Question about flowering from seed.

Do you HAVE to have an auto-flowering strain or can any flower if you give them 12/12 from seed?

Also, if I veg and flower with 400w hps what will the effect be on my buds?

auto flower strains you usually leave the light at 18/6 the whole grow.
yes you can do a seed from start to finish on 12/12 but imo the plant really wont go into flower until it matures enough and is ready to flower. so why not veg at 18/6 until the plant matures. a mature plant going to 12/12 will respond to the 12/12 switch better than a seed started at 12/12.
you will have some nice buds with an hps the whole grow.

pretty much exactly what smoke and coke said, yes, you can grow 12/12 all the way. they wouldnt get so big mind, or they might take longer to flower than if u had them on 18/6 for a few weeks first.
a 400w hps would give u big dense nugs, and also give u a higher yeild than cfls or a mh for flowering.

remember that buds are related to roots. I've done the seed to flower and it isn't efficient. Some plants die as a result of giving up on a weak root system to flower. I would let them veg for at least 2 weeks, otherwise they may not be strong enough to flower. Oh and the 400W is the money shot.

i would also like to add.
dont get me wrong, im not saying do not do a 12/12 from seed. ive tried it and was ok but i will veg for minimum of 4 weeks with either fluoros of 400 mh before the switch.
i like to look at it that the longer veg, the more you will yeild. as long as you have the lighting to cover the taller plants.

ive seen some impressive 12/12 from start to finish. and one that comes to mind is randy rockets grow. heres the link.

https://www.rollitup.org/grow-journals/151253-12-12-seed-harvest-1-a.html

Thanks for the advice, I'll 18/6 with the HPS for now.. but also, i have a problem.. the hood I bought was the basic one from HTG.. and I didn't know it didn't have an exhaust area.. It has a round 4" panel to the right with a circular plate you can remove, but it just exposes wires.. and a smaller hole for the wires to go into the mogul socket.

I attached a 4" exhaust to this, will that work? or is this hood not exhaustable?

So is this exhaustable?

What hood exaclty do you have? Do you have a picture or a link?
I have a 400 watt hps and I love it. I do not need an exhaust for it because it doesnt put out alot of heat and I have a fairly big grow room. If you are growing in a small room you may need to vent it.
You can run the 4" duct to the light if you want. It will pull heat dirrectly from the bulb out of the room. Its not as efficent as a cool tuble, but for a 400 watter it should work fine.
Peace!

usually you can make your own 4" holes in the ends of the hood and get a couple of adapters to mount over or through the holes then connect exhaust.