Plants need light for photosynthesis and without light they can’t grow. But not all light is equal.
If you remember from your middle school science class, sunlight contains many colors or wave lengths of light. Plants mainly use the blue and red part of the light spectrum and not much else.
Seedlings need good quality light to thrive. The ideal place to grow seedlings of course, is in a greenhouse or sun-room where there is plenty of natural sunlight. However, not everyone has access to a space like a greenhouse. A south window can help, but even in that case, supplemental lighting may be needed.
An adequate substitute for natural sunlight is light from fluorescent bulbs. Special “grow lights” are available but are quite a bit more expensive than standard fluorescent tubes and they don’t last as long. Research has shown that plants do as well or even better under “cool white” bulbs. Cool white bulbs provide plenty of blue light.
Even with the most recent research, some gardeners still feel that seedlings grow better if the light is “blended”. So, they’ll add a “soft white” bulb to a florescent fixture to provide some red light for their seedlings. Shining light from an incandescent bulb onto the seedlings will also add some red light.
Most vegetable and flower garden seedlings need bright light, at least 500 to 1,000 foot candles. Placing the light fixture within six inches or so will provide them with that amount of light. Still, that is not a bright as a sunny day where there can be 10,000 foot candles shining on a plant.
Plants require some darkness every day so lamps must be on a timer. Six to eight hours of darkness is sufficient for most plants — just about the same number of hours as a good night’s sleep.
If you are really serious about growing a large number of plants under artificial light, special high output light fixtures are available starting at around $300 each.