Does it really conserve energy? I mean, you grow them for 4 weeks at 24/0 and they are X inches tall. If you grow them with 18/6, it might take them 5 or more weeks to reach the same X inches tall. So, you use less electricity per day, but you then have to go more days to reach the same point. All in all, unless you have a reason to slow down the growth (can't handle the heat without the 6-hour cooling down period, flowering rooms/cabs won't be ready for a while, whatever), then using 18/6 seems like sort of a waste of time, literally. On the other hand, as long as you're in no hurry to get to harvest day, it doesn't really matter.