Re: Is artificial light or natural light better for growing plants from seed?

If you use one or more 4 foot long shop fixtures with cool white fluorescent 
bulbs you should get substantially  more light than natural sunlight on a 
windowsill at that time of year. Run the lights 16 or 18 hours per day to 
maximize light and keep the top of the plants a few centimeters from the bulbs. 
The cool white bulbs are low in far red wavelengths so plants are often a bit 
shorter than with sunlight. That is usually an advantage because seedlings 
grown indoors tend to get overly tall. The lights also provide some heat which 
can speed growth.

Reference

Hershey, D.R. 1995. Plant Biology Science Projects. Wiley: New York.