appears to be more black and white.

    Perhaps if you were to clarify why the non-relective black coating you described, is described by them as a reflective white coating, it would help to clarify what you meant?

    --------------------

    Tim - It sounds like a lot of factors might be cancelling out in a nice way here.

    Your losses in light due to the transmission through the glass plate used to stand the light on to fix the height/alignment are subtracting from the lumens into the pipe.

    Your reflection of the light by the PVC inside the pipe might be increasing the detected lumens...according to the above post, but I don't think absorbing light would change the lumens except by reducing the amount making it to the end of the pipe/detector...and reflectance can't increase the OTF lumens themselves, as only what is there can be reflected, etc.

    Your losses to the pipe opening (Light reflected back out the top, around the light) would reduce the lumens detected.

    Your losses to the lumens lost around the detector would reduce the lumens detected.

    Your meter may or may not be reporting an accurate lux value.


    You already know you are currently getting good correlation of lumen values with known references...and your Lux = Lumens ratio is a happy coincidence.

    This says to me that while you are losing light from both open ends of the pipe, and due to the glass plate the light stands on, the square footage of the interior surfaces and the involved angles, whatever your meter is reporting, etc, all seem to be in a good ratio to have your end result work.



    Having your meter calibrated, and having some reference lights across a broad spectrum of light sources calibrated, would of course help...but may simply result in your current Lux = Lumen ratio being skewed - and you needing to use a conversion factor to get back to what you already get.

    Food for thought.

    Last edited by TEEJ; 04-24-2012 at 06:10 AM.

  30. #30
    Flashaholic* ti-force's Avatar
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    Default Re: Lumens measuring contraption (feedback please!)

    Quote Originally Posted by turboBB View Post
    Thx for feedback guys!

    @0dBm, the paint that Labsphere uses (Spectralon) is prohibitively expensive so not an option for me at this time and if I were to splurge on that kind of money, I may as well save up for a real IS.

    For creating better diffusion, I'll likely sand down the inside w/steel wool and acetone. This should scruff up the surface enough to provide a nice matte finish, besides it'll be hard to evenly coat the insides w/paint anyways (which has also been a challenge for styrofoam spheres as well).
    Sanding bare styrofoam actually works very well, and may work well with pvc also. I have sanded pvc before by hand and it tends to leave fine pieces of pvc sticking up. I'm guessing that's why you're planning to use the acetone while sanding? Anyhow, if you haven't already, see the following link for some interesting reading, and a comparison of light reflectance from styrofoam using three different surface finishes. 1- bare styrofoam, 2- sanded styrofaom, and 3- white paint/barium sulfate mixture coated styrofoam. CPF member Saabluster did all testing. The results for the sanded styrofoam are posted after post #20, but the entire thread is informative for some. Barium sulfate is a cheap alternative (for budget minded diy guys) to Spectralon, and the like. Link to thread- http://www.candlepowerforums.com/vb/...=1#post3624709

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