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Resistor for a blue LED on 9 volts
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300 Ω
resistor for a blue LED on 9 V at 20 mA (calculated 290 Ω)
Blue LED on 9 V by current
| LED current | Exact resistor | Standard value |
|---|---|---|
| 5 mA | 1,160 Ω | 1,200 Ω |
| 10 mA | 580 Ω | 620 Ω |
| 15 mA | 387 Ω | 390 Ω |
| 20 mA | 290 Ω | 300 Ω |
Assumes 3.2 V forward voltage; check your LED datasheet. One LED per resistor; for several LEDs in series subtract each forward voltage from the supply.
Other LED colors on 9 V
FAQ
What resistor for a blue LED on 9V?
For a blue LED (about 3.2 V forward voltage) at 20 mA on 9 V: R = (9 − 3.2) ÷ 0.020 = 290 Ω. The next standard value is 300 Ω, which gives 19.3 mA.
What resistor is safe for an Arduino or breadboard with a blue LED on 9V?
A 620 Ω resistor limits the current to about 9 mA - dimmer but safe and long-lived. Use 300 Ω for full brightness.
What power rating does the resistor need?
At 19.3 mA it dissipates about 112 mW, so a 1/4 W resistor is enough.
LED resistor calculator · all supply voltages · Ohm’s law
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