Usually they're talking about the sum of the whole system. But pay attention to the ratios. If you have a 200ws light a 20ws light won't do you a whole lot of good as there's more than a 3 stop difference between the two. Try to keep the lights winthin one stop of each other like a 400ws and a 200ws pair. Generally more is better, because you can always reduce the power of a light.
-James
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