LEDs are light-emitting diodes that emit light when electricity is applied, similar to a light bulb. LEDs are part of a group of lighting technologies called solid-state lighting and come in multiple styles, colours and light temperatures. LEDs provide greater energy efficiency than both incandescent and fluorescent lamps, and have a longer life cycle. A standard 3-volt LED lamp can be connected to a 9- volt battery, provided that a current limiting resistor is connected between the battery and LED.
Calculate the value of the resistor needed by dividing six volts by the LED 's current requirement in amps. The value calculated will be the resistor value in ohms. Use a resistor as close to this value as possible. Six volts is the remaining battery voltage across the resistor when there is three volts at the LED.
Solder the positive wire of the battery connector to one lead of the resistor. Solder the remaining resistor lead to one connection on the switch.
Solder the positive lead of the LED to the remaining switch connection. Solder the negative lead of the LED to the negative wire of the battery connector.
Verify that the switch is in the "off" position. Connect the battery connector to the 9-Volt battery. Turn the switch to the "on" position and verify that the LED illuminates.
Always verify all connections are correct prior to applying power to the LED
Use caution when soldering - irons are hot and can cause burns.