48 hours of darkness is a very popular answer. However, this is as stated above a very debatable topic. I think the correct answer is personal opinion, which can only be formed by true trial and error. You can learn a lot by research and reading but somethingā??s you just have to do to learn. I do not do anything special with my harvests anymore, I have tried the 48hours of dark and did not notice a huge difference, and now that I am running a perpetual grow my options are limited more than others. I have been doing some research on UVB but at this point, I am not ready to try it. This is a great topic for discussion, and I am looking forward to seeing what some of the other experienced growers have to say.