This LED flasher give similar circuit with the previous transistor LED flasher, but this circuit use a 555  integrated circuit chip as the active component. Here is the schematic diagram of the LED flasher circuit:

led flasher 555 circuit schematic

This circuit gives alternating LED flashing, but with different flashing period between LED 1 and LED 2. The ON period of the LED 1 is proportional to the R2 value, and the ON period of the LED 2 is proportional to R1 + R2 value. If you use a 1M variable resitor in series with a 22k resitor to replace R1, then you get a variable period flasher. The power consumption will be much lower if you use only LED 1 (remove the LED 2 and R4), and choose R2 value to be much lower than R1. This would give you a strobe effect since the ON period will be much shorter than the OFF period.