In short, the earth sits a a 23.5 degree angle in relation to the sun. During our summer the sun's rays have the shortest distance of travel through our atmosphere. They are the most intense and least filtered by our atmosphere at this time. As we move into the fall outdoors, the sun's rays no longer encounter the atmosphere at a 90 degree angle, this angle begins to decrease, eventually down to 30 degrees. The Sunbeam entering at the shallower angle must also travel twice as far through the Earth's
atmosphere, which reflects some of the energy back into space. Much of the reflected light is in the far red and ultraviolet spectra. (blah blah blah)
So by switching to LED in week 6 you are, in a way, simulating nature since your GrowBlu fixture will have a higher amount of blue light and no UV.