Depending on your LED's forward voltage that could well be a perfect value resistor for the job. This relies on Ohm's law (link to calculator online) to calculate.
If your source voltage is 5V and the voltage drop across your LED is 2V, you put 3V in that calculation (the voltage that will be dropped over the resistor 5V - 2V = 3V) and 220 as your resistor value in and it will calculate 13mA as the current. 20mA is your upper limit for a pin on your Arduino so that's well within the capability.
Hope that explanation makes sense, Geoff
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