We have learned a lot about cannabis since I started growing. We used to always use 18/6 because we did not know that cannabis did not need a rest period. However, like mentioned, now most of use 24/0 because of what we now know about cannabis and how it grows. I do want to do some research to see if Hackerman's theory is correct--that you get better root development if you start out at 18/6 and then go to 24/0. But right now, I do like everyone else and veg 24 hours a day. I just think of the 18/6 light schedule as "old school" and only used by those that don't really understand how cannabis grows.