Darkness can make MOB rescue efforts infinitely more difficult unless the victim is equipped with a strobe light; in that case, you might be able to spot him more readily than in daylight. That’s why most PLBs and AIS MOB devices are equipped with strobe lights.
Yet you can also add a stand-alone strobe light to your person. One of the newest and most compact MOB rescue lights is the ACR C-Strobe. Available in manual ($19) and water-activated ($29) models, the Coast Guard-approved C-Strobe has a 45-lumen white LED that operates continuously for 120 hours on two AA batteries. The 5-inch-long waterproof strobe can clip to a life jacket.