cycle of light (help)

i just finished with my 21 days and i dont know wat cycle of light some people tell me 12/12 some say 18/6 so is good if some one could explain or give me a link that would help me thanks

it depends on how big you want the plant to grow and how long you;re willing to wait. keep on a 18/6 schedule until the plant is about 1/2 the height you want/have, then switch to 12/12