I want to wire up an IR LED on a battery. I've seen many tutorials telling me that I should add a resistor, but none says what resistor to use to maximize battery life. So a 680ohm resistor will do the job of powering up the LED, but will a 47k resistor do the job too and keep the current still running (which will be more beneficial for the battery)?
I wonder if the LED (and all the diodes) need a minimum current, or a minimum voltage to operate, because I want to know how will adding one more diode in series or in parallel affect my choice of a resistor.
Also is my thinking correct? Say I have a 9V battery and a 0.7V drop LED. This means that if I place a resistor in series, the voltage drop through the resistor will always be 8.3V. So the current through both the resistor and the LED will be determined by the current through the resistor R which will be 8.3V / R.