And the winters are long, too. We can supplement the natural light with artificial light. A simple way to do that is with a standard fluorescent fixture, like this one that's available from most discount or hardware stores. This fixture has standard cool white bulbs in it. They are very strong in the blue wavelengths.
Photosynthesis requires energy in both the blue and the red wavelengths.
So, in order to be best, you need both blue and red light. Or, you can simply replace these bulbs with the grow tubes. It would give you the full spectrum. This is a quartz halogen fixture. Again, they're available at most discount and hardware stores.