If I was growing outdoors in direct sunlight and my plants weren't getting fried by the sun. I would just assume it was dirt , I mean in an outdoor grow the guy can't run extension cords outside and run leds in sunlight LOL. The sunlight can't really be too weak unless it's winter time where you live. Sunlight is the best light for plants, I know people have problems growing tomatoes in some dirt and they use cages and stakes to keep them up.