Father Nature...The science is all in my semi logical thinking mind, lol. Basically in the morning the lower light comes on first (the sun rising). Then a little later the top light comes on and the middle light kicks in for mid day (in the light cycle, which is also mid day in real life anyway). So by midday through to late afternoon the lights run at 100%. Then late afternoon the 400 goes off, and in the start I have the top 600 off for a bit, but in the middle of the grow I have it on through the late afternoon (peak summer time in my eyes). Then when the buds have packed on their weight and are filling up in the last couple I'll put them back to the same regime as at the start of the grow. Kushes by all accounts like to be given a bit of breathing space in the end. Last few weeks I am going to stick the 400MH in there and get the 400 hps out for heavier resin production.