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Thread: Just build my own "poor man's" integrating sphere

  1. #1

    Default Just build my own "poor man's" integrating sphere

    Take a look:

    *Pictures removed*

    What do you think? Of course I know that this can't be absolutly correct measurement. But it gives me a value for comparison.

    Here are some measured values in mV:

    Nuwai ALX-352L
    High 332
    Med 310
    Low 287

    Gladius
    Max 316
    Low 42

    Nuwai Q3 295

    Fenix L1P 2.5 291

    GlooTob FX Blue
    100% 174
    25% 53

    Arc-AAA Premium (2005) 266

    NoName 3W 3xAAA 313

    What do you think about these measurements? Are they correct? They seem to be logarithmic. I'll have to look for the charactieristic curve of that photo diode I used.
    Last edited by Xygen; 01-03-2013 at 07:09 PM. Reason: had to remove the pictures
    Nuwai ALX-352L - Gladius - Q3 - Arc-AAA P v4 - Glo-Toob FX - Jil 1.3 Up - L1P - L0P - Petzl Myo XP - PT EOS - E1L - Orb RAW NS - Fire~Fly 3 - VG FB1 - P1 - L4 - P1D-CE - L5 - KL3 - KL5 - KL4 - L2D-CE - L0D-CE - P2D-CE - L6 - L1-Cree - EDC120P - NiteCore EX10 + D20-R2

  2. #2
    *Flashaholic* wquiles's Avatar
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    Default Re: Just build my own "poor man's" integrating sphere

    Very cool . I am in the process of also building my own "light box". Like yours, it will not give me "absolute" measurements, but it should give enough information to do A to B comparisons

    Will
    Please no PM/Visitor Msg's. Email for questions/Paypal: wquiles [at] gmail {dot} com. Please visit my new website.

  3. #3
    Farewell our Curmudgeon Administrator Roy's Avatar
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    Default Re: Just build my own "poor man's" integrating sphere

    Now alll you need is a logging DMM and you can start doing runtime plots!!!

  4. #4
    Flashaholic*
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    Default Re: Just build my own "poor man's" integrating sphere

    I just have to ask. Gladius measures 316 units on high and Arc AAA measures 266?? You sure meant Arc AAA or Arc-something-else-that's-definitely-brighter? That means the Gladius is only 1.2x as bright as a AAA light?

  5. #5

    Default Re: Just build my own "poor man's" integrating sphere

    I'm sorry. I have no exact information about this photodiode I use. As I said, it seems to be some kind of logarithmic value.
    With absolute darkness I measure 0 milliVolt. When lifting the the lid a little, the measurement rises very quickly. At higher brightness, the measurement rises not so quickly. I think I have to calculate them, to get a e.g. "Gladius is x times brighter then ARC-AAA" result. Or just to get a true lux value.
    The diode is a EG&G UV-040BG 8911.
    I just used it in the absence of a luxmeter.

    Another thing is, that its not good, to put the flashlight in the box. A dark object (like the Gladius) absorbs light and gets a lower reading than a silver flashlight. I can measure a difference, when I put a black piece of plasic in the box. Even if its not in the way of light.

    Of course you can find better info about the brightness of specific flashlights from the well known review sites.
    It's just some kind of experiment I wanted to try and to get some feedback from you.

    Thanks for your concern!
    Last edited by Xygen; 11-22-2005 at 07:30 PM.
    Nuwai ALX-352L - Gladius - Q3 - Arc-AAA P v4 - Glo-Toob FX - Jil 1.3 Up - L1P - L0P - Petzl Myo XP - PT EOS - E1L - Orb RAW NS - Fire~Fly 3 - VG FB1 - P1 - L4 - P1D-CE - L5 - KL3 - KL5 - KL4 - L2D-CE - L0D-CE - P2D-CE - L6 - L1-Cree - EDC120P - NiteCore EX10 + D20-R2

  6. #6

    Default Re: Just build my own "poor man's" integrating sphere

    This is a good idea and similar to others light measuring devices. What would be cool is a standardized recipe for building a device like this that is made from components that are easily available pretty much world wide. Then , as long as folks were mindfull to follow the directions we would have CPF standardized measurements that could be verified from user to user. In time, the measurements based on a CPF standard recipe lightbox just might become more meaningful than those that come from 10 thousand dollar devices belonging to a few elite companies.

  7. #7

    Default Re: Just build my own "poor man's" integrating sphere

    Yes that would be great, but hard to realize.
    Alone the material of the box must be nearly the same. Must not be mirroring (glossy) and must not absorb too much light. I think there are a lot of different shoe-boxes out there...
    Last edited by Xygen; 11-22-2005 at 07:32 PM.
    Nuwai ALX-352L - Gladius - Q3 - Arc-AAA P v4 - Glo-Toob FX - Jil 1.3 Up - L1P - L0P - Petzl Myo XP - PT EOS - E1L - Orb RAW NS - Fire~Fly 3 - VG FB1 - P1 - L4 - P1D-CE - L5 - KL3 - KL5 - KL4 - L2D-CE - L0D-CE - P2D-CE - L6 - L1-Cree - EDC120P - NiteCore EX10 + D20-R2

  8. #8
    Flashaholic* zespectre's Avatar
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    Default Re: Just build my own "poor man's" integrating sphere

    My thoughts

    1) The box should have some sort of "portal" into which you put the light vs placing the light inside. With the light sitting inside you have a LOT of variables, not the least of which would be that the exact same light would probably read differently with a matte black finish vs a polished silver finish.

    2) Create a tray of some sort so that the lights are always alligned the same.

    Just my .02 worth.
    "Notorious collector of things that glow, shine, or blink"
    CPF # 9435

  9. #9

    Default Re: Just build my own "poor man's" integrating sphere

    Quote Originally Posted by Xygen
    [edit]
    What do you think about these measurements? Are they correct? They seem to be logarithmic. I'll have to look for the charactieristic curve of that photo diode I used.
    Photodiodes produce a current proportional to irradiance, not voltage. So connect your photodiode to the current terminals of the meter (microamperes scale setting) and see what you get. Those results should make a lot more sense.

    Here is a good reference:

    http://www.udt.com/Datasheets/Other/...cteristics.pdf

    Photodiodes operated in photoconductive mode (with a bias voltage) are typically more linear, but for these purposes photovoltaic mode should be just fine as it will still give at least 6 decades of linear response, provided you have a decent photodiode.

    Photodiodes also have varying responsivity as a function of wavelength, so comparing the results of significantly different colored lights will not be valid. For white sources, you can probably get away with ignoring this. This assumption is more acceptable if the phosphor is the same for the sources in question. But if different phosphors are used between different vendors, then discrepancies can arise.

    As for the homemade integrating box, it would be better to install some baffles. Consider a baffle in the center, and shine the light onto it from the face opposite the photodiode. The baffle must be diffuse white reflective, and opaque so no light seeps though it. The scattering of light will be much better this way, so hopefully the variations in light intensity reaching the detector vs. the angle, divergence, and distribution of the incoming light beam will be less.

    Folks seem to think they should put the light into the integrating sphere. This is not necessary. Just have an aperture that the light shines into. You can qualitatively tell if the integrator is doing a good job if when you move the light source around a bit (pointing the beam at different spots on the baffle) that the light intesity seen by the detector doesn't vary much.

    A better test would be to take a laser and shine it at different points on the baffle. If the detector signal doesn't vary much, then it is working well.
    ________
    Good day!

  10. #10
    Flashaholic* CroMAGnet's Avatar
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    Default Re: Just build my own "poor man's" integrating sphere

    It would be ultra great to have a CPF member to log LUMEN graphs on our favorite lights. I hope you have some success at the "poor man's" IS

    Gadget_Lover has a kewl version of his "poor man's" makeshift IS. He usually brings it along to the CPF get-togethers and he's coming to the one we're having in a couple of weeks in the San Jose bay area.

    http://www.candlepowerforums.com/vb/...ad.php?t=98111

  11. #11

    Default Re: Just build my own "poor man's" integrating sphere

    Xe54: I'm impressed by your knowledge! Thank you very much.
    I'll evade this photodiode-thing. I ordered a cheap ($30) luxmeter today.
    I'll think about that baffle... I've found this description of a IS:

    Integrating Spheres
    An integrating sphere is a hollow
    sphere coated inside with Barium Sulfate, a
    diffuse white reflectance coating that offers
    greater than 97% reflectance between 450
    and 900 nm. The sphere is baffled internally
    to block direct and first-bounce light.
    Integrating spheres are used as sources of
    uniform radiance and as input optics for
    measuring total power. Often, a lamp is
    place inside the sphere to capture light that
    is emitted in any direction.

    Source
    Nuwai ALX-352L - Gladius - Q3 - Arc-AAA P v4 - Glo-Toob FX - Jil 1.3 Up - L1P - L0P - Petzl Myo XP - PT EOS - E1L - Orb RAW NS - Fire~Fly 3 - VG FB1 - P1 - L4 - P1D-CE - L5 - KL3 - KL5 - KL4 - L2D-CE - L0D-CE - P2D-CE - L6 - L1-Cree - EDC120P - NiteCore EX10 + D20-R2

  12. #12
    *Flashaholic* jtice's Avatar
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    Default Re: Just build my own "poor man's" integrating sphere

    Looks great to me, I have been thinking of doing this also.

    Only suggestion I have is, that for example.
    The Fenix you have laying in there,
    If you were to lay the Gladius in there, the front of the bezel would be closer to the box walls.
    Since the light is longer,
    you need to try to make the front of the bezel be the same distance from the walls all the time.
    Then again, I guess I could be REAL picky, and say that the different diameter bezels will hold each up off the bottom at different levels.

    Nice work, will be great for reference, better than my ceiling bounce test

    ~John

  13. #13

    Default Re: Just build my own "poor man's" integrating sphere

    Yes, you're right John. The distance from the reflecting wall and the angle in which the light shines onto it makes a little difference. But not very much. I tested that. I put the lights in different locations and w/ different angles into the box. Measured only a few mV difference. I think this cardboard box diffuses the light very good.
    But as mentioned above, I must not put the light into the box, because it "eats" light. And that would solve this problem too.

    I just did another test: Take a flashlight and aim it at the ceiling. Now look at a white item on the floor. Now vary the distance to the ceiling. You will see that the item will be lit at the same intensity. Ok, you'll need a dark room for that!!!

    Greetings... and thanks for your comments!
    Nuwai ALX-352L - Gladius - Q3 - Arc-AAA P v4 - Glo-Toob FX - Jil 1.3 Up - L1P - L0P - Petzl Myo XP - PT EOS - E1L - Orb RAW NS - Fire~Fly 3 - VG FB1 - P1 - L4 - P1D-CE - L5 - KL3 - KL5 - KL4 - L2D-CE - L0D-CE - P2D-CE - L6 - L1-Cree - EDC120P - NiteCore EX10 + D20-R2

  14. #14

    Default Re: Just build my own "poor man's" integrating sphere

    Argh! Where did the pictures go? I just started a thread asking about how to measure lumens on the cheap (http://www.candlepowerforums.com/vb/...emitter-lumens), and then I just noticed this thread.

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