i use 11/13 myself after 2 weeks of 12/12, this allows the plant to finish on its finishing date. like grim said during the dark period the plant releases hormone whick promotes flower growth, this one is the reasons ur turn ur fans off during the dark. also if i find if u leave ur plants in the dark for the last 3/5 days before cutting the will bud out like mad is a last dying act to produce seed . IMO the produce flowers at night and use the light during the day to produce new veg growth.
i am probably wrong but with my own grows i found these things