Photoperiod is a term used in cannabis growing to refer to a standard type of seed. With latin roots in the words ‘light,’ and ‘time’—photoperiod seeds are standard seeds that flower based on the amount of darkness they receive each night. Photoperiod seeds will keep growing as long as they do not get more than about 12 hours of complete darkness each night. Photoperiods are the opposite of autoflower seeds, which flower automatically, and without regard to the length of night.