LEDs are great devices, small, very bright, efficient run cold and easy to use. They are quite hardy too, with one exception: excessive forward current. Forward WHAT? Sorry, if you don’t limit te current flowing through the LED it will smoke and die. It could also damage your output circuit too. So how do we limit the current? Simple a series resistor.
How to select a resistor.
This is a simple ohm’s law calculation and a data sheet lookup for your LED. If you don’t have the data sheet you can make a basic assumption that the voltage potential difference between the anode and cathode of approximately 2V. LEDs also have a maximum forward current Iforward of between 10-20mA. The more current, the harder the LED will be driven.
Don’t forget about power dissipation:
so a 0.125Watt resistor will be fine.
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