Given the following circuit, it seems like we could use ohms law to conclude that current = voltage / resistance. With a source voltage of 3.3 and a resistance value of 220, current = 3.3 / 220 = .015 amps, however, after measuring the current with a multimeter, this value was wrong.
The actual measured current was .0061 amps.
So it seems that we need to subtract another value from the source voltage to get the right current result, I believe this value is the voltage drop.
What value do we subtract from the source voltage? Do we select the voltage drop of the resistor or the voltage drop of the LED and why?
It seems that based on the obvious values of a source voltage and a resistor, we need to include less obvious values in the calculation of current which seem to be only available by circuit measurements or by consulting a spec sheet of some sort.