I'll give you an answer icey but like turtle said read read then read some more.

You don't need a hps to flower but they will give you the best yield per watt and the most potent buds but they do run hot so you'll need good ventilation. A good alternative to the hps are cfls, the advantage being they run a lot cooler than hps so you can get away without spending money on heavy duty fans. Check out a couple of grows using both hps and cfl and see which one suits what you want.

Start 12/12 when the plants are roughly half the size you want them to be when they finish flowering. Most people switch to 12/12 when plants are between 1 and 2 feet, usually 4-8 weeks after germinating.
hudson88 Reviewed by hudson88 on . lights wut kind of light should i get to start out. and do i need an hps light for flowering, wut alternative could i use. how do i know when to start 12/12 Rating: 5