Growing plants indoors is a popular activity, but it can be hard to provide enough light. Many plants, especially herbs and vegetables, require a lot of direct sunlight. Artificial lights can help with growth, but it can be tricky to choose the right one. Learning the difference between incandescent and fluorescent lights, and their effects on plant growth, can help novice gardeners make the right decision.
Plants need light that is relatively balanced in color in order to grow correctly. Most incandescent lights provide a poor color balance. They have high percentages of red-spectrum light but produce very little blue-spectrum light. Cool white fluorescent tubes are in common use by gardeners and produce blue, yellow-green and orange light but very little red light. Supplementing cool white fluorescent tubes with a few incandescent lights or light from a window can provide the appropriate balance. "Daylight" fluorescent bulbs seem as though they might provide the right balance but usually work poorly in practice.
Heat is another consideration. Light bulbs that are too close to the surface of a plant can burn the leaves, preventing healthy growth. Incandescent bulbs are only about 1/3 as efficient in converting electricity into light as fluorescent bulbs. This means they produce much more heat, and must be positioned at a greater distance from the plants in order to be effective.
While incandescent bulbs are much less expensive per unit than fluorescent ones, they also last for a much shorter period of time. The average incandescent light has only about 1,000 hours of life in it compared with around 10,000 to 34,000 hours in a fluorescent bulb. This greater longevity means that gardeners who use fluorescent lighting don't need to change bulbs as often and spend less money buying new ones.
Artificial lighting is a much more expensive way to grow plants than simply putting them out in the sun. Fluorescent bulbs tend to be much more energy and cost efficient than their incandescent cousins. A 25-watt fluorescent bulb provides as much light as a 100-watt incandescent bulb, using 1/4 the electricity to provide the same illumination.
While some manufacturers offer special bulbs with the right color balance for growing plants, these can be very expensive. A mix of cool white fluorescent bulbs with redder incandescent bulbs may provide the same quality of light but be less expensive. According to the University of Missouri Extension, the best ratio is to provide 3 watts of incandescent light for every 10 watts of fluorescent.