You could use a compact fluorescent bulb, which should fit in the incandescent lamp socket. I've read there are bulbs at Wal-Mart that work well, in their aquarium dept, and are around $5. They're made by Lights of America, or All-Glass aquarium.
It's better to use the U-shaped bulbs, rather than the spirally ones.
Also, you'll want to use bulbs that are at least 5500K (Kelvin rating, aka lighting temp) - which will be good for the plants.
The long fluorescent strip bulbs won't work.
25g Marineland Eclipse (30w T-8 ):
- java ferns, anacharis, corkscrew vals, giant hygros, marimo balls, java moss
- zebra danios (5), otos (2), others TBD
6g Marineland Eclipse (8w T-5):
- anacharis, asian ambulia, java moss
- white cloud mountain minnows (10 = 6-7 inches total)