LED's and Ohm's Law

[crazy legs]

I heard that they don't obey it, is it true. If so, why? Thanks.

[Clanad]

They don't appear to when wired directly to the power source, however, the LED needs a resistor. Without one, the only resistance is the wiring between the supply and the LED. Normal wire has a very low resistance. By Ohm's Law, a very large current will flow and probably destroy the LED. Therefore the requirement for the resistor... When taking the resistance of the resistor into account the device certainly obeys Ohm's law...

[mibn2cweus]

LEDs only appear to violate Ohm's Law because they are a non-linear device consisting of a semiconductor PN junction in which the resistance changes in relation to the polarity and potential of the applied voltage.

A standard light bulb also has a non-linear response to the applied voltage, in this case due to an increase in resistance that results when the filament is heated by the flow of current through it. Once the change in resistance is taken into account, conformity with Ohm�s Law is observed.

The operational properties of several semiconductors are explained here