LEDs (Light Emitting Diodes) are current-driven devices. Unlike light bulbs, they have very low internal resistance. If you connect an LED directly to a battery without a resistor, it will draw excessive current and burn out instantly.
Why do I need a resistor?
To limit current. LEDs try to draw infinite current if voltage exceeds their forward voltage (Vf). The resistor acts as a bottleneck to keep current safe (e.g., 20mA).
What if I have multiple LEDs?
You can wire them in series (daisy-chain). The voltages add up (e.g., 3 LEDs × 2V = 6V needed). This calculator now supports series calculation. If wiring in parallel, each LED should have its own resistor.
Can I put resistors in parallel to handle more power?
Yes. Two 1kΩ resistors in parallel = 500Ω, but they can handle 2x the power (heat).
What power rating (Watts) resistor do I need?
The calculator below the result shows "Power Dissipated". Use a resistor rated for at least 2x that value (e.g., if dissipated is 0.1W, use a 1/4W resistor).