Quick Tour Video:
Circuit is basically a "gated" blocking oscillator (joule thief) . IC1 CD4001 requires 3V and will not run from 1.5V (AA cell) when first connected. By shorting the header pins 1-2 momentarily, circuit oscillates and flyback voltage pulses appear at collector of transistor Q1. These pulses are rectified by LED and charge capacitor C3 while at the same time light is emitted by LED. Now, CD4001 is powered from C3 with adequate supply voltage, and produces short pulses (1.5mS) at a rate of 1Hz (header pins disconnected). Cycle repeats until 1.5v cell is depleted.
Led should be of maximum efficiency (current is very small).