I prefer a natural 12.5hr on/11.5hr off photoperiod during late spring until the end of summer.I then revert back to a 12on/12off photoperiod for the remaining of the yr.This light cycle i use and recommend for all flourescents.With metal halides,I run my actinincs for the full 12 to 12.5hr photoperiod and my halides run for a 6 hr cycle.