How close can I keep my light?

Hello all, I have some hopefully simple and straightforward questions concerning HPS lighting. I am in the process of working a grow with CFL's but am already making plans for my next grow along with a new grow environment (is it just me or is gathering all the materials and putting together the enclosure etc. half the fun?).

I have no prior experience with HPS lighting so here goes. I want to use a 150 watt HPS light to cover two or possibly three plants that will be heavily LST'd to keep them real low. The enclosure I am working with is going to be about six sq/ft. The ambient temperature in the area I intend to work in is very consistently in the low sixties fahrenheit. I plan to use a cooltube that will intake on one side of the box, go across the length of it and dump out on the other side with no bends or curves at all except necessary light blocking mechanisms. In total this will be about three feet of ducting and tube. First, are these circumstances such that you think a 90 CFM computer case fan could do the job rather than a bulkier and more expensive inline unit? Further ventilation will be provided by a second fan pushing about 40 CFM through a small DIY carbon filter in the actual grow area. If not, then what is the recommended CFM that my cooltube fan needs to push, keeping in mind that this is only a 150 watt HPS.

With this in mind, about how much space do the experts think I would need to allow between my cooltubed light and the point where the tops of the plants would eventually be? Could I leave as little as a foot? 18 inches?

Lastly, knowing that I have about six sq/ft. to work with, would the 150 watt HPS be enough to pack 'em dense or would you recommend an upgrade to a 250 watter?

Thanks in advance, so far this has proven to be a great community!

wow, nothing?

im no expert but a good rule of thumb is 30 to 50 watts per sq ft,i have a 400 hps and keep it about 18 inches with a fan blowing across the canopy and works for me welcome to RIU,HANG in there people will help in just takes a little time.

for ventilation all u need is a exhaust fan (bathroom ones are a very cheap option, they make a little noise though attatch with rubber to surface to avoid rattling), id recomend a 400 hps for your growing if u want big buds... i have a 600 hps and i keep it 6 inches from tops of plants making sure to have constant air flow and osciliating fans going between lights and tops of plants...

i keep mine about 8-10 inches from the plants in a cool tube. works well for me.

-GT

You can go really close with 150W. I have 250W 6" away no problem. Put the back of your hand where you want the top of your plants-if it feels hot then it's too close-but keep it as close as possible.

Based on how things have worked out with my 250W, 6 square feet is too much for 150W IMHO. I am using about 4-5 square feet with 250, to get any more I would have to raise the light too far away to be effective.

Thanks guys, I think that pretty much answers my Q's. Might want to upgrade to a 250 HPS for better coverage, less than a foot from the plants shouldn't be a problem as long as there is adequate ventilation, and my plan for a strong case fan should be enough for the cooltube. Sounds great, I think i can go forth with this build worry free, hehe.