You cannot just put a light in a large room--you do need some kind of enclosed space that is sized to the light you plan on using. Otherwise the light disburses throughout the entire space leaving you deficient in lumens. In addition, when the plants are put into 12/12, you need 100% total darkness for the 12 hours of dark with absolutely no interruptions of the dark. A 600W HPS (high pressure sodium) light is sufficient for a space that is 4' x 4' or 120cm x 120 cm. You also need some kind of centrifuge type fan to exhaust air within your space. In addition to controlling heat, the exhaust fan supplies fresh air to the plants--plants need a continual supply of fresh air all the time the lights are on for proper photosynthesis. The space also needs some kind of oscillating fan to move the air around and help the plants develop strong stems.
For the vegging space, which can be about 1/2 the size of your flowering space, most of us use high output T5 fluorescent tubes. I have a 4 tube fixture in my 2 x 4' vegging space. You need fans for this space too, but they can be smaller.