Hi there! I tried autos outside with limited direct sunlight (7-8hours) and plenty of indirect sunlight (5hours extra). I also gave some seeds from same batch to a friend with led lighting to compare.
We found that:
1. LED lights on 18 hour schedule makes huge difference (2-3x the size plant during veg)
2. Supplementing with CFLs made huge difference. I started with a single 85w cfl but eventually added more to get to total 500w in cfls. The difference at around week 4 across my three grows should give you some indication of the impact.
My take away from this was that if you can't supply >12hours direct light to autos then it is better to grow photo periods instead and be patient. If you do grow autos with limited light then supplementing should produce a big payoff.