sorry but i have to ask this HELP : )

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sorry but i have to ask this HELP : )

please let me know if there is a better place to post this

ok is there a difference between 500mA at 12V Vs. 500mA at say 4 or 6 or 8 V


is it the same power ? does the led show a difference in brightness


let me lump another one thats been avoiding me if you want to go for the bonus prize

can anyone link me to a chart of a measurement of heat outputted by an XML at say 100mA to 3A or so ....

for example at 300mA it makes X amount of heat and need X amount of heatsinking at room temp of X , anythign general to pretty involved would help alot


thank you in advance , sorry this has just been eluding me

Edited by: df2dot on 06/15/2011 - 17:27
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Ok, i'm not an expert but i'll try to give you an answer..

You can use this law to calculate "power"


Where p=power (watt), v=voltage (volt) and i=current (A). So you can have different watt with same current if you use a higher voltage.
I hope i didn't say something stupid.. this are all school memories.Embarassed


In this post you can find a spreadsheet to calculate the led temp. i don't think you can have a perfect equation to calculate the temperature at any current. There are too many variables

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power is relative to voltage AND amperage


for instance, a 3 volt battery putting out 10 amps (not a reality) would be 30 watts.

wheres a 12 volt battery putting out 10 amps would be 120 watts...

so you can see where 500mA draw is multiplied by the voltage. that gives you the power or wattage; which sums up it up in basic terms

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0.5A x 12v = 6Watts 

0.5A X 6v = 3Watts 

And so forth ...  Power is expressed in Watts 

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Last seen: 1 year 9 months ago
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btw thank you for posting

... so .5A @ 12v is not the same POWER OR BRIGHTNESS as .5A @ 4.5V 

 i have so much to learn

my intention it to hook up some LED( S ) , xmls preferably to a power adapter, like one that would go into you cable modem for instance

i was looking for something in the 1A range , found some 300mA @ 4,5v to 1.2A @ 12v

just didnt want to fry my precious XML : D



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XM-L's should be powered from a 3.3v source, this is referred to at it's forward voltage or Vf. 


Our batteries generally have a higher voltage than that, but battery voltages sag significantly under load so with that factored in we generally are pretty close to the recommended VF.


Generally for testing purposes you would only want to power them from a power supply you can set the voltage and current on. For long term use you are probably better using a driver circuit.