I try to keep my plants, in both phases of life, between 40% and 60% RH. Consistency is the key, and can save you from lots of headaches.
As for the soda bottles, no, the roots will not like light, not good. Get a can of black spray paint and give those bottles about 2 coats ea. Light in there with all that moisture would cause all kinds of nasty algae's to grow, and ya don't what that in yer roots.:holysheep:
ISO