wvmarle:
A diode is NOT a resistor and also doesn't at all act like it, if only because it conducts in only one direction, which is the most common use of a diode. The voltage drop is fairly constant over the allowed current range, usually increasing slowly with increasing current. Check the data sheet of individual diodes on the actual voltage drop.To calculate the power dissipated by a diode, take the voltage drop (0.6V) and multiply this by the current (for an Arduino typically about 150 mA - depending on peripherals), and you get 90 mW.
I'm a bit confused. If a resistor causes a drop and a diode creates a voltage drop isn't the diode acting like a resitor. Could one not get a 0.6 voltage drop using a resitor. (Would't a 4 ohm resitor do thing as the diode in this circuit.