Sounds like your using an open face reflector and very little air is actually being sucked through the tent, or maybe isn't leaving through the top?

Point is, If you are using an A/C reflector with a glass seal. You pull air from the top of the tent, through the hood and out. This allows you to keep heat down not only in the tent, but the hood stays cooler and thus you can get the light closer to the plants.

Like this one:

EURO AIR COOLABLE GROW LIGHT REFLECTOR HOOD cooled dome - eBay (item 400069759887 end time Feb-22-10 12:03:12 PST)

I'm not saying THAT is the best or cheapest either, It's just the first one I found.