I had mine under 18 hours of light. It stretched a a lot and left very distant bud sites. Of course the outdoor sun will outperform my 2 600s. I havnt seen a od auto vs id auto. I know autos thrive the best in 20/4 light depending on who you talk to so I dont know exactly how a lack of light exposure outside from the day not being 20 hours long in most places would compare with the huge increase in light energy. Its a good question.