Light Emitting Diode or LED is suitable for ON/OFF indicator since it has high durability, almost free of maintenance. The most common usage is in low voltage application since the operating voltage is low DC. Taking the benefit of its high durability of LED in high AC voltage from line voltage can be done using this circuit:
The capacitor is used to limit the current, and the zener diode is used to limit the voltage. The zener diode also provide a path to dischage capacitor at the half cycle when the direction is backward to the LED. Since the current amount is limited by the capacitor, you can select the capacitor value to adjust the current to suit your need. It gives about 4 mA at 100nF, and about 20 mA at 470 nF. Please note that the lower the current, the longer the LED’s lifetime.
