Serfas Thunderbolt USB Rear Light Serfas Thunderbolt (UTL-6) Taillight gives you style & safety in one high-powered & affordable package. Being seen on your bike at night never looked so good with Serfas’ Thunderbolt (UTL-6) Taillight. This USB rechargeable gem comes with 35 lumens of firepower while giving riders’ several different rear facing mounting options. The 30 micro-LED strip will let your presence be known to cars and bikes alike. Charge up, light up & get riding safely with the Thunderbolt.