Sucker Punch dropped the date in a tweet (via IGN) following the date briefly appearing on the PlayStation Store. First Light will follow Fetch, the neon-powered character who appears in Second Son. Her story will revolve around her time in Curdun Cay, the Conduit prison, and her subsequent plans to get revenge on her captors.
As previously reported, First Light will work as a standalone game. Owning both it and Second Son, though, will net you some extra content.