Thanks for the quick reply..
the grow space is a small bedroom prob about 3m x 3m with 2 trays on each side of the wall and 2 600w lights..
i dont really have a cooling plan besides an extractor blowing air out of the room and a small inline fan blowing air in..
the transformer will be outside the grow room so that should save a bit of heat... how big of a difference is it between the 600 and the 400? is it worth the extra cash? price vs yield in comparison to the 400w....