The Hub Lights (SL120) are very sensitive and need to be mounted correctly. It is important to ensure that the distance between the magnet and the light does not exceed 3 mm. You should also be aware that the capacitor is completely empty when you take the lights in use for the first time. When they are put in use for the first time, we recommend that you ride the bike for about 15 minutes in order to charge the capacitor. When the capacitor is fully charged your ReePower function should be working.
You may find that the rear light does not flash as brightly as the front light, as the LEDs in the rear light require more energy. The capacitor is empty at delivery, and in order to charge it as quickly as possible, you will need to make a long, quick trip the first time you go out on the bike. This will help clarify whether the light beams as it should.