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LED series resistor calculator

Picks the series resistor for one LED or a string: exact value, nearest preferred value, actual current, and power per resistor.

Enter the LED and the supply to size the resistor.

This is a plain series resistor for an indicator or a low-power string. It assumes one resistor in series with the whole string, so every LED carries the same current. It does not model LED binning, thermal runaway, or constant-current drivers, and a parallel string needs one resistor per leg. The suggested rating doubles the calculated dissipation because running a resistor near its rating cooks it and drifts its value.
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