Heck, I'd never noticed they had serial numbers. Twisted mine to on and dawg-gone if there wasn't a serial number.
47 lumen SN starts with SL, a few zeros and what appears to be just over 100 thousand (presuming each is stamped in series).
47 lumen SN starts with SL, a few zeros and what appears to be just over 100 thousand (presuming each is stamped in series).