Should the exhaust run with lights off??????

Hey everyone, I'm alittle confused on this last piece of the puzzle. I'll make it short....2x4x7 tent,400 watt air-cooled light,6" exhaust (530 cfm's)w/ speed control,carbon filter,passive intake. 1st-when the lights are on does the exhaust run all the time or should I set a thermostat on it. When the lights are off do I still need a exhaust or does the smaller fans inside the tent help circulate the air from the passive intake? I understand the air has to be replaced every so often, but when and how? what is the best order to set-up carbon filter,light,fan,duct,etc. I think you pros are getting the picture of what I'm trying to do. Have everything else in place and ready to fire this baby up as soon as getsome advise here.Any comments good/bad,indifferent are welcomed. Thanks to everyone for all the great advise.

I'm not a world class grower but your plants need oxygen at night right? I leave my exhaust fan on during dark period to bring in fresh air. I could be wrong but it has worked for my small grows since 2006. Also I like to bring down my temps during darkness 10-20F degrees. Hope that helps and good luck!

Night is when the humidity has a tendency to rise. When flowering you do not want the humidity higher than 50%. I keep my RH (relative humidity) at around 35% in my flower room. If you are in veg than humidity can be higher where 65 - 75% is optimal. So leaving the exhaust on will not hurt your plants. If you use CO2 than that needs to be turned off in the dark cycle as it is only usable with the lights on. Good luck

turning fans off is ok as long as you don't have heat,humdity issues. I would use a small fan in the tent just to keep air moving.