What is the min lighting requirements for growing?

I have a resonabley sized green house and intend to start growing on a small scale in it. Money is currently tight and i will require lighting for sure as i live in a cold area and the days are getting very short.

Could some kind soul please tell me what the bare requirements as far as lights go are?

Cheers all.

depends on the sq foot of the area the plants are in but basically 3x3 =400watt lights 4x4 foot are 600 watts and 5x5 =1000 watts of light

thanks very much mate,
are we talking heat lights here? or flouresent bulbs?

I'm gonna have up too 10 plants on the go at one point in time but most likely we'll stick to 5.
What types of light do i actually NEED?
If i need Infra red heat lamps can i use chick brooder style gas heat lamps as these are cheaper for me to run and easier to get hold off for me also(i live in a farm style environment).
Are high pressure sodium lamps essential?
I also have a massive chest freezer, is this suitable to blank out and use for the stages in which i require darkness?

ta mice much