???????????????????????

First off u grow the plants not the light a lot of factors come into play soil,hydro, strain and health and plant numbers

2-3 days...

420 hours

E.

Come on buddy, I always said there is no such thing as a stupid question but I think you just killed that phrase. Do some research, man.

My experience with hsp lights is on the dim side but it would probably grow the plants as fast as a woodchuck could chuck wood

leejohn90 said:

https://www.rollitup.org/grow-room-design-setup/581778-how-fast-would-400w-hsp.html

Click to expand...

WTF dude, only idiots put up topics like???????????????????

The answer to your question is very complex. Since, we don't know many factors that can and will effect your grow beside 400w hps
So, here is my guess. "They will grow as fast as they want to grow"

superstoner1 said:

2-3 days...

Click to expand...

yes but which ones? cn

You could do an Indica in one day on Mercury. If you wanted to.

as fast as a plant can grow in the climate that its in.