Actually, I would'nt call a single 400 beefy at all. Great starter light.

You will probabley have to set up some kind of active air extraction from the space- could be as simple as a fan blowing out the door.

Couple of questions before we can give specific advice-

What are the dimensions of the closet, including height?
How important is stealth?
What's your budget?
Is anybody going to freak out if you modify the closet door or walls?
Do you have a window?

Ventilation design goes hand in hand with odor control. How critical is odor control inside your living space? Outside?

How long do you think you'll be running just the one 400? Keep in mind that this is a hobby that often results in a condition referred to as GAS ( Gear Aquisition Syndrome). Does it make sense to build in a bunch of headroom?

Other than that, all I can tell you is that you'll need to move hot air out of the space, and draw cooler air in, almost inevitabley with some kind of fan. It's generally more efficent to push or pull air out of the space than to push air into the space- nature abhors a vacuum , more than a high pressure zone.

Hope that helps.
rhizome Reviewed by rhizome on . Hot! So I just purchased a 400 watt HPS setup today, and I got it up and running. I have to say that I am pretty blown away at the difference in power from what I was using (4-26 watt CFL's). I nearly get blind from looking at my plant! Unfortunately, my temps have risen about 8 degrees also. Now my closet is 93 degrees, and I need a way to cool it! Rating: 5