Calculate the right series resistor (and power rating) for an LED given supply voltage, forward voltage and current. Single or multi-LED series, E12/E24/E48 rounding.
| Metric | Value |
|---|
R = (Vs − n × Vf) / I, where I is in amps. Power dissipated by the resistor: P = (Vs − n × Vf) × I. Pick a rating at least 2× the calculated power for headroom.
If (n × Vf) ≥ Vs the LED won't light — drop one from the chain or raise the supply. Use the nearest higher standard value to avoid over-driving.
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