Until last year, Greenpoint’s St. Cecilia church housed an active nunnery, but tonight the church’s closed convent will reopen with new secular inhabitants. 25 artists have taken over the 97-year-old building for “Room Tones,” an exhibition organized by Nathan Spondike. The nuns’ former quarters now showcase individual artists’ work, including paintings, sculptures and film, while common areas feature their collaborations. Like other holy houses repurposed for artistic endeavors, the show’s hours will be limited following tonight’s opening from 6 to 9 PM at 21 Monitor Street.