Ok...you turned off your lights (all but the 400) and the temps went way down....duh
But im guessing, (like you said) you would like to use all of them. This goes directly back to a ducting system you just need exhaust registers (or even open sucking tubes) as near the light as possible. You need SERIOUS airflow to cool this room, and aim for temps in the 70s, not 80s to make this stadium grow worth it.
You dont want to invest in cooltubes or ducted glass or anything? Ecen using glass tubes ducted with aluminum will seperate your bulbs from your growroom air.
But anyway....You need a high cfm blower and duct an exhaust to each of the lights so the hot air is being constantly evacuated. If you can get some good suction on your ducts and get them close, like directly above the sockets, you will effectivly get the effect of ducted air cooling. It should remove all the hot air and draw in cool air from your intake, which can be a smaller passive fan.
These steps are neccessary for your grow, you need a good HVAC system for climate controll. Get those temps to 75 look up fans at buisnesslights.com or buisnesslighting or something im to stoned to look for a link
EDIT: Dude, THINK before you add air movement in your room, right now if you increase airflow in your room your only going to circulate more air by the bulbs thus heating it faster. Youll be doing nothing but help equalize the heat unless you figure out an exhaust solution.