Windowpanes or Grow Lights

The final consideration for starting seeds indoors is their individual light requirements. Most seeds germinate best in darkness, but some won't sprout without a little light. Knowing the light requirements of the seeds you sow prevents mysterious disappointments.
The light level is just as important after the seeds sprout. If grown at room temperature, they need supplemental light to prevent spindly growth. Plants grown on windowsills will do fine if the microclimate near the window is cool enough.

The alternative is to purchase cool-watt fluorescent lights. Sold as shop lights in 4- and 8-foot lengths, the lights are inexpensive and perfectly adequate for the task. They do not radiate the full sun spectrum, but unless you intend to hold seedlings until they flower, they won't need the full sun spectrum. The range of light waves from shop lights are just what seedlings need. Hang the lights within a few inches of the plants' tops, and adjust the lights as the seedlings grow.