Topeak RedLite DX USB Rear Light (Red with Red LED) 4 Super Bright Red LEDs, 3.7V 240mAh Lithium Ion Battery 2 Modes. Constant/Blinking, Burn Time (approx) 11 hrs / 30 hrs, Reserve Time (approx) 1 hour Lamp Housing Silicon Mount Seatpost (25.4 - 31.6mm) Size (L x W x H) 4.5 x 4.2 x 2.8 cm / 1.8 x 1.7 x 1.1 Weight 40 g / 1.41 oz (light only)