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

1. ## 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. ## 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.
P

3. ## 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!

5. ## 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.

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

Originally Posted by LogicalBeard
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.

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