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Thread: Methodology and factors contributing to guesstimating lumen outputs based on amps

  1. #1

    Thinking Methodology and factors contributing to guesstimating lumen outputs based on amps

    I was curious if there was a shorthand way to guesstimate the lumens a light puts out by knowing the amount of amps it pulls.

    For example, if I know a flashlight pulls 1 amp on the high mode with a 3.7 volt battery with an xm-l emitter, and is constant current, is a reasonable guess possible?

    Related, if the same flashlight used a 3 volt primary, would the guess be the same?

  2. #2
    peter yetman's Avatar
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    Default Re: Methodology and factors contributing to guesstimating lumen outputs based on amps

    If you look at the spec sheets for various emitters they give the luminous flux at a defined current. I have seen some graphs also which give the results.
    As for the flashlight on Li-ion or primaries, it would depend on the driver. A boost driver would raise the voltage seen by the emitter on a primary so no difference would be seen. You really need to know the currecnt being supplied to the emitter rather than the driver.
    I think I understand what I'm trying to say.
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    Last edited by peter yetman; 08-12-2018 at 06:09 AM.

  3. #3
    Flashaholic*
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    Default Re: Methodology and factors contributing to guesstimating lumen outputs based on amps

    For Cree LEDs, you can also use their interactive Product Characterisation Tool:

    http://pct.cree.com/dt/index.html

    As Peter Yetman says, you need to know the LED current.

    For ordinary linear drivers - the sort of thing you'll see in most single-cell Li-Ion flashlights, like the Convoy S2+ or BLF A6 - the LED current is essentially the same as the cell current you measure at the tailcap, minus a milliamp or two for the driver itself.

    For switching boost or buck drivers, you either have to measure the LED current directly, or calculate an estimate using the LED voltage, the cell voltage, the cell current and the driver efficiency. That last part gets complicated, as driver efficiency varies with changes in most of the other parameters!
    Phlogiston is the main constituent of Magic Smoke.

  4. #4
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    Default Re: Methodology and factors contributing to guesstimating lumen outputs based on amps

    Moving thread to "Flashlight Electronics"
    ... is the archimedes peak

  5. #5

    Default Re: Methodology and factors contributing to guesstimating lumen outputs based on amps

    Cool stuff. Thanks for the info fellas. And thanks Archimedes, I wasn't sure where to post the thread at.

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    Default Re: Methodology and factors contributing to guesstimating lumen outputs based on amps

    Quote Originally Posted by LogicalBeard View Post
    Cool stuff. Thanks for the info fellas. And thanks Archimedes, I wasn't sure where to post the thread at.
    Certainly, it is an interesting topic.
    ... is the archimedes peak

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