12 hours light / 12 hours dark...which simulates the normal proces off the world...to be honest i would wack that thing under it as soon asap..try an get the most out of ur plant but to be honest i doubt ur gona get much bud! so put it nder the HPS bout 15" away from the top of the plant on 12 hours light 12 hours dark ull need onea those 24r timers to get 12/12 automaticly but you can do it manually i spose... gd luck