That’s similar to the temp swings I get in my grow. It just brings a lot of purple out due to the lower temps. It doesn’t really have a negative effect. If anything it may slow their growth, but not noticeably. This is my last basement run.
I used to have my ducting running out the window through a plastic cover type of thing from a portable air conditioner. It’s just a strip of plastic with a hole cut for the ducting and it keeps wind and rain and stuff from coming in from the open window. That worked well for me but it could depend on your situation.
There is locks that go in the window track so it can be fixed in place. With a curtain it looks like an ac unit coming from the window and its securely locked. Other than that you could try running the exhaust out the door instead if you don’t have to be discreet about it at home.
It’s more about temperature control, the exhaust will be warmer than the room temp and eventually it warms the room up. If you can keep a door open to give some fresh air it wouldn’t be a problem and could even work to your advantage in winter.
Otherwise, the only other thing that comes to mind is what I was once advised.
Is your light source definitely an LED?
I was told that while sodium vapor lamps are a bit more expensive in terms of consumption, they are quite cheap to purchase. AND they practically warm your tent for free.