LED Resistor Calculator
Physics & EngineeringCalculate the resistor value needed to safely power an LED at a target current.
Required Resistor Value
The required resistor value in ohms to safely limit current to the LED at the target current, given the supply and LED forward voltage.
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Odeh Ahwal0people find this calculator helpful
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Physics & Engineering calculators
Frequently Asked Questions
Why does an LED need a current-limiting resistor?
LEDs have very low internal resistance and would draw excessive current without a limiting resistor, leading to overheating and rapid failure — the resistor protects the LED by limiting current to a safe operating level.
What is LED forward voltage?
Forward voltage is the voltage drop across an LED when it is conducting current in its normal operating direction, varying by LED color and type, commonly listed in the component datasheet.
What happens if the supply voltage is lower than the LED forward voltage?
If supply voltage is lower than the LED forward voltage, the LED will not illuminate properly or at all, since there is insufficient voltage to overcome its forward voltage threshold and allow significant current flow.
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