i have grown for a good long while, always in the same space with a 400hps(430hps for a bit as well). imo if you have the space and means of cooling don't get less than 1kw. you put alot of time and effort into growing so you might as well get a large payback on your investment. with practice i was able to yeild close to a lb with the 400hps growing scrog style, just imagine if i had been using a 1kw light instead. with the same time and effort(slightly higher energy expense) i could have well over doubled that yeild. with all that being said i have only 1 more thing to say...... 1KW HPS COOLTUBE