Florescent lights are much more efficient than incandescent, The "pretzel-shaped" compact fluorescent bulbs that screw into standard fixtures are more convenient for house plants than 4 foot "shop lights".
However, if you want to keep the plants warmer without heating the whole house, maybe an incandescent bulb would work.
However, that will also dry out ferns and African Violets something fierce.
Winter indoors in the NE is DRY. The cold air outside is dry becuase it's cold. Then when that air filters into a warm house, it becomes extremely dry. Ferns and African Violets don't like "dry". I would suggest spritzing the ferns several times per day, but I don't know if leaves of African Violets would like having water standing on them.
The trick with heat and humidity is keeping them where you want them! Heated air especially will just float up and away, so that you're warming your ceiling, not your plants.
You can buy a 2'x2' square of drywall ("gypsum board") from Home Depot for $5, and that will direct ALL the heat from a heat pad straight upwards towards pots or into your terrarium.
However, keeping heat "down" and near the plants seems to require a tent, like from clear plastic film. Maybe a dry-cleaning bag?
Your terrarium is a great idea for maintaining humidity . I assume you keep a layer of gravel wet. But I would expect it to allow heated air to rise and escape, perhaps caryying away too much humidity as it rose.
If you love fiddling with gadgets, there are low-pressure misters for 70 cents that can run off the water pressure in your pipes. One of those near a plant would keep it (and that whole room) much less dry, or even comfortably humid for humans. That might make your skin happier, too, if the whole house became less dry! Then maybe you could also keep it warmer.
But you would have to run 1/4" tubing from a faucet to each plant. And if someone tripped over it and unplugged it, the jet of water that comes out of 1/4" tubing at 30-40 PSI will soak an entire room in seconds!
http://www.dripworks.com/produ...
If you have enough mass of foliage in one spot, and the plants are warm enough to be growing and metabolizing happily, they will transpire enough humidity to keep their immediate area somewhat less dry. Grouping may plants into one spot may let them tolerate a dry atmosphere better than being spread out over many rooms.
Or you could find some tough plants with lots of foliage, keep them well-watered, and surround your delicate flowers with a lot of foliage.
(Four foot shop lights are ideal for starting seedlings indoors in winter and spring, if you plan to get into that.)
