If we make good choices in the type of light, how long the light is left on, and the distance between the light source and the plants, we can have success in growing seedlings even without the sun. The type of light we choose will effect the intensity or amount of light. The lights we are most familiar are incandescent and fluorescent. Incandescent, or the traditional light bulb, is an inefficient light source producing a lot of heat with not much light. They are also high in red wavelengths, but deficient in blue.
Plants absorb light of many wavelengths, but mostly in the blue and red range.
They absorb little in the green range, which is why leaves look green to us. To get an idea of wavelengths, just look closely at the colors of a rainbow. You can see red and orange on one end and blue and violet on the other end. Light also includes infrared and ultra violet light on the far ends of the rainbow. Intensity is traditionally measured in footcandles, which is the amount of light an international candle casts over a one square foot surface area from one foot away.