Many electronic circuits need an indication that they are under power; for most ac circuits, a neon lamp is
the device of choice. A bidirectional tricolor LED can be used if a capacitor is connected in series with the LED to limit the current through the LED. 1-Â¥, 250-WVdc capacitor, which has a reactance of 2 650 ohms at 60 Hz, is used in series with an LED to limit the current through the unit to 43 mA. The impedance of the LED is low compared to the reactance of the capacitor, so nearly all the impedance will be caused by the capacitor with the added advantage of no energy loss caused by the capacitor. The power of the LED is 1.175 V 0,043 A = 50 mW compared to an NE-2H at 250 mW. For 230 V, use a 0.47-^F, 400-WVdc capacitor.