A good question mate and a good answer by cruzer but depends 1000w light is not as efficient as 10x100w lights placed in strategic positions around the grow room 500 w on top of canopy and 500 watt below this way the bottom portion of the plant turn their leaves to face the lower source light so in effect you could grow more bud as a result I discovered this fact as I have only 2.5 meters long and 1m 200 high so I could not put my lights directly over the top of my plants but they have done so well I will always use low watt CFLs to illuminate the underneath of the canopy if you are using just 1000w HPS then you need to have a rotation system for the 6 pots so they all share the centre spot were the light is most concentrated at least once a week.