Humidity Problem, Need Advice, Please help

I just got a grow tent to flower my girls in, right now I'm using a 1000w hps with Co2 for an enclosed system and the only vent I have is for my hps. During the day photo period the climate is almost perfect, around 75 degrees and about 30 percent humidity but at night the humidity jumps to about 80. I was thinking about another vent to help circulate the air in the tent. The problem I'm having is that in the area where I live, the air outside drops to the mid to low 40's at night. So I can't pull it from outside and I can't pull it from the room because I use the rest of the room to veg and I'm worried about letting any light into the tent, thinking it might screw up the dark period. can I still run another vent without screwing up the dark period? that is, if I use a certain length of vent ducting, will that keep the light out?

What is the humidity in the room? What are the options for getting room air into the tent. I suspect that an exhaust fan set to turn on when the lights go out with a passive intake would help. Is the room Co2 or just the tent?

you should try to install a 6" ducting, from the grow tent going into another room. you can do this as a passive vent or if the humidity dosent go down too much u may want to put an intake fan in the duct

humidity is usually around 30% in the room and the tent is set up for Co2 not the room. I'm doing SOG so trying to focus more on the girls flowering (with using Co2).

ok, I'll give both a try and see what happens, thanks for the advice!

not sure but could you use a dehumidifier we get them here in the £1 shop just put it in before lights go off i used one when i was growing in my shed as humidity was a slight problem and it worked well

something like this

http://www.amazon.co.uk/151-Interior-dehumidifier-Absorbs-damp/dp/B000X1ERW8

Cool, I'll check it out.