The illumination is created by the LED. Once the Forward Voltage (VF) and Current (IF) is achieved, the LED will illuminate. If the voltage is reversed and exceeds the Reversed Voltage (VR), the LED can be damaged. A ballast resistor must be used to properly illuminate the lamp. An alternative to the ballast resistor is a constant current source circuit, but NKK’s LB and YB Series have LED options with built-in resistors. The LED is generally used in DC applications. If an AC circuit is used, a rectifier circuit along the ballast resistor is required to generate the appropriate DC voltage.