The sun is superior of course but 8 hours and then 4 more hours of hps you mean right??Oh and if you move the plants(i am assuming you are) this would cause some stress but I used to grow in a closet and when the sun was shining in I would move the plants from the closet to where the light hit.I got some nice nugs but hated the extra work
Thanks for the reply jesus420 and dhhbomb.What i meant was 8 hours of total sunlight not direct or shaded.Like say the sun rises at 8am and it sets at 4 pm.
Oh its actually like it is actually 9 hours of light instead of 8 which would be better.12 hours of 400w hps or 8-9 hours of total sunlight.
unlike an hps whitch is the same intensity for 12 hrs and the sun gets brighter throught the day and peaks then fades and if thers clouds in the sky it drops it even more so the having 12 hrs of proper hid lighting is whay better than the ever changing sun at 8 hrs a day.....
It can also depend on where you live and the time of year.
If the sun is only out for 8 hours a day then it is likely to be quite weak sunlight.
But where I live in the sub tropics the winter sun is about 9 1/2 hours but it will
still give you sunburn, so in my case I would prefer the sun.
If I lived in the UK or Canada I'd go for the HID's.