What you will need:
- 3 relay coils (I had some with 200 and others with 600 windings);
- 1 HD magnet;
- 3 diodes (general purpose diodes are ok, I used 1n5818 schottky for the low voltage drop);
- 18 blue LEDs (you may use how many you want or even other colors - white is also cool).
For the continuous mode just add:
- 1 capacitor (4700uF seemed fine, you could test some other values);
- 1 switch to be able to choose between modes.
Step 1: Circuit diagram
When the capacitor is connected to the circuit, it will be charged and will keep the LEDs on for some time when no coil is providing power.