This little laser beam tail light will ensure your safety while riding in the darkness. It has 3 LEDs and 2 laser bulbs. The LED and the laser work independently.There are three modes of the LEDs: Slow Strobe/Fast Strobe/Normal.Powered by two AAA batteries (not included). The working time depends on the batteries employed: with two 900 mAh batteries it can generate the laser beam for 8 to 9 hours.This safety light can be mounted on 16-36mm seatpost. The length and position of the laser beam varies with the angle you mount the lamp.