For a single bottle you could cut your power to 1/5th and use one of those 20W CF bulbs that fit incandescent fixtures. Phillips and GE both have "daylight" bulbs that are in the 5500K to 6500K range for color temperature.
For the last 8 months I've just used a shelf by one of our south-facing basement windows that has a heat vent nearby, the cultures take a little longer lately cuz our days are pretty short up here in the winter but they've been doing fine so far -- plus the bubbling green bottles in the window keep the neighbors intrigued
