Blackburn's Click USB Rear Light throws 20 lumens from its single LED for ample visibility at night, and it's designed to shine light from the sides as well for visibility to cross traffic. A universal rubber mounting strap is compatible with seatposts and frames 15 mm - 35 mm in diameter, and the integrated Li-Po battery is USB rechargeable in 3 hours using the included cable. Remaining battery life is shown with a built-in indicator.
Runs for 1.5 hours on constant and 3 hours on blinking mode. IP65 waterproof rating. Claimed weight is 20 g. Available in multiple colors.