I'm a real newbie and I hope I'm posting this in the right place. I recently got a new light with a Cree LED-XM-L. The spec sheet says the emitter output is 25 - 580 lumens and the input voltage is 2.8v to 12v. The flashlight is designed to hold either 2-123A batteries (6v) or 1-18650 (3.7v) battery. Am I right in assuming that if I use 2-123A batteries for a total of 6V I'm not going to get any where near the 580 lumens the flashlight is capable of putting out?
Lumens & voltage question
- Thread starter Telman2
- Start date
AnAppleSnail
Flashlight Enthusiast
The LED will not take over 5V, but the driver can. The honest answer is: "It depends on the driver." Cheap drivers tend to get brighter with more voltage input. Also I doubt you'll see 580 lumens out of this on any setting.
Now I'll really show my ignorance, I don't know what a driver is. Let me ask this, when I'm buying a flashlight how do I know what I'm getting if I can't go by what the dealer is saying? The light I have was purchased from a popular dealer I see mentioned here on CPF many times and the manufacture has a forum here on CPF. I would say it's a quality product not something cheaply made, I paid just over $100.00 for it so how do you know what you're really getting?
You did not mention a higher quality light, so AnAppleSnail typed for the "typical" cheapo light (where the boasts usually are way overrated)
As to Your questions:
a (white) led needs ~ 3.7-4 V input power. The driver (= circuit) guarantees, that this is delivered to the led.
f.e. when the input is lower (2*AA cells) then it pushes the voltage up, if its too high (like Your 2*CR123 cells) then it gets down.
A single Li-Ion is a special case, thats almost the voltage the led "needs". The better the driver, the less losses it has, the more power goes to the led.
In General a typical "better" light will run the led on high output:
* all the time with the 2*CR123, (till one is depleted)
* a very long time for the single 18650 (it has to reduce getting power from the single cell, just be4 it gets depleted).
You can do a few very rough (but astoundingly correct) and easy measurements:
* first: let light run for some mins, open battery end and hook a current meter between negative end of battery and flashlight body. That way You get the current to the driver;
in a single cell setup this is almost the same, that is what goes to the led.
For 600 Lumen the XM-L has to see almost full power, so You should get a reading of about 2.3-2.5 Amperes.
* heat: switch light on and wrap Your fingers around. You should - within some seconds, lastest 1 minute - notice it getting hot.
And after - say - 15 mins (without holding it) it should almost be to hot to grip again.
Then the XM-L will be run on high power.
* runtime: switch it on and it should run about 50 mins - 1 hour at one 18650.
(2.5 Amp current from a 2.500-2.900 mAh cell --> 1 hour runtime)
((I recommend fully putting it in a box of water then, for cooling))
PS: imho the 1*18650 setup is the better one.
same size of the light, less "loose" cells, no chance to mix loaded and depleted cells by accident, more power in the single cell than the 2*CR123 have together, ...
only con: primary cells can not be purchased in a store; in case the cells brought to "work" are empty and can not be recharged
(to bring enough and use the light on levels and runtimes to still have enought light left --> is users skill)
;)
PPS: sorry for the long post, i hope it is still readable.
What light did You get?
As to Your questions:
a (white) led needs ~ 3.7-4 V input power. The driver (= circuit) guarantees, that this is delivered to the led.
f.e. when the input is lower (2*AA cells) then it pushes the voltage up, if its too high (like Your 2*CR123 cells) then it gets down.
A single Li-Ion is a special case, thats almost the voltage the led "needs". The better the driver, the less losses it has, the more power goes to the led.
In General a typical "better" light will run the led on high output:
* all the time with the 2*CR123, (till one is depleted)
* a very long time for the single 18650 (it has to reduce getting power from the single cell, just be4 it gets depleted).
You can do a few very rough (but astoundingly correct) and easy measurements:
* first: let light run for some mins, open battery end and hook a current meter between negative end of battery and flashlight body. That way You get the current to the driver;
in a single cell setup this is almost the same, that is what goes to the led.
For 600 Lumen the XM-L has to see almost full power, so You should get a reading of about 2.3-2.5 Amperes.
* heat: switch light on and wrap Your fingers around. You should - within some seconds, lastest 1 minute - notice it getting hot.
And after - say - 15 mins (without holding it) it should almost be to hot to grip again.
Then the XM-L will be run on high power.
* runtime: switch it on and it should run about 50 mins - 1 hour at one 18650.
(2.5 Amp current from a 2.500-2.900 mAh cell --> 1 hour runtime)
((I recommend fully putting it in a box of water then, for cooling))
PS: imho the 1*18650 setup is the better one.
same size of the light, less "loose" cells, no chance to mix loaded and depleted cells by accident, more power in the single cell than the 2*CR123 have together, ...
only con: primary cells can not be purchased in a store; in case the cells brought to "work" are empty and can not be recharged
(to bring enough and use the light on levels and runtimes to still have enought light left --> is users skill)
;)
PPS: sorry for the long post, i hope it is still readable.
What light did You get?
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