It all varies on what ur able to do, there r diff lights cause of diff factors, if ur grow room is really small and ur worried bout heat use t5 t8 etc. or cfls, if u have plenty of room and can afford anything u could get some 1000w HID lights, or u could get some LED lights that produce very little heat but r expensive as hell. If u've never grown and wanna start ur cheapest bet is to go get some cfl bulbs, u can get like 125w or 200w or 85w 105w, or like some 2ft or 4ft Tube fluorescents. The reason he asked seiously is cause if u know anything its a very vague and general question that no one serious with growing would ask without saying anything else.