Many, MANY THANKS for your EXCELLENT article on choosing resistors for LEDs - http://www.evilmadscientist.com/2012/resistors-for-leds/
We learned a great deal from it and from the comments too.
How would we use that formula to calculate the resistors needed to: 1) Replace one CR2032 with 2 C or D batteries to extend battery life for existing LED lights used with model trains; and 2) Replace three LR44 button batteries with three C or D batteries for an existing LED fixture we want in a dollhouse? We are trying to get the equivalent current using larger, longer life batteries and don't want to tear the lights apart to see if we can find the specs on the LEDs they use.
Is this a straight forward application of Ohm's Law using the mAh we find for these batteries? Is there anything else we should consider? I don't want to blow up the little LEDs they are currently using, just extend the battery life.
Is there a procedure we could use with a multimeter to determine the correct resistor? Or can you suggest a topic we could Google?