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  1. #1
    *Flashaholic* precisionworks's Avatar
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    Default Building an Integrating Sphere ...

    There are already articles on CPF about different light measurement designs, but none that I found on Integrating Sphere construction. For me, finding a hollow, white sphere was the first challenge. After quite a few searches, a 12" hollow styrene sphere was found at Barnard (phone 888-584-3637). Price with shipping was about $38 - the shipping seemed high until the sphere arrived in a carton almost twice as big as the item.




    A top and bottom plate were cut from 1/2" plywood. The sphere measured exactly 12" diameter, and the plywood was cut to 11 7/8" (square) to give the sphere a small amount of compression when assembled.



    Four posts (also 11 7/8") were cut to connect the upper & lower plates, and the posts and plates were assembled with yellow glue & brad nails.






    The sphere was placed inside the assembly, and four side panels were cut from 1/8" plywood. These are attached with yellow glue & brad nails.



    The upper hole is cut with a holesaw to match the diameter of the light meter sensor. The light port is also cut with a holesaw to fit the light tube.



    A piece of 2 3/4" stainless tube is used here, but PVC pipe would work just as well. The light tube was coated with Satellite City Special T Super Glue, the inside of the hole was misted with accelerator, and the tube was inserted & twisted until the glue set (about 5 seconds)




    Except for applying a finish to the wood, the IS is complete. The light meter is an Extech EA31 (range to 20,000 Lux). It was found on Amazon for under $100 & gives repeatable readings. Since the IS is a comparative device, my concern is that the readings are the same every time a light is retested.

    Here are the first Lux readings obtained:


    Malkoff M60 in Surefire 6P host - 10,400

    Surefire E1B on high setting - 6,540

    Surefire U2 on high setting - 6,350

    Novatac 120P on high setting - 5,790

    Muyshondt Nautilus high setting - 4,900

    Surefire L4 - 3,840

    Malkoff M60LL in Surefire G2 - 3,330

    Surefire E2L (single stage Cree) - 2,970

    McGizmo Sundrop - 2,550

    Surefire E1L (single stage Cree) - 2,180

    Muyshondt CR2 Ion - 1,580

    Again, these are comparative readings ... they are not absolute.
    Last edited by precisionworks; 06-15-2008 at 05:59 PM.
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  2. #2

    Default Re: Building an Integrating Sphere ...

    That is a cool set up.

    What difference in readings do you get with and without the sphere

  3. #3
    Flashaholic* adamlau's Avatar
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    Default Re: Building an Integrating Sphere ...

    Very interesting. Now to measure some light with big power .
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    Flashaholic* half-watt's Avatar
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    Default Re: Building an Integrating Sphere ...

    very nice construction job. kudos to you for your fine effort and excellent fabrication.

    based upon some of the comparative readings, not sure if the setup is truly integrating. obviously, the meter is still reading in Lux. that said, in some respects it still seems to be reading mainly "hotspot" (Lux) readings (plus some, perhaps???) and may not be truly integrating. why would i say this? well,...

    unless i have my head screwed on totally backwards, just compare two or three of the SF lights. SF rates the E1B at, IIRC, 80lm, the U2 and L4 at 100lm. now, the lux (hotspot) readings of these three lights are quite different, i would imagine, based upon hotspot (E1B > U2 > L4). your readings are ordered in accordance with what i would imagine it would be if only HOTSPOT was considered (again, E1B > U2 > L4).

    your readings indicate, comparatively, for those three SF lights what one might expect from Lux/hotspot readings and not what SF claims for Lumen ratings.

    i would like to know what the Lux readings are at a straight line linear distance equivalent to the diameter of the sphere. how different are they from the Lux readings using the sphere? how do they compare to each other?

    all this is *NOT* said to denigrate in any way either your exemplary initiative, nor your fine efforts. i just have these questions based upon the readings obtained and published in your Post.
    Last edited by half-watt; 06-14-2008 at 02:51 PM.

  5. #5
    *Flashaholic* precisionworks's Avatar
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    Default Re: Building an Integrating Sphere ...

    it still seems to be reading mainly "hotspot"
    I understand your thoughts, and agree that some of the readings are not what I expected. Perhaps 12" is too small for full integration of the reflected light. However, the diffusion dome of the meter is looking straight down at the bottom of the sphere, where it sees no direct light. The hotspot from the light is projected against the sphere wall opposite the light port.

    I may need to fabricate & install a baffle at the bottom of the sensor dome port. This would lower all readings by an equal amount & eliminate any overreading from a hotspot.

    FWIW, Chevrofreak used essentially the same locations for both light port & sensor port:

    Last edited by precisionworks; 06-14-2008 at 03:07 PM.
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    Flashaholic* half-watt's Avatar
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    Default Re: Building an Integrating Sphere ...

    understood about the relative positions of the light source and sensor. just having the right angle relationship between source and sensor does NOT guarantee that proper integration is occurring. one could use one flat mirror to reflect light at a right angle from source to sensor. this obviously would not be integration, and the meter would only read the hotspot/highest/brightest portion of the reflected light. i'd like to try to determine how much (in a purely gross qualitative sense; not a quantitative sense) integration is really taking place in your sphere.

    it still seems to be reading the reflected hotspot plus possibly some non-hotspot reflected light, and NOT integrating more/"all" of the light output. if it did the U2 and L4 ought to read higher than the E1B (again, unless i have my head screwed on backwards).

    if you measure the Lux output straight on at 12" (the diameter of your sphere) without the sphere, there are only three relative possibilites. the readings of each will be higher, lower, or the same when compared to the "in sphere" readings.

    if higher, then your sphere [readings] and Lux meter are only measuring SOME of the reflected light which appears to the meter to be reduced by the reflection in the sphere.

    if lower [, but still the same relative relationship E1B > U2 > L4], then there is some integrating taking place, but probably (again, based upon U2 and L4 being SF rated at 100lm vs. E1B rated at 80lm) still to a degree only measuring the brightest portions of the beam output.

    if lower, but a different relationship (e.g. E1B, NOT being the highest reader), then there may be something amiss in the straight line Lux readings as one would expect the E1B to be the brightest (i really don't know how they compare in Lux testing; i'm just guessing here based upon the brightspot of each light - i own all three of these SF lights).

    if the same (i don't expect this to be the case), then no integration is taking place.

    this is the values of performing a "sanity" check by taking normal straight line/linear Lux readings. i suggest using the very close 12" distance since that is the diameter of your sphere, or use 24" (or any other distance - easier to use a multiple of the sphere's diameter - makes purely mental calculation of the inverse square easier; i can't easily do inverse square with decimals in my head) and use the inverse square law of radiating energy to compare the results to the sphere's Lux reading.

    again, excellent work on the concept and fabrication. obviously, a valuable original Thread and Post on your part.
    Last edited by half-watt; 06-14-2008 at 03:33 PM.

  7. #7
    Retired Administrator Norm's Avatar
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    Default Re: Building an Integrating Sphere ...

    I'll start by saying I know nothing about this subject but I would have thought the best position for the light sensor would be close to the input port, if the tube at the input was set an inch or two into the sphere it would also act as a baffle.
    Norm

  8. #8
    *Flashaholic* precisionworks's Avatar
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    Default Re: Building an Integrating Sphere ...

    I looked again in the sensor port (which is 1/2" plywood followed by 1" of styrene foam) and saw that the styrene foam is capturing a some of the spillbeam, leading to an inflated reading on some lights.

    Since the sensor port is 2" diameter x 1 1/2" thickness (to the inside of the sphere), a piece of 2" tubing was painted flat black inside, and pushed into the port. The new readings are as follows:

    Malkoff M60 in Surefire 6P host - 2,880

    Surefire E1B on high setting - 1,780

    Surefire U2 on high setting - 1,774

    Novatac 120P on high setting - 1,582

    Muyshondt Nautilus high setting - 1,370

    Surefire L4 - 1,203

    Malkoff M60LL in Surefire G2 - 935

    Surefire E2L (single stage Cree) - 864

    McGizmo Sundrop - 727

    Surefire E1L (single stage Cree) - 614

    Muyshondt CR2 Ion - 454

    If you look at these numbers as a percentage, they are nearly identical to the first test without the black tube baffle. The numbers below are in percent, with the Malkoff M60 used as a 100% standard (numbers are test 1/test 2)


    Malkoff M60 in Surefire 6P host - 100/100

    Surefire E1B on high setting - 63/62

    Surefire U2 on high setting - 61/61

    Novatac 120P on high setting - 56/55

    Muyshondt Nautilus high setting - 47/48

    Surefire L4 - 37/42

    Malkoff M60LL in Surefire G2 - 32/32

    Surefire E2L (single stage Cree) - 29/30

    McGizmo Sundrop - 25/25

    Surefire E1L (single stage Cree) - 21/21

    Muyshondt CR2 Ion - 15/16

    To me, the only reading that falls outside the expected lumen curve is the E1B. I bought a few of these and sold all but this one (which is on a McGizmo Ti McClicky Pak host, not the standard SF body). It has about the same low setting as any other E1B, but the high is the brightest of any that I've seen. Maybe SF put the wrong driver board in this head, maybe the emitter bin is at the top of the XR-E series, but without a doubt it is brighter than the U2 on a ten foot, white wall bounce.

    A five foot ceiling bounce gives the U2 @ 42, the E1B @ 44.
    Last edited by precisionworks; 06-15-2008 at 06:00 PM.
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  9. #9

    Default Re: Building an Integrating Sphere ...

    Very interesting work indeed, Can you see white light coming through the sphere to the outside world? Is it glowing? If so you are losing light because the material is not as reflective as it should be. What ever amount of light is coming out is not being internally reflected.

    Half-watt's test sounds valid as a way to determine if its integrating or just getting most of the hot spot readings.

    Also what does IIRC mean?

  10. #10
    Flashaholic* half-watt's Avatar
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    Default Re: Building an Integrating Sphere ...

    IIRC = if i recall correctly

  11. #11

    Default Re: Building an Integrating Sphere ...

    Very cool!! You might want to install a PTFE or other white type baffle blocking the meter from direct viewing of your source port. I believe most IS have such a baffle.
    EDIT: Nevermind!

    BTW, I have a 6" sphere with 1.250" port access and it seems to do fine with anything I can introduce properly to the sphere.
    Last edited by McGizmo; 06-14-2008 at 03:11 PM.
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