Backup LED Light

Tiny automatic light powered by a backup capacitor

This circuit will light the LED when the supply voltage is removed. In normal operation the base of the transistor is grounded and no current will flow through the LED. When the supply voltage is removed the diode will isolate the base from the negative on the capacitor and the 10K pull-up resistor will make sure the transistor is conducting. The capacitor is 1F, 5.5V.