Hi I am a beginner I am making an LED flasher of 55 LED's. there are 6 lines of 8 LED's and 1 line of 7 LED's. The start voltage will be 15 volts prior to the 555 chip and drop to about 13 volts by the time it leaves the 555 chip. I will be having a resistor before each line of LED's. I would like each LED to run at about 20MA, but am unsure what to put in the ohm's law equation as the voltage. Is it 13 volts, or the voltage drop of an LED, or the full voltage drop of the series of LED's, or the voltage leaving the LED's.?