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Forget HD's and HPS in that case, it'll get much too hot.
You'll have to go all CFL's. I started off in a similiar space with excellent vent but with a 250 HPS and it's still been a struggle. I LST'd like mad but when flowering time came along, I realized I was still in height trouble.
So now I've built a new room , 2*2 sqm, and am just testing it for heat issues right now.

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