Nicole, you must be thinking of the lighthouse on Plum Island. I know they were doing lighthouse dinners a few years back, but I didn't realize they were still available. I know they used to book at least a couple of months in advance, so if your husband b'day is in summer, good time to scope it out is now. I can't vouch for anyplace to stay in Newburyport, since I lived so close. The only time I sleep in Newburyport is if we tie up the boat on the boardwalk to get an early start on fishing
You'd want to definitely arrive early to enjoy the town during daylight hours, maybe take a harbor cruise or something. You just don't want to schedule this for Yankee Homecoming Week(end) which is usually around the last week of July, 1st week of August. The town is WAY too full at that time, no parking, long lines everywhere, just not the best time to visit.