bell arella 250 led bike tail light. the five led design puts out an intensely bright 20 lumens and offers three attention grabbing modes; steady, flash and rapid flash. it features an extra wide beam pattern that stretches more than 180 degrees and provides excellent rear and side visibility. the run time is ten to fifteen hours depending on mode and attaches to any bar or seat post without tools by using the included silicone strap. the light runs on two aaa batteries which are not included.