Topeak rear bike light AlienLux Lamp 2 Red LEDs / (2) CR2032 Batteries (Included) 2 Modes Constant/Blinking - Burn Time (approx) 60 hrs / 100 hrs Engineering Grade Plastic / Mount Seatpost onTopeak Bags Size (L x W x H) 4.8 x 3.5 x 3 cm / 1.9 x 1.4 x 1.2 Weight 20.6 g / 0.73 oz