You can successfully grow plants under artificial light indoors, but it's important to get your setup right. Light consists of several different wavelengths, each of which produces its own color. These colors are what you see when you run light through a prism to create a rainbow. Sunlight is rich in red and blue hues, both of which are extremely important to plant growth. Unfortunately, many artificial light sources produce more of the green and yellow wavelengths, which provide very little energy for plants. Others emit red or blue light but not both. When growing plants indoors, you must understand not only what parts of the light spectrum you are provided but also how much heat. The same is true of sunlight, which can provide the right light but may bake indoor plants when too intense.
Free and plentiful, sunlight gives plants exactly what they need. The blue portion of the spectrum promotes healthy leaf growth while red hues foster flowering and fruiting. As good as sunlight is, it is possible to provide your indoor plants with too much of a good thing. Plants that need a lot of sun do best in a south-facing window unobstructed by trees, roof overhangs or other obstacles. Plants that need less light do better in west or east facing windows. Low light plants need a north-facing window.
Make note of the temperature on your windowsills as well as light levels. Most houseplants do best in temperatures between 60 and 75 degrees Fahrenheit. Window glass can amplify direct sunlight and generate intense heat, causing issues for some plants. In the winter, a draft from the window can harm sensitive plants. If the windowsill itself is too hot or cold, move the plant to a stand or table a few inches away from the window rather than placing it directly on the windowsill or against the window glass.
Whether you opt for the traditional long tubes or more modern compact fluorescent light bulbs (CFL), you'll be using the most popular type of light for indoor growing. Fluorescent bulbs last about 10,000 hours and run cool, so they need only sit about one foot away from your plants. Although these bulbs emit lots of the blue light wavelength that plants need, they tend to lack the equally important red hues. To counter this, buy the whitest fluorescent bulb because white light encompasses all the colors of the spectrum. If you can't find a fluorescent bulb with enough warm light, supplement your lighting with at least one traditional incandescent bulb.
When it comes to the light they emit, incandescent bulbs are the opposite of fluorescents. Incandescent bulbs emit a very warm light that is rich in red wavelengths. Though great for promoting flowering, incandescent bulbs lack the blue light that plants need for healthy leaves. Incandescent bulbs also generate a lot of heat and so must be at least one foot away from plant foliage at all times. For optimal health, your plants will need a combination of both fluorescent and incandescent bulbs at a two to one ratio. You can expect a lifetime of about 1,000 hours from most incandescent bulbs.
Cool to the touch and extremely energy efficient, LED lights are a great indoor growing option if you choose the right ones. Basic LED lights tend to have a blue hue but are sorely lacking on the red end of the spectrum. You can combat this problem by looking for horticultural LED lights. Made specifically for plants, these lights are rich in both red and blue lights. LED bulbs are inexpensive to operate and last up to 50,000 hours.
Halogen and Horticultural Lighting
Halogen and horticultural bulbs are both champions at emitting a full spectrum of light. In spite of this, they may not make for the best choices when growing plants indoors. Halogen bulbs give off as much or more heat than incandescent bulbs and generally cost more. Horticultural bulbs, too, demand a higher price than other light sources. They do promote healthy plants, but most indoor gardeners find full spectrum fluorescent lights equally effective and less expensive.
Remember that how much light your plants receive matters as much as the type of light. Outdoors, plants experience a natural cycle of light and darkness, with the amount of light changing with the seasons. Exposing your indoor plant to constant light may actually weaken its health. Plants should generally receive 16 to 18 hours of light a day, but low light plants may only need 12 to 14 hours. When in doubt, adjust the timer on your lights to mimic what is currently happening with the sun in your region.