LEDs are low‑current devices that must be protected from excessive current. A resistor placed in series limits the current, ensuring the LED (or LED string) operates safely within its rated parameters—typically a few milliamps and a maximum of 3 V DC. A 100‑Ω resistor is a common choice for a standard 5 mm red LED.
Tin a 100‑Ω resistor and a 5 mm red LED by applying a small amount of rosin‑core solder to their leads.
Solder one end of the resistor to the cathode (short lead) of the LED. Resistors are non‑polar, so the orientation of the resistor does not matter, but the LED’s polarity must be observed.
Solder a copper wire to the free end of the resistor. Solder another copper wire to the anode (long lead) of the LED. These wires will serve as the connection points to your power source.
Connect the wire attached to the resistor’s free end to the negative terminal of a 1.5‑ to 3.0‑V battery. Attach the wire connected to the LED’s anode to the battery’s positive terminal. The LED should illuminate brightly without overheating.
Adjust the resistor value to control brightness: higher resistance dims the LED, lower resistance brightens it. However, using a resistor that is too low or a battery that is too high can over‑drive the LED, causing heat and eventual failure.
Soldering irons can reach temperatures that cause third‑degree burns—handle with care. Inhaling solder fumes exposes you to trace amounts of lead, a known neurotoxin. Use a fume extractor or work in a well‑ventilated area.
