Every LED needs a current-limiting resistor to prevent burnout.
R = (Vsupply − Vforward) / Iforward.
Standard LED forward voltages: Red 1.8V, Green 2.1V, Blue 3.2V, White 3.3V.
Reach for this calculator when a quick, verified engineering computation is needed without opening specialised software. The formula used follows the relevant standard and is documented for reference.
A frequent mistake is using nominal or rated values when actual measured values are required. Calculations based on nominal dimensions or catalogue specifications may not match field conditions — always use measured values where precision matters.
A mechanical engineer verifies a beam's deflection under a specified load using standard formulas. Running the calculation with exact dimensions confirms the design meets deflection limits before fabrication — catching an issue that would be expensive to correct in the field.
An LED has very low resistance. Without a resistor, too much current flows and the LED burns out.
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